Plasma corticosterone levels in stressed rats following the administration of pentobarbital, morphine and diphenylhydantoin

Abstract

Plasma corticosterone concentrations were determined in serial plasma samples from individual rats as a measure of pituitary-adrenal activity. Pentobarbital produced a fall in corticosterone concentration in the absence of noxious stimuli but did not block the rise in plasma corticoids following mild stress. Morphine, in large doses, stimulated the pituitary-adrenal mechanism while smaller doses, in combination with pentobarbital, had a blocking effect on the pituitary response to surgery and hemorrhage. Some degree of tolerance developed to the ability of morphine to prevent the rise in plasma corticosterone when given in combination with pentobarbital. Chronic administration of diphenylhydantoin diminished the pituitary-adrenal response to stress under the conditions of this study but it did not block the ACTH releasing effect of high doses of morphine.