Effect of norepinephrine, prenalterol and metoprolol on the histochemical localization of adenylate cyclase activity in the brown adipose tissue of newborn rat.

Norepinephrine-stimulated adenylate cyclase enzyme (EC 4.6.1.1.) was histochemically demonstrated by electron microscope in the plasmalemmas of the newborn rat adipocytes. The precipitating agent in the histochemical reaction was cobalt salt. Metoprolol, a selective beta 1-blocker given in vivo abolished almost totally the reaction products from the outer surfaces of the plasmalemmas. In vitro treatment did not yield constantly reproducible results. Prenalterol (H 133/22-CGP 7760/B Hässle) a selective beta-agonist given in vivo stimulated enzyme activity in the plasmalemmas. The reaction, however, showed different localization patterns and enhanced amounts of reaction products in the membranes. It is proposed that the histochemical demonstration of amine-stimulated adenylate cyclase activity in the adipocyte plasmalemmas corresponds to the hormonal receptor sites. The question of the sensitivity of the receptors is discussed.