SummaryThe effects of oleuropein, a phenolic compound in extra virgin olive oil (EVolive oil), on triglyceride metabolism were investigated by measuring the degree of thermogenesis in interscapular brown adipose tissue (IBAT), and noradrenaline and adrenaline secretions in rats. In Experiment 1, rats were given a high-fat diet (control diet) with the oleuropein supplementation of 1, 2 or 4 mg/kg of diet (0.1, 0.2 or 0.4% oleuropein diet, respectively). After 28 d of feeding, body weight, perirenal adipose tissue, epididymal fat pad, and plasma triglyceride, free fatty acid and total cholesterol concentrations were reduced by the 0.1, 0.2 or 0.4% oleuropein diet and were significantly lowest in rats fed the 0.4% oleuropein diet, as compared with those of rats fed with the control diet. The content of uncoupling protein 1 (UCP1) in IBAT and urinary noradrenaline and adrenaline excretions were significantly higher in rats fed the 0.1 or 0.2% oleuropein diet, as compared with those of rats fed with the control diet, although there were no significant differences in rats fed the 0.4% oleuropein diet. In Experiment 2, the effects of oleuropein on noradrenaline and adrenaline secretion were evaluated. The intravenous administration of oleuropein and oleuropein aglycone significantly increased plasma noradrenaline and adrenaline concentrations. Furthermore, oleuropein aglycone induced the secretions of noradrenaline and adrenaline about ten fold more potently than oleuropein. These results suggest that the phenolic compound oleuropein in EV-olive oil enhances thermogenesis by increasing the UCP1 content in IBAT and noradrenaline and adrenaline secretions in rats.