Prostaglandin synthesis inhibition during volume expansion: collecting duct function.

The aim of this study was to examine the possible role of renal prostaglandins in the response of the inner medullary collecting duct (IMCD) to acute volume expansion. Collecting duct microcatheterization and clearance studies were carried out in anesthetized rats, volume-expanded with isotonic Ringer's solution. In volume-expanded control animals, there was no significant sodium or chloride reabsorption between the beginning and end (papillary tip) of the IMCD. Administration of indomethacin or meclofenamate prior to and during volume expansion in two other groups of rats resulted in significant water, sodium, and chloride reabsorption along the IMCD and markedly blunted the diuretic, natriuretic and chloriuretic response to volume expansion. Because delivery to the beginning of the duct was not significantly decreased, enhanced reabsorption in the IMCD largely accounted for the decrease in natriuresis and chloriuresis. Inner medullary tissue fluid chloride concentration increased after inhibition of prostaglandin synthesis. The results indicate that renal prostaglandins, perhaps by directly decreasing sodium chloride reabsorption, have an important role in the decrease in collecting duct reabsorption of sodium and chloride observed with acute volume expansion.