Effects of osmolality and antidiuretic hormone on prostaglandin synthesis by renal papilla. Study in Brattleboro rats with diabetes insipidus.

Prostaglandin (PG) production by the kidney is known to be reduced both in vivo and in vitro in rats with hereditary diabetes insipidus (DI), totally lacking ADH. Exogenous ADH restores normal PG excretion in these rats. On the other hand, osmolality in vitro, and urine flow rate in vivo have been shown to influence PG synthesis rate. In order to determine whether the decreased PG synthesis of DI rats is due to the lack of antidiuretic hormone itself or to low tissue osmolality, we studied in vivo and in vitro PG production in DI rats in which urine osmolality had been raised either with ADH (infused by Alzet minipumps), or without ADH (by dehydratation) and in control DI rats. PGE2 and PGF2 alpha were measured by radioimmunoassay in the urines and in supernatants of papillary homogenates incubated at 37 degrees C for 15-120 min. ADH administration and dehydration led to similar urine osmolalities (congruent to 900-1,000 mosmol/kg H2O versus 150 in controls). However, only ADH administration but not dehydration increased PG urinary excretion (X 5, P less than 0.001) and subsequent in vitro papillary synthesis (X 1.6, P less than 0.01). These results show that antidiuretic hormone increases PG-synthesis of the renal papilla directly and not through its effects on papillary osmolality.