Effect of melatonin on the luteinizing hormone release induced by clomiphene and luteinizing hormone-releasing hormone.

The effect of melatonin on the LH-release response after the administration of synthetic LH-RH and clomiphene citrate was investigated in adult male rats. The sc administration of melatonin (1 mg/day) for 6 days produced a significant decrease in serum LH levels and in seminal vesicles and ventral prostate weights. On the other hand, the daily injection of 0.01 mg/100 g of body weight of clomiphene citrate during 6 days significantly stimulated LH levels and the weights of the accessory sex glands. Simultaneous treatment with melatonin and clomiphene produced an inhibitory effect similar to that obtained with melatonin alone. Neither pretreatment with melatonin alone. Neither pretreatment with melatonin (1 mg/day, sc for 6 days) nor its simultaneous iv administration (500 mug) with 75 ng of LH-RH modified the LH-release in response to the hypothalamic hormone. The fact that melatonin was able to suppress the effect of clomiphene, which is probably exerted at the hypothalamic level, but not the actiion of LH-RH on the pituitary, appears to indicate that the hypothalamus may be the site involved in the inhibitory effect of the pineal principle on the reproductive function.