INTERACTION BETWEEN INHALATIONAL ANESTHETICS 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. Concen tration-response curves were obtained for the positive inotropic effec ts of enoximone on electrically stimulated left atria. 3. Enoximone si gnificantly (P < 0.01) increased the contractile force (56% maximum) w ith 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 e noximone alone. 5. Similar results were obtained with enoximone in the presence of halothane plus diltiazem. Isoflurane (1.5% v/v) did not s ignificantly 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. Th ese results shows that halothane, but not isoflurane, decreased the po tency of enoximone on the isolated left atria and suggests that this e ffect may be mediated by the blocking of the influx of extracellular c alcium through voltage-dependent calcium channels inhibited by diltiaz em.