Positive inotropic and chronotropic effects of beraprost sodium, a stable analogue of prostacyclin, in isolated guinea pig myocardium

Abstract

1. 1. Inotropic and chronotropic effects of beraprost sodium (beraprost), a chemically stable prostacyclin analogue, were examined in isolated myocardial preparations of guinea pigs. 2. 2. In the left atria, 10 −9-10 −7 M beraprost had no significant effect on the contractile force, but 10 −6 and 10 −5 M produced a concentration-dependent positive inotropic response. This effect was antagonized by S-145, a potent and selective thromboxane A 2 (TXA 2) receptor antagonist, but not by propranolol. 3. 3. Beraprost, from 10 −9 to 10 −5 M, had no significant inotropic effect in the right ventricular papillary muscles. 4. 4. In the right atria, 10 −9 and 10 −8 M beraprost had no significant effect, but 10 −7-10 −5 M caused an increase in beating rate; this effect was not affected by S-145. 5. 5. The present study demonstrates that beraprost has positive inotropic and chronotropic effects at high doses on isolated guinea pig atria. The inotropic effect may be mediated by the TXA 2 receptor, but some mechanism other than the TXA 2 receptor is responsible for the chronotropic effect.