Effect of renal interstitial infusion of arachidonic acid on proximal sodium reabsorption

The effect of prostaglandins (PGs) on proximal sodium reabsorption has not been fully defined. The objective of the present study was to determine the response of proximal tubular sodium reabsorption to infusions of arachidonic acid and specific PGs into the renal interstitium in rats. Renal interstitial infusions of arachidonic acid as well as the individual PGs, I2, E2, and F2 alpha, were employed to elevate the concentration of these PGs in the kidney. Infusion of 10(-4) M arachidonic acid elicited a marked increase of urinary excretion of 6-keto-PGF1 alpha (a stable metabolite of PGI2) from 260.1 +/- 52.7 to 507.4 +/- 129.5 pg/min (P less than 0.05) and a smaller increase of PGE2 from 18.4 +/- 11.2 to 25.9 +/- 10.9 pg/min (P less than 0.05). When micropuncture samples were obtained from superficial late proximal tubules, infusion of arachidonic acid increased the fractional delivery of sodium (FDNa) from 47.8 +/- 5.9 to 58.3 +/- 4.6% (n = 6, P less than 0.01). In the presence of indomethacin, arachidonic acid failed to augment FDNa. Infusion of 10(-5) M PGI2 also increased FDNa from 51.4 +/- 3.4 to 64.0 +/- 4.4% (n = 10, P less than 0.01). PGF2 alpha did not change FDNa and PGE2 decreased it from 53.1 +/- 5.4 to 37.4 +/- 3.3% (n = 8, P less than 0.01). In summary, the present study demonstrates that renal interstitial infusion of arachidonic acid decreases sodium reabsorption by the superficial proximal tubules possibly through the stimulation of PGI2 production.