Inhibition of Immunoreactive Corticotropin-Releasing Factor Secretion into the Hypophysial-Portal Circulation by Delayed Glucocorticoid Feedback*

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Abstract
Nitroprusside-induced hypotension evokes ACTH secretion which is primarily mediated by enhanced secretion of immunoreactive corticotropin-releasing factor (irCRF) into the hypophysial-portal circulation. Portal plasma concentrations of neither arginine vasopressin nor oxytocin are significantly altered in this paradigm. Application of a delayed feedback signal, in the form of a 2-h systemic corticosterone infusion in urethane-anesthetized rats with pharmacological blockade of glucocorticoid synthesis, is without effect on the resting secretion of arginine vasopressin and oxytocin at any corticosterone feedback dose tested. Resting irCRF levels are suppressed only at the highest corticosterone infusion rate, which resulted in systemic corticosterone levels of 40 .mu.g/dl. Suppression of irCRF secretion in response to nitroprusside-induced hypotension is observed and occurs at a plasma corticosterone level between 8-12 .mu.g/dl. These studies provide further evidence for a strong central component of the delayed feedback process which is mediated by modulation of irCRF release.

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