Alpha-adrenoceptor reserve in the canine cephalic vein.
In the canine cephalic vein, the pD2 for the selective alpha 1-agonist, phenylephrine, was 6.08 +/- 0.08 (n = 14) and that for the selective alpha 2-agonist, UK-14,304, was 8.32 +/- 0.06 (n = 10). The pA2 values for the antagonism exerted by the selective alpha 1-antagonist, prazosin, against phenylephrine and UK-14,304 were 7.74 +/- 0.05 (n = 14) and 6.28 +/- 0.03 (n = 8), respectively, while those for the antagonism exerted by the selective alpha 2-antagonist, yohimbine, against phenylephrine and UK-14,304 were 7.40 +/- 0.02 (n = 14) and 8.93 +/- 0.05 (n = 14), respectively. Furthermore, the concentration-response curve for UK-14,304 was typically biphasic, the first phase being antagonized by yohimbine and the second phase by prazosin and phenoxybenzamine. These results show that there are postsynaptic alpha 1- and alpha 2-adrenoceptors in the canine cephalic vein. In such a preparation, only one concentration of phenoxybenzamine (1 nM) shifted the concentration-response curves for noradrenaline, adrenaline and isoprenaline to the right without reducing the maximum. However, at the concentrations tested, phenoxybenzamine did not shift the concentration-response curve for phenylephrine to the right without depressing its maximum. It is concluded that: (1) the canine cephalic vein is a suitable preparation to study postsynaptic alpha 1- and alpha 2-adrenoceptors; (2) according to the original definition of 'spare receptors', there is no alpha 1-adrenoceptor reserve in canine cephalic vein; (3) UK-14,304 is a partial agonist at alpha 1-adrenoceptors.
Moura
D
D
Department of Pharmacology, Faculty of Medicine, Porto, Portugal.
Vaz-da-Silva
M J
MJ
Guimarães
S
S
D000818:Animals; D000068438:Brimonidine Tartrate; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D005260:Female; D005552:Forelimb / Q000098:blood supply*; D008297:Male; D010643:Phenoxybenzamine / Q000032:analysis / Q000494:pharmacology*; D010656:Phenylephrine / Q000037:antagonists & inhibitors*; D011224:Prazosin / Q000494:pharmacology*; D011810:Quinoxalines / Q000037:antagonists & inhibitors*; D011942:Receptors, Adrenergic, alpha / Q000032:analysis / Q000187:drug effects*; D014661:Vasoconstriction; D014680:Veins; D015016:Yohimbine / Q000494:pharmacology*
D011810:Quinoxalines; D011942:Receptors, Adrenergic, alpha; D010643:Phenoxybenzamine; D010656:Phenylephrine; D015016:Yohimbine; D000068438:Brimonidine Tartrate; D011224:Prazosin