The positive inotropic effect of troglitazone is not mediated via the cyclic AMP-PKA pathway or the PLC-PKC pathway. (A) Representative tracings of LVP before and after administration of isoproterenol (bolus injection of 5 pmol) or troglitazone (bolus injection of 1 μmol) after treatment with carbachol (3 μM) in isolated rat hearts. (B) The summarized data for the effect of vehicle, isoproterenol or troglitazone on LVPmax, dP/dtmax and dP/dtmin (n=5, respectively). While the positive inotropic effect of isoproterenol was completely inhibited by carbachol, the inotropic effect of troglitazone was not. (C) The positive inotropic effect of troglitazone was not inhibited by H89, U73122 or H7, either (n=5, respectively). (D) The cyclic AMP concentration in the left ventricle, as measured by radioimmunoassay (n=7, respectively), did not differ significantly between hearts perfused with vehicle and those perfused with troglitazone. Changes of parameters are expressed as per cent changes from the baseline values (B and C). *P<0.05 vs vehicle.