 Individuals with reduced plasma concentration of high-density lipoprotein HDL cholesterol are more susceptible to oxidative stress and often present reduced endothelial function, which has been mainly related to this susceptibility. Studies in animal and cell models have demonstrated that niacin activates both GPR-109A in leukocytes and heme oxygenase-1 HO-1 pathway promoting strong anti-inflammatory and anti-oxidative effects. . In this context, the aim of this study was to investigate the short-term effect of niacin on endothelial function and verify the existence of interaction of PGD2 receptor antagonist, i.e. laropiprant LRPT, in subjects with low HDL-cholesterol HDL -C. 