Leptin, which is secreted mainly by adipocytes and some other tissues including pituitary, informs the brain about the mass of adipose tissue and has an important role in energy homeostasis. We have previously shown that melatonin decreases circulating leptin levels. Whether melatonin has an effect on leptin synthesis in pituitary is currently unknown. Therefore, the aim of this study was to immunohistochemically examine the effects of pinealectomy and administration of melatonin on leptin production in the rat anterior pituitary. Eighteen male Wistar rats were divided into three groups. Groups I and II were designated as control (sham-pinealectomized) and pinealectomized rats, respectively. They received 10% ethanol (0.1 ml s.c.) alone. Rats in group III were pinealectomized and injected daily with melatonin (3 mg/kg dissolved in 0.1 ml 10% ethanol s.c.) for 2 months commencing on day 7 after surgery. The pituitary glands of all rats were removed and fixed in Bouin's solution. The specimens were embedded in paraffin, serially sectioned and processed for immunohistochemistry. It was seen that immunostaining of leptin was moderate (3+) in sham-pinealectomized rats, heavy (5+) in pinealectomized rats and low (1+) in melatonin - treated pinealectomized rats, respectively. The present findings indicate that pinealectomy induces leptin secretion in anterior pituitary cells, and this increase in leptin synthesis can be prevented by administration of melatonin. It is thus suggested that melatonin may have both physiological and pharmacological effects on leptin synthesis in the anterior pituitary of male rat.
22 - 24 Mar 2004
British Endocrine Societies