However, Di Bona suggested that hyperleptinemia could Vismodegib induce a reduction in the RPF, renal vasoconstriction, enhanced renin secretion and de novo Ang II synthesis. Our results are in accordance with Di Bona0s findings because in rats treated with leptin for 7 days, we observed a slight decrease in the RPF, and this decrease was progressive and achieved statistical significance in rats treated for 28 days. In both treatment periods, the RPF was normalized in the leptin plus losartan group, indicating that leptin acting on the sympathetic nervous system can induce vasoconstriction in the renal arterioles and activate the RAS. The discrepancy between our results and Gunduz`s findings can be justified by the different methods used. Gunduz et al. evaluated the RBF by an indirect method, using a laser module system, whereas in our study, the RPF was analyzed through PAH clearance. In the present study, leptin treatment for 7 or 28 days did not result in GFR changes. However, although not significantly different, the alterations of the GFR and RPF observed in the present study are physiologically relevant because the FF was significantly higher in rats treated with leptin for 7 and 28 days. Only the leptin plus losartan rats treated for 7 days displayed a completely normalized FF, suggesting that in the 28-day group, not only the Ang II/AT1 receptor, but also other factors such as ET-1 and NO participates in the FF enhancement. ET-1 is the main peptide of the endothelin family, which includes ET-2 and ET-3. ET-1 binds to two different receptors: ETA, which mediates vasoconstriction and ETB, which mediates vasodilation and inflammatory processes. Furthermore, in many diseases, the synthesis and activity of ET-1 is increased in the kidneys. Gunduz et al., studying hyperleptinemic rats, demonstrated an increase in the plasma ET-1 levels, which were normalized by co-treatment with losartan. In the present study, we did not observe changes in plasma ET-1 levels. However, of note, in the study performed by Gunduz et al., the leptin dose was much higher compared with the doses used by us. Furthermore, Beltowski et al. demonstrated that leptin treatment induces renal oxidative stress and decreases NO availability. The NO deficiency contributes to the intrarenal resistance and induces hemodynamic changes, by modulating the FF. The urinary flow rate increased in the leptin-treated rats for 7 days and was normalized in the leptin plus losartan group. In contrast, the rats treated for 28 days exhibited no differences in the urinary flow rate. Controversy exists regarding Na+ regulation with chronic leptin infusion. Kuo et al. did not observe any differences in Na+ excretion, whereas Beltowski et al. showed Na+ retention and Gunduz et al. demonstrated a natriuretic effect. Villarreal et al. suggested that the increase in the fractional excretion of Na+ without changes in the GFR could be due to a tubular mechanism. In fact, the identification of the long leptin receptor in the renal medulla, primarily in the MLN4924 medullary collecting ducts, indicates that this segment is a possible target for leptin��s direct action.