The effect of nicotine on the

coronary circulation of dogs

Gordon Ross* Marta I. Bless*”

Los Angeles, Cc&f.

A lthough the effects of nicotine on coro- nary blood flow have been exten-

sively investigated, most of the studies have been concerned with average flow deter- minations and with coronary venous out- flow rather than coronary arterial inflow. The present study reports the action of nicotine on instantaneous coronary arterial flow in anesthetized dogs. Instantaneous coronary flow measurements provide much more information than average flow and permit a better assessment of some of the important determinants of coronary flow which might be altered by the drug, e.g., extravascular compression, relative dura- tion of systole and diastole, and end-dia- stolic vascular resistance.‘v2 In order to avoid the complex systemic actions of nicotine, injections were made directly into the coro- nary arterial system in doses insufficient to produce systemic responses. Because of the reported liberation of catecholamines in the heart by nicotine3 the effects of this drug were examined before and after the induc- tion of beta-adrenergic blockade with propranolol.

venous pentobarbital sodium, 40 mg. per kilogram, and intubated. The chest was opened in the fifth left intercostal space, while ventilation was maintained with a Bird Mark 8 respirator. After incising the pericardium, the anterior descending branch of the left coronary artery was care- fully dissected over a distance of approxi- mately 1 cm. and a noncannulating flow probe was placed on the vessel. Flow was determined by means of a Biotronex BL-610 flowmeter. The zero reference point was frequently determined during each experiment by mechanically occluding the vessel distal to its probe. Calibration was performed by placing the probe on a branch of the femoral artery and withdrawing a known amount of blood from this vessel at rates from 5 to 80 ml. per minute with a Harvard infusion-withdrawal pump.

Aortic pressure was determined with a Statham P23Db transducer via a polyethyl- ene tube (PE200) approximately twelve artery inches long inserted into the carotid and advanced into the arch of the aorta. The frequency response of both the flow and pressure measuring systems was 25 Hz (-3 db). Methods

A total of ten dogs weighing 10 to 18 Drugs were injected directly into the kilograms were anesthetized with intra- coronary artery through an indwelling 30

From the Department of Physiology, U.C.L.A. School of Medicine, Los Angeles, Calif. 90024. This study was aided by a grant from the American Medical Association Education and Research Foundation. Received for publication April 8, 1969. *This work was done during the tenure of an Established Investigatorship of the American Heart Association. Reprint

requests to: Dr. Gordon Ross, Department of Physiology. U.C.L.A. School of Medicine, Los Angeles. Calif. 90024. **Postdoctoral Trainee supported by United States Public Health Service Training Grant No. 5 T I HE 5696.

96 American Heart Journal Jattltary, 1970 Vol. 79, Vo. 1, pp. 96-102

Effect of nicotine on coronary circulation 97

gauge needle connected by polyethylene tubing to a microsyringe. The presence of this needle had no effect on either mean or instantaneous flow. Supplementary anes- thetic and pharmacologic blocking agents were injected through a catheter in the jugular vein.

A Walton-Brodie strain-gauge arch was sutured on a portion of myocardium within the area of distribution of the anterior descending coronary artery so that changes in contractile force produced by nicotine could be determined at the same time as the coronary flow changes. In two dogs an additional strain gauge was placed in a zone of myocardium in the distribution of the anterior descending coronary artery, but upstream from the point of injection of the drug.

The parameters measured were regis- tered on a Beckman S II Dynograph re- corder. The drugs used were: norepineph- rine bitartrate, (Levophed, Winthrop), nic- otine acid tartrate (K and K Laboratories), propranolol hydrochloride (Ayerst Labora- tories, Inc.), and pentolinium tartrate (Wyeth). Doses are referred to in terms of salt except for norepinephrine which is referred to in terms of base.

Diastolic and systolic coronary blood flow were calculated by planimetry of the appropriate area under the flow curve. Diastole was considered to start with the inflection in the flow trace coincident with the closure of the aortic valves and marked by the incisura of the aortic pressure record. Systole was considered to begin with the onset of coronary flow deceleration immedi- ately preceding the systolic upstroke of the pressure curve. All measurements were averaged over three cycles.

Results

The mean control values and the stan- dard deviations for coronary flow, arterial pressure and heart rate in the ten dogs were as follows:

Systolic arterial pressure Diastolic arterial pressure Heart rate

Duration of “systole” Duration of “diastole” Stroke systolic coronary flow Stroke diastolic coronary

BOW

Total stroke coronary flow

122 * 22 mm. Hg 87 * 16 mm. He

18.5 * 22 beats per min.

166 * 22 msec. 159 * 27 msec.

0.029 * 0.018 ml.

0.065 * 0.022 ml. 0.091 f 0.047 ml.

Effects of intracoronary nicotine. The threshold dose was the same for both the coronary flow and myocardial contractile force responses in each animal and varied from one to 10 pg. Maximal effects occurred with 80 to 100 pg. Effective doses increased contractile force and reduced the duration of myocardial contraction and the time to peak tension. These changes appeared to occur only downstream from the site of injection since no changes were registered by an additional strain gauge arch up- stream from this point. This apparent local- ization of the response to a relatively small portion of the myocardium probably ac- counts for the fact that changes in aortic pressure were not observed except with doses above 50 pg. Heart rate was un- changed but the duration of “systole” of the myocardium downstream from the injection site was reduced (mean reduction 20 per cent, standard deviation 10 per cent) and the duration of “diastole” was corre- spondingly increased. Total stroke systolic coronary flow and systolic flow per milli- second systole were reduced and total stroke diastolic coronary flow and diastolic coronary flow per millisecond were in- creased. Total stroke coronary flow in- creased and end-diastolic coronary vascular resistance diminished. All these changes began within 4 seconds of injection, reached a maximum 4 to 8 seconds later, and re- turned to normal within 3 minutes.

The over-all effects of increasing doses of nicotine are shown at slow paper speed in Fig. 1 and the details of the instantaneous coronary flow and contractile force changes are seen at rapid paper speed in Fig. 2. The changes produced by the intracoronary injection of 20 pg of nicotine in all ten ani- mals are shown in Fig. 3.

The effects of nicotine on coronary flow and myocardial contraction were compared with those of norepinephrine in four of the ten dogs. The responses to both agents were very similar (Fig. 4) and were blocked by intravenous propranolol, 1 mg. per kilo- gram (Fig. 5). The nicotine responses were also blocked by intravenous pentolinium, 0.5 mg. per kilogram, in each of another four animals (Fig. 6). Note that both pro- pranolol and pentolinium produced con- siderable depression of contractile force pre- sumably because of the high degree of sympathetic tone exhibited by open-chest

98 Ross and Hlesn

30

CF

‘0

INTRA CORONARY NICOTINE

Fig. 1. Effect of increasing doses of intracoronary nicotine on arterial pressure (AP), instantaneous arterior descending coronary artery flow (CF), and contractile force of segments of myocardium downstream (SGr) and upstream (SG,) from the point of nicotine injection. In this, and all subsequent figures, pressures are measured in millimeters of Hg and flows in milliliters per minute.

150 AP

C 100 --J -L,j % &+r?h -J-w. -J--L -.-, %-.. J‘

75

CF

0

SG

A B

Fig. 2. Effect of intracoronary nicotine on arterial pressure (AP), instantaneous coronary flow (CF), and myo- cardial contractile force (SG). A, Pre-injection record. B, Eight seconds after 20 pg intracoronary nicotine.

Volttme 79 Number 1 Effect of nicotine on coronary circulation 99

200

15c

is 100 2 5

2 Y 5 a 50

0

-5c

Systolic

Flow Stroke per Systolic msec

Fig. 3. Mean per cent changes * standard deviations produced by 20 s of intracoronary nicotine in ten dogs. The numerical values were as follows: stroke systolic coronary flow, -55 * 24 per cent; systolic coronary flow

per millisecond, -37 * 26 per cent; stroke diastolic coronary flow, $62 * 24 per cent; diastolic coronary flow per millisecond, +42 * 3.5 per cent; total stroke coronary flow, +32 * 21 per cent; end-diastolic vascular resistance, -22 * 13 per cent; contractile force, +132 * 63 per cent.

Control Nicotine 20 pg Control Norepinephrine 004pg

Fig. 4. Similarity of instantaneous coronary flow (CF) and contractile force (SG) changes produced by intra- coronary nicotine and intracoronary norepinephrine. A, Control. B, Eight seconds after intracoronary nicotine, 20 a. C, Control. D, Eight seconds after 0.4 pg of intracoronary norepinephrine.

100 Boss and Nesu

AP

CF

SG

too

B

inl

dogs anesthetized \I-ith pentol)arbital. ‘I‘he effects of nicotine were not affected 1)~. ,Itropine, 1 Illg. per liilOgratl1, or vagotoni\-

in any of the ten animals.

Discussion

‘I

4 300

Fig. 5. Blockade of coronary and myocardial re- soonses to nicotine bv orooranolol. A. Effects of intracoronarv nicotine, 100 WEI. on arteiial pressure

An evaluation of the voluminous litera- ture on the effects of nicotine on coronary flow is difficult because of the variety of species used, and the differences in doses and routes of administration. The many studies with intravenous nicotine are par- ticularly difficult to interpret because of the complex pharmacological effects of this agent a-hich has been shown to stimulate and inhibit autonomic ganglia,4 to liberate catecholamines from the adrenal medulla,” to elicit axon reflexes, and to have direct effects on vessels.” An added difliculty has been that until recently there has been no direct method of measuring rapid coronary flow changes. Most of the published reports indicate that nicotine increases coronary flow7 although some earlier investigations found onlv a flow reduction.7

(AP), instantaneous coronary flow (CF), and myo- cardial contractile force (SG). B, Effects after intra- venous propranolol, 1 mg. per kilogram. Note that 300 rg of intracoronary nicotine produced no response.

100

AP

0

The p&sent study showed that intra- coronary nicotine in doses that produce no systemic effects and that do not elicit the Bezold-Jarisch reflex produce a simulta-

B

75 CF

0

SG

Fig. 6. Effects of intracoronary nicotine on arterial pressure (=1P), coronary flow (CF), and contractile force (SG). A, Before pentolinium. B, After intravenous pentolinium, 0.5 mg. per kilogram. Before pentolinium the responses to 40, 60, and 80 pg of nicotine are shown. After pentolinium these doses were without effect, and even increasing the dose to 300 fig failed to produce a response.

Voll4me 79 Number 1 Effect of nicotine on coronary circulation 101

neous increased force of myocardial con- traction and an increase in coronary flow. These changes began within 4 seconds of injection, i.e., before the drug could have reached the systemic circulation, and were unaccompanied by changes in heart rate and arterial pressure or by changes in myo- cardial force upstream from the point of injection. Examination of the instantaneous coronary flow records showed that the in- creased coronary flow was partly due to coronary vasodilatation as shown by the reduced end-diastolic vascular resistance and partly to an increase in the duration of diastole during which most of the coronary inflow takes place. Systolic flow was reduced and even reversed. All the coronary flow changes, which were blocked by proprano- 101, were strikingly similar to those pro- duced by norepinephrine8 (see Fig. 4) and by sympathetic nerve stimulation9 and were blocked by propranolol. This suggests that the effects of nicotine on the myo- cardium and on coronary flow are mediated by catecholamines. This view is supported by previous studies which have shown that propranolol blocks the tachycardia induced by the injection of nicotine into the sinus node artery in dogslo and the increased cardiac output and rise in arterial pressure produced by intravenous nicotine in cats.” Pretreatment with reserpine also blocks the coronary flow increase produced by nicotine in the isolated cat hear@ and inhibits the chronotropic effect of nicotine in the isolated rabbit atrium.3

The rapid onset of the inotropic response to nicotine in our experiments and its ap- parent localization to the area downstream from the point of injection indicate that any catecholamine release or potentiation must have occurred from sites within the ventricular myocardium. Chromaffin cells have been described in the atria of dogs’3 but not in the ventricIe. It therefore seems likely, that nicotine released norepinephrine from adrenergic nerve terminals within the muscle. The coronary flow changes we observed may have been entirely secondary to the metabolic and mechanical effects of myocardial stimulation. Certainly we never saw any alteration of coronary flow in the absence of an inotropic response and when the latter was blocked by propranolol, nico- tine had no effect on coronary flow. On the

other hand, it is possible that norepineph- rine was liberated simultaneously in the coronary resistance vessels and in the myo- cardium. Studies of the effects of nicotine on isolated small coronary vessels would be helpful in clarifying this point.

Our results have confirmed previous ob- servations that the cardiac effects of nico- tine are prevented by pretreatment with ganglionic blocking agents.14 As far as we are aware, adrenergic ganglion cells have never been described in the canine ventricle. The nicotine-blocking effect of pentolinium in our experiments must therefore have occurred at a nonganglionic site. During recent years, the cholinergic link hypothe- sis of adrenergic transmission has excited much interest.‘5 According to this hypothe- sis, the action potential passing down the postganglionic sympathetic nerve fiber causes the release of acetylcholine which in turn releases norepinephrine. Hexametho- nium and pentolinium have been found to block the adrenergic effect of acetylcholine but not that of sympathetic nerve stimu- lation.16 Burn and Gibbons” have sug- gested that certain ganglionic blocking agents might block the sympathomimetic effects of acetylcholine by preventing the entry of acetylcholine into the postgangli- onic fiber. Nicotine, like acetylcholine, can produce adrenergic effects in many organs.i6 It is therefore conceivable that nicotine enters postganglionic fibers within the myo- cardium and causes the release of norepi- nephrine by an action involving the “choli- nergic link” mechanism. Pentolinium, by preventing the entry of nicotine into the fiber, would therefore block its sympa- thomimetic effects. These ideas concerning the interaction of nicotine and pentolinium at the cardiac sympathetic postganglionic nerve terminals are admittedly speculative, but they are put forward since it should be possible to test them. One obvious approach would be to study the uptake of labelled nicotine by nerve fibers before and after pentolinium.

The authors wish to acknowledge the able tech- nical assistance of Miss Madeline Kurrasch.

REFERENCES

1. Green, H. D., Wbgria, R., and Boyer, H. H.: Effect of epinephrine and pitressin on the coro-

2.

3.

4.

5.

6.

7.

8.

9.

nary artery inflow in anesthetized dogs, J. Pharmacol. & Exper. Therap. 76:378, 1962. Gregg, D. E., and Fisher, L. C.: Blood supply to the heart, in Hamilton, W. F., and Dow, I’., editors: Handbook of Physiology, Section 2: Circulation, Vol. 2, W’ashington, D. C., 1963, American Physiological Society, p. 1517. Burn, J. H., and Rand, M. J.: Action of nico- tine on the heart, Brit. M. J. 1:137, 1958. Feldberg, W., and Vartiainen, A.: Further ob- servations on the physiology and pharmacology of the sympathetic ganglia, J. Physiol. (Lond.) 83:103, 1935. Van Slyke, C. B., and Larson, P. S.: Observn- tion on the role of the adrenal medulla in the blood pressure response to nicotine, J. Phar- macol. & Exper. Therap. 98:400, 1950. Hilton, S. M.: The effects of nicotine on the blood vessels of skeletal muscle in the cat. An investigation of vasomotor axon rellexes, J. Physiol. (Lond.) 123:289, 1954. Larson, P. S., Haag, H. B., and Silvette, H.: Tobacco, experimental and clinical studies, Baltimore, 1961, The Williams & Wilkins Com-

pany. Gaal, P. G., Kattus, A. A., Kolin, A., and Ross, G.: Effects of adrenaline and noradrenaline on coronary blood flow before and after beta ad- renergic blockade, Brit. J. Pharmacol. 26:713, 1966. Granata, L., Olsson, R. A., Huvos, A., and Gregg, D. E. : Coronary inflow and oxygen usage following cardiac sympathetic nerve stimula- tion, Circulation Res. 16:114, 1965.

10.

11.

12.

13.

14.

15.

16.

17.

Nadeau, Ii. A., and James, ‘I. 1.: Etfccts of nicotine on heart rate studied by direct per- fusion of sinus node. Am. 1. Phvsiol. 212:911. 1967. Papacostas, C. A., and Reed, J. I’.: Influence of beta receptor blockade on certain cardiovascular actions of nicotine, Arch. Internat. Pharmn- codyn. 164:167, 1966. Romero, T., and Talesnik, J.: Influence of nico- tine on the coronary circulation of the isolated heart of the cat, J. Pharm. Pharmacol. 19:322, 1967. Jacobowitz, D.: Histochemical studies of the relationship of chromaffin cells and adrenergic nerve fibers to the cardiac ganglia of several species, J. Pharmacol. & Exper. Therap. 158:227, 1967. West, J. W., Guzman, S. V., and Bellet, S.: Cardiac effects of intracoronary arterial injec- tions of nicotine, Circulation Res. 6:389, 19.55. Ferry, C. B.: Cholinergic link hypothesis in adrenergic neuroeffector transmission, Physiol. Rev, 46:420, 1966. Daly, M. de B., and Scott, M. J.: The effects of acetylcholine on the volume and vascular re- sistance of the dog’s spleen, J. Physiol. (Lond.) 156:246, 1961. Burn, J. H., and Gibbons, W. R.: The sympa- thetic postganglionic fibre and the block by bretylium, the block prevented by hexamethon- ium and imitated by mecamylamine, Brit. J. Pharmacol. 22:549, 1964.