Prostaglandin synthesis inhibition during volume expansion: Collecting duct function

Abstract

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.

Papillary collecting tubule synthesis of prostaglandin E2 in Dahl rats.

“…24 There is also indirect evidence, in vivo, of prostaglandin-mediated inhibition of sodium reabsorption in the medullary collecting tubule of the rat. 10 To investigate the onset phase of hypertension in Dahl rats, we conducted our initial studies in young, prehypertensive animals. Urinary PGEj excretion, which is predominantly of renal inner medullary origin, 6 was clearly decreased in the DS compared with the DR, confirming die work of others.…”

“…8 Renal medullary microsomes from DS also underproduced PGEj as compared with microsomes from DR. 9 Reduction of medullary PGEj may be important in the defective natriuresis observed in the DS strain. Prostaglandins have a role in promoting natriuresis in the inner medullary collecting duct in volume-expanded rats, 10 a situation somewhat analogous to high salt feeding. Indeed, the inner medullary collecting duct may reabsorb up to 6% of the filtered sodium load" in volume expansion.…”

Effect of bradykinin B2 receptor antagonist and indomethacin on natriuretic and hypotensive responses to atrial natriuretic factor

“…However, on a per kilogram body weight basis, the Indo dose was at least an order of magnitude lower than in the present experiments. At doses similar to those used here, Endo blunts the natriuretic response to extracellular fluid volume expansion by increasing reabsorption in the ascending limb of Henale's loop (Higashhara et al 1979) and the medullary collecting duet (Wilson et d. 1982). These effects are due to prostaglandin inhibition, since the stmcturdly dissimilar drug meclofenamate shows similar responses Wigashihara et al0 1979; Wilson et d. 1982).…”

Effect of acetylcholine and secretin on medullary collecting duct function in the rat

“…The full expression of the natriuretic effect of Ach requires an intact prostaglandin system (Yun et al 1984). Since prostaglandin inhibition increases sodium reabsorption from the medullary collecting duct (Wilson et al 1982), stimulation of prostaglandin release by acetylcholine could account for the specific inhibition of duct transport.…”