Antidiuretic hormone reduces the high PGE2 synthesis in papillary collecting duct of DI rats.

PGE2 synthesis was measured along the nephron of Brattleboro (DI) rats, lacking ADH, and control LE rats, using an enzyme immunoassay. Experiments were performed in vitro, in the absence of exogenous arachidonic acid, using microdissected tubular segments. The effect of a chronic treatment of dDAVP was tested on three ADH sensitive tubular segments, medullary thick ascending limb (MTAL), medullary collecting tubule (OMCD) and papillary collecting duct (IMCD). No difference in PGE2 synthesis was present between LE and DI in glomerulus and tubular segments up to OMCD. In both strains, values were low in the proximal tubule and the loop of Henle, and gradually increased along the collecting tubule. In IMCD, PGE2 synthesis was much higher in DI (12.8 +/- 2.0 pg per 30 min per mm tubular length) than in LE (3.8 +/- 0.5, LE vs. DI p less than 0.001). In MTAL and OMCD, dDAVP treatment did not affect PGE2 synthesis. In IMCD, dDAVP reduced PGE2 synthesis to values (5.3 +/- 0.8 pg per 30 min per mm tubular length), which were not significantly different from those of LE. Neither oxytocin, which has been shown to be elevated in DI rats, nor furosemide, that reduced papillary osmolarity to values comparable to those of DI rats, were able to increase PGE2 synthesis in IMCD of LE rats. The mechanism of the increase in PGE2 synthesis in IMCD of DI rats, and of the inhibitory effect of dDAVP is yet unknown; it may participate to compensate for the lack of ADH in the Brattleboro rat.