Fluroxene and isolated heart muscle.
The direct myocardial effects of fluroxene were examined in isometrically and isotonically contracting isolated rat heart muscle. MAC, the minimum anesthetic concentration needed to prevent movement in response to tail clamping, was found to be 5.0 vol per cent fluroxene in the rat. At 4.6 vol per cent fluroxene, peak developed isometric tension and maximum rate of tension development were decreased 29 and 24 per cent, respectively. At 11 vol per cent, the depressions were 39 and 33 per cent. At 26.4 vol per cent, the depressions were around 60 per cent. Vmax (the maximum shortening velocity of unloaded muscle) of the force-velocity relation was unaltered by fluroxene concentrations of 0.8, 4.6, and 11 vol per cent. Even at 26.4 vol per cent, the depression in Vmax was only 25 per cent. Po (the maximum force at zero velocity), work, and power were lowered much more, with reductions ranging from 15 to 27 per cent at 4.6 vol per cent, from 40 to 42 per cent at 11.0 vol per cent, and from 65 to 69 per cent at the 26.4 vol per cent. Series elastic extension was unchanged at 0.8 and 4.6 vol per cent fluroxene, but was decreased 16 per cent at 11.0 vol per cent and 46 per cent at 26.4 vol per cent fluroxene. The data indicate the fluroxene has a direct negative inotropic effect that is associated with increased series elastic stiffness, but does not involve Vmax of the force-velocity relation until quite high anesthestic concentrations are reached. Comparative studies were also carried out with halothane. MAC for halothane in the rat was 1.0 vol per cent. The relative potency of halothane compared with fluroxene in depression of Vmax was 13.2, and its relative potency in depression of Po, 4.0.
D000769:Anesthesia, Inhalation; D000818:Animals; D004548:Elasticity; D004987:Ethers / Q000494:pharmacology*; D006221:Halothane / Q000494:pharmacology; D006352:Heart Ventricles / Q000187:drug effects; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000187:drug effects*; D051381:Rats
D004987:Ethers; D006221:Halothane