The objective of this study was to compare renal interstitial hydrostatic pressure (RIHP) and sodium excretion in female and male Sprague-Dawley (SD) rats. The RIHP and pressure natriuresis responses were determined in female (n=13) and male (n=8) SD rats. Renal perfusion pressure (RPP) was controlled at two levels (100 and 120 mm Hg). Clearances were taken at each level and RIHP was measured with a chronically implanted polyethylene matrix in all rats. At the lower RPP level, RIHP was similar in both groups of rats (5.2+/-0.2 mm Hg for female, and 5.5+/-0.4 mm Hg for male), whereas fractional excretion of sodium (FENa) was significantly lower (P < .05) in male (1.10+/-0.27%) as compared to female (2.23+/-0.32%) rats at similar lower RPP. Allowing RPP to increase from 100 to 120 mm Hg resulted in similar increases in FENa (deltaFENa), urine flow rate (deltaV), and RIHP (deltaRIHP) in both groups of rats. The deltaFENa, deltaV, and deltaRIHP were 1.67+/-0.43%, 38.45+/-4.74 microL/min/g kidney weight, and 2.7+/-0.2 mm Hg for female, and 1.79+/-0.42%, 30.40+/-4.37 microl/min/g kidney weight, and 2.8+/-0.3 mm Hg for male rats. In conclusion, RIHP is similar in female and male SD rats at similar RPP levels. Both female and male SD rats increase RIHP and sodium excretion similarly in response to increases in RPP. The lower basal FENa in male as compared to female rats may play an important role in the more significant elevation of blood pressure in males with age.