The dopamine receptor in the intermediate lobe of the rat pituitary gland: pharmacological characterization.

The dopamine receptor in the intermediate lobe (IL) of the hypophysis of the rat is characterized on the basis of the ability of dopamine and other dopaminergic agonists to decrease the consequences of activation of the beta-adrenoceptor. Stimulation of the dopamine receptor diminishes the L-isoproterenol-induced accumulation of cAMP and the catecholamine-stimulated enhancement of adenylate cyclase activity. The dopamine receptor in the IL can be assigned to the category of dopamine receptor designated D-2 on the basis of the following criteria: 1) occupancy of the dopamine receptor does not result in enhancement of adenylate cyclase activity or an accumulation of cAMP, 2) the dopaminergic ergots and apomorphine mimic the inhibitory effect of dopamine upon cAMP formation or alpha MSH release, and 3) metoclopramide and sulpiride, substituted benzamides, block the inhibitory effect of dopamine. The sympathetic neurotransmitter, norepinephrine, interacts with the dopamine receptor and the beta-adrenoceptor in the IL.