title: Heterogeneity of postjunctional alpha-adrenoceptors in isolated mesenteric resistance arteries from rats, rabbits, pigs, and humans.
abstract: Mesenteric resistance arteries (internal diameter 174-337 microns) from rats, rabbits, pigs, and humans were isolated and mounted in a myograph. In all preparations, phenylephrine (alpha 1-adrenoceptor agonist) evoked concentration-dependent contractions that were antagonized by prazosin (alpha 1-adrenoceptor antagonist). B-HT 933 (alpha 2-adrenoceptor agonist), however, did not evoke contractions in any rat or rabbit vessels. In contrast, this agonist elicited contractions in some (five of 15) porcine and all (18) human vessels; in the vessels responsive to B-HT 933, the maximum responses amounted to 53 +/- 7 and 79 +/- 6%, respectively, of the responses to high potassium. The affinities of yohimbine (alpha 2-adrenoceptor antagonist) for the receptors mediating responses to B-HT 933 were 7.46 +/- 0.13 (pKB) and 7.57 +/- 0.10 (pA2), respectively. Prazosin (10(-8) M) antagonized the responses to norepinephrine in all preparations, whereas yohimbine (10(-7) M) caused significant inhibition of these responses in human vessels only; moreover, the inhibition in these vessels of the responses to norepinephrine caused by the combination of these two antagonists was greater than the antagonism caused by either antagonist alone. These results suggest the presence of postjunctional alpha 1-adrenoceptors that are involved in responses to norepinephrine in mesenteric resistance arteries from all species examined. Functional, postjunctional alpha 2-adrenoceptors appear to be present in porcine and human vessels, but this receptor seems to be involved in responses to norepinephrine in human vessels only.
authors.affiliation: Institute of Pharmacology, University of Aarhus, Denmark.
authors.forename: H
authors.initials: H
authors.lastname: Nielsen
authors.forename: H K
authors.initials: HK
authors.lastname: Pilegaard
authors.forename: J M
authors.initials: JM
authors.lastname: Hasenkam
authors.forename: F V
authors.initials: FV
authors.lastname: Mortensen
authors.forename: M J
authors.initials: MJ
authors.lastname: Mulvany
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D001381:Azepines / Q000494:pharmacology; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008638:Mesenteric Arteries / Q000502:physiology; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000502:physiology*; D009638:Norepinephrine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011817:Rabbits; D051381:Rats; D011919:Rats, Inbred Strains; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D013045:Species Specificity; D013552:Swine; D014655:Vascular Resistance / Q000502:physiology; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D000318:Adrenergic beta-Agonists; D001381:Azepines; D011943:Receptors, Adrenergic, beta; D010656:Phenylephrine; D015016:Yohimbine; C015603:azepexole; D009638:Norepinephrine; D011224:Prazosin