The catecholamine-mediated positive inotropic effect of simple quinones is related to superoxide anion generation.

In guinea pig and rat cardiac tissue, redox cycling benzoquinones (2,5-dimethyl-p-benzoquinone and duroquinone) and naphthoquinones (menadione and 2,3-dimethoxy-1,4-naphthoquinone) generated superoxide anion (O2-.) both through one- and two-electron reductions, the generation being significantly greater in guinea pig than in rat tissue. In electrically driven left atria isolated from guinea pig and rat, menadione and 2,5-dimethyl-p-benzoquinone but not duroquinone caused a concentration-dependent positive inotropic effect. Unlike guinea pig, 2,3-dimethoxy-1,4-naphthoquinone had no effect in rat tissue. Naphthoquinones and 2,5-dimethyl-p-benzoquinone were more active in guinea pig than in rat tissue, their effect being dependent on the release of catecholamines from adrenergic stores. A linear relationship (r = 0.90) between the amount of O2-. generated by benzo- and naphthoquinones in guinea pig and rat heart and the extent of catecholamine-dependent positive inotropic effect was evident. An amount of O2-. higher than 600 nmol/g of tissue per min was calculated to be necessary to determine the catecholamine-mediated increase in contractility. Lipid peroxidation was not involved in quinone-induced catecholamine release.