Toxicology Letters, 17 (1983) 259-261 Elsevier

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ATROPINE INHIBITS BONE RESORPTION INDUCED BY HIGH DOSE OF ZINC IN RATS

(Zinc; calcium; bone resorption; atropine)

MASAYOSHI YAMAGUCHI

Department of Environmental Biochemistry, Shizuoka College of Pharmacy, 2-2-1, Oshika, Shizuoka-

city, 422 (Japan)

(Received December 6th, 1982) (Revision received January 12th, 1983) (Accepted January 29th, 1983)

SUMMARY

A single oral administration of high amounts of zinc (Zn) induced hypocalcemia and bone resorption in rats. Atropine inhibited both effects thus supporting the hypothesis that the effect of Zn administra- tion on bone results from the hypocalcemia mediated by acetylcholine.

INTRODUCTION

Zn has been demonstrated to have a wide variety of roles in mammalian systems [ 11. The metal may play a physiological role in the growth and calcification of bone tissue [3]. Zn-deficient rats have reduced calcium (Ca) balance, and rate of bone anabolism and resorption [4]. Zn is also required for the complete physiological ac- tion of vitamin D on Ca metabolism in rats [5]. On the other hand, high Zn diets exert a porotic effect in bone [2]. However, the mechanism of Zn action on Ca metabolism in mammals remains to be elucidated.

Recently, Yamaguchi et al. [12] have reported that oral administration of a com- paratively high dose of Zn stimulates bone resorption in rats, although a low dose of Zn stimulates the bone growth of weanling rats at early stage. Thus Zn-induced bone resorption is mediated by parathyroid hormone secreted to maintain Ca homeostatis; Zn causes a hypocalcemia in rats [ 10, 111. The hypocalcemic effect of Zn results from the stimulation of gastric Ca secretion mediated through acetylcholine action [B, 91. Therefore, the present study was designed to clarify whether atropine inhibits Zn-induced bone resorption in rats.

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METHODS

Male Wistar rats (5 weeks old) were kept at room temperature (25 -t 1’C) and fed a laboratory chow containing 1.1% Ca, 1.1% P and 0.012% Zn, with tap water ad lib. Zinc sulfate was dissolved in distilled water to a concentration of 10 mg Z&ml. This solution (1 ml/l00 g body weight) was given as a single oral dose to rats and the rats were killed after 3.5 h. In separate experiments, groups of rats oral- ly administered Zn (10 mg/lOO g) were treated S.C. 3 times at 1 h intervals, with atropine (0.1 yg10.5 ml/100 g) dissolved in distilled water, 30 min after the metal administration. The rats were killed 1 h after the last treatment with the drug. Con- trol animals received the solvent alone.

Rats were bled by cardiac puncture under light ether anesthesia and the femur and blood removed. Ca in the femoral epiphysis was measured by methods reported previously [IO, 1 I], and serum Ca was determined by the method of Willis [7].

The results were subjected to analysis of variance, and the SE calculated from the residual error term. Statistical significance is expressed as P values from Student’s t-test.

RESULTS AND DISCUSSION

The effects of atropine on the changes of serum Ca levels and in the femoral epiphysis of rats administered Zn are shown in Fig. 1. A significant decrease in serum Ca caused by Zn administration was completely prevented by atropine (0.1 t

II i_ Control Atropine Control Atropine

Fig. 1. Effect of atropine on the change of Ca levels in the serum and the femoral epiphysis of rats orally administered zinc sulfate. The rats received administration of distilled water or zinc (10 mg/lOO g), and 30 min later distilled water or atropine (0.1 ag/lOO g) was subcutaneously administered 3 times at 1 h intervals. The rats were sacrificed 1 h after the last administration. Each bar represents the mean value of 6 animals. The vertical lines give the SE. *P<O.Ol, as compared with control. q , control rats; m, zinc-treated rats.

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pg/lOO g) treatment in comparison with that of control. Also, administration of Zn to control rats caused a significant decrease in Ca content in the femoral epiphysis,

but not diaphysis (data not shown). This decrease was completely inhibited by atropine treatment.

Thus, atropine treatment completely prevented the hypocalcemia and bone resorption induced by high amounts of Zn in rats. This fact further supports the hypothesis that Zn-induced bone resorption may result from the hypocalcemia mediated by acetylcholine.

REFERENCES

1 R.E. Burch, H.K. Hahn and J.F. Sullivan, Newer aspects of the roles of zinc, manganeses, and cop- per in human nutrition, Clin. Chem., 21 (1975) 501-520.

2 H.W. Ferguson and A.G. Leaver, Effects of diets high in zinc at different levels of calcium and vitamin D on the rat humerus and incisor, Calcif. Tissue Res., 8 (1972) 265-275.

3 S. Haumont and J. Vincent, Zn65 and calcification of the skeleton, Experimentia, 17 (1961) 296-297. 4 L.S. Hurley, J. Cowan and G. Milhaud, Calcium metabolism in manganeses-deficient and zinc-

deficient rats, Proc. Sot. Exp. Biol. Med., 130 (1969) 856-860. 5 B. Sivakumar and B. Bhavani, Effect of zinc on vitamin D-dependent calcium uptake in rat intestine,

Indian J. Biochem. Biophys., 12 (1975) 386-388. 6 G. Vaes, in J.T. Dingle and H.B. Fell (Eds.), Lysosomes in Biology Pathology, Vol. I, North-

Holland, Amsterdam, 1969, pp. 217-253. 7 J.B. Willis, Determination of calcium in blood serum by atomic absorption spectrophotometry,

Nature, 186 (1960) 249-250. 8 M. Yamaguchi, T. Yoshino and S. Okada, Effect of zinc on the acidity of gastric secretion in rats,

Toxicol. Appl. Pharmacol., 54 (1980) 526-530. 9 M. Yamaguchi, K. Katayama and S. Okada, Hypocalcemic effect of zinc and its mechanism in rats,

J. Pharmacobio-Dyn., 4 (1981) 656-663. 10 M. Yamaguchi, A. Mochizuki and S. Okada, Stimulation of bone resorption by comparitively high

dose of zinc in rats, J. Pharmacobio-Dyn., 5 (1982) 501-504. 11 M. Yamaguchi, K. Takahashi and S. Okada, Zinc-induced hypocalcemia and bone resorption, Tox-

icol. Appl. Pharmacol., (1982) in press. 12 M. Yamaguchi, A. Mochizuki and S. Okada, Stimulatory effect of zinc on bone growth in weanling

rats, J. Pharm. Dyn., 5 (1982) 619-626.