CELLULAR ASPECTS OF THE STRESS RESPONSE IN PRECOCIAL NEONATES

The extent to which control over adrenal steroidogenic function is established during embryogenesis, and therefore the ability of precocial neonates to withstand stress, is probably an important determinant of breeding success. Studies on the ontogeny of adrenal steroidogenic function in birds, however, have been limited to the chicken Gallus domesticus and the duckling Anas platyrhynchos. Up to the 21st day of embryogenesis, the temporal patterns of adrenal gland development in these species are similar. By the 15th day the adrenal anlage is encapsulated and consists of islands of chromaffin cells distributed throughout a mass of structurally typical steroidogenic cells: at this time the steroidogenic cells are responsive to 1-24 ACTH and they contain small quantities of corticosterone and aldosterone. During the next six days the corticotropic responsiveness increases although the inducible response of cells from the 21 day-old emerging chick embryo is less than that of cells from the 21 day-old duck embryo. In the duckling, corticotropic responsiveness increases further during the next week preceding emergence. Also the steroidogenic cells in the emerging duck embryo, but not those in the emerging chicken embryo, preferentially synthesize aldosterone in response to angiotensin II. Although catecholamines and acetylcholine each suppress basal unstimulated rates of corticosterone and aldosterone release from the steroidogenic tissue, none has an effect on 1-24 ACTH-inducible corticosteroid release.