Altered Ratios of Beta‐Endorphin : Beta‐Lipotropin Released from Anterior Lobe Corticotropes with Increased Secretory Drive. I. Effects of Diminished Glucocorticoid Secretion

Abstract

Previous studies have demonstrated that acute stress or ovine corticotropin-releasing hormone (oCRH) in vivo, or oCRH in vitro, stimulates release of beta-endorphin over beta-lipotropin from anterior pituitary corticotropes. This occurs despite the predominance of beta-lipotropin in corticotrope peptide stores. In vitro studies with primary anterior pituitary cultures suggested that chronic exposure to oCRH results in a shift towards more beta-lipotropin secretion into the media than with short-term exposure. The current studies explored whether increased secretory drive in vivo results in a similar shift towards more beta-lipotropin. We used removal of glucocorticoids by adrenalectomy or metyrapone blockade of corticosterone synthesis, to stimulate endogenous secretion of CRH and vasopressin. Both treatments resulted in shifts of the ratio of beta-endorphin: beta-lipotropin in plasma of experimental animals in comparison to the sham-treated control rats. In vitro testing with oCRH of anterior lobe cultures from adrenalectomized or metyrapone-treated rats demonstrated similar effects of these treatments on the ratio of beta-endorphin:beta-lipotropin. These changes occurred despite similar ratios of beta-endorphin:beta-lipotropin in anterior pituitary peptide stores.