Previous studies have shown that the elevation of renal interstitial hydrostatic pressure by the direct expansion of renal interstitial volume increases urinary sodium excretion. The objective of the present study was to investigate whether proximal tubules respond to the elevated renal interstitial hydrostatic pressure and whether the inhibition of prostaglandin synthesis would alter the effect of elevated renal interstitial hydrostatic pressure on proximal sodium reabsorption. Expansion of renal interstitial volume by injecting 100 μl of 2.5percent; albumin solution through a chronically implanted matrix increased renal interstitial hydrostatic pressure similarly in control rats (n=8) and in indomethacin (n=8) or meclofenamate-treated (n=7) rats. In the absence of prostaglandin synthesis inhibition, renal interstitial volume expansion significantly increased the fractional delivery of sodium at the superficial late proximal tubules from 56.5±6.1 to 67.0±6.5percent; (p<0.01) with an accompanying increase in fractional excretion of sodium from 2.1±0.5 to 3.0±0.4percent; (p<0.01). In the presence of indomethacin or meclofenamate, renal interstitial volume expansion failed to augment the fractional delivery of sodium and the fractional excretion of sodium. In summary, these studies demonstrate that the synthesis of prostaglandins plays a role in the regulation of sodium reabsorption by the proximal tubules in response to elevated renal interstitial hydrostatic pressure.