1. Urinary prostaglandin (PG) E2 excretion and plasma renin were measured in five healthy volunteer subjects for 2 h after intravenous injection of frusemide (protocol A) and during salt restriction for 7 days with frusemide added on the 2 last days (protocol B).
2. In protocol A, peak values in PGE2 and urine flow were reached in 10–20 min, after which the values rapidly subsided. Plasma renin increased twofold in 60 min.
3. In protocol B, even during severe anti-natriuresis (day 5) and during maximal negative sodium balance (day 7), no change in urinary PGE2 excretion was observed. Plasma renin increased twofold on day 5 and increased tenfold on day 7.
4. The result of protocol B does not suggest any essential role of renal PGE2 for sodium excretion or sodium homeostasis in man. The result of protocol A may point to a role of renal prostaglandins for the diuretic action of frusemide.