Somatostatin Inhibits the Isoproterenol-Stimulated Adenylate Cyclase in the Intermediate Lobe of the Male Rat Pituitary Gland

Somatostatin-14 inhibited the isoproterenol-stimulated adenylate cyclase in cell-free homogenates of pituitary intermediate lobe of the male rat with a Ki of 7.25 +/- 0.31 X 10(-7) M. Somatostatin-28 was found to be a partial agonist. Other neuropeptides (met- and leu-enkephalin, beta-endorphin, alpha-melanocyte-stimulating hormone, ACTH, neurotensin, substance P, vasoactive intestinal polypeptide, and vasopressin) were without effect. Our results suggest a role for pituitary and/or brain somatostatin in the physiological regulation of the intermediate pituitary lobe, and the possibility of an interaction between somatostatins and catecholamines on the regulation of intermediate lobe adenylate cyclase.