Modifications of the inotropic responses to α- and β-adrenoceptor stimulation by propofol in rat myocardium

Propofol induces cardiovascular depression but without significant effect on intrinsic myocardial contractility in many species. However, its interactions with adrenoceptor stimulation are unknown. We studied the effects of propofol (1 and 10 mu g/mL) and its solvent on the inotropic response induced by phenylephrine (10(-8)-10(-4) M) or isoproterenol (10(-8)-10(-4) M) in rat left Ventricular papillary muscles in vitro (Krebs-Henseleit solution, 29 degrees C, pH 7.40, calcium 0.5 mM, stimulation frequency 12 pulses/min). We also studied the lusitropic effects in isotonic and isometric conditions. Zn control groups, phenylephrine (127% +/- 3% of baseline; P < 0.05) and isoproterenol (169% +/- 11% of baseline; P < 0.05) induced a positive inotropic effect. Propofol (10 mu g/mL) completely abolished the positive inotropic effect of phenylephrine (100% +/- 3% of baseline; P = not significant). In contrast, at the lowest concentration (1 mu g/mL), propofol did not modify the positive inotropic ef feet of phenylephrine. Propofol did not modify the inotropic effect of isoproterenol. Propofol (10 mu g/mL) enhanced the positive lusitropic effect of isoproterenol under low-load (P < 0.05) but not under high-load conditions. Implications: A high concentration of propofol abolished the positive inotropic effect of alpha- but not beta-adrenoceptor stimulation and enhanced the positive lusitropic effect of beta-adrenoceptor stimulation.