Autoradiographic localization and function of β‐adrenoceptors on the human internal mammary artery and saphenous vein

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Abstract
1 Receptor autoradiography with (−)-[125 I]-cyanopindolol (CYP) was used to study the distribution of β1 and β2-adrenoceptor subtypes in the human internal mammary artery and saphenous vein. 2 Images from X-ray film and nuclear emulsion coated coverslips, exposed to [125 I]-CYP labelled sections, showed a high density of β2-adrenoceptors localized to the endothelium of the internal mammary artery and fewer β2-adrenoceptors on the smooth muscle. 3 The function of β-adrenoceptors in ring preparations of the internal mammary artery was investigated in organ bath studies. (−)-Isoprenaline produced concentration-dependent relaxation of phenylephrine contracted rings. The potency and maximal effects of (−)-isoprenaline were not influenced by the presence of the endothelium. 4 Images of [125 I]-CYP binding to the saphenous vein, from X-ray film and nuclear emulsion coated coverslips, showed localization of β2-adrenoceptors to the outer smooth muscle and not to the endothelium. 5 Relaxation of mammary artery and saphenous vein to (−)-isoprenaline is mediated via β2-adrenoceptors located on the smooth muscle. Endothelial β2-adrenoceptors, although present on the internal mammary artery, mediate other functions.