zinc cortisol

9 1990 by the Humana Press, Inc. All rights of any nature, whatsoever, reserved. 0163-4984/90/2401-0083 $02.00

Zinc Acutely and Temporarily Inhibits Adrenal Cortisol Secretion in Humans

A Preliminary Report

J. BRAND/~O-NETO,*" B. B. DE MENDON~A, 2 T. SHUHAMA, 3 J. S. MARCHINI,' W. P. PIMENTA,' AND M. T. T. TORNERO 1

1Department of Internal ,a'ledicine, Faculdade de ,a,ledicina de Botucatu, Universidade Estadual Paulista, 18610, Botucatu, SP;

2Department of Internal ,a'ledicine, Faculdade de ,a'ledicina, Universidade de S~o Paulo, 05403, S~o Paulo, SP; and 3Department

of Physical Chemistry, Faculdade de Ci6ncias Farrnac6uticas de Ribeir~o Preto, Universidade de S~o Paulo, I4.049,

Ribeir~o Preto, SP, Brazil

ABSTRACT

Hypo- and hyperzincemia has been reported to cause alterations in the adrenal secretion. To determine the acute effect of zinc on cortisol levels, we studied 27 normal individuals of both sexes aged 20-27 y after a 12-h fast. The tests were initiated at 7:00 AM when an antecubital vein was punctured and a device for infusion was in- stalled and maintained with physiological saline. Zinc was administered orally at 8:00 AM. Subjects were divided into an experimental group of 13 individuals who received doses of 25, 37.5, and 50 mg of zinc and a control group of 14 individual who received 20 mL of physiological saline. Serial blood samples were collected over a period of 240 rain after basal samples ( -30 and 0 min). We detected an acute inhibitory effect of zinc on cortisol secretion during 240 min of the study period in the experimental group.

Index Entries: Acute hyperzincemia; zinc supplement, effects of on cortisol secretion; plasma zinc and cortisol levels; normal individuals.

Author to whom all correspondence and reprint requests should be addressed.

Biological Trace Element Research 83 Vol. 24, 1990

84 Brand, o-Nero et al.

INTRODUCTION

The adrenals of vertebrates are known to be rich in zinc (1), but few data are available in the literature about the effects of zinc on cortisol synthesis and secretion. The adrenal cortex may be affected by zinc in some aspects. For example, rats with zinc deficiency have high choles- terol and ascorbic acid levels in their adrenals in relation to control animals and increased plasma 11-hydroxysteroid levels under basal con- ditions or when stimulated with ACTH (2). However, excess zinc has an opposite effect on plasma steroid levels, since it significantly inhibits plasma 11-hydroxysteroids in rats (3).

Conversely, the effect of glucocorticoids on zinc has been detected both in humans and in experimental animals. Patients with adrenal insufficiency and Cushing syndrome, respectively, show increased and decreased serum zinc levels (4). These results have also been obtained for adrenalectomized cats (4) and rats supplemented with dexamethasone (5), thus corroborating the existence of an inverse correlation between zinc and glucocorticoids.

On the basis of these considerations, the objective of the present study was to determine the possible existence of an acute effect of zinc on basal cortisol secretion in humans, a phenomenon that has not yet been reported in the literature.

MATERIAL AND METHODS

We studied 27 normal individuals (medical students) aged 20-27 y after obtaining informed consent in writing, according to the recommen- dations of the Declaration of Helsinki. The individuals had no history of endocrinopathy, used no type of drugs, and had ideal weights. The test .was started at 7:00 AM after a 12-h fast. A no. 19 infusion device was initially inserted into an antecubital vein. Basal blood samples were collected at 7:30 and 8:00 AM ( - 30 and 0 min) and all individuals maintained resting decubitus from the beginning to the end of the test. The control group consisted of 14 subjects of both sexes who received 20 mL physiological saline, p.o. Serial blood samples were collected from 8 of these individuals at the following time points: 30, 60, 90, 120, 150, 180, 210, and 240 min, and at 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 110 and 120 rain from the remaining 6. Heptahydrate zinc sulfate diluted in 20 mL deionized water was administered to the experimental group after the basal collection. Three men and 4 women ingested 25 mg zinc and 3 women ingested 37.5 mg zinc. Blood samples were collected from each subject at 30-min intervals for 240 rain. Three other women received 50 mg zinc and blood samples were collected from them at 10-min intervals

Biological Trace Element Research Vol. 24, 1990

Zinc and Cott/sol Secretion 85

for 120 min. The objective of this reduction in time scale was to guard against the possibility that some hormonal alteration may go undetected. Plastic syringes and tubes and zinc-free EDTA were used to obtain plasma. Plasma samples were stored at -20~ for zinc and cortisol determination. All tubes and pipets used were previously washed with acetone, 3 N hydrochloric acid, 0.1% EDTA, and deionized water.

Zinc was measured by atomic absorption spectrophotometry (6). Intrassay variation was 2.5% and sensitivity 0.02 ~g/mL. Samples were measured in triplicate and those showing hemolysis were excluded. Cortisol was measured by radioimmunoassay by the double-antibody method using kits of Diagnostic Products Corporation, US. Intra- and interassay variation was 6.4 and 7.4%, respectively, and sensitivity was 1.0 ~,g/dL. Samples were measured in duplicate.

The basal levels of zinc and cortisol were defined as the mean concentration of the -30 and 0 values. Data were analyzed statistically by the Sign test, by the t-test for independent samples, and by the Mann- Whitney test (7).

RESULTS

Since the individuals in the control group showed plasma cortisol levels of 3.4-18.5 p,g/dL during the basal period, we defined individuals within this range as the sample for the experimental group. Thus, we had a total of 14 individuals in the control group and 12 in experimental group (1 individual showing a basal level of 24.1 p,g/dL was excluded from the study). Plasma zinc and cortisol are presented in Figs. 1, 2, and 3.

For data analysis, the direction and magnitude of the basal differences (basal cortisol minus cortisol level at time t) were observed, each individual serving as his/her own control. Direction was analyzed by the Sign test. The number of individuals with a fall in cortisol levels was statistically significant at all times, in the control group, except for 210 min, and in the experimental group (Table 1). Comparison of the magni- tudes of the differences in cortisol levels between the control and the experimental group showed that the mean difference was statistically higher (t-test) in the the experimental group at all times analyzed (Table 2). The maximum difference in cortisol level within each individual was also measured, regardless of the occasion when the maximum and mini- mum peaks had occurred. The comparison of the magnitude of the maximum difference in cortisol between the two study groups revealed that the maximum difference was statistically higher (Mann-Whitney test) in the experimental group up to 120 rain, thus corroborating the data in Table 1.

Biological Trace Element Research 1/ol. 24, 1990

86 Brand&o-Neto et aL

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Fig. 1. Plasma cortisol in the control group (o-o) and experimental group (o--o), and plasma zinc in the experimental group (nt), according to oral zinc dose (25 mg) and collection time. The results are reported as means (~) ___ standard deviation (SD).

DISCUSSION

The acute inhibitory effect of zinc on cortisol secretion in vivo was demonstrated in the present experiment. The fall in cortisol in the experimental group in relation to the control group occurred during the 240 min of the study period. The intrinsic mechanism of this phenomenon is still to be elucidated. At the moment, evaluation of the interrelationship between this loss of cortisol and the different zinc doses was made difficult by the small sampling in each subgroup.

Very little is known about the effects of zinc on the physiological processes of cortisol secretion. The fact that zinc inhibits basal cortisol secretion in humans may be related to a direct blockade of cortisol synthesis and secretion in the adrenal cortex. This cause-effect relation- ship has been supported by reports of other authors who observed adrenal hyperplasia and a decrease in plasma 11-hydroxysteroids in rats on zinc-rich diets. (3). This trace element is known to be important for the structural and functional integrity of the cell membrane, since, by acting

Biological Trace Element Research 1/ol. 24, 1990

Zinc and Cortisol Secretion 87

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Fig. 2. Plasma cortisol in the control group (o--o) and experimental group (o--o), and plasma zinc in the experimental group (B-N), according to oral zinc dose (37.5 mg) and collection time. The results are reported as means (2) + standard deviation (SD).

on the sulfhydryl group, it can inhibit several membrane enzymes, among them ATPase and adenyl cyclase (8), and, through this effect, it may block cortisol secretion by the fasciculated and reticular cells of the adrenal cortex.

Moreover, many plasma membrane receptors have been reported to have the function of transmitting hormonal information to the interior of the cell (9). We know that zinc, by acting on membrane receptors for mast cells and platelets, can inhibit histamine and serotonin release, respectively (10,11). In this respect, it is plausible to postulate an inhibitory effect of zinc also on ACTH-receptor sites.

A study is currently underway in our laboratory to determine the site(s) of action and the intrinsic mechanisms of these processes.

SUMMARY

The ability of the adrenal cortex to decrease cortisol secretion in response to ingestion of zinc was studied in 13 normal individuals of both sexes aged 20 to 27 y. Plasma cortisol levels fell significant in all


88

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Brand&o-Neto et aL

I I I I I I I I I I I I I BASAL I0 20 30 40 50 60 70 80 90 I00 II0 120

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Fig. 3. Plasma cortisol in the control group (e--i) and experimental group (o--o), and plasma zinc in the experimental group ( ! t ) , according to oral zinc dose (50 mg) and collection time. The results are reported as means (Y) + standard deviation (SD).

k\ T T ~- ""

Table 1 Number of Individuals Showing Decreased Cortisol Levels (X) During Basal Time, Total Number of Individuals (N),

and Test of Significance ~ for the Different Collection Times for the Control and Experimental Groups

Control Experimetal

Time, min X (N) X (N) 120 13"* (14) 12"* (12) 150 7* (8) 9** (9) 180 7* (8) 9** (9) 210 5 NS (8) 9** (9) 240 7* (8) 9** (9)

'Sign test for Ho: P [Yo > Yt] = 89 vs H,: P [Yo > Yt] > 89 and NS P [X < X] > 5%.

*Indicates 1% P [X < X] < 5% and ** indicates P [X < X] < 1%.

individuals in relation to the control group throughout the study. These results demonstrate that acute high blood zinc levels were able to inhibit basal cortisol levels in normal individuals.

ACKNOWLED~NTS

This work was supported by FAPESP (Proc. no. 86/2511-3; 88/0950-5) and FUNDUNESP (Proc. no. 289/88, DFP). We acknowledge the techni- cal assistance of Maria Nice da S. Tavares.

Biological Trace Element Research VoL 24, 1990

Zinc and Cortisol Secretion 89

Table 2 Mean Difference (d) in Cortisol Level During Basal Time,

Number of Individuals (N), and t-Test" Comparing the Control and Experimental Groups for the Various Collection Times

Control Experimental

Time, rain d (N) d (N) t-Test

120 2.76 (14) 8.09 (12) ** 150 3.00 (8) 7.12 (9) * 180 2.60 (8) 8.04 (9) ** 210 3.15 (8) 8.96 (9) ** 240 2.05 (8) 7.41 (9) **

9 t-Test for H0: u~ = uE vs Hi: Uc < uE. **Indicates P [T < tl < 1%, and * indicates 1% < P I T < t] < 5%.

REFERENCES

1. E.J. Underwood, Trace Elements in Human and Animal Nutrition, 4th ed., E. J. Underwood, ed., Academic, NY, 1977, pp. 196-242.

2. J. Quarterman, Proc. Nutr. Soc. 31, 74-A (1972). 3. J. Quarterman, Trace Element Metabolism in Animals-2, W. G. Hoekstra, J. W.

Suttie, H. E. Ganther, and W. Mertz, eds., University Park Press, Baltimore, 1974, pp. 742-744.

4. R. I. Henkin, Trace Element Metabolism in Animals-2, W. G. Hoekstra, ]. W. Suttie, H. E. Ganther, and W. Mertz, eds., University Park Press, Baltimore, 1974, pp. 647-651.

5. K. R. Etzel, S. G. Shapiro, and R. J. Cousins, Biochem. Biophys. Res. Commun. 89, 1120 (1979).

6. M. M. Parker, F. L. Humoller, and D. J. Mahler, Clin. Chem. 13, 40 (1967). 7. S. Siegel, Nonparametric Statistics for the Behavioral Sciences, 1st ed., S. Siegel,

ed., McGraw-Hill, NY, 1956, pp. 61-158. 8. W. J. Bettger and B. L. O'dell, Life Sci. 28, 1425 (1981). 9. K. J. Catt and M. L. Dufau, Ann. Rev. Physiol. 39, 529 (1977).

10. W. Kazimierczak and C. Maslinski, Agentes and Actions 4, 203 (1974). 11. M. Chvapil, Med. Clin. North America 60, 799 (1976).


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