Niacin (nicotinic acid) has recently been shown to increase serum adiponectin concentrations in men with the metabolic syndrome. However, little is known about the mechanism(s) by which niacin regulates the intracellular trafficking and secretion of adiponectin. Since niacin appears to exert its effects on lipolysis through receptor (GPR109A)-dependent and -independent pathways, the purpose of this investigation was to examine the role of the recently identified GPR109A receptor in adiponectin secretion. Initial in vivo studies in rats demonstrated that niacin (30 mg/kg po) acutely increases serum adiponectin concentrations, whereas it decreases NEFAs. Further in vitro studies demonstrated an increase in adiponectin secretion and a decrease in lipolysis in primary adipocytes following treatment with niacin or -hydroxybutyrate (an endogenous ligand of the GPR109A receptor), but these effects were blocked when adipocytes were pretreated with pertussis toxin. Niacin had no effect on adiponectin secretion or lipolysis in 3T3-L1 adipocytes, which have limited cell surface expression of the GPR109A receptor. To further substantiate these in vitro findings, wild-type and GPR109A receptor knockout mice were administered a single dose of niacin or placebo, and serum was obtained for the determination of adiponectin and NEFA concentrations. Serum adiponectin concentrations increased and serum NEFAs decreased in the wild-type mice within 10 min following niacin administration. However, niacin administration had no effect on adiponectin and NEFA concentrations in the GPR109A receptor knockout mice. These results demonstrate that the GPR109A receptor plays an important role in the dual regulation of adiponectin secretion and lipolysis. nicotinic acid; PUMA-G; HM74A; nonesterified fatty acids; lipolysis NIACIN (NICOTINIC ACID) HAS BEEN USED for more than 50 years as a pharmacological agent for the treatment of dyslipidemia and remains an effective strategy to decrease serum triglycerides and increase HDL cholesterol concentrations (6,19). In one of the first randomized clinical trials of heart disease prevention, niacin reduced serum triglyceride concentrations by 27% and nonfatal myocardial infarctions and cardiovascular disease (CVD) mortality by 27 and 26%, respectively (6a). More recent studies provide evidence that niacin is associated with a reduction in the number of angiographically documented vascular lesions and carotid artery intima-media thickness in patients with CVD (16, 31).The cardioprotective benefits of niacin have been attributed primarily to improvements in blood lipid and lipoprotein characteristics and reductions in vascular inflammation and thrombosis (18). However, recent studies have demonstrated that niacin significantly modulates serum adipokine concentrations. Westphal et al. (36) demonstrated that 6 wk of niacin treatment increased serum adiponectin concentrations by 54% in obese men with the metabolic syndrome. Investigations from our laboratory support these findings and further demonstrate th...