Contributions of alpha 1- and alpha 2-adrenoceptors to contractile response in canine blood vessels.
Strips of canine saphenous vein, inferior vena cava, and femoral artery were studied isometrically in vitro to compare quantitatively the alpha 1- and postsynaptic alpha 2-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 alpha 1-receptors with prazosin, or alpha 2-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 alpha 1-adrenoceptors was larger than that of alpha 2-receptors in all vessels. The alpha 2-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 alpha 1-receptors was almost linear, without the marked upward convexity reported in some other vessels. alpha 2-Occupation-response curves were convex towards the occupation axis, with a relatively small response at low levels of occupation.
Milnor
W R
WR
Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, Md.
Stone
D N
DN
Sastre
A
A
D000818:Animals; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D005260:Female; D005263:Femoral Artery; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D009638:Norepinephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D012501:Saphenous Vein; D014682:Vena Cava, Inferior; D015016:Yohimbine / Q000494:pharmacology
D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D009638:Norepinephrine; D011224:Prazosin