Effects of melatonin on adrenal function in male rats

Effect of a ten-day melatonin treatment on adrenal function in male rats was studied. The weight of adrenal gland was decreased by treatments with the highest dose of melatonin (30 mg/kg, s.c., injection time: 1700) once daily for ten days. And also corticosterone levels in adrenal gland and in serum were significantly decreased. Lower doses (1, 5 and 15 mg/kg) had no effect. The increase of corticosterone levels in adrenal gland by successive treatments with ACTH, were suppressed by simultaneous injections of melatonin. On the other hand, after dexamethasone, the increase in corticosterone levels induced by ACTH were also suppressed by melatonin treatment. These results suggest that melatonin may have an inhibitory action on the effect of ACTH on rat adrenal gland.