The purpose of the present study was to investigate the effects of chronic methionine treatment on vascular smooth muscle contractility for angiotensin II (Ang II). Methionine at 0.1, 1 and 2 g/kg body weight was administered daily in the drinking water for 2, 4, 8 and 16 weeks. Rat carotid rings from control and treated animals were placed in an organ chamber containing Krebs solution. Concentration-response curves for Ang II and potassium chloride (KCl) were determined. Methionine-rich diet enhanced the plasmatic homocysteine concentration, and the magnitude of the contractile response to Ang II was increased in carotid rings from treated animals after 8 and 16 weeks. However, the treatment did not alter KCl-induced contraction. In another set of experiments, the rings were incubated with indomethacin and curves for Ang II were obtained. Exposure of the rings to indomethacin inhibited the enhancement in the contractile response to Ang II. The present findings show that chronic methionine treatment enhances homocysteine plasmatic concentration leading to an enhanced Ang-II-induced contraction, which appears to be related to the release of vasoconstrictor prostanoid(s).
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