Effect of Zinc on the Uptake of Human Chorionic Gonadotropin (hCG) in Rat Testis and Testosterone Response in vivo

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Abstract
The effect of zinc on the uptake of 125I-labeled human chorionic gonadotropin (hCG) in vivo and the subsequent testosterone (T) response was studied. The testes of male rats were injected intratesticularly with 100 μl of 5 mM ZnCl2, the controls receiving only the vehicle (0.9% NaCl). Immediately afterwards the animals received [125I] i.v.; hCG uptake in the testes and serum and testicular T levels were studied at 1, 3, 6, and 24 h. The uptake of hCG in the zinc-treated testes was significantly higher than in the control testes throughout the 24 h observation period, the increase being dependent on the dose of zinc. Analysis of testicular radioactivity by gel filtration and displacement tests with an excess of unlabeled hCG showed that zinc treatment increased receptor-hormone complex formation. The T response to hCG-stimulation was rapid and biphasic in both treatment groups with maxima at 1 and 6 h, but the primary increase was significantly lower both in sera and testicular tissue in the zinc-treated animals. The free receptor level of the zinc-treated testes did not differ from that of the vehicle-treated testes. A significant down-regulation of the receptors was found at 24 h after hCG-injection in both groups. These results show that intratesticular administration of zinc results in increased fromation of receptor-hCG complexes and reduces the primary T response.
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