Urinary prostaglandins: site of entry into renal tubular fluid.

The stop-flow technique was used in dogs to determine the site of entry of urinary prostaglandins (PG) into tubular fluid. The proximal tubule was localized by the peak (U/PPAH)/(U/PIn) and the distal tubule and collecting duct by the peak U/PIn and the minimum (U/PNa)/(U/PIn). The peak of prostaglandin E (PGE) concentration was located 4.8+/-0.8 (SEM) ml distal to the proximal tubule and 4.6+/-0.8 (SEM) ml proximal to the distal nephron. At its peak, PGE was concentrated 6.3-fold over baseline, whereas inulin was concentrated 1.4-fold at its peak. The height of the PGE peak but not its location was increased by an i.v. infusion of angiotensin II at 20 ng/kg of body wt per min. Indomethacin abolished the PG peak. In a single experiment, prostaglandin F2alpha (PGF2alpha) exhibited an excretion pattern similar to PGE. These data indicate that the site of entry of PG into tubular fluid is most likely in the loop of Henle. This is consistent with the hypothesis that PG synthesized in the medulla can be transported to the cortex via tubular fluid. Whether PG in the tubular fluid can influence renal function remains to be determined.