To test the hypothesis that an acute increase in plasma homocysteine concentration (Hcy) produced by methionine loading is associated with an acute decrease in brachial artery blood flow measured by flow-mediated dilatation (FMD) using forearm plesthysmography.

A double-blind, cross-over, placebo controlled design was used and FMD of the brachial artery, plasma Hcy, plasma methionine, total cholesterol, high density lipoprotein (HDL) cholesterol, low density lipoprotein (LDL) cholesterol, plasma triglyceride, oxidised LDL, apolipoproteins (Apo) A1 and B and C reactive protein (CRP) were measured between 12 and 20 hours after methionine loading or placebo.

Between 12 and 20 hours, after a methionine loading test, acute hyperhomocysteinaemia had no significant effect on mean FMD compared to placebo (57.08±6.18ml/100ml/min versus 63.46±5.87ml/100ml/min, p<0.5). The mean age of the eight subjects was 71.5±6.9 years. Twelve hours after methionine, mean triglyceride concentration was significantly increased by 23.0% compared to placebo (1.51±0.47mmol/l versus 1.23±0.44mmol/l, p<0.02).

In elderly volunteers, acute hyperhomocysteinaemia induced by methionine loading resulted in no significant late impairment of endothelial function although further investigation is recommended. Acute hyperhomocysteinaemia resulted in a significant increase in plasma triglyceride concentration.