Pharmacological differentiation of postsynaptic alpha adrenoceptors in the dog saphenous vein

PJ Fowler, M Grous, W Price and WD Matthews

The dog saphenous vein has postsynaptic subpopulations of both alpha-1 and alpha-2 adrenoceptors which are easily demonstrable using selective agonists and antagonists. Specific alpha-1 (methoxamine and SK&F 89748) or mixed alpha-1, alpha-2 (l-norepinephrine and M7) agonists as well as the specific alpha-2 agonist, BHT 920, cause concentration-related contraction of this tissue. However, maximum contractions produced by alpha-2 activation are significantly less than maximum contractions produced by alpha-1 or combined alpha-1, alpha-2 adrenoceptor activation. SK&F 89748-induced contractions are competitively inhibited by prazosin (pA2 = 7.74) and rauwolscine (pA2 = 6.63); BHT 920-induced contractions are unaffected by prazosin but inhibited by rauwolscine (pA2 = 8.93). Contractile responses to l-norepinephrine are inhibited by prazosin, rauwolscine or phenoxybenzamine in a manner that suggests that norepinephrine interacts with two subtypes of alpha adrenoceptors in this tissue. These data indicate that the dog saphenous vein strip is a suitable in vitro preparation for study of drug action at both postsynaptic adrenoceptors inasmuch as either subpopulation of alpha adrenoceptor can be studied independently using specific agonists or antagonists.

Volume 229, Issue 3, pp. 712-718, 06/01/1984
Copyright © 1984 by American Society for Pharmacology and Experimental Therapeutics

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