Abstract
A study was made on the characteristics of β-adrenoceptors in the isolated canine facial, portal and saphenous veins. Ring segments of the facial and saphenous veins and longitudinal strips of the portal vein were suspended in tissue baths containing Krebs solution oxygenated and maintained at 37°C. They were moderately contracted with prostaglandin F2α before examining their relaxation responses. The facial and saphenous veins fully relaxed to isoproterenol, while the aortal vein relaxed to a small extent (20% of maximum relaxation) even in the presence of an α-adrenoceptor blockade. In contrast, both forskolin, a direct activator of adenylate cyclase, and membrane-permeable dibutyryl cyclic AMP similarly relaxed all the veins studied. Thus, the reduction of coupling between β-adrenoceptors and the adenylate cyclase system may be involved in the decreased responsiveness of the portal vein to β-adrenoceptor agonists. In addition, analyses of β-adrenoceptor agonism and antagonism, using selective (β1: T-1583, β2: procaterol) and non-selective (isoproterenol) agonists as well as selective (β1: atenolol, β2: IC1 118, 551) and non-selective (propranolol) antagonists, confirmed that beta;-adrenoceptors in the canine facial vein are not homogeneous, with the β1-subtype predominating over the β2-subtype, and that the canine saphenous vein has a homogeneous population of the β2-subtype, as reported in the other species.
