Release ofα-Melanocyte-Stimulating Hormone from Dispersed Cells of the Intermediate Lobe of the Rat Pituitary Gland: Involvement of Catecholamines and Adenosine 3′,5′-Monophosphate

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Abstract
Treatment of the neurointermediate lobe of the rat pituitary gland with mechanical agitation in the presence of trypsin and DNAse results in a preparation of cells which secrete αMSH and synthesize cAMP. The receptors for catecholamines present in the intact intermediate lobe remain functional on the dispersed cells. Thus, stimulation of a β-adrenoceptor with (l)isoproterenol enhances the secretion of aMSH. This receptor is stereospecific and responds to low concentrations of isoproterenol (EC50 = 0.4 nm). Activation of a β-adrenoceptor also increases the accumulation of cAMP. Furthermore, dopamine inhibits the basal release of αMSH but has no effect on basal levels of cAMP. In addition, dopamine inhibits the isoproterenolenhanced release of αMSH as well as the isoproterenol-induced accumulation of cAMP (Endocrinology106: 1795, 1980)