SIMILARITY BETWEEN THE EFFECTS OF SUPRACHIASMATIC NUCLEI LESIONS AND OF PINEALECTOMY ON GONADOTROPIN-RELEASE IN OVARIECTOMIZED, SULPIRIDE-TREATED AND MELATONIN-REPLACED RATS

The aim of this study1 was to compare the effects of pineal indole tre atments on LH and FSH release in pinealectomized and suprachiasmatic l esioned and ovariectomized rats rendered hyperprolactinemic by acute s ulpiride treatment. Pinealectomy or suprachiasmatic nuclei lesions in female rats both decreased plasma LH and FHS at 10, but not at 20 d af ter surgery, whereas the daily afternoon administration of melatonin e ffectively restored levels of both gonadotropins to control values. In ovariectomized rats, pinealectomy or suprachiasmatic nuclei lesions w ere ineffective in counteracting the high plasma levels of LH and FSH. However, sulpiride treatment in both pinealectomized and suprachiasma tic nuclei lesioned and castrated female rats significantly decreased the levels of LH and FSH, an effect which was counteracted by daily af ternoon melatonin administration. Other pineal indoles tested, i.e., 5 -hydroxy- and 5-methoxytryptophol, were ineffective in regulating gona dotropin levels. The results suggest that the pineal gland, through it s hormone melatonin, can modulate gonadotropin secretion by acting on a dopamine mechanism independent of hypothalamic suprachiasmatic areas .