INFLUENCE OF THE PINEAL AND MELATONIN ADMINISTRATION ON THE DAY-NIGHT CHANGES IN THE ADRENAL CATECHOLAMINES OF YOUNG CHICKS

The effects of pinealectomy with or without substitutive administration of melatonin on the concentrations of epinephrine (E) and norepinephrine (NE) in the adrenals of young chicks were studied at mid-day and mid-night. The two-week old chicks were either non-operated (NO), or sham-operated (SO), or pinealectomized (Px) and maintained in LD 12:12 for 15 days. During this period, half of the total number of NO, SO, and Px chicks were injected daily in the afternoon with melatonin (Mel; 10 ug/100 g body wt) and the remaining birds from the same groups were administered daily only with the vehicle (V; ethanol-saline) of the hormone. The control (Con) birds were maintained under natural conditions without any treatment. In the adrenals of both the Con and NO-V birds, a significant nocturnal increase in the concentration of E was noted compared to the same at mid-day. But the night-time value of adrenal E was lowered in SO-V birds and raised in SO-Mel chicks. Exogenous melatonin in intact (NO-Mel) and sham-operated (SO-Mel) chicks caused a significant reduction in the nocturnal value of NE. Pinealectomy resulted in a nocturnally increased value for NE. The amount of E in the adrenals of Px-Mel birds was significantly elevated at mid-day and depleted at mid-night resulting into inverse day-night changes in E and NE compared to those in NO-V chicks. The results suggest a possible influence of the pineal organ and its secretion of melatonin on the day-night changes in adrenal catecholamines of chicks.