Hydroxylated chlorpromazine metabolites: positive inotropic action and the release of catecholamines

Temma, K.; Akera, T.; Brody, T.M.

Molecular Pharmacology 13(6): 1076-1085

1977


ISSN/ISBN: 0026-895X
PMID: 201831
Accession: 068523866

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Abstract
The mechanism of the positive inotropic action of the 7-mono- and 7,8-dihydroxylated metabolites of chlorpromazine was studied in isolated guinea pig hearts. In electrically driven left atrial preparations, these metabolites and 3,7,8-trihydroxychlorpromazine produced positive inotropic effects, which were prevented by prior treatment with either reserpine or propranolol. Although 7,8-dihydroxychlorpromazine is a potent inhibitor of (Na+ + K+)-ATPase in vitro, it failed to affect Na pump activity in Langendorff preparations at the time of the positive inotropic effect, indicating that this compound cannot gain access to the site of inhibition on the Na pump during the relatively short perfusion period. 7,8-Dihydroxychlorpromazine altered the transmembrane action potential configuration. These changes were similar to those produced by catecholamines. 7,8-Dihydroxychlorpromazine also increased the cyclic-AMP concentration in atrial muscles, an effect that appeared to be related to the positive inotropic action. Both these effects were prevented by prior treatment with reserpine. In electrically driven left atrial preparations, 7,8-dihydroxychlorpromazine released previously loaded [3H] metaraminol without affecting its uptake. The hydroxylated metabolites of chlorpromazine probably release catecholamines from cardiac sympathetic nerve terminals and increase myocardial contractile force.