Effect of Melatonin on the Adrenl and Gonad of the Common Mynah Acridtheres tristis

Abstract

Exogenous intraperitoneal administration of melatonin (10 �g per day for 30 days) during peak activity phase ofthe annual reproductive cycle caused atrophy of the adrenal and gonad in the common mynah, Acridotheres tristis. The adrenal activity was assessed by weight, histology, cortical cord width, cortico-medullary ratio and total cholesterol content; the gonadal activity by weight, histology, cytometric measurements (seminiferous tubule, Leydig cell nuclei and follicular diameter) and total cholesterol content. Single injection of 300 and 600 �g melatonin suppressed the activity of the adrenal as well as the gonad via the neuro-endocrine complex to the same extent as did the daily injections. The present study suggests that melatonin may influence the adrenal and the reproduction of seasonally breeding subtropical common mynahs, although in birds the extent and nature of melatonin control is not yet clear.