Pituitary extract, compared with

In order to determine the site of action of these two differing effects of peripherally administered catecholamines, the corticotropin releasing activity (as measured by the increase in adrenal corticosterone) of a crude acid extract of rat median eminence (MEE) was compared in rats in which the endogenous secretion of CRF was effectively Inhibited by a single subcutaneous injection of prednisolone (2.5 mg/lOO hours earlier) with animals given phentolamine only, steroid plus phentolamine, or normal saline only (see Table 3) Phentolamine injected 3-l/2 hours after the steroid and 30 minutes before use of the animals was without effect in preventing the stress of ether and intravenous saline and the response of the pituitary to MEE, nor did it affect the sensitivity of the adrenal cortex to injected ACTH. 

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