Renal prostaglandin E₂ synthesis in the brattleboro homozygous diabetes insipidus rat

The effect of vasopressin (VP) on prostaglandin (PG) synthesis in the renal collecting tubule remains equivocal. To further address this issue, the present study determined the effects of chronic absence of VP on renal medullary collecting tubule PG synthesis. Prostaglandin E₂ (PGE₂) synthesis was measured in both inner and outer medullary slices and collecting tubules microdissected from the inner medulla (PCD) and outer medulla (MCT) of Brattleboro homozygous diabetes insipidus (DI) rats, which are genetically devoid of VP, and from Long Evans (LE) control rats. In vitro PGE₂ synthesis was significantly lower in. both inner medulary (Δ - 56%; p < 0.001) and outer medullary (Δ - 56%; p < 0.01) slices of DI rats compared to controls. Vasopressin tannate treatment (0.5 U/day for 5 days) increased urinary PG excretion, and increased in vitro PGE₂ synthesis in both inner and outer medullary slices of DI rats to levels that did not differ from vehicle-treated LE controls. In contrast, PGE₂ synthesis in both PCD and MCT of DI rats did not differ from LE controls when incubated either in an isotonic (300 mOsm) medium, or in an hypertonic (1000 mOsm) medium. These results suggest that PGE₂ biosynthetic capacity of medullary collecting tubules in the DI rat is not dependent on VP, while depressed PGE₂ synthesis in renal medullary slices of DI rats, suggests that the interstitial cell is the primary medullary site of PG synthesis which is modulated by VP.