Exogenous nitric oxide stress on endothelial cells and macrophages.

Bovine endothelial cells (ECs, P1) and lipopolysaccharide/gamma-interferon-induced mouse macrophages (MMs) were incubated in the presence of SIN-1 and C 3754 (1 microM to 1 mM), sydnonimine metabolites of the antianginal predrugs molsidomine and pirsidomine, respectively up to 48 h. No change of the endogenous nitric oxide output from MMs and A23187- or adenosine triphosphate-stimulated ECs was found by means of the methemoglobin method. Data indicate that downregulation of the nitric oxide (NO) synthase is not obvious within the intact cells under exogenous NO stress supplied by high concentrations of the spontaneous NO donors. Cytosolic MM NO synthase extracts, however, revealed reduction in the enzymic [3H]arginine turnover to [3H]citrulline by SIN-1, but not by C 3786, the pharmacologically active metabolite of pirsidomine.