STIMULATORY EFFECT OF CALCITONIN-GENE-RELATED PEPTIDE ON ADRENOCORTICOTROPIN RELEASE FROM RAT ANTERIOR-PITUITARY-CELLS

In the present study, we examined the direct regulatory effect of rat calcitonin gene-related peptide (CGRP) on adrenocorticotropin (ACTH) r elease from rat cultured anterior pituitary cells. CGRP significantly increased ACTH release at concentrations of 10(-8)-10(-11) M. The ACTH release was gradually increased by CGRP concentrations lower than 10( -10) M, and was decreased at concentrations higher than 10(-9) M, pres enting a bell-shaped dose-response curve. As well as having an additiv e effect on corticotropin-releasing factor-induced ACTH release, CGRP stimulated the accumulation of intracellular cAMP. The CGRP-induced AC TH release was inhibited by a protein kinase A inhibitor, suggesting t hat its stimulatory effect on the ACTH release was mediated via an ade nylate-cyclase-protein kinase system. CGRP-like immunoreactive nerve f ibers have been reported to innervate the anterior pituitary, so that the stimulatory effect of CGRP on the ACTH release suggests that this peptide may be involved in neural regulation of hormone secretion in t he anterior pituitary.