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Department of Physiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655
Adenosine
A2a-receptor activation enhances shortening of isolated
cardiomyocytes. In the present study the effect of
A2a-receptor activation on the contractile performance of
isolated rat hearts was investigated by recording left ventricular
pressure (LVP) and the maximal rate of LVP development
(+dP/dtmax). With constant-pressure perfusion,
adenosine caused concentration-dependent increases in LVP and
+dP/dtmax, with detectable increases of 4.1 and
4.8% at 10
6 M and maximal increases of 12.0 and 11.1%
at 10
4 M, respectively. The contractile responses were
prevented by the A2a-receptor antagonists
chlorostyryl-caffeine and aminofuryltriazolotriazinyl-aminoethylphenol (ZM-241385) but were not affected by the
1-adrenergic antagonist atenolol. The adenosine
A1-receptor antagonist dipropylcyclopentylxanthine and
pertussis toxin potentiated the positive inotropic effects of
adenosine. The A2a-receptor agonists
ethylcarboxamidoadenosine and
dimethoxyphenyl-methylphenylethyl-adenosine also enhanced contractility. With constant-flow perfusion, 10
5 M
adenosine increased LVP and +dP/dtmax by 5.5 and
6.0%, respectively. In the presence of the coronary vasodilator
hydralazine, adenosine increased LVP and
+dP/dtmax by 7.5 and 7.4%, respectively.
Dipropylcyclopentylxanthine potentiated the adenosine contractile
responses with constant-flow perfusion in the absence and presence
of hydralazine. These increases in contractile performance were also
antagonized by chlorostyryl-caffeine and ZM-241385. The results
indicate that adenosine increases contractile performance via
activation of A2a receptors in the intact heart independent
of
1-adrenergic receptor activation or changes in coronary flow.
adenosine A1 receptor;
1-adrenergic receptor; myocardial contractility; constant-pressure-perfused heart; constant-flow-perfused heart; A1 antagonists; A2a antagonists; hydralazine
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