Vitamin C improves endothelial dysfunction in renal allograft recipients.

BACKGROUND Endothelial function is impaired in renal allograft recipients but the effects of antioxidant vitamin therapy on endothelial function in such patients is unknown. METHODS Thirteen renal allograft recipients were randomized to vitamin C or placebo in a double blind cross-over study design. Flow-mediated endothelium-dependent dilation and glyceryltrinitrate-induced endothelium-independent dilation of the brachial artery were assessed before and 2 h after oral administration of 2 g vitamin C or placebo. RESULTS Plasma vitamin C levels increased from 33.5+/-17.0 micromol/l to 98.8+/-60.2 micromol/l after treatment (P=0.0001). Endothelium-dependent dilation improved (from 1.6+/-2.6 to 4.5+/-2.5%) after vitamin C administration but was unchanged after placebo (1.9+/-1.5 to 1.8+/-2.5%; P=0.003 for vitamin C vs placebo). There was no significant change in endothelium-independent dilation in response to vitamin C. Vitamin C was also associated with a significant increase in the lag time in dilute serum oxidation (P=0.001). CONCLUSIONS Vitamin C acutely improves flow-mediated, endothelium-dependent dilation and increases the resistance of lipoproteins in dilute serum to oxidation in renal transplant recipients.