Role of melatonin in the control of growth and growth hormone secretion inpoultry

The pineal hormone melatonin controls reproduction of photoperiodic mammals and is an integral part of the circadian organization in birds. Recent fin dings indicate an involvement of this hormone also in more basic physiologi cal processes, including growth, development, and aging. Melatonin may modu late growth in poultry through interaction with transcriptional factors, th rough interaction with hormones involved in growth control, and by modulati on of energy metabolism and decreasing physical activity. Our studies showe d that a single melatonin injection increased plasma growth hormone (GH) co ncentrations in the Japanese quail. Specific serotonin receptor blocker ket anserin did not preclude a stimulatory action of melatonin on GH synthesis. Serotonin agonist quipazine increased GH levels but failed to enhance the stimulatory effect of melatonin. Pretreatment with melatonin in drinking wa ter did not affect the magnitude of the GH response to subcutaneous (s.c.) administration of thyrotropin releasing hormone (TRH) that considerably sti mulated GH secretion. Present data suggest that melatonin modulates rather central neural pathways involved in the control of GH synthesis at the hypo thalamic level than the sensitivity of the pituitary gland. (C) 1999 Elsevi er Science Inc. All rights reserved.