Time-dependent effect of leptin on renal Na+,K+-ATPase activity

Leptin, secreted by adipose tissue, is involved in the pathogenesis of arterial hypertension, however, the mechanisms through which leptin increases blood pressure are incompletely elucidated. We investigated the effect of leptin, administered for different time periods, on renal Na+,K+-ATPase activity in the rat. Leptin was infused under anesthesia into the abdominal aorta proximally to the renal arteries for 0.5-3 h. Leptin administered at doses of 1 and 10 mu g/min per kg for 30 min decreased the Na+,K+-ATPase activity in the renal medulla. This effect disappeared when the hormone was infused for 2:1 h. Leptin infused for 3 h increased the Na+,K+-ATPase activity in the renal cortex and medulla. The stimulatory effect was abolished by a specific inhibitor of Janus kinases (JAKs), tyrphostin AG490, as well as by an NAD(P)H oxidase inhibitor, apocynin. Leptin increased urinary excretion of hydrogen peroxide (H 202) between 2 and 3 h of infusion. The effect of leptin on renal Na+,K+-ATPase and urinary H2O2 was augmented by a superoxide dismutase mimetic, tempol, and was abolished by catalase. In addition, infusion of H2O2 for 30 min increased the Na+.K+-ATPase activity. Inhibitors of extracellular signal regulated kinases (ERKs), PD98059 or U0126, prevented Na+,K+-ATPase stimulation by leptin and H2O2. These data indicate that leptin, by acting directly within the kidney, has a delayed stimulatory effect on Na+,K+-ATPase, mediated by JAKs, H2O2 and ERKs. This mechanism may contribute to the abnormal renal Na+ handling in diseases associated with chronic hyperleptinemia such as diabetes and obesity.