DIFFERENTIAL RESPONSES TO VARIOUS ACTH-RELEASING STIMULI IN RATS WITH HYPOTHALAMIC IMPLANTS OF CORTICOSTEROIDS

The eflects of hypothalamic implants of corticosterone and cortisol on adrenocortical responses to different repeated stresses - as measured by plasma corticosterone levels -were studied in rats, and compared with cholcsterol-implanted and intact animals. Both corticosteroids depressed the response to auditory and photic stimulation, but the adrenocortical responses to immobilization and hemorrhage were depressed by cortisol only. Similarly, cortisol was more effective than corticosterone in inhibiting the adrenocortical responses to ether stress. The response to exogenous ACTH demonstrated a reduced adrenal sensitivity in the cortisol implanted animals; however, this could not account for the decreased adrenocortical responses to the various stimuli. These studies thus demonstrate the inhibitory etfect of hypothalamic cortisol and corticosterone implants, the differential effects of corticosteroids on various stresses, and that the blockage of the response to stress in animals with corticostcroid implants is due to inhibition of ACTH secretion. © 1969 S. Karger AG, Basel.