A reduction of endogenous asymmetric dimethylarginine contributes to the effect of captopril on endothelial dysfunction induced by homocysteine in rats

We examined whether captopril exerts beneficial effect on homocysteine-induced endothelial dysfunction in vivo and whether this effect of captopril is associated with a reduction of endogenous inhibitor of nitric oxide synthase (NOS) asymmetric dimethylarginine (ADMA) in rats. Male Sprague-Dawley rats were given intravenous injections of homocysteine (10 mg/kg/day) to induce endothelial dysfunction. Captopril treatment (3 mg/kg/day, i.v.) was taken in some rats after homocysteine administration. Endothelium-dependent relaxation was tested in aortic rings. Serum levels of ADMA, nitrite/nitrate, malondialdehyde (MDA), and creatinine were measured. Furthermore, superoxide dismutase activity in liver and angiotensin converting enzyme activity in serum were also assayed. Administration of homocysteine to rats for 4 weeks significantly impaired endothelium-dependent relaxation compared with control rats. This impairment of endothelium-dependent relaxation was accompanied by elevated serum concentration of ADMA and decreased serum content of nitrite/nitrate. Moreover, serum concentration of MDA was remarkably increased, whereas liver superoxide dismutase activity was decreased in homocysteine-treated group compared with control. Chronic captopril treatment not only improved the impaired endothelium-dependent relaxation, but also prevented the elevation of serum ADMA and MDA levels, as well as reduction of serum nitrite/nitrate contents and liver superoxide dismutase activity. Serum angiotensin converting enzyme activity and creatinine had no significant difference between the three groups. These results suggest that chronic captopril treatment reduces endogenous inhibitor of NOS in rats with homocysteine injection, which may contribute to the beneficial effect of captopril on homocysteine-induced endothelial dysfunction in vivo, and may be secondary to the antioxidative action of captopril.