Interactions between thiopental and volatile anesthetics (halothane and isoflurane) in isolated heart preparations of the rat.

Thiopental uptake into heart muscle tissue was studied in spontaneously beating rat hearts (Langendorff preparation, 0.13-0.27 mmol/l thiopental in the perfusion fluid). Up to 0.19 mmol/l the concentration of thiopental in heart muscle tissue was increased vs. control when halothane (0.8 vol%) was present. Using a constant thiopental concentration (0.13 mmol/l) and 0.8, 1.5 or 2.0 vol% halothane +12%, +29% or +43% more thiopental was taken up into heart muscle tissue compared to the control. This increased uptake was not seen in the presence of 1.2 and 2.0 vol% isoflurane. Frequency of right rat atria was decreased by increasing thiopental concentrations (0.02-0.23 mmol/l in the incubation medium). Halothane (0.8 and 1.5 vol%) and isoflurane (1.0 and 2.0 vol%) alone had no influence on frequency of right atria. Both volatile anesthetics additionally increased the negative chronotropic action of thiopental when the corresponding higher concentration was applied. Contractile force of left rat atria was decreased concentration-dependently by thiopental (0.02-0.23 mmol/l). Halothane and isoflurane alone decreased contractility. Dependent on the concentration used, both volatile anesthetics further increased the negative inotropic action of thiopental, yet preferentially at higher barbiturate concentrations.