Comparison of the adrenal sensitivity to ACTH of laying hens with immobilization and plasma baseline levels of corticosterone.

The effects of mammalian ACTH (0.01-10.0 IU/kg) given intraarterially on plasma corticosterone levels in laying hens were determined. A rectilinear dose-response relationship was found, y = 24.545 + 8.691x. Daily ACTH injections of 0.1 IU/kg on 3 successive days showed a good reproducibility in response in plasma corticosterone levels. Immobilization by hand also increases plasma corticosterone to a plateau level of about 4 ng/ml. The effects of ACTH and immobilization in individual birds showed a good correlation (r = 0.87). A rather low correlation (r = 0.49) existed between individual baseline levels of plasma corticosterone and adrenal sensitivity for ACTH. The adrenal sensitivity for ACTH was nearly two times higher in the morning than in the evening. A diurnal pattern, however, could not be shown in the corticosterone response to immobilization.