Renal prostaglandins and sodium balance in normal man

We investigated the relationship between urinary prostaglandin E (PGE) excretion and sodium and water balance. PGE excretion was measured in thirteen healthy male volunteers on the metabolic ward during conditions of high sodium (200 mmols/day) and low sodium diets (40 mmols/day) and during intravenous administration of saline and of dextrose and water, using each subject as his own control. PGE excretion was higher on the high sodium than on the low sodium diet (191±37 SE versus 98±41 ng/6h, p<0.01). Saline and dextrose and water infusions significantly increased PGE excretion while subjects were on low sodium diets (to 314±74 and 443±152 ng/6h, respectively, p<0.01). while on high sodium diets the increase in PGE excretion during infusions was not significant. To further evaluate the role of prostaglandins in sodium excretion the study was repeated with simultaneous administration of indomethacin or ibuprofen to inhibit prostaglandin synthesis. Sodium excretion from saline and dextrose and water infusions were unaltered. The data suggest that dietary content of sodium may alter PGE excretion, but that acute changes in PGE excretion during saline administration reflect water balance rather than sodium load.