Effects of pethidine and nalorphine on the mechanical and electrical activities of mammalian isolated ventricular muscle

Abstract

Summary1. The strength of the isometric mechanical contraction of electricallydriven ventricular muscle has been recorded simultaneously with the resting and action potentials; the effects of pethidine and of nalorphine on these parameters have been studied. 2. When lower concentrations of pethidine (0 22-6 5 ,ug/ml) were perfused, isometric peak tension was decreased in parallel with the maximum upstroke velocity of the action potential; these actions are considered to result from membrane stabilization. At higher concentrations (11-8-109 ,ug/ml) pethidine usually produced, in addition, a progressive decrease in the resting and action potentials associated with marked irregularities in, or even abolition of, the mechanical response. It is suggested that these effects of the higher doses might be due to a depression of ATPase activity in the myocardial membrane. 3. Compared with pethidine, nalorphine had similar, but weaker, actions. IntroductionThe following circulatory actions of pethidine and of nalorphine have been reported previously (Grundy, 1971). In the anaesthetized cat or rabbit, after intravenous doses of 2-10 mg/kg pethidine, the blood pressure responses typically consist of transient pressor or depressor changes preceding a more prolonged hypotensive phase, which is the result of direct musculotropic peripheral vasodilation and cardiac depression. In respect of this latter effect, on the Langendorff preparation of the guinea-pig heart a single administration of pethidine (10 p,g-2 mg) predominantly produces a dose-dependent decrease in the amplitude of the mechanical contraction accompanied, at the higher doses, by bradycardia and cardiac irregularities including arrest of the heart. In these preparations nalorphine, when given alone, acts like pethidine but is a much weaker agonist. Although nalorphine, in up to five times the pethidine dosage, does not usually prevent the cardiovascular actions of pethidine administered subsequently, it can

Arrhythmogenic, Antiarrhythmic and Inotropic Properties of Opioids

“…Most class III an tiarrhythmic agents under clinical and ex perimental evaluation have a more or less positive inotropic effect, and a possible link between class III antiarrhythmic action and positive inotropic action has been suggested [Platou and Refsum, 1983;Platou et al, 1986a, b]. The few previous studies on pe thidine's inotropic effect have yielded con flicting results [Grundy and Tritthart, 1972;Strauer, 1972: Rendig et al, 1980, but our study is in agreement with Rendig et al [1980] who demonstrated a consistent in crease in peak isometric tension and dT/dt at concentrations from 10~8 to 10~5 mol/1.…”