Autoradiographic characterization of beta-adrenoceptors in rat heart valve leaflets

beta-Adrenoceptors were localized and characterized in valve leaflets of the rat heart. Sixteen micrometer-thick tissue sections containing the mitral and aortic valves were incubated with (-)3-[125I]iodocyanopindolol followed by autoradiography with computerized microdensitometry and comparison with 125I-labeled standards. beta-Adrenoceptors were present in all the valves studied. The selective beta 1-adrenoceptor antagonist CGP 20712 A (100 nM) displaced not more than 20% of the total binding sites, suggesting that most of the beta-adrenoceptors in the valve leaflets are of the beta 2-subtype. Forskolin-binding sites were detected in the mitral valve leaflet by incubation of adjacent tissue sections with [12-3H]forskolin. Our results indicate that catecholamines could regulate the function of the heart valves through stimulation of beta 2-adrenoceptors.