Characterization of beta-adrenoceptors in pig basilar artery from functional and radioligand binding studies.
beta-Adrenoceptors in pig basilar arteries were investigated by measuring the relaxation response to norepinephrine and by a radioligand binding assay with [3H]-dihydroalprenolol (DHA). Norepinephrine induced concentration-dependent relaxations. The relaxation responses were independent of the presence of endothelial cells, and they were competitively antagonized by (+/-)-propranolol, atenolol, butoxamine and ICI 118,551. Specific [3H]-DHA binding to beta-adrenoceptors was saturable, reversible and high affinity (Kd = 1.4 nM), with a Bmax of 48.7 fmol/mg protein. Computer analysis of inhibition of [3H]-DHA binding by atenolol, butoxamine and ICI 118,551 gave a beta 1: beta 2-adrenoceptor ratio of approximately 65:35. The pA2 values of these antagonists were significantly correlated with the Ki values for beta 1-adrenoceptor determined by the radioligand binding assay. The present findings indicate that the relaxation responses to norepinephrine are predominantly mediated through the stimulation of beta 1-adrenoceptors on vascular smooth muscle cells in a pig basilar artery.
Miyamoto
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A
Department of Veterinary Pharmacology, Faculty of Agriculture, Kagoshima University, Japan.
Ito
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K
Nishio
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D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000818:Animals; D001488:Basilar Artery / Q000187:drug effects / Q000378:metabolism*; D004082:Dihydroalprenolol; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D066298:In Vitro Techniques; D009126:Muscle Relaxation / Q000187:drug effects; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011869:Radioligand Assay; D011943:Receptors, Adrenergic, beta / Q000187:drug effects / Q000378:metabolism*; D013552:Swine
D000319:Adrenergic beta-Antagonists; D011943:Receptors, Adrenergic, beta; D004082:Dihydroalprenolol; D011433:Propranolol; D009638:Norepinephrine; D010646:Phentolamine