Contribution of 4-hydroxy-2,3-trans-nonenal to the reduction of β-adrenoceptor function in the heart by oxidative stress

Oxidative stress reduces adenylate cyclase activity and also the maximal response to β-adrnoceptor stimulation in the rat heart, while β-adrenoceptor density is not affected or increased. Since free sulfhydryl groups are essential to β-adrenoceptor function and the sulfhydryl reactive substance 4-hydroxy-2,3- trans-nonenal (HNE) is responsible for part of the effects of oxidative stress, the effect of HNE on β-adrenoceptor function in field stimulated left atria of the rat was determined. To this end field stimulated atria were incubated with 10 μM, 100 μM and 1 mM HNE for 25 min. After removing the excess of HNE, β-adrenoceptor function was determined by measuring the positive inotropic response to (-)-isoproterenol. It was found that 10 μM HNE had no effect on β-adrenoceptor function, whereas 100 μM HNE reduced the maximal effect to (-)-isoproterenol without affecting the pD 2 (-log EC 50). At these concentrations, HNE had no effect on either β-adrenoceptor density or on c-AMP production. After 1 mM HNE, the atria stopped contracting. Since the effects of the synthetic thiol inactivator N-ethyl maleimide were similar to those of HNE, it was concluded that the reduction of β-adrenoceptor function by HNE is probably the result of alkylation of free sulfhydryl groups. Our results indicate that the reduction of adenylate cyclase activity by oxidative stress is not mediated by the production of HNE, however oxidative stress and HNE both reduce the maximal response to β-adrenoceptor stimulation.