Heterogeneity of smooth muscle alpha adrenoceptors in rat tail artery in vitro
Vascular smooth muscle alpha adrenoceptors in the proximal end of the rat isolated tail artery have been classified by determining pA2 values and -log KB values for the antagonists prazosin, corynanthine and idazoxan (RX 781094, a new synthetic alpha-2 adrenoceptor antagonist) against norepinephrine...
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Published in | The Journal of pharmacology and experimental therapeutics Vol. 229; no. 3; pp. 823 - 830 |
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Main Authors | , |
Format | Journal Article |
Language | English |
Published |
Bethesda, MD
American Society for Pharmacology and Experimental Therapeutics
01.06.1984
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Subjects | |
Online Access | Get full text |
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Summary: | Vascular smooth muscle alpha adrenoceptors in the proximal end of the rat isolated tail artery have been classified by determining
pA2 values and -log KB values for the antagonists prazosin, corynanthine and idazoxan (RX 781094, a new synthetic alpha-2
adrenoceptor antagonist) against norepinephrine. The effects of the antagonists on responses to intramural sympathetic nerve
stimulation were also assessed. Artery segments were perfused and superfused with Krebs' solution containing cocaine (4 microM)
and propranolol (1 microM). Maximum responses to KCl, norepinephrine and nerve stimulation were not significantly different
from one another. Corynanthine (0.1-100 microM), prazosin (10 nM-1 microM) and idazoxan (1-100 microM) caused competitive
antagonism of norepinephrine responses with pA2 values consistent with the presence of alpha-1 adrenoceptors. However, idazoxan
(10-100 nM) also caused parallel shifts in the concentration-response curves to norepinephrine with -log KB values higher
than those consistent with the presence of alpha-1 adrenoceptors. The results have been interpreted to suggest a predominance
of smooth muscle alpha-1 adrenoceptors in addition to a subpopulation of smooth muscle alpha-2 adrenoceptors which also contribute
to vasoconstrictor responses to norepinephrine. In contrast to the results obtained with exogenous norepinephrine, responses
to electrical stimulation were exquisitely sensitive to blockade by prazosin but resistant to idazoxan , suggesting an involvement
of an alpha-1 adrenoceptor in these responses. It is concluded that idazoxan may be used to distinguish alpha-1 and alpha-2
adrenoceptors on vascular smooth muscle in vitro and that the results favor the existence of alpha-1 and alpha-2 adrenoceptors
in terms of the existing subclassification scheme for alpha adrenoceptor subtypes. |
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Bibliography: | ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23 ObjectType-Article-1 ObjectType-Feature-2 |
ISSN: | 0022-3565 1521-0103 |