THIE FATE OF SUGAR IN THE ANIMAL BODY. Without an accurate ...

THIE FATE OF SUGAR IN THE ANIMAL BODY.

I. THE RATE OF ABSORPTION OF HEXOSES AND PENTOSES FROMTHE INTESTINAL TRACT.

BY CARL F. CORI.

(From the State Institute for the Study of Malignant Disease, Buffalo.)

(Received for publication, May 13, 1925.)

CONTENTS.PAGE

I. Introduction ................................................ 691II. A method for the quantitative study of intestinal absorption.. 692

III. The loss of body weight of rats fasted for 48 hours .............. 696IV. The relation of the absorbing surface of the intestine to the

body weight .............................................. 696V. The absorption coefficient .................................... 697

VI. The graphic representation of the rate of absorption of sugars.. 701VII. The comparison of the rate of absorption of hexoses and pentoses. 705

VIII. The dilution mechanism in the stomach and intestine and thewater content of blood and tissues during the absorption of ahypertonic sugar solution ................................. 706

IX. The sugar and nitrogen excretion in the urine, the blood sugarconcentration, and the relation of the absorption of sugar fromthe intestine to the disposal of sugar in the tissues .......... 708

X. Discussion ................... ................................ 710XI. Summary ................................................... 714

I.

INTRODUCTION.

Without an accurate knowledge of the laws of intestinal ab-sorption it would seem impossible to follow the fate of sugar inthe animal organism on a quantitative basis. For convenience,the fate of sugar in the animal body may be divided into foursteps: first, the absorption from the intestinal tract; second,the passage through the blood and occasionally elimination in

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Absorption of Hexoses and Pentoses

the urine; third, the penetration into the tissues;' and fourth,the disposal in the tissues. The first and second steps are com-paratively easy to follow quantitatively and form the content ofthis paper. It was originally intended to investigate only thefate of glucose. The other sugars as galactose, mannose, fructose,and pentoses were later on included, partly because some of themare frequently ingested with our food and are also physiologicalcell constituents, partly because it was found that they serve as anexcellent illustration of the selective permeability of the intestinalmembrane.

II.

A Method for the Quantitative Study of Intestinal Absorption.

Hitherto, most of the experiments on intestinal absorption havebeen performed on isolated intestinal loops of dogs, cats, or rab-bits and generally one of two principles was followed. Eitheran acute experiment was made, which involved narcosis of theanimal, a laparotomy, and the tying off of the desired portion ofthe intestine or a Vella fistula was established in a preceding opera.tion. Both methods have their merits and demerits which neednot be discussed here. Their chief disadvantage is that by work-ing only on a part of the intestine, they do not allow the study ofthe mechanism of absorption of the whole intestinal tract as aphysiological unity.

For our purpose, a method had to be devised, which wouldallow of estimating quantitatively the absorbing capacity of thewhole intestine and which would permit of basing the results on aunit of body weight. Since only small laboratory animals can beobtained in sufficient number and of the desired uniformity ofstock, age, and nutritional condition, the method was worked outon rats. The principle is briefly as follows: A known amountof the substance under investigation is fed by stomach tube.After a given time, the rats are killed and the amount of substanceremaining in the intestines is determined quantitatively. Thedifference between the amount fed and the amount recovered from

1 While this paper was in press the permeability of liver and musclesfor hexoses and pentoses has been determined (Cori and Goltz, 1925, a).

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the whole intestinal tract is then the amount of substance ab-sorbed. The method is described in detail below.

Male and female albino rats of an inbred strain, originally derived fromThe Wistar Institute, Philadelphia, were used. They received a basalration which was composed as follows: Ground scratch feed, 24 per cent;ground wheat, 20 per cent; ground fish, 20 per cent; milk powder, 20 percent; lard, 15 per cent; cod liver oil, 1 per cent.2 In addition, they receivedtwice a week, some fresh vegetables. The growth of the rats maintained onthis diet was entirely normal.

Rats between 2 and 3 months of age, weighing from 120 to 180 gm. werefound most suitable. They were weighed 48 hours prior to the experimentand each rat was placed in a small wire screen cage. The feces droppedthrough the wire screen and were not accessible to the animals. Solid foodwas withheld throughout the 48 hours, but water was left at their disposal.After 48 hours, the rats were again weighed and the solution under investi-gation was fed by stomach tube. Urethral catheters Nos. 4 and 5 werevery satisfactory for this purpose. These catheters soften when they areplunged for a moment into boiling water without making them permeableto liquids. A small mouthpiece served as a protection and a mark indicatedthe depth to which the catheter had to be introduced in order to reach thestomach. As a rule, the rats could be fed without causing excitement orinflicting pain. The only point that sometimes offered resistance was thediaphragmatic portion of the esophagus. If the catheter could not beintroduced beyond this point while the rats were held in a ventral posi-tion, they were turned in a dorsal position and stretched. The catheterslides then easily into the stomach. A hypodermic needle was tightlyfitted into the outside end of the catheter and the fluid was introduced byattaching a syringe to this needle. Preference was given to the Recordtype of syringe which has a metal plunger rather than the all glasssyringes of the Luer type. Generally, between 1.25 to 2.5 cc. of a 25 to80 per cent sugar solution, warmed up to 40°C., were given. Largeramounts of sugar solution of such a high percentage were found dis-advantageous, since they sometimes caused diarrhea. After the fluidwas delivered the catheter with the syringe still attached was quicklywithdrawn from the esophagus. The very small diameter of the catheterprevents the escape of fluid that is still located in it and any liquid thatadheres to the outside of the catheter is wiped off on the wall of theesophagus.

For reasons to be advanced later, it was not found necessary to give aconstant amount of sugar per unit of body weight. This simplified themethod to a great extent and allowed feeding the sugar with a high degreeof accuracy. If each rat had to be given an amount of sugar according to

2 This ration was furnished by Mr. C. Congdon from the Department ofNutritional Research of Park and Pollard Co.


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694 Absorption of Hexoses and Pentoses

weight, one would have to introduce different amounts of sugar solutioninto each rat, which would involve a rather high error in the amounts offluid measured. It is also difficult to set the plunger with the desired de-gree of accuracy at a certain graduation mark of the syringe. This wasavoided by introducing special stops into the syringe against which theplunger could firmly be brought to rest.

On each experimental day a larger number of rats received the sameamount of sugar solution. The amount of sugar thus introduced wasdetermined by delivering into a volumetric flask the same amount of sugarsolution under exactly the same conditions as when the rats were fed.Even if the same sugar solution was used on subsequent days it was foundnecessary to determine anew the amount of sugar delivered. The ratswere killed at hourly intervals after the sugar administration. Any ratsthat showed diarrhea subsequent to the sugar feeding were discarded. Theabdominal cavity was opened and ligatures were placed around the eso-phagus and the rectum. The stomach, small intestine, and the wholelarge intestine were carefully detached from the mesentery and placed in abeaker. The whole intestinal tract was cut open, the instruments usedcarefully rinsed off, and the intestine washed out with successive portions ofhot distilled water. Generally 500 cc. of water were used and the washingsdecanted into a volumetric flask. The interfering substances in theintestinal washings were precipitated with Merck's colloidal iron on theaddition of a small amount of sodium sulfate. The flask was cooled, madeup to the mark, well mixed, and the contents filtered. Aliquot parts ofthe clear filtrate were then taken for analysis but not until almost thewhole amount of fluid had filtered through.

The following control experiments were performed in order to test theaccuracy of the different steps involved in this method.

1. The Determination of the Amount of Sugar Fed to the Rats.-2 cc. of anapproximately 50 per cent glucose solution at 40°C. were drawn up into thesyringe, the syringe attached to the catheter, and the fluid delivered into a1000 cc. volumetric flask. Another 2 cc. were delivered into a second flask.Both flasks were made up to the mark and aliquot parts taken for sugardeterminations. The first flask contained 1.097 gm. glucose, the secondflask 1.10 gin. glucose.

2. The Amount of Sugar Adhering to the Outside of the Catheter afterWithdrawing It from the Esophagus.-After feeding rats with 2.5 cc. of a 50per cent glucose solution, the outside of the withdrawn catheter was care-fully rinsed off. 2.1 mg. glucose were recovered as an average of fourexperiments.

S. The Amount of Sugar Recovered from the Intestine When the Rats WereKilled Immediately after the Sugar Feeding.-Three rats, fasted previouslyfor 48 hours, received 2.5 cc. each of a 50 per cent glucose solution and werekilled immediately. From 99.4 to 99.8 per cent glucose was recovered.

4. The Amount of Reducing Substances Normally Present in the Intestineof Rats That Were Fasted for 48 Hours.-In three experiments, using themicro method of Hagedorn and Jensen, 13.9, 9.0, and 12.7 mg. reducing sub-


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stances were found respectively. This amount, when compared with theamount of sugar fed, seemed so small that it was neglected in the calcula-tions.

5. How Soon after the Sugar Feeding Does Absorption Begin?-Since partof the sugar solution is forced during the injection, into the small intestine,the absorption begins at once. A rat killed 2 minutes after sugar feedingalready showed half of the small intestine filled with sugar solution.

6. Is There Any Loss of Sugar From the Intestine Due to Bacterial Action?-This was determined for each sugar in the following way. Rats fastedfor 48 hours were killed immediately after feeding 2.5 cc. of a 50 per centsugar solution and 2.5 cc. of distilled water. Ligatures were made aroundthe esophagus and the lowest portion of the ileum. The stomach and smallintestine were removed and the contents evenly distributed by gentle mas-sage. After incubating for 3 to 5 hours at 37C., stomach and small in-testine were cut open and the sugar content was determined in the manneralready described. The losses of sugar due to bacterial action were sosmall that they were neglected in the calculations.

The following sugars were used in our experiments.

d-Glucose Merck ........................................ 52.45" Pfanstiehl .................................... 52.5

d-Galactose Kahlbaum ................................. 79.8" Pfanstiehl ................................... 80.0

d-Mannose " .................................. 14.25d-Fructose " ...................................- 91.66l-Arabinose " ................................. 104.5l-Xylose " .................................. 18.5

25, 50, and 80 per cent solutions from glucose and 50 per centsolutions from the other sugars were fed. The sugars were broughtinto solution in distilled water at least 24 hours before they wereused, so that any possible complication due to a displacement ofthe usual a and : equilibrium of the sugars might be avoided.For all sugar determinations Bertrand's method was used. Thepermanganate used for the titration was standardized againstc.p. glucose. For mannose, arabinose, and xylose which are notrecorded in the original Bertrand table, the copper equivalentsfor the range of 10 to 20 mg. sugar were especially determined.For blood sugar Hagedorn and Jensen's (1923) method was used.

THE JOURNAL OF BIOLOGICAL CHEMISTRY, VOL. LXVI, NO. 2


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III.

The Loss of Body Weight of Rats Fastedfor 48 Hours.

The loss of body weight, expressed in per cent of the body weightat the beginning of the fasting period, is recorded in Tables Ito VIII. It was 12.92 per cent as an average of 124 observations,the maximum being 16.02 and the minimum 8.34 per cent. Ratsthat did not show a loss of weight falling within this range wereconsidered abnormal and were not used. The variation in the lossof body weight is in part due to an individual variability of therats, in part to irregular food intake prior to the fasting period,and also to some extent to the uncertainty with which the originalbody weight of the rats can be determined. Rats which are notfasted may change their weight by 1 to 2 gm. in the course of avery short time by the loss of feces and urine. All calculationswere based on the weight of the rats after fasting for 48 hours.

IV.

The Relation of the Absorbing Surface of the Intestine to the BodyWeight.

The amount of a given substance that is absorbed should beproportional to the absorbing surface of the intestinal tract.Since the surface of the intestine will vary with the body weight,larger animals will have a greater intestinal surface and willabsorb more than smaller ones. In order to use animals of differ-ent weight one would have to show that the absorbing surface isstrictly proportional to the body weight or in other words that the

intestinal surface amount absorbed is a constant.quotient or is a constant.body weight body weight

Our experiments reveal that within the range of body weightsinvestigated, namely between 100 and 180 gm., both sexes show aproportionality between the amount absorbed and hence betweenintestinal surface and body weight. An example taken fromTable II might illustrate this. A female rat weighing 117.7

0.219 X 100gm. absorbed in 1 hour 0.219 gm. glucose or 117 = 0.186

117.7gm. glucose per 100 gm. of body weight. A male rat weighing

0.320 X 100 173.7 gn. absorbed in 1 hour 0.320 gm. glucose or 1

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0.184 gm. glucose per 100 gin. of body weight. It should be notedthat this proportionality between the amount absorbed and thebody weight was found in rats that were still in a period of activegrowth. It may not be valid for fully grown rats, where varia-tions in the fat depots and other factors might play a r61le.

v.

The Absorption Coefficient.

On the basis of the preceding section the mathematical expPes-sion of intestinal absorption is very simple. The absorptioncoefficient (C) is the amount of substance absorbed per 100 gm.of body weight in 1 hour and can be represented by the followingformula.

A X 100 ()WXT

where A is the total amount of substance absorbed in a givenperiod, W the weight of the rat after fasting for 48 hours and Tthe length of the period in hours.

TABLE I.

The Absorption of 25 Per cent Glucose Solution.

Glucose absorbedper 100gm. of body weight

in 1 hr.(Absorption coefficient.)

gm.

0.172 (max. 0.203)(min. 0.152)

Remarks.

Absorption period 1 hour.Average of six rats.

Loss oforiginal

bodyweight

in 48 hrs.

per cent

13.24

Bloodsugar.

per cent

0.162

Glucosefed per100 gm.of bodyweight.

gm.

0.399


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TABLE II.

The Absorption of 50 Per Cent Glucose Solution.The amount of fluid introduced was 2.5 cc., with the exception of two

rats marked with an asterisk, which received 1.25 cc.

Glucose ab-Loss Glucose fed Total sorbed per

Bodyweight of original Blood per 100gm. amountof 100 gm.in ofSex. after fasting body weight sugar. boy glucose bOdy eight

48hrs. in48 hrs. arbdody absorbed.weight. (Absorption

coefficient.)

Absorption period 1 hr.

gm. per cent per cent gm. gm. gm.

M. 169.5 13.16 0.204 0.649 0.334 0.197"4 170.2 13.38 0.171 0.646 0.330 0.194"4 173.7 12.53 0.168 0.659 0.320 0.184II 151.8 13.15 0.170 0.754 0.298 0.196it 160.1 11.87 0.195 0.715 0.311 0.194"t 118.1 13.28 0.168 0.442* 0.241 0.204F. 148.9 14.52 0.186 0.772 0.316 0.212"t 117.7 0.149 0.469* 0.219 0.186

Average......... 13.12 0.176 0.638 0.196

Absorption period 2 hrs.

M. 157.8 12.81 0.177 0.713 0.478 0.151"1 155.0 14.78 0.240 0.726 0.546 0.176

159.4 12.00 0.261 0.706 0.450 0.141149.6 12.76 0.219 0.715 0.540 0.180158.2 12.05 0.213 0.676 0.431 0.136155.2 12.01 0.214 0.747 0.568 0.183

Average......... 12.73 0.220 0.713 0.161

Absorption period 3 hrs.

M. 137.5 13.19 0.226 0.834 0.744 0.180" 144.8 13.24 0.233 0.801 0.692 0.159" 158.8 16.02 0.231 0.705 1.010 0.212" 144.6 14.43 0.255 0.774 0.760 0.180"' 152.7 12.14 0.193 0.733 0.734 0.160

Average......... 13.80 0.227 0.769 0.178

Average of 1, 2, and 3 hr. absorption periods .................. 0.178


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Carl F. Cori

TABLE III.

The Absorption of 80 Per Cent Glucose Solution.

Loss oforiginal

bodyweight

in 48 hrs.

per cent

11.57

12.35

11.15

12.62

13.92

Bloodsugar.

per cent

0.157

0.187

0.167

0.162

0.201

Glucosefed per100 gm.of bodyweight.

gm.

0.819

1.082

1.253

1.323

1.459

Average of 1, 2, 3,4, and 5 hr. ab-sorption periods..

Glucose absorbedper 100 gm. of body weight

in I hr.(Absorption coefficient.)

gm.

0.143 (max. 0.183)(min. 0.126)

0.159 (max. 0.214)(min. 0. 131)

0.153 (max. 0.180)(min. 0.122)

0.171 (max. 0.219)(min. 0.134)

0. 184 (max. 0.203)(min. 0.170)

0.162

Remarks.

Absorption period 1 hr.Average of seven rats.

Absorption period 2 hrs.Average of six rats.

Absorption period 3 hrs.Average of five rats.



TABLE IV.

The Absorption of 50 Per Cent Galactose Solution.

Loss of GalatoseLoss of Galatose Galatose absorbedoriginal Blood fed per

body Blood 100 per 100 gm. of body weight Remarks.body S 00 gm. in 1 hr.

in 48 hrs. weight.in 48 hrs . weight' .(Absorption coefficient.)

per cent per cent gm. gna.

14.30 0.298 0.791 0.220 (max. 0.247) Absorption period 1 hr.(min. 0. 190) Average of five rats.

14.51 0.325 0.905 0.186 (max. 0.201) Absorption period 2 hrs.(min. 0.172) Average of four rats.

12.32 0.361 0.946 0.184 (max. 0.196) Absorption period 3 hrs.(min. 0.177) Average of five rats.

Average of 1, 2, and3 hr. absorptionperiods ........... 0.196

699

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TABLE V.

The Absorption of 60 Per Cent Fructose Solution.

Loss oforiginal

bodyweight

in48 hrs.

per cent

12.18

12.56

11.82

12.46

13.43

Bloodsugar.

per cent

0.144

0.130

0.150

0.177

0.176

Fructosefed per100 gm.of bodyweight.

gm.

0.716

0.485

0.583

0.601

0.708

Average of 1, 2, 3,4, and 5 hr. ab-sorption periods..

Fructose absorbedper 100 gmin. of body weight

in 1 hr.(Absorption coefficient.)

gm.

0.075 (max. 0.096)(min. 0.059)

0.073 (max. 0 090)(min. 0.063)

0.079 (max. 0.097)(min. 0.063)

0.077 (max. 0.091)(min. 0.065)

0.080 (max. 0.087)(min. 0.071)

0.077

Remarks.

Absorption period 1 hr.Average of five rats.

Absorption period 2 hrs.Average of four rats.




TABLE VI.

The Absorption of 50 Per Cent Mannose Solution.

Loss of Mannose Mannoseabsorbedoriginal Blood fed per per 100 gm. of body weight Remarks.body 100 gm. Remarks.weight sugar. in 1 hr.

n egoftbody (Absorption coefficient.)in 48 hrs. weight.

per cent per cent ginm. gin.

13.66 0.106 0.851 0.033 (max. 0.036) Absorption period 1 hr.(min. 0.028) Average of thiee rats.


11.78 0.099 0.581 0.037 (max. 0.041) Absorption period 3 hrs.(min. 0.031) Average of three rats.


12.83 0.112 0.538 0.036 (max. 0.038) Absorption period 5 hrs.(min. 0.034) Average of two rats.

Average of 1, 2, 3,4, and 5 hr. ab-sorption periods.. 0.034

700

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TABLE VII.

The Absorption of 50 Per Cent Xylose Solution.

Loss of Xylose Xylose absorbedoriginal Blood fedper per 100 gm. of body weight Remarks.

body 100 g . in 1 hr.weight s,,ar. ofbody (Absorption coefficient.)

in 48 hrs. weight.

per cent per cent ginm. gm.

12.04 0.125 0.411 0.062 (max. 0.074) Absorption period 1 hr.(min. 0.055) Average of six rats.





Average of 2, 3,4, and 5 hr. ab-sorption periods. . 0.028

TABLE VIII.

The Absorption of 50 Per Cent Arabinose Solution.

Loss of Arabi-iLoss nose Arabi nose absorbedoriginal Blood fed per per 100 gm. of body weight remarks.

body Remarks.wei ht sugar. 100 gin. in 1 hr.of body (Absorption coefficient.)

in 48 . weight.

per cent per cent gm. gm.

14.13 0.095 0.509 0.016 (max. 0.022) Absorption period 2 hrs.(min. 0.012) Average of eight rats.

VI.

The Graphic Representation of the Rate of Absorption of Sugars.

When the amount of sugar that is absorbed per 100 gm. of bodyweight is plotted against time, a straight line is obtained, as isillustrated in Fig. 1. The observations show a maximal deviationfrom the straight lines of 4- 10 per cent, which is as close an


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agreement as can be expected from a biological method such as theone used for this work. Fig. 1 serves also as an illustration of therate of absorption of the different sugars. The more the straightlines are slanting to the right, the slower is the rate of absorptionand vice versa.

Arabinose has not been included in this figure, because notenough data for a graphic representation could be secured. This

250

I I I I I 1 ' I I I .i TeI

i 2. 3 4 5 ,aGa/actose

......... ....... Fructose . .._ . MannoseFroIG. 1. Graphic representation of the rate of absorption of hexoses.

The figures for the absorption coefficients in Tables II and IV to VI havebeen used for the construction of the straight lines.

sugar is absorbed so slowly that when the absorption is allowedto proceed over 2 hours, diarrhea developes in the majority ofthe rats. Xylose, on the other hand, differs from the rest of thesugars investigated since much more is absorbed in the 1st hourthan in the following hours (see Table VII). From the 2nd to5th hour the absorption of xylose follows a straight line in ac-

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150

100

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I411, �- - I � I I I I I I i I i 1i 1 ' i I I I 1 1


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Carl F. Cori 703

cordance with the other sugars. The reason for the higher rateof absorption in the 1st hour needs further investigation.

The fact that the absorption of sugar follows a straight linemeans that in 2 hours twice as much sugar is absorbed as in 1hour and in 3 hours three times as much as in 1 hour and so on;in other words, the absorption proceeds at a constant rate. Theamount and also the concentration of the sugar originally intro-duced into the intestine diminishes more and more the longer theabsorption is allowed to proceed. Does this finally lead to a de-crease of the rate of absorption? Or how far may the sugar pre-sent in the intestine diminish without causing a decrease in therate of absorption? The straight lines in Fig. 1, with the exceptionof that of mannose, extend to a point where about 60 to 70 percent of the sugar originally introduced has been absorbed. Acalculation made from Table II may illustrate this for glucose.In the 3 hour period, as an average, 0.769 gm. glucose was fed and0.534 ginm. glucose was absorbed per 100 gm. of body weight. Thedifference between these two values, namely 0.235 gm. glucose,represents the amount of glucose that was still present'in theintestine at the end of the 3 hour period. Up to this point, orwhen 69.5 per cent of the sugar originally introduced was absorbed,the rate of absorption had not diminished as can be seen from acomparison of the average absorption coefficient of this periodwith that of the preceding period. If individual experiments ofthe 3 hour period of Table II are examined one finds still smalleramounts of sugar remaining in the intestine, without a diminutionof the rate of absorption. The third rat, for instance, received 0.705gm. glucose and absorbed 0.636 gm. glucose per 100 gm. of thebody weight. This corresponds to an absorption of 90.2 per centof the glucose originally introduced. In spite of the fact that only69 mg. glucose remained in the intestine of this rat, the rate ofabsorption had not diminished as can be seen from the absorptioncoefficient. Similar calculations can be made from Tables IVand V for galactose and fructose. It can, therefore, be concludedthat these sugars and probably also the other sugars investigatedare absorbed up to the point of their complete disappearance fromthe intestine at a constant rate. From this it follows that therate of absorption must be independent of both the absoluteamount and the concentration of sugar present in the intestine,


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which means that neither an increase nor a decrease of these twofactors can change the rate of absorption, or that there is only onerate of absorption for each particular sugar. These conclusionsare the logical consequence of the fact that the absorption of sugarfollows a straight line. Other experimental evidence points inthe same direction.

If in Tables I to VIII, 3 the amounts of sugar given per 100 gm.of body weight are compared with the absorption coefficients itwill be noted that the rate of absorption is independent of theabsolute amount of sugar fed. An example from Table III mayserve as an illustration. Thus a rat weighing 174.4 gm. received0.496 gm. glucose per 100 gm. of body weight and absorbed 0.130gm. glucose per 100 gm. of body weight per hour. Another ratalso weighing 174.4 gm. received 1.037 gm. glucose per 100 gm.of body weight or twice as much and absorbed 0.126 gm. glucoseper 100 gm. of body weight per hour. This means that the rateof absorption cannot be increased by increasing the amount ofsugar fed. This example serves also as an illustration that therate of absorption is within certain limits independent of theabsolute amount of fluid introduced, since the first rat received1.25 cc. of an 80 per cent glucose solution, while the second ratreceived 2.5 cc. of an 80 per cent glucose solution.

The sugar solution does not maintain its original concentrationwhen it is introduced into the alimentary canal of the rats. Evenin the stomach a dilution mechanism sets in and a further diminu-tion of the sugar concentration occurs in the small intestine.Since the rate of absorption is independent of the constant dimi-nution of the sugar concentration that is taking place during ab-sorption, it should also be independent of the sugar concentrationoriginally introduced. This has been tested experimentally forglucose solutions ranging from 25 to 80 per cent. The data aresummarized in Table IX.

The average figures of Table IX agree within the limits of errorof the method and are considered as additional evidence that therate of absorption of sugar is independent of the actual sugarconcentration in the intestine. The experiments recorded in Table

3 Due to lack of space Tables I and III to VIII had to be represented in a,condensed form. For this reason the figures for the example given belowswill not be found in the tables referred to.

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IX were also undertaken in order to see which sugar concentrationwould be best suited for a comparative study of the rate of ab-sorption of different sugars. If the absorption coefficients of the1 hour period in Table IX are compared with each other it willbe noted that less sugar is absorbed from the 80 per cent solutionthan from the 25 and 50 per cent solution. This anomaly maybe due to the high viscosity of the 80 per cent solution, sincemore sugar is absorbed in the subsequent periods where a dilutionand consequently a decrease in the viscosity has occurred. The50 per cent solution has the advantage over the 25 per cent solu-tion that enough sugar can be introduced to let the absorptionproceed for at least 3 hours. Absorption periods of severalhours are desirable for a graphic representation. In order to usethe 25 per cent solution one would have to introduce too largevolumes of fluid, which are apt to cause diarrhea. For thesereasons a 50 per cent sugar solution has been chosen for comparative studies.

TABLE IX.

The Influence of a 25, 50, and 80 Per Cent Glucose Solution on the Rate ofAbsorption (see Tables I, II, and 11l).

Length of absorption Absorption coefficients for glucose solutionlls of:period.

25 per cent. 50 per cent. 80 per cent.

hrs.

1 0.172 0.196 0.1432 0.161 0.1593 0.178 0.1534 0.1715 0.184

Average ........ 0. 172 0.178 0.162

VII.

The Comparison of the Rate of Absorption of Hexoses and Pentoses.

Table X contains the average absorption coefficients of thedifferent sugars investigated. The most important factor thatdetermines the rate of absorption of a particular sugar seems tobe the structure of its molecule. A relatively slight change in thesugar molecule affects the rate of absorption very markedly.


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The keto-sugar fructose is absorbed with a rate less than one-halfof that of glucose. A stereoisomeric change from glucose to man-nose reduces the rate of absorption to one-fifth. The pentoses areabsorbed at still slower rates. All this indicates that the intestinalmembrane is possessed of a high degree of selective permeabilityfor sugars.

TABLE X.

Comparison of the Rate of Absorption of 60 Per Cent Solution of Hexoses andPentoses.

Average RatioAverageType of sugar. blood sugar. abscoefrficient (glucose 100).

per cent ginm.

d-Galactose ...................... 0.328 0.196 110d-Glucose .......................... 0.207 0.178 100d-Fructose ................... 0.... 0.155 0.077 43d-Mannose ........................ .106 0.034 19I-Xylose ......................... 0.125 0.028 15I-Arabinose ...................... 0.095 0.016 9

VIII.

The Dilution Mechanism in the Stomach and Intestine and the WaterContent of Blood and Tissues during the Absorption of a

Hypertonic Sugar Solution.

It was noted that the rats showed a greatly distended stomach,when examined 1 to 3 hours after sugar feeding. This suggestedthat in the stomach water was attracted by the hypertonic solu-tion. An examination of the sugar concentration in the stomachin different time intervals after giving 2.5 cc. of an 80 per centglucose solution showed:

Hrs....................... 0 1 2 3 4Per cent.....73.2 38.0 30.9 24.5 14.3

Since the stomach does not have a very marked absorbing capacityfor sugar, the diminution of the sugar concentration in the stomachis mainly due to the excretion of water.

The sugar concentration in the duodenum and jejunum isalways lower than in the stomach and falls off more and more inthe lower parts of the small intestine. A rat weighing 191.6 gm.,


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Carl F. Cori 707

with a total length of the small intestine of 87 cm., showed thefollowing sugar concentrations 3 hours after giving 2.5 cc. of an80 per cent glucose solution. Stomach, 25.0 per cent; smallintestine, 0 to 33 cm., 14.2 per cent; small intestine, 33 to 50 cm.,almost empty; small intestine 50 to 87 cm., 2.65 per cent. Thetotal amount of fluid recovered from stomach and small intestinewas 5.1 cc. The diminution of the sugar concentration in the smallintestine is partly due to the absorption of sugar, partly to thesecretion of water and it is difficult to separate both factors. Itis said that in the upper part of the small intestine relatively moresugar is absorbed than water, while the opposite is true in the lowerpart of the small intestine. This point has not been investigatedin connection with our experiments.

TABLE XI.

The Effect of the Absorption of a Hypertonic Glucose Solution on the WaterContent of the Organs and the Blood.

The rats, fasted previously for 48 hours, were killed in hourly intervalsafter giving 2.5 cc. of an 80 per cent glucose solution. The values of eachperiod are an average of several experiments.

Water content of:

Blood.

per cent

78.21

77.2378.4778.7778.2878.47

Muscle.

per cent

75.48

Liver.

per cent

69.26

74.90 70.0674.45 69.9574.69 70.5574.04 70.0974.53 69.80

Skin.

per cent

53.31

45.5846.9546.2445.9845.05

It seemed of importance to know if the high sugar concentra-tions that were given to the rats caused any unphysiological con-ditions. The animals did not show signs of distress subsequentto the sugar feeding nor did the blood sugar rise abnormally high.However, there might have been an excessive dehydration ofblood and tissues due to the secretion of water into the intestine.This would have been undoubtedly a serious disturbance. Forthese reasons the water content of the blood, liver, muscle, andskin has been examined in different time intervals after the sugar

Length ofabsorption

period.

hrs.

0(Controls.)

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feeding. The tissues were dried for 1 week at 97C. in a constanttemperature oven. The weighing bottles were then stopperedand allowed to cool in a CaC12 desiccator. Table XI shows theresult of this examination. With the exception of the skin nosignificant changes occurred in the water content of the othertissues and of the blood. The skin serves as the principal waterdepot of the organism, while the vital organs are apparently pro-tected against dehydration. During the absorption of a hyper-tonic sugar solution from the intestine, water is constantly with-drawn from the blood. Since the water content of the blood didnot diminish, the mechanism of release of water from the skinmust be very accurately adjusted and must be set in motion veryrapidly. It may be concluded that the use of sugar solutions ofhigh concentrations for absorption work does not result in ab-normal conditions.

IX.

The Sugar and Nitrogen Excretion in the Urine, the Blood SugarConcentration, and the Relation of the Absorption of Sugar from

the Intestine to the Disposal of Sugar in the Tissues.

Table XII shows that a negligible amount of glucose is excretedin the urine, even if as much as 15 gm. per kilo are fed. Theexcretion, after the subtraction of the amount of reducing sub-stances normally eliminated in the urine, amounts to 1 mg. ofsugar per 100 gm. of body weight per hour. The nitrogen ex-cretion of the sugar-fed rats is lower than that of the fastingcontrols, which corresponds to the well known sparing action ofcarbohydrate ingestion on the protein metabolism. Whetherthe small amount of reducing substances eliminated in the urineof fasting rats is actually sugar has not been determined.

The blood sugar concentration during absorption is dependenton three factors: the rate of absorption of sugar from the intes-tine; the rate of disposal of sugar in the tissues; the amount ofsugar excreted in the urine. The relation between the blood sugarconcentration and the rate of absorption of different sugars isshown in Table X. The slower the rate of absorption, the loweris the blood sugar concentration and vice versa. If the first and


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Carl F. Cori 709

the last factor are known an insight is gained into the rate of dis-posal of sugar in the tissues. The first factor can be considered asconstant, since the rate of absorption proceeds as a straight lineand since it is independent of the total amount and concentrationof sugar present in the intestine. The excretion in the urine ofother sugars than glucose has not been extensively enough studied.For glucose one can conclude that under the conditions of ourexperiments the rate of disposal in the tissues is parallel to the rateof absorption, since practically no sugar is excreted in the urineand since the blood sugar does not rise very high. The free sugar

TABLE XII.

The sugar and nitrogen excretion in the urine after giving:(a) 2.5 cc. of water (controls).(b) 2.5 cc. of an 80 per cent glucose solution (sugar-fed rats).(c) The same as (b) plus 20 units of insulin subcutaneously (sugar-fed

and insulinized rats).All experiments were performed on the same group of rats. The animals

were fasted for 48 hours previously. The analyses were made on the com-bined urine of the animals used for each experiment.

Nitrogen SugarGlucose excreted excreted

f Combined Length of fed per per 100 per 100r.No body absorption 100 gi. gm. of gin. of Remarks.rats. weight. period. of body body body

weight. weight in weight inl hr. 1 hr.

gm. hrs. ginm. mng. mg.

9 1212 5 2.45 0.32 Controls.6 872 5 1.471 2.33 1 36 Sugar-fed rats.8 1162 5 1.498 2.31 0.71 Sugar-fed and insulin-

ized rats.

concentration in the tissues is dependent on the blood sugar con-centration. If the blood sugar would rise abnormally high, partof the glucose could be held by the tissues as such without beingmetabolized. At blood sugar concentrations such as were ob-served during the absorption of glucose, a retention of sugar in thefree state by the tissues plays a minor role, so that all the glucosethat is absorbed in a given period is also metabolized in that period.If the rate of disposal in the tissues would fall even slightly belowthe rate of absorption the blood sugar would rise, as can be seenfrom the following calculation. If we assume that the blood


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volume of a rat weighing 100 gm. is 7 cc. and if we assume ablood sugar of 0.1 per cent, 7 mg. sugar would be held by theblood. During 1 hour 178 mg. glucose or twenty-five times asmuch enter the blood from the intestine and have also to leavethe blood if the blood sugar concentration is to remain the same.If in 1 hour, 7 mg. less glucose would be metabolized than are ab-sorbed, the blood sugar would rise to 0.2 per cent. If this wouldgo on for another hour, the blood sugar would rise to 0.3 per centand so forth, not considering the sugar excretion in the urine. If,however, the rate of disposal of glucose in the tissues is parallelto the rate of absorption, the blood sugar values of successiveabsorption periods should remain the same. In Table III, theabsorption was allowed to proceed for 5 hours. The average bloodsugar at the end of the 1st hour was 0.157 per cent, at the end ofthe 5th hour 0.201 per cent, which is an insignificant change onthe basis of the calculation just given.

x.

DISCUSSION.

An outline of an investigation of the fate of sugar in the animalorganism has been given in the introduction. The object of theexperiments recorded in this paper was to study the intestinalabsorption of sugars, particularly that of glucose, on a quantita-tive basis. For this purpose a method has been worked out, whichallowed us to measure and express absorption in terms of unit ofbody weight and unit of time. One result of the use of this methodwas that the absorption of hexoses was found to follow a straightline. What can be learned from this fact in regard to the mech-anism of absorption in general it would be too early to discuss,since it has not been investigated as to whether or not othernon-electrolytes show the same behavior as sugars. Nor has theabsorption of lipoid-soluble substances and of electrolytes beenstudied with this method. The results of previous investigatorsare not strictly comparable, since they are based on observationson isolated parts of the intestine. The study of absorption bythe whole intestinal tract as a physiological unity and the pos-sibility of constructing definite absorption curves for each sub-stance may give results differing in many respects. For thesereasons it seemed advisable to postpone a discussion of the

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Carl F. Cori 711

mechanism of absorption until these experiments have beenperformed.

Another result was that stereoisomeric sugars were found to beabsorbed at different rates from the intestine. This is a confirma-tion of data to be found in the literature. Nagano (1902) usedfour dogs with a Vella fistula of the small intestine of 18 to 27 cm.in length. 30 cc. of 1 to 7.5 per cent sugar solutions were intro-duced and allowed to remain in contact with the intestine for 1hour. On Dog 1 all sugars were tested in succession. The fol-lowing order in the rate of absorption was found: galactose>glucose > fructose > mannose > xylose > arabinose. Similar resultswere obtained on the other dogs on which only some of the sugarsjust mentioned were tested. Hewitt (1924) made experiments onrabbits and cats. Approximately 2 per cent solutions of glucose,fructose, and galactose were used. In the series with rabbitsether narcosis was applied. The author mentions that the experi-ments were not strictly comparable since varying lengths of in-testine were isolated in the different animals and since the sugarswere apparently not tested in succession on the same intestinalloop. He merely draws the conclusion that glucose is more readilyabsorbed than fructose. In the series with cats more stringentexperimental conditions were attained. The animals were pithedin deep ether narcosis, artificial respiration was started, and theapplication of the anesthetic discontinued. Two or all threesugars were tested in succession on the same intestinal loop andthe order of introduction of the sugars was changed in the differ-ent animals. The absorption time was 10 minutes. Five experi-ments are recorded. Galactose was absorbed at about half therate of that of glucose, fructose at a still smaller rate. In ourexperiments and in those of Nagano galactose was absorbed at aslightly greater rate than glucose and this was also the case inobservations of Hoeber (1899) on dogs and H6don (1900) on rab-bits. It is possible that the results of Hewitt as regards galactosewere due to the different species used. On the other hand it isinteresting to note that our experiments on rats, with ten timesmore concentrated sugar solutions, gave the same order in therate of absorption of the different sugars as those of Nagano ondogs.

These results offer another striking example of the selectivepermeability of living membranes and in this connection reference


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might be made to the work of Hamburger (1922) on the perfusedfrog kidney. He showed that of the isomeric sugars some areretained by the glomerular membrane, 4 while others are allowed topass unhindered into the urine. Still more remarkable is the factthat the glomerular membrane is sensitive to such insignificantchanges in the sugar molecule as are represented by the a and3 modifications. From d-galactose and l-xylose only the a formis retained while the P form is completely excreted in the urine.Hamburger on the basis of the well known scheme of Clowes ofthe transformation of an oil in water into a water in oil emulsionbelieves that the sieve theory is an adequate explanation for theselective permeability of the glomerular membrane.

Since equal amounts of sugar pass from the intestine into theblood stream in equal periods of time, the absorption is compar-able with a continuous intravenous infusion at a constant rate.Woodyatt, Sansum, and Wilder (1915) determined the sugartolerance of normal rabbits, dogs, and men by the continuousintravenous infusion method. They found that if glucose wasinfused at a rate of 0.85 gm. per kilo of body weight, per hour, noglycosuria was produced, even if the infusion was extended overmany hours. This is a much lower tolerance than was observedon rats during intestinal absorption. These animals after a 48hour fast absorb 1.78 gm. glucose per kilo per hour over long periodswithout showing glycosuria. This value would be reduced to 1.54gm. per kilo per hour if the original body weight is taken as a basis.It could be objected that the rats showed no glycosuria on accountof their depleted glycogen stores. This might have increased theircapacity to assimilate glucose. However, in control experimentson non-fasting rats the same amount of glucose could be givenwithout causing sugar excretion in the urine. There is also noreason to believe that rats that have not been fasted absorb glu-cose at a slower rate than fasted animals. It would seem, there-

4 In the light of recent work on the physiology of the kidney it seems moreprobable that the selective permeability of the kidney is due to a selectivereabsorption in the tubular apparatus rather than to a selective filtrationthrough the glomerular membrane. It seems of interest in this connectionthat in recent experiments the rate of absorption of different hexoses andpentoses from the peritoneal cavity was found to be identical (Cori andGoltz, 1925, b).


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Carl F. Cori 713

fore, that the glucose tolerance when tested by the intestinal routeis higher than when tested by the intravenous route. This dis-crepancy could be explained by assuming that the rat has a higherglucose tolerance than rabbit, dog, or man. Yet Sansum andWoodyatt (1917) in recalculating the data of Fisher and Wishart(1912-13) found that dogs absorb between 1.6 to 1.7 gm. glucoseper kilo per hour, a value which approaches closely that found inour experiments on rats. A still greater discrepancy between thetolerance when measured by the intestinal and the intravenousroute exists for fructose. The intravenous tolerance limit for thissugar, as determined by Woodyatt, was 0.15 gm. per kilo per hour.The rats absorbed this sugar at a rate of 0.77 gm. per kilo perhour or 0.67 gm. per kilo per hour if the original body weight istaken as basis. Fructose was not excreted in the urine. Thetolerance by the intestinal route was therefore four to five timeshigher than by the intravenous route. Since it could again beobjected that the results obtained on different species are notstrictly comparable, it is proposed to determine the intravenoustolerance limit for glucose and fructose on rats.5 There arenumerous experiments on record which were taken as evidencethat fructose is better tolerated and better utilized than glu-cose. Fructose has also been given on that assumption to dia-betic patients. The literature on this subject has recently beensummarized by Isaac (1920). The apparently better utilizationof fructose than glucose has been deducted from a comparison ofthe blood sugar curves and the sugar excretion in the urine fol-lowing the ingestion of these sugars by the same patient. How-ever, the fact that fructose is absorbed at a much slower rate thanglucose has not been taken into consideration in these experimentsand the results might equally well be explained on that basis.

Woodyatt found an intravenous tolerance limit for galactoseof about 0.1 gm. per kilo per hour. The rats absorbed this sugarat a rate of 1.96 gm. per kilo per hour or 1.69 gm. per kilo perhour, if based on the original body weight. In several experi-ments close to 50 per cent of the total amount of galactoseabsorbed was eliminated in the urine. Experiments are in prog-ress to elucidate this observation further.J

5 Since the above has been written the intravenous tolerance of rats wasfound to be between 2.2 and 2.5 gm. glucose per kilo per hour (Cori, 1925).


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XI.

SUMMARY.

1. A method for the quantitative study of absorption by thewhole intestinal tract has been described. The amount of sub-stance absorbed per unit of body weight per hour of time has beencalled absorption coefficient.

2. A proportionality between the absorbing surface of theintestine and the body weight has been demonstrated for growingmale and female rats.

3. 50 per cent solutions of hexoses (glucose, galactose, fructose,and mannose) are absorbed from the intestine at a rate which isconstant for each sugar. Even after the absorption of 70 per centof the sugar originally introduced the rate of absorption is notdiminished. Hence the rate of absorption of hexoses is independ-ent of the absolute amount and also of the concentration of sugarpresent in the intestine. If the amount of sugar absorbed isplotted against time a straight line is obtained (see Fig. 1).

4. 25, 50, and 80 per cent glucose solutions are absorbed at thesame rate, which is considered as additional evidence that therate of absorption is independent of the sugar concentrationpresent in the intestine.

5. The following order in the rate of absorption has been found:galactose > glucose > fructose > mannose > xylose > arabinose.The selective permeability of the intestinal membrane for stereo-isomeric sugars has been emphasized.

6. It has been shown that a hypertonic sugar solution is dilutedin the stomach by the excretion of water.

7. The water content of the blood, liver, and muscle is notchanged during the absorption of a hypertonic sugar solution,showing that the vital organs are protected against dehydration,whereas the skin shows a marked diminution in the water content.

8. Glucose, when fed to rats in as large amounts as 15 gm. perkilo does not lead to a sugar excretion in the urine. From galac-tose close to 50 per cent of the total amount absorbed is eliminatedin the urine.

Acknowledgment is due to Miss Hilda L. Goltz for valuable as-sistance in this work.

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Carl F. Cori 715

BIBLIOGRAPHY.

Cori, C. F., Proc. Soc. Exp. Biol. and Med., 1925, xxiii, 127.Cori, C. F., and Goltz, H. L., Proc. Soc. Ep. Biol. and Med., 1925, a,

xxiii, 124.Cori, C. F., and Goltz, H. L., Proc. Soc. Exp. Biol. and Med., 1925, b,

xxiii, 122.Fisher, G., and Wishart, M. B., J. Biol. Chem., 1912-13, xiii, 49.Hagedorn, H. C., and Jensen, B. N., Biochem. Z., 1923, cxxxv, 46.Hamburger, H. J., Biochem. Z., 1922, cxxviii, 185, 207.Hdon, E., Compt. rend. Soc. biol., 1900, ii, 41.Hewitt, J. A., Biochem. J., 1924, xviii, 161.Hoeber, R., Arch. ges. Physiol., 1899, lxxiv, 246.Isaac, S., Med. Klin., 1920, xvi, 1207.Nagano, J., Arch. ges. Physiol., 1902, xc, 389.Sansum, W. D., and Woodyatt, R. T., J. Biol. Chem., 1917, xxx, 155.Woodyatt, R. T., Sansum, W. D., and Wilder, R. M., J. Am. Med. Assn.,

1915, lxv, 2067.


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Carl F. CoriINTESTINAL TRACT

HEXOSES AND PENTOSES FROM THEBODY: I. THE RATE OF ABSORPTION OF

THE FATE OF SUGAR IN THE ANIMAL

1925, 66:691-715.J. Biol. Chem.

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