Increased urinary 6-keto-PGF1 alpha excretion during water immersion is blunted by metoclopramide in normal man

Urinary excretion of 6-keto-PGF1 alpha and 2,3 dinor-6-keto-PGF1 alpha, as indices of the renal and systemic production of prostaglandins, was measured during water immersion in a group of 6 healthy volunteers both in the presence and absence of dopamine blockade by the dopamine receptor antagonist, metoclopramide. Urinary flow rate and excretion of both sodium and 6-keto-PGF1 alpha increased during water immersion, while plasma renin activity and plasma aldosterone were reduced. Urinary kallikrein and 2,3 dinor-6-keto-PGF1 alpha also tended to increase during water immersion. Administration of metoclopramide significantly reduced 6-keto-PGF1 alpha and sodium excretion during water immersion, but produced no changes in plasma renin activity or in 2,3 dinor-6-keto-PGF1 alpha. Plasma aldosterone concentrations after metoclopramide were similar to those observed in the pre-immersion period. An increased synthesis of the vasodilator and natriuretic prostacyclin in the kidney might play a role in the response to water immersion. The reduced sodium and 6-keto-PGF1 alpha excretion observed after metoclopramide administration suggests that dopamine might induce prostacyclin synthesis in the kidney during water immersion.