[Effect of melatonin on the function of the pituitary-gonadal axis in food restriction states]

The effects of melatonin (25 micrograms s.c. daily in the late afternoon during ten days) on the ovarian morphometry and the gonadotropin secretion were investigated in food-restricted and fed ad libitum rats. It was found that in food-restricted rats melatonin produced the significant decrease of the surface area of the whole ovary and of zona granulosa. Moreover melatonin treatment of food-restricted rats resulted in significant decrease of the relative areas of graafian follicles and zona granulosa estimated in relation to the whole ovary cross-section surface area. On the other hand melatonin did not produced significant alterations of the morphometric indices of the ovary in fed ad libitum rats. Melatonin administration was found to inhibit the effects of gonadotropin release in food-restricted but not in normally fed rats. These findings suggest that food restriction sensitizes the pituitary ovarian axis to antigonadotropic melatonin action.