Influence of age and splanchnic nerve on the action of melatonin in the adrenomedullary catecholamine content and blood glucose level in the avian group

Abstract

A single intraperitoneal (IP) melatonin injection (0.5 mg/100 g body wt.) caused an increase in norepinephrine (NE) fluorescence and elevation of NE content in newly-hatched pigeons (Columba livia), but a reduction of NE fluorescence and depletion of NE content in the adrenal medulla of newly-hatched crows (Corvus splendens) after 0.5 h of treatment. In contrast, in adults melatonin caused increase in NE fluorescence and elevation of NE content only in the parakeet (Psittacula krameri). Half an hour of IP melatonin treatment (0.5 mg/100 g body wt.) induced release of epinephrine (E) from the adrenal medulla of newly-hatched pigeon and parakeet. In contrast, in the adults melatonin caused more than a two-fold increase in E in the pigeon, and a significant increase in the crow. Single IP melatonin injection (0.5 mg/100 g body wt.) caused hypoglycemia in the newly-hatched parakeet and adult pigeon, and hyperglycemia in newly-hatched pigeon after 0.5 h of treatment. Melatonin failed to regulate glucose homoeostasis in newly-hatched and adult crow. Splanchnic denervation of the left adrenal gland was performed in the adult pigeon. The right adrenal served as the innervated gland. Melatonin-induced modulation of catecholamines following a single IP injection (0.5 mg/100 g body wt.) revealed significant increases in NE fluorescence and NE content at 4 and 12 h after treatment in the denervated gland only, which gradually approached normal levels 9 days after treatment. In contrast, E content showed more than a two-fold increase over the control value in both the innervated and denervated glands 0.5 and 24 h after treatment. At 9 days after treatment, E content showed significant depletion in the innervated gland. The results of this study indicate that melatonin modulates catechol hormone content in avian adrenal medulla, and also regulates glucose homoeostasis (except in the crow). The splanchnic nerve plays a vital role in the synthesis of NE but has no effect on E.