Interaction of isoflurane and sevoflurane with α- and β-adrenoceptor stimulations in rat myocardium

Background: Halothane potentiates the positive inotropic effects of alpha- and beta-adrenoceptor stimulations but impairs the positive lusitropic effect of beta-adrenoceptor stimulations. Dow ever, the interactions of isoflurane and sevoflurane with alpha- and beta-adrenoceptor stimulation have not been entirely defined. Methods: The effects of 1 minimum alveolar concentration isoflurane and sevoflurane on the inotropic responses induced by phenylephrine (10(-8) to 10(-4) M) or isoproterenol (10(-8) to 10(-4) M) were studied in rat left ventricular papillary muscles in vitro (Krebs-Henseleit solution, 29 degrees C; pH, 7.4; 0.5 mM calcium; stimulation frequency, 12 pulses/min). The positive lusitropic effects of alpha- and beta-adrenoceptor stimulations were studied under isotonic and isometric conditions. Data are mean percentages of baseline +/- SEM. Results: In control groups, phenylephrine (134 +/- 8%; P < 0.05) and isoproterenol (171 +/- 7%; P < 0.05) induced a positive inotropic effect. Isoflurane enhanced the positive inotropic effects of phenylephrine (185 +/- 10%; P < 0.05) and of isoproterenol (203 +/- 11%; P < 0.05). Sevoflurane enhanced the positive inotropic effects of phenylephrine (187 +/- 10%; P < 0.05) and of isoproterenol (228 +/- 11%; P < 0.05). These potentiations were similar to those previously reported with halothane. Isoflurane and sevoflurane did not modify the positive lusitropic effects under low and high loads of isoproterenol. Conclusion: Although isoflurane and sevoflurane have moderate negative inotropic effects, they potentiated the positive inotropic effects of alpha- and beta-adrenoceptor stimulations but did not modify the positive lusitropic effects of beta-adrenoceptor stimulation.