Stimulation of a D-2 Dopamine Receptor in the Intermediate Lobe of the Rat Pituitary Gland Decreases the Responsiveness of the β-Adrenoceptor: Biochemical Mechanism

In experiments using a cell-free homogenate of the intermediate lobe of the hypophysis of the rat, apomorphine, a dopaminergic agonist, diminished both basal and L-isoproterenol-stimulated adenylate cyclase activity; dopaminergic antagonists from several chemical families reversed these inhibitory effects of apomorphine. Apomorphine diminished the ability of GTP to enhance both basal and L-isoproterenol-stimulated adenylate cyclase activity but did not directly interfere with the interaction between the beta-adrenoceptor and L-isoproterenol. The affinity of the D-2 dopamine receptor in the intermediate lobe for each dopaminergic antagonist used in this study was estimated from a mathematical analysis of the data. (Endocrinology 108: 420, 1981)