The objectives of the present study were to evaluate the effects of a methionine-supplemented diet on systolic blood pressure (BP) and vasomotor functions in Sprague–Dawley (SD) and deoxycorticosterone acetate (DOCA)–salt hypertensive rats. SD and DOCA rats were fed a normal or a methionine (8 g/kg)-supplemented diet for 10 weeks. Systolic BP was monitored and plasma homocysteine, methionine and cysteine levels were determined at the end of the experiment. Vasoconstriction and vasodilatation of aortic rings were measured. The methionine-supplemented diet induced a greater increase in homocysteinaemia concentration in DOCA rats than in SD rats and an increase in plasma cysteine concentration in DOCA rats. This diet was associated with an increase in systolic BP in SD rats and with a lesser development of DOCA–salt hypertension. An enhanced aortic constriction and a decreased responsiveness to acetylcholine, bradykinin and sodium nitroprusside in the SD rats fed the methionine-rich diet were consistent with the elevated systolic BP. In DOCA rats the increased responsiveness to bradykinin was in accordance with the systolic BP-lowering effect. In conclusion, the methionine-enriched diet cannot simply be considered as model of hyperhomocysteinaemia, since other metabolites and mechanisms seemed to be implicated in these complex interactions. The differential vasopressive effect of the methionine supplementation in SD and DOCA rats, and in particular the lowering of systolic BP obtained with a greater degree of hyperhomocysteinaemia in DOCA rats, suggest that more complex interactions exist between hyperhomocysteinaemia and BP than the simple positive association described previously.

The objectives of the present work were to evaluate the effect of a methionine-supplemented diet as a model of hyperhomocysteinaemia on the systolic blood pressure (BP) and vasomotor functions of aortic rings in Wistar–Kyoto (WKY) and spontaneously hypertensive rats (SHR). WKY and SHR rats, randomised into four groups, were fed a normal semisynthetic diet or a methionine (8 g/kg)-supplemented diet for 10 weeks. Systolic BP was measured non-invasively. At the end of the experiment, plasma homocysteine, methionine, cysteine and glutathione levels were determined. Vasoconstriction and vasodilatation of aortic rings were measured. The methionine-supplemented diet induced a significant increase in plasma homocysteine and methionine concentration in both WKY and SHR rats, an increase in plasma cysteine concentrations in WKY rats and an increase in the glutathione concentration in SHR. The systolic BP of WKY rats fed the methionine-supplemented diet increased significantly (P<0·01), whereas systolic BP was reduced in SHR. An enhanced aortic responsiveness to noradrenaline and a decreased relaxation induced by acetylcholine and bradykinin were observed in the WKY rats fed the methionine-enriched diet. In SHR, the bradykinin-induced relaxation was reduced, but the sodium nitroprusside response was increased. In conclusion, a methionine-enriched diet induced a moderate hyperhomocysteinaemia and an elevated systolic BP in WKY rats that was consistent with the observed endothelial dysfunction. In SHR, discrepancies between the decreased systolic BP and the vascular alterations suggest more complex interactions of the methionine-enriched diet on the systolic BP. Further investigations are needed to understand the paradoxical effect of a methionine-rich diet on systolic BP.