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(Hypertension. 1999;33:145-152.)
© 1999 American Heart Association, Inc.

Scientific Contributions

Inotropic Effects of Endothelin-1

Interaction With Molsidomine and With BQ 610

Martin E. Beyer; Günther Slesak; Tobias Hövelborn; Silke Kazmaier; Stefan Nerz; Hans Martin Hoffmeister

From the Medizinische Klinik, Abt III, Eberhard-Karls-Universität, Tübingen, Germany.

Correspondence to Dr Martin E. Beyer, Medizinische Universitätsklinik, Abteilung III, Otfried-Müller-Str 10, 72076 Tübingen, Germany. E-mail martin-eberhard.beyer{at}dgn.de

Abstract—In vivo studies could not detect a positive inotropy of endothelin (ET)-1 as described in in vitro experiments. ET-induced direct positive inotropy, which seems to be mediated by ET_B receptors, may be antagonized in vivo by an indirect cardiodepressive effect owing to an ET-induced coronary vasoconstriction via ET_A receptors. This study compares the effects of a dose of 1 nmol/kg ET-1 alone on myocardial contractility and myocardial energy metabolism with the effects of 1 nmol/kg ET-1 after pretreatment with 5 mg/kg molsidomine or with 100 µg/kg of the ET_A receptor antagonist BQ 610. We investigated the effects of ET-1 versus saline controls in open-chest rats. In addition to measurements in the intact circulation, myocardial function was examined by isovolumic registrations independent of peripheral vascular effects. We also studied the effect of ET-1 on myocardial high-energy phosphates. Pretreatment with molsidomine and BQ 610 attenuated the ET-induced reduction of cardiac output (ET-1: -62%; molsidomine+ET-1: -47%; BQ 610+ET-1: -27% different from controls). After a transient initial vasodilation, ET-1 raised total peripheral resistance (ET-1: +190%; molsidomine+ET-1: +171%; BQ 610+ET-1: +89%). BQ 610 was more effective in preventing ET-induced vasoconstriction. The increase of isovolumic peak first derivative of left ventricular pressure (ET-1: -2%; molsidomine+ET-1: +16%; BQ 610+ET-1: +19%) after pretreatment with molsidomine or BQ 610 indicates that these drugs unmask the positive inotropy of ET-1. ET-induced myocardial ischemia was abolished by molsidomine and BQ 610. Pretreatment with molsidomine or blockade of ET_A receptors by BQ 610 can unmask the positive inotropy of ET-1 by preventing ET-induced myocardial ischemia. The positive inotropic effect of ET-1 seems to be mediated by ET_B receptors.

Key Words: endothelin • BQ 610 • molsidomine • contractility • phosphates, high-energy • rats

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