ABSTRACT
To study the effect of melatonin on the gonads, seminal vesicles and prostates, melatonin was injected subcutaneously [at 3 p.m] into mature male rats in a dose of 50, 100 and 500 ug. daily for 20 days. A significant decrease [P < 0.01] in the average weight of the testes occurred in the groups treated with the second and third dose of melatonin. A moderate inhibition of spermatogenesis and spermatocytogenesis in most tubules of the testes in the groups treated with lowest dose was observed. Drastic inhibition of spermatogenesis and spermatocytogenesis in the tests of treated groups with the second and third doses was noticed. The number of leydig cells and the diameter of seminiferous tubules were significantly decreased [P < 0.01] in first dose] and [P 0.001 in the second and third doses.] A highly significant decrease [P < 0.001] in the average weights, drastic hypoactive and atrophy of seminal vesicles and prostates in all treated groups was noticed. A significant decrease [P < 0.01] in serum testosterone of the group treated with the lowest dose, and the results of moderate and highest doses were below the sensitivity of the curve [less than 0.3 ng/ml]. From this work, it is clear that the suppressive effects of melatonin on gonadal functions was dose dependant. A maximum inhibitory action resulted from injection of the moderate dose. The suppressive effects of melatonin on gonadal functions may be due to a direct effect on the gonods. Also, may be due to suppression of the gonadotrophin hormone or reduction of the gonadotrophin releasing hormone from the hypothalamus by endorphin. May be also, due to decrease of the prolactin hormone which decreased the sensitivity of LH and FSH receptors in the testes