EFFECTS OF SEX-HORMONES ON THE PINEAL RESPONSE TO ISOPROTERENOL AND ON PINEAL BETA-ADRENERGIC RECEPTORS

Several studies have shown sex hormone effects on pineal function. In order to clarify the role of adrenergic mechanisms in these effects, w e investigated the pineal response to adrenergic stimulation and pinea l beta-adrenergic receptors following castration and/or sex hormone tr eatment in 2-month-old male and female Sprague-Dawley rats. The urinar y 6-sulphatoxymelatonin (aMT6s) response to isoproterenol(ISO) was com pared in castrated and sham-operated animals. Ovariectomy caused an in crease and orchiectomy a decrease in ISO-induced urinary aMT6s excreti on. The melatonin response to ISO was examined in pineal glands and se rum samples obtained from castrated, sex-hormone-treated castrated and sham-operated rats. Consistently, ovariectomy increased pineal and se rum melatonin responses to ISO, while orchiectomy decreased the respon ses; oestradiol and testosterone treatments, respectively, reversed th ese effects. H-3-dihydroalprenolol binding was measured in single pine al glands from castrated, sex-hormone-treated castrated and sham-opera ted rats. Ovariectomy increased the density of beta-adrenoceptors, whe reas orchiectomy decreased the density; oestradiol and testosterone re placement, respectively, blocked these effects. No significant effect on receptor K-d values was found. These data suggest that sex hormones regulate pineal melatonin production by modifying beta-adrenergic mec hanisms.