text: It was found that a single intragastric gavage by << L-methionine >> resulted in inhibition of endothelium-dependent relaxation, markedly increased the serum level of malondialdehyde and decreased the activity of PON1 and [[ SOD ]], similarly decreased the level of NO in the serum; but had no effects on endothelium-independent relaxation and angiotensin-converting enzyme activity compared with the control group.