Beta-Adrenergic stimulation of the release of ACTH- and LPH-related peptides from the pars intermedia of the rat pituitary gland.

Abstract

The intermediate lobe of the rat pituitary gland produces a series of peptides related to ACTH and LPH. The spontaneous and isoproterenol-stimulated release of such peptides was studied during in vitro superfusion of rat neurointermediate lobes with Krebs-Ringer medium. Products released into the superfusion medium were quantified by direct measurement or after chromatography on Sephadex G-50. ACTH bioactivity was determined by use of adrenal cortical cell suspension assay. In addition, NH2-terminal ACTH, CO2H-terminal ACTH, alpha-MSH and beta-endorphin radioimmunoassays were used. The results show that 1. neurointermediate lobes of rats secret spontaneously various ACTH- and LPH-related peptides in amounts proportional to the amounts in which these peptides are found in extracts of the neurointermediate lobe; 2. the beta-adrenergic agonist, isoproterenol, stimulated the spontaneous release of various peptides, including alpha-MSH, ACTH, CLIP, glycosylated CLIP, and beta-endorphin-like peptides; 3. isoproterenol induced a dose-dependent (10(-9)-10(-7) M), parallel increase in the release of alpha-MSH and ACTH following similar time courses and showing identical EC50 values (about 10(-8)M). Although the spontaneous release of alpha-MSH and ACTH from rat neurointermediate lobes is not strictly coupled under the conditions used in this study, isoproterenol seems to affect the spontaneous release of these peptides to the same relative extent.