Relationship between alpha 2-adrenoceptor occupancy and response for B-HT 933 in canine saphenous vein.
The relationship between alpha 2-adrenoceptor occupancy and contractile response for B-HT 933 was investigated in canine saphenous vein. B-HT 933 produced a concentration-dependent, alpha 2-adrenoceptor mediated contractile response in canine saphenous vein with an ED50 of 0.65 microM. The dissociation constant (KA) of B-HT 933 was calculated to be 5 microM. The relationship between alpha 2-adrenoceptor occupancy and contractile response for B-HT 933 in canine saphenous vein was hyperbolic, typical of full agonists or agonists with high intrinsic efficacies. B-HT 933 produced a half-maximal response in canine saphenous vein at only 11% alpha 2-adrenoceptor occupancy, with a maximal response being obtained with 40-60% alpha 2-adrenoceptor occupancy. We conclude that the selective alpha 2-adrenoceptor agonist, B-HT 933, has high efficacy at alpha 2-adrenoceptors, such that a significant alpha 2-adrenoceptor reserve, or spare alpha 2-adrenoceptors, exists for this compound in canine saphenous vein.
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D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D001381:Azepines / Q000378:metabolism / Q000494:pharmacology*; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D012501:Saphenous Vein / Q000187:drug effects / Q000378:metabolism; D014661:Vasoconstriction / Q000187:drug effects
D000316:Adrenergic alpha-Agonists; D001381:Azepines; D011942:Receptors, Adrenergic, alpha; C015603:azepexole