Circadian variation in activity of the duck (Anas platyrhynchos) adrenal gland

Duck adrenal glands were studied with respect to circadian activity by incubating with progesterone-4-¹⁴C at 2-hour intervals for 24 hr. The production of deoxycorticosterone, corticosterone, and aldosterone was studied in quadruplicate incubations. Results show that peak production of corticosterone and aldosterone occurred at early morning at 06.00–08.00 hr and again in the late afternoon, 16.00–20.00 hr. Production of these two hormones was at minimum at midday and midnight. Unlike the mammalian species studied which exhibit a 24-hr cycle change in adrenal activity, the duck shows a characteristic 12-hr cycle. This pattern of circadian activity of the adrenal reflects to some degree the physiology of the animals in that the peaks of adrenal activity coincide with times of maximal body activity.