Interaction between inhalational anaesthetics and enoximone on isolated heart muscle

1. The present study describes the effects of halothane or isoflurane on enoximone activity in the isolated left atria of the rat. 2. Concentration-response curves were obtained for the positive inotropic effects of enoximone on electrically stimulated left atria. 3. Enoximone significantly (P < 0.01) increased the contractile force (56% maximum) with all the concentrations tested (10(-9) -10(-3) M). 4. When halothane (1.5% v/v) was present in the organ bath, the maximum effect obtained with enoximone (9%) was significantly lower than that obtained with enoximone alone. 5. Similar results were obtained with enoximone in the presence of halothane plus diltiazem. Isoflurane (1.5% v/v) did not significantly modify the maximum effect obtained with enoximone alone. 6. The administration of diltiazem antagonized the positive inotropic effects of enoximone in the presence of isoflurane or halothane. 7. These results shows that halothane, but not isoflurane, decreased the potency of enoximone on the isolated left atria and suggests that this effect may be mediated by the blocking of the influx of extracellular calcium through voltage-dependent calcium channels inhibited by diltiazem.