Contributions of Alpha₁ and Alpha₂-Adrenoceptors to Contractile Response in Canine Blood Vessels

Abstract

Strips of canine saphenous vein, inferior vena cava, and femoral artery were studied isometrically in vitro to compare quantitatively the α₁- and postsynaptic α₂-adrenoceptor contributions to the contractile force generated by l-norepinephrine (NE). Effects mediated by each receptor type were measured independently by quantitative blockade of virtually all α₁ -receptors with prazosin, or α₂-receptors with rauwolscine. Appropriate concentrations of the antagonists were calculated from dissociation constants previously determined by binding or competition with [³H]prazosin or [³H]rauwolscine in tissue homogenates. The contribution of α₁-adrenoceptors was larger than that of α₂-receptors in all vessels. The α₂-type was responsible for 38% of the maximum unblocked response to NE in saphenous vein, 32% in vena cava, and 28% in femoral artery. The occupation-response relationship for α₁-receptors was almost linear, without the marked upward convexity reported in some other vessels. α₂-Occupation-response curves were convex towards the occupation axis, with a relatively small response at low levels of occupation.

Effects of Serotonin on Vascular Tone of Isolated Human Placental Chorionic Veins

“…Because of the fragmentary infor mation on the physiology and pharmacology of placental vessels, it is supposed that such blood flow could be influenced by activation of various hormones and ago nist receptors present in the intravascular tissue, as has been reported for other vascular preparations [11,12].…”