Role of the Pineal Gland in the Control of Gonadotropins and Androgen-reducing Enzymes in the Rat

Abstract

It has been claimed that, in some mammalian species (for example, the hamster, the rat, the ferret, etc.) the hormone of the pineal gland melatonin may exert an inhibitory activity on the secretion of LH or on both LH and FSH. It has also been found that the administration of melatonin to intact rats results in a decrease of testis and ventral prostate weight, which is significantly more pronounced than that which follows hypophysectomy. Moreover, Alonso and others (1978) have found that the concomitant injection of melatonin decreases the effectiveness of exogenous testosterone on prostate and seminal vesicle weights in adult castrated male rats. It has been suggested that melatonin may also exert a peripheral antiandrogenic activity. It is now well established that both the peripheral androgenic activity and the central feedback effects of testosterone are exerted in mammals through a fundamentally similar mechanism: circulating testosterone is first bound to specific receptors. Consequently, it may be hypothesized that the antigonadotropic activity of melatonin and its antiandrogenic effect might be exerted either via an interference on specific testosterone receptors, or through an influence on the activity of the α-reductase.