Effect of prolonged treatment with tetracosactrin on hypothalamo‐pituitary‐adrenal function in the rat

Abstract

Summary1. The functional integrity of the hypothalamo-pituitary adrenal (HPA) system was assessed in rats after prolonged treatment with tetracosactrin. 2. Adrenal size and sensitivity to corticotrophin were increased. 3. Both the circadian rhythm and the stress-induced increase in HPA activity were inhibited. The circadian rhythm recovered before the response to stress. 4. Tetracosactrin given after betamethasone treatment delayed the return of a normal HPA response to stress. 5. Suppression of HPA activity appeared to be the result of a direct action of tetracosactrin and not entirely due to the elevations in the plasma corticosterone concentration which it caused.

Natural variations in brain phenylethanolamine-N-methyltransferase activity during different phases of the oestrous cycle: Effect of chronic dexamethasone treatment.

“…The action of chronic administration of dexamethasone to rats in the oestrous cycle on central PNMT activity appears to be dependent on the status and function of the hypothalamo-pituitary-adrenal function which has been shown to be impaired after therapy with corticosteroids or corticotrophin (37). These authors observed that beta methasone-treated rats showed adrenal atrophy and insensitivity to exogenous cor ticotrophin.…”

“…These authors observed that beta methasone-treated rats showed adrenal atrophy and insensitivity to exogenous cor ticotrophin. In addition to this, similar treat ment with the synthetic corticoid prevented the normal circadian rhythm and the stress induced rise in plasma corticosterone con centration (37). The impairment of hypo thalamo-pituitary-adrenal function resulting from chronic dexamethasone administration prevents the mobilization of endogenous corticotrophin which is required to maintain normal corticosterone levels in the plasma as well as in the central nervous system.…”