Toxicology Letters, 6 1 (1992) 205-2 12

0 1992 Elsevier Science Publishers B.V. All rights reserved 0378-42741921s 5.00

205

TOXLET 02733

The renal handling of sodium and potassium in environmental cadmium-exposed subjects with renal dysfunction

Teruhiko Kido”, Koji Nogawa”, Masayoshi Ohmichi”,

Ryumon Hondab, Ikiko Tsuritanib, Masao Ishizakib and

Yuichi Yamadab

“Department of Hygiene, Chiba University School of Medicine, Cllibu und hDepurtment of Hygiene,

Kanrrruwu Medical Universit~~. Ishikuwu I Jupan)

(Received 19 December 1991)

(Accepted 19 February 1992)

Key ww&; Sodium; Potassium: Renal handling: Cadmium: Renal dysfunction

SUMMARY

To clarify using clearance methods the renal handling of sodium and potassium in a population with

environmental cadmium (Cd)-induced renal dysfunction, 76 Cd-exposed subjects (32 men and 44 women)

and 36 non-exposed subjects (18 men and 18 women) were selected. Fractional excretions of potassium and

&microglobulin were higher in the Cd-exposed subjects than in the non-exposed subjects. while the frac-

tional excretion of sodium in the Cd-exposed subjects was equal to that of the non-exposed subjects. The

urinary excretion rate of sodium was significantly lower in the Cd-exposed subjects than in the non-

exposed subjects, while no significant difference was found in the urinary potassium excretion rate. Frac-

tional excretion of sodium showed a significant correlation with age in all the subjects, while that of

potassium significantly correlated with serum /I?-microglobulin. These results indicate that increases in the

fractional excretion of sodium or potassium do not directly signify increased urinary excretion of sodium

or potassium in Cd-induced renal tubular dysfunction. The fractional excretion of potassium may be more

affected by Cd-induced renal dysfunction, while that of sodium appears to be more related to age.

INTRODUCTION

Exposure to environmental cadmium (Cd) initially causes renal tubular dysfunc-

tion [1,2]. Low-molecular-weight proteins in the urine, e.g., &microglobulin (j??-

Correspondence to: T. Kido, Department of Hygiene, Chiba University School of Medicine, Chiba, Japan

206

MG), a,-microglobulin, and metallothionein are useful markers of this renal dysfunc-

tion [224]. Exposure to Cd also causes decreased renal glomerular filtration [2,5], and

Cd-induced renal dysfunction is aggravated even after cessation of Cd exposure [6,7],

progressing in some cases to renal failure or uremia [7,8]. Itai-itai disease is the most

severe stage of environmental exposure to Cd and it is accompanied by renal and

bone damage [9]. In itai-itai disease patients and inhabitants in the Cd-polluted area

in which this disease is endemic, it is reported that the fractional excretions of sodium

and potassium increase in proportion to the degree of renal dysfunction [lo. 1 11. It is

also reported that mortality rates due to all causes, specifically cerebrovascular dis-

ease, of the inhabitants in the Cd-polluted area are lower than those of a non-exposed

area [12]. This is thought to be attributable to an increase in urinary sodium ex-

cretion because renal tubular dysfunction may cause decreased reabsorption of

sodium in the renal tubuli. However, little information is available on the relation-

ship between electrolytes such as sodium and potassium and Cd-induced renal disor-

der.

In the present study, the renal handling of sodium and potassium in inhabitants

with renal dysfunction in a Cd-polluted area other than the area in which itai-itai

disease is endemic is assessed using clearance methods.

MATERIALS AND METHODS

Target population The subjects in this study consisted of 32 men and 44 women, all of whom were over

50 years of age and lived in the Cd-polluted Kakehashi River basin in Ishikawa

Prefecture. They all showed Cd-induced renal tubular dysfunction and were officially

recognized as ‘subjects requiring observation’ by the Research Committee organized

by the Prefectural Health Authority [13]. Cd compounds were transported by the

Kakehashi River from a mine upstream to rice fields where river water was used for

irrigation. As non-Cd-exposed subjects, 18 men and 18 women over 50 years of age

living in a non-Cd-polluted area were selected. They presented for an annual routine

health checkup.

Analysis of blood and urine In the morning, urine specimens were obtained for clearance methods 2 h after the

subjects drank approximately 300 ml of water. Blood specimens were drawn at the

midpoint of the collection period. Serum sodium (S-Na) and potassium (S-K) were

determined by electrode methods. Urinary sodium (U-Na) and potassium (U-K) were

measured by flame atomic absorption spectrometry. The &MG levels in serum and

urine were analyzed by the Phadebas B2-microtest (Pharmacia, Sweden). Creatinine

concentrations in serum and urine were determined by Jaffe’s method [14]. Phospho-

rus levels in serum and urine were analyzed by Taussky’s method using a kit (P-Test

Wako, Wako Inc., Japan) and Allen’s method [ 151, respectively. Fractional excretion

of sodium (FENa), filtered load of sodium (F-Na), urinary excretion rate of sodium

207

(E-Na), and tubular reabsorption rate of sodium (R-Na) were estimated according to the formula [16]:

FENa (%) = CCr C* x 100 (%) = SUZ,x x”;C; x 100

where UV = urinary volume (ml/min); F-Na (mEq/min) = S-Na x CCr; E-Na (mEq/ min) = UV x U-Na; R-Na (mEq/min) = F-Na - E-Na. Both poassium and P,-MG were also estimated according to the same method used for sodium. It should be noted that the tubular reabsorption rate of potassium is less than the real reabsorp- tion rate since potassium is secreted at the distal tubule, and this secretion value is included in the urinary excretion rate in this calculation.

TABLE I

RESULTS OF SERUM AND URINARY ANALYSIS IN Cd-EXPOSED AND NON-EXPOSED SUB-

JECTS

Cd-exposed subjects Non-exposed subjects

Men Women Men Women

Number

Age”

Serum Na (mEq/l)

K (mEq/l)

B,-MG @s/l)

Creatinine (mgi100 ml)

Urine

t%-MG Olgiw.)

Cd @gig.cr.)

4 4 11 9

28 40 7 9

59.0 k 2.8 58.8 k 1.5 56.4 f 5.5 56.0 f 4.7

75.9 k 5.4 14.1 +_ 5.8 73.1 f 5.0 71.8 k 3.3

139.6 I .o** 140.6 1.0 136.1 1.0 136.5 1.0

140.3 1.0** 141.6 l.O** 135.8 1.0 138.0 1.0

4.25 1.13 4.18 1.19 4.16 I .08 3.94 1.11

4.15 1.10 4.13 1.09’ 3.90 1.08 3.91 1.06

2065 1.2’ 2371 2.1 1618 1.3 1510 1.2

3006 1.3** 2710 1.5** 1919 1.4 1950 1.2

1.25 1.12+ 1.14 1.72 I .03 1.22 0.72 1.09

1.45 1.24** 1.19 1.38** 1.03 1.16 0.80 1.13

1472 14.0** 4295 11.4** 6 5.0 30 6.3

6918 5.9** 10914 5.5** 60 3.7 306 3.7

10.16 2.05** 10.30 2.05** 1.60 1.58 4.08 1.44

8.87 1.60** 11.69 1.68** 2.38 1.72 5.70 1.39

Upper values: subjects aged under 65 years; lower values: subjects aged 65 years or over.

a Arithmetic mean and SD. Others are expressed as geometric mean and geometric SD.

‘Difference (PcO.1) between Cd-exposed and non-exposed subjwts,

*Significant difference (P c 0.05) between Cd-exposed and non-exposed subjects.

*%ignificant difference (P < 0.01) between Cd-exposed and non-exposed subjects.

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TABLE II

RESULTS OF PARAMETERS OF RENAL CLEARANCE IN Cd-EXPOSED AND NON-EXPOSED

SUBJECTS

Cd-exposed subjects Non-exposed subjects

Men Women Men Women

Number 4 4 II 9

28 40 7 9

Cc,(ml/min) 53.6 2 17.5’ 47.9 I23.6’ 87.1 -t 30.5 86.2 i 8.8

43.5 k 19.3** 40.9 + 14.5** 76.0 k 16.4 69.3 -t 16.9

% TRP” 75.9 + 0.8** 79.9 k 8.9’ 85.6 k 5.1 86.9 i 5.1

76.6 -t 5.9 76.8 -t 10.3** 80.8 i 6.2 X6.X I 4.2

Frcrctionul cscwtion (%)

FENa 2.13 I .32** 1.89 1.35 0.91 1.5x 1.40 1.55

1.38 1.67 1.97 1.80 1.89 1.40 2.07 1.33

FEK 18.41 I .32** 20.46 I .48** 9.16 I.41 II.56 1.19

16.33 1.50 20.84 I .49** 12.65 1.32 13.96 I.33

FEB,-MC 0.89 0.13** 2.05 0.1 I’ 0.03 0.04 0.06 0.02

3.35 0.06** 4.81 0.05** 0.05 0.07 0.13 0.03

Filterd loud

F-Na (x10-’ mEq/min) 7129 1.5- 6053 1.7 11143 1.5 11722 I.1

5521 I .6** 5370 I .5** 10093 1.3 9290 I.3

F-K (x10-’ mEq/min) 217 1.5- 180 1.6- 340 I.5 338 I.’

163 I .6’* 157 1.5** 290 I.3 263 1.3 F-/&-MC @g/mitt) IO’ 0.00 I 102 0.00 I I32 0.001 I30 0.001

II8 0.002’ 103 0.001* 143 tl.001 131 0.001

(irinuql~ cscretion rcrtr

E-Na (x10-’ mEq/min) 155.2 1.5 119.9 1.3 113.0 I.4 157.0 1.6

76.0 2.1** YO.8 1.7** 202.8 1.5 179.9 1.5

E-K (x10 ’ mEq/min) 40.7 2.2 38.5 I .2 34.6 1.5 37.6 1.3

26.1 2.0 ‘8.1 1.5 39.1 I.5 34.5 1.5 E-/&-MC ug/min) 0.96 0.01 I ** 2.21 0.010~ 0.04 0.004 0.07 0.002

3.96 0.007** 4.27 0.005** 0.08 0.006 0.16 0.003

Tuhulur rrtrhsorption rut<’

R-Na (x10-’ mEq/min) 6966 1.5’ 5929 I .8 I IO15 I.5 II535 I.1

5433 I .6** 5262 I .5** 9886 1.3 9120 I .3

R-K (xl0 ’ mEq/min) 174 1.5* 137 1.8’ 304 I .5 299 I .2

134 1.6** 125 l.6** 250 1.3 228 I.3

R-&MG uglmin) 101 0.001 95 0.001 I32 0.001 129 0.001

107 0.002* 88 0.002% I43 0.001 131 0.001

Upper values: subjects aged under 65 years; lower values: subjects aged 65 years or over.

*Arithmetic mean and SD. Others are expressed as geometric mean and geometric SD.

‘Difference (P<O. I) between Cd-exposed and non-exposed subjects.

*Significant difference (P < 0.05) between Cd-exposed and non-exposed subjects.

**Significant difference (P < 0.01) between Cd-exposed and non-exposed subjects.

209

Statistical analysis Depending on the homogeneity of variance, statistical differences between two

groups were tested by Student’s t-test or Welch method. Relationships between varia-

bles were tested with multiple regression and shown as values of partial correlation

coefficients.

RESULTS

The results of biological indicators in serum and urine are shown in Table I. Each

group was divided into two subgroups according to age, with one group under 65

years and the other 65 years and over. Levels of sodium, &MG and creatinine in

serum and&MG and Cd in urine in most subgroups of the Cd-exposed subjects were

significantly higher than those in the non-exposed subjects.

The results of variables of renal handling of sodium, potassium and &MG are

shown in Table II. Creatinine clearance and percent TRP were significantly lower or

tended to be lower in most subgroups of the Cd-exposed subjects than in the corre-

sponding subgroups of the non-exposed subjects. Fractional excretions of potassium

(FEK) and p,-MG in most subgroups of the Cd-exposed subjects were significantly

higher than those in the corresponding subgroups of the non-exposed subjects. Con-

TABLE III

MATRIX OF PARTIAL CORRELATION COEFFICIENTS FOR FRACTIONAL EXCRETION OF

SODIUM AND POTASSIUM WITH AGE AND SERUM &MICROGLOBULIN

Age S-&MG

Men

Fractional excretion

FENa (%)

FEK (%)

0.331* -0.124

-0.096 -0.078

0.835** -0.295

0.093 0.328*

-0.252 0.221

0.431’ 0.051

Women

Fractional excretion

FENa (%)

FEK (%)

0.270* 0.232’

0.244 0.307*

0.571* -0.100

0.206 0.576**

0.126 0.557**

0.222 0.065

Upper values; all the subjects; middle values: Cd-exposed subjects; lower values: non-exposed subjects.

‘Difference (PC 0.1); *significant difference (PcO.05); **significant difference (P < 0.01).

210

cerning the filtered load, urinary excretion rate and tubular reabsorption rate, most variables of sodium and potassium showed signififant decreases or tended to decrease in the Cd-exposed subjects as compared to the non-exposed subjects. The urinary excretion rate of sodium was lower and that of &MC was higher in the Cd-exposed subjects than in the non-exposed subjects. However, the urinary excretion rate of potassium was equal to that of the non-exposed subjects.

The matrix of partial correlation coefficients for fractional excretion of sodium and potassium with age and serum/&MC is shown in Table III. FENa correlated signifi- cantly with age in all the subjects (male and female} and the nonexposed subjects (male and female), while FEK did not correlate significantly with age when &-MG was fixed. FEK showed a significant correlation with /&-MG in all the subjects (male and female) and the female exposed subjects, while FENa showed a significant corre- lation with &MG only in the Cd-exposed female subjects when age was fixed.

DISCUSSION

There are many Cd-polluted areas in Japan [17], and a health survey of residents in areas with environmental Cd pollution reported that 202 of 13 570 persons participat- ing in detailed medical examinations have proximal renal tubular dysfunction, where- as none of 7 196 residents in non-polluted areas were found to have this renal dysfunc- tion 1181. Thus, the prevalence rate of renal tubular dysfunction was 1.5% in the Cd-polluted areas in this health survey [I 81, with this Cd-induced renal disorder con- sidered to be uncommon.

Renal clearance methods are well-known as a practicable means of studying human renal physiology. Clearance techniques are used for estimating the fractional excre- tion of sodium, potassium and &MG [16,19,20]. However, it should be noted that these methods have some disadvantages such as the impossibility of separating reab- sorption and secretion in the case of substances undergoing both [ 191.

In Cd-exposed subjects including itai-itai disease patients, the fractional excretion of sodium or potassium has been estimated using clearance methods [ IO,1 11. In these studies, FENa and FEK were shown to increase in proportion to the increase in urinary,&-MG or serum creatinine, and it was suggested that excessive urinary excre- tion of sodium may reduce the blood pressure [I 11. This low blood pressure is often seen in Cd-exposed subjects with renal dysfunction. However, the present study clari- fied that the filtered loads of sodium and potassium were significantly lower in the Cd-exposed subjects than in the non-exposed subjects. Concerning the urinary excre- tion rate, the sodium excretion rate was also si~ificantly lower in the Cd-exposed subjects than in the non-exposed subjects, with no significant difference found in the potassium excretion rate. These phenomena may be explained by tubuloglomerular feedback [21]. Therefore, it can be said that the increase in FENa paralleling the degree of renal dysfunction does not directly result in increased urinary sodium excre- tion.

According to the partial correlation coefficients, FEK showed a closer correlation

211

with serum &MG, while FENa was more correlated with age. These results mean that potassium is more affected by Cd than is sodium.

From the viewpoint of renal function tests, the urinary excretion rate of sodium is lower in the subjects with Cd-induced renal dysfunction than in control subjects. However, this does not mean that the total sodium excretion in urine is smaller in the subjects with Cd-induced renal dysfunction since some mechanism may act to main- tain sodium homeostasis. A study on the urinary excretion of sodium and potassium under normal living conditions is in progress.

REFERENCES

1 Kellstrom, T. (1986) Renal effects. In: L. Friberg, C.G. Elinder, T. Kellstrom and G.F. Nordberg

(Eds.), Cadmium and Health: A Toxicological and Epidemiological Appraisal. Vol. II. Effects and

Response. CRC Press, Boca Raton, FL, pp. 21-l 09.

2 Nogawa, K. (1984) Biologic indicators of cadmium nephrotoxicity in persons with low-level cadmium

exposure. Environ. Hlth Perspect. 54, 163-169.

3 Kido, T., Honda, R., Yamada, Y., Tsuritani, I., Ishizaki, M. and Nogawa, K. (1985) cr,-Microglobulin

determination in urine for the early detection of renal tubular dysfunction caused by exposure to

cadmium. Toxicol. Lett. 24, 195-201.

4 Shaikh, Z.A., Kido, T., Kito, H., Honda, R. and Nogawa, K. (1990) Prevalence of metaliothioneinuria

among the population living in the Kakehashi River basin in Japan: an epidemiological study. Toxicol.

64, 59-69.

5 Lauwerys, R.R., Buchet, J.P., Roels. H.A., Brouwers, J. and Stanescu, D. (1974) Epidemiological

survey of workers exposed to cadmium: effect on lung, kidney and several biological indices. Arch.

Environ. Hlth 28, 145.-148.

6 Kido, T.. Honda, R., Tsuritani, I., Yamaya, H., Ishizaki, M., Yamada, Y. and Nogawa, K. (1988)

Progress of renal dysfunction in inhabitants environmentally exposed to cadmium. Arch. Environ. Hlth

43.213-317.

7 Kido, T., Nogawa, K.. Ishizaki. M.. Honda. R., Tsuritani, I., Yamada, Y.. Nakagawa. H. and Nishi,

M. (I 990) Long-term observation of serum creatinine and arterial blood pH in persons with cadmium-

induced renal dysfunction. Arch. Environ. Hhh 45. 3541.

8 Kajikawa, K. (1978) Pathogenesis of Itai-itai disease based on post-mortem studies. In: K. Tsuchiya

(Ed.), Cadmium Studies in Japan: A Review. Kodansha-Elsevier, Tokyo, pp. 286295.

9 Nogawa. K. (1981) Itai-itai disease and follow up studies. In: J.O. Nriagu (Ed.), cadmium in the

Environment. Part II: Health Effects. John Wiiey and Sons, New York. pp. I- 37.

IO Shinoda, A.. Yuri. T. and Nakagawa, A. (1977) Clinical findings of itai-itai disease patients. Kankyo

Woken Report 41,44-52 (in Japanese).

11 Aoshima, K. and Kasuya. M. (1988) Environmental exposure to cadmium and effects on human health.

Part 3. The results of blood examinations and blood pressure in inhabitants of the cadmium-polluted

Jinzu River basin in Toyama Prefecture. Jpn. J. Hyg. 43. 949-955 (in Japanese).

12 Shigematsu, i.. Minowa. M.. Nagai, M., Ohmura. T. and Takeuchi, K. (1982) An epidemiological study

on mortality of the inhabitants in the Cd-polluted areas in Japan. Kankyo Hokcn Report 48. 118-136 (in Japanese).

13 Ishikawa Prefecture. Results of the epidomiological study on the health effects of cadmium on the

population in the Kakehashi River basin. lshikawa Prefecture, Kanazawa. pp. 1-56 (in Japanese).

14 Bonsnes, R.W. and Taussky. H.H. f 2945) On the calorimetric determination of creatinine by the Jaffe

reaction. J. Biol. Chem. 1%. 581 591.

15 Alien. R.J.L. (1940) The estimation of phosphorus. Biochem. J. 34, X58-865.

212

16 Chesney, R.W. (1985) Phosphaturic syndromes. In: H.C. Gonick and V.M. Buckalew (Ed%), Renal

Tubular Disorders: Pathophysiology, Diagnosis, and Management. Marcel Dekker, Inc.. New York

and Base], pp. 201-238.

17 Yamagata, N. (1978) Cadmium in the environment and in humans. In: K. Tsuchiya (Ed.), Cadmium

Studies in Japan. A Review. Kodansha-Elsevier, Tokyo, pp. 19-37.

18 Japan Public Health Association Cadmium Research Committee (1989) Summary Report on Studies of

Health Effects of Cadmium. Japan Public Health Association, Tokyo, pp. 53367.

19 Schuster, V.L. and Seldin, D.W. (1985) Renal clearance. In: D.W. Seldin and G. Giebisch (Eds.), The

Kidney: Physiology and Pathophysiology. Raven Press, New York, pp. 365-395.

20 Elinder, C.G.. Edling. C., Lindberg. E., Kagedal, B. and Vesterberg, 0. (1985) Assessment of renal

function in workers previously exposed to cadmium. Br. J. Ind. Med. 42. 754 760.

21 Thurau, K. und Schnermann, J. (1965) Die Natriumkonzentration an den Macula densa-Zellen als

regulierender Faktor fur das Glomeruhtmfiltrdt (Mikropunktionsversuche). Klin. Wochenschr. 43.

410-416.