Some age-related changes in pituitary-adrenal function in the male laboratory rat

Changes in the pituitary-adrenal axis have been investigated as a function of age (2 1/2 to 26 mo) in the male laboratory rat (CFY-Sprague Dawley). Ether stress was used to challenge the pituitary-adrenal axis and blood samples (peripheral and adrenal venous effluent) taken for measurement of corticosterone using the competitive protein-binding assay and ACTH by the increase in corticosteroidogenesis in isolated rat adrenal cells. The results show that there was an increase of basal ACTH levels with increase in age which might be correlated with the degenerative changes in the adrenal cortex at old age. No age difference was observed in the 2 1/2-min stress levels. However, 15-min stress resulted in a further increment of ACTH levels, which was not found in old animals. No age-related differences in the basal and stress levels of corticosterone was observed, and, hence, adrenocortical function would seem not to be impaired in old age.