Hypothalamo-pituitary-adrenal function in the rat after prolonged treatment with cortisol.

1. Cortisol, administered subcutaneously every day for long periods, caused growth retardation, adrenal atrophy and impaired hypothalamo-pituitary-adrenal (HPA) function in the rat.2. The growth rate and the functional activity of the HPA system gradually returned to normal after steroid withdrawal.3. Normal adrenal sensitivity to corticotrophin returned more rapidly than normal pituitary corticotrophic function, suggesting that the initial impairment of HPA function was due both to reduced responsiveness of the adrenal gland to corticotrophin and failure of the pituitary gland to secrete the hormone.