Effect of Dexamethasone on Immunoreactive Corticotropin-Releasing Factor in the Rat Median Eminence and Intermediate-Posterior Pituitary*

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Abstract
Immunoreactive ACTH (I-ACTH) concentrations in the anterior pituitary, intermediate-posterior pituitary (IP) and plasma and immunoreactive corticotropin-releasing factor (I-CRF) concentrations in the median eminence and IP were determined in rats receiving dexamethasone for various periods from 16 h to 10 days. Plasma I-ACTH concentrations were decreased 16 h after a single injection of dexamethasone. Anterior pituitary I-ACTH concentrations did not increase until 4 days after the start of dexamethasone medication. IP I-ACTH concentrations did not change throughout these periods. I-CRF concentrations in median eminence and IP rapidly decreased after dexamethasone administration. These results raise the possibility that the source of I-CRF in the IP is hypothalamic.