Temperature-dependent effects of halothane and isoflurane on the isolated left atrium.

The aim of the present study was to examine whether changes in temperature alter the effects of halothane and isoflurane on isolated left atria. Concentration-response curves for inotropic effects at different temperatures (30 degrees C, 37 degrees C, 40 degrees C) on electrically stimulated left atria of the rat were obtained. The change of temperature modified the maximal negative inotropic response to halothane. The maximal decrease induced by halothane was 12 +/- 2.3 per cent at 37 degrees C and 18 +/- 2.5 per cent at 30 degrees C. When the temperature increased up to 40 degrees C the maximal decrease of atrial inotropism was 46 +/- 2.1 per cent--significantly higher than obtained at 37 degrees C. However, the maximal effect obtained by isoflurane was not significantly affected by temperature (30 degrees C = 7 +/- 1.6 per cent; 37 degrees C = 8 +/- 1.8 per cent; 40 degrees C = 2 +/- 0.8 per cent). Furthermore the potency of halothane (expressed as the concentration which produced 50 per cent inhibition - IC 50 per cent), decreased significantly at 30 degrees C (IC 50 = 1.34 +/- 0.18) and increased at 40 degrees C (IC 50 = 0.44 +/- 0.17) when compared with its potency at 37 degrees C (IC 50 = 0.96 +/- 0.08). On the other hand changes in temperature did not significantly modify the IC 50 for isoflurane obtained at 37 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)