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  • Title: Heterogeneity of postjunctional alpha-adrenoceptors in isolated mesenteric resistance arteries from rats, rabbits, pigs, and humans.
    Author: Nielsen H, Pilegaard HK, Hasenkam JM, Mortensen FV, Mulvany MJ.
    Journal: J Cardiovasc Pharmacol; 1991 Jul; 18(1):4-10. PubMed ID: 1719290.
    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.
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