Recent studies suggested that leptin in white adipose tissue (WAT) affected the sympathetic out flow to several tissues. We examined whether elevations of renal sympathetic nerve activity (RSNA) and blood pressure (BP) could be observed by leptin injection into WAT in rats. Injections of leptin (10 and 100 ng/ml per kg) into WAT evoked the activation of RSNA dose-dependently. Circulating sympathetic nerve activators, such as leptin, insulin, glucose and lactate, were unchanged by any doses of leptin. In addition, BP was not affected by leptin injections during a 90 min experimental period. These data suggested that leptin activated the afferent nerves through the sensors in WAT, resulting in elevation of RSNA.