Renal effects of urodilatin in healthy subjects are independent of blockade of the cyclooxygenase and angiotensin II receptor.

Abstract

Objective: Little is known about the role of the renin-angiotensin-aldosterone system and the renal prostaglandins in modulating the renal vasoconstrictive and natriuretic effects of synthetic urodilatin (URO) in healthy humans.

Material and methods: Twelve volunteers were pretreated in a randomized, single-blind, crossover study with losartan 50 mg a day or placebo for 5 days. Another 12 healthy subjects received indomethacin 25 mg three times a day or placebo for 4 days and a single dose on day 5. All subjects received a URO infusion (15 ng kg(-1) min(-1)) on day 5. Radioactive tracers and the lithium clearance technique were used.

Results: The effective renal plasma flow (ERPF) decreased significantly during URO infusion: losartan pretreatment 573+/-63 to 461+/-76 mL/min versus placebo 540+/-89 to 432+/-90 mL/min. The urinary sodium excretion rate (UNa) increased significantly during URO infusion: losartan 335+/-115 to 502+/-134 umol/min (micromol/min) (UNa) versus placebo 386+/-142 to 476+/-137 umol/min (micromol/min) (UNa). In the indomethacin pretreated subjects, ERPF decreased significantly from 530+/-109 to 446+/-55 mL/min versus 533+/-89 to 449+/-69 mL/min in the placebo group. UNa increased significantly from 395+/-142 to 768+/-254 umol/min (micromol/min) (UNa) in the indomethacin group versus 282+/-117 to 552+/-242 umol/min (micromol/min) (UNa) in placebo.

Conclusion: The renal vasoconstrictive and natriuretic effects of synthetic URO are not modified by sustained inhibition of the angiotensin II receptor or the cyclooxygenase in man in a sodium replete state.