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

Abstract

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. 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. 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. 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. 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. 1988 British Pharmacological Society