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Am J Physiol Heart Circ Physiol 261: H762-H767, 1991;
0363-6135/91 $5.00
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AJP - Heart and Circulatory Physiology, Vol 261, Issue 3 762-H767, Copyright © 1991 by American Physiological Society

ARTICLES

Alpha-adrenoceptors in human resistance arteries from colon, pericardial fat, and skeletal muscle

H. Nielsen, J. M. Hasenkam, H. K. Pilegaard, F. V. Mortensen and M. J. Mulvany
Institute of Pharmacology, University of Aarhus, Denmark.

Human resistance arteries (144-332 microns diam) from colon, pericardial fat, and skeletal muscle were mounted in a myograph for measurements of isometric contractions under conditions of partial depolarization by potassium chloride. In all preparations, both phenylephrine (alpha 1-selective agonist) and B-HT 933 (alpha 2-selective agonist) evoked concentration-dependent contractions that were antagonized by the alpha 1-selective antagonist prazosin (10(-8) M) and the alpha 2-selective antagonist yohimbine (10(-7) M), respectively. The affinities (expressed as pKB values) of prazosin for the receptor mediating the responses to phenylephrine were 8.88-9.41, whereas the affinities of yohimbine for the receptor mediating the responses to B-HT 933 were 7.71-7.97. Norepinephrine (mixed alpha 1-agonist/alpha 2-agonist) also elicited concentration-dependent responses that were modestly, but significantly, antagonized by prazosin alone and yohimbine alone at the above-mentioned concentrations. The two antagonists in combination, however, effectively antagonized the responses to this agonist. These findings strongly suggest the presence of functional, postjunctional alpha 1- and alpha 2-adrenoceptors in isolated human resistance arteries from colon, pericardial fat, and skeletal muscle and that responses to norepinephrine in these vessels are mediated by both alpha-adrenoceptor subtypes.


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