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, we investigated the pineal response to adrenergic stimulation and pineal beta-adrenergic receptors following castration and/or sex hormone treatment in 2-month-old male and female Sprague-Dawley rats. The urinary 6-sulphatoxymelatonin (aMT6s) response to isoproterenol (ISO) was compared in castrated and sham-operated animals. Ovariectomy caused an increase and orchiectomy a decrease in ISO-induced urinary aMT6s excretion. The melatonin response to ISO was examined in pineal glands and serum samples obtained from castrated, sex-hormone-treated castrated and sham-operated rats. Consistently, ovariectomy increased pineal and serum melatonin responses to ISO, while orchiectomy decreased the responses; oestradiol and testosterone treatments, respectively, reversed these effects. 3H-dihydroalprenolol binding was measured in single pineal glands from castrated, sex-hormone-treated castrated and sham-operated rats. Ovariectomy increased the density of beta-adrenoceptors, whereas orchiectomy decreased the density; oestradiol and testosterone replacement, respectively, blocked these effects. No significant effect on receptor Kd values was found. These data suggest that sex hormones regulate pineal melatonin production by modifying beta-adrenergic mechanisms.