Adrenocortical cell function in the hypophysectomized domestic fowl: Effects of growth hormone and 3,5,3′- triiodothyronine replacement

The control of adrenocortical function in the domestic fowl (Gallus domesticus) was investigated using adrenocortical cells isolated from hypophysectomized (hypox) and intact cockerels and from hypox cockerels injected with T₃, purified chicken GH (cGH), and T₃ plus cGH. Corticosterone in plasma and cell incubations was measured by RIA. Cellular responses to varying concentrations of steroidogenic agents were fitted and statistically analyzed by computer. Hypophysectomy reduced the basal plasma corticosterone (B) concentration to 53% of the value in intact birds and eliminated a stress response. Although hypophysectomy reduced adrenal weight by 20%, it did not change relative adrenal weight (milligrams per 100 g BW). However, replacement with cGH increased relative adrenal weight by 24%, whereas replacement with T₃ or T₃ plus cGH reduced relative adrenal weight by 16%. In the absence of steroidogenic agents, there were no detectable differences in B production by adrenocortical cells isolated from various experimental groups. However, with a maximal steroidogenic concentration of ACTH, B production by isolated adrenocortical cells from hypox birds was 61% of that by cells from intact birds. The ED₆₀ of ACTH for cells from hypox cockerels was 2.7 times greater than that of cells from intact cockerels, thus indicating a loss of cell sensitivity to ACTH after hypophysectomy (the greater the EDso, the lesser the cell sensitivity). Although cGH replacement increased maximal B production (Bmai) induced by ACTH to 329% that by cells from hypox cockerels, it increased the ACTH ED₅₀ 3.6 times, thus decreasing cell sensitivity more than hypophysectomy alone. In contrast to cGH, T₃ replacement maintained the cell sensitivity to ACTH at the level of cells from intact birds, but lowered B_max to 54% that of cells from hypox cockerels. The combination of cGH and T₃ administered to hypox cockerels both maintained cell sensitivity to ACTH and raised the B_max to 358% that of cells from hypox animals. These treatments also affected 8-bromo-cAMP-induced B_max and pregnenolone-supported B_max, but did not significantly alter the ED₅₀ of these agents. Data from this study of domestic fowl suggest that 1) hypophysectomy lowers the activity of adrenal steroidogenic loci before the formation of cAMP and pregnenolone, 2) hypophysectomy lowers steroidogenic enzyme content, and 3) these effects of hypophysectomy can be prevented by T₃ and cGH administered in vivo in the absence of exogenous ACTH; T₃ maintains cell sensitivity to ACTH and cGH maintains steroidogenic enzyme content.