Enriched prostaglandin E-9 ketoreductase activity in outer medullary cells of the rabbit kidney

PGE2 metabolism was examined in rabbit renal slices and cell suspensions from the outer medulla, enriched (TALH) and depleted (OMC) for the thick ascending limb of Henle's loop. Metabolism was negligible in intact cells, either OMC or TALH fractions. However, in OMC and TALH homogenates, transformation of PGE2 to PGF2 alpha by NADPH-dependent prostaglandin E-9 ketoreductase (PGE-9KR) was observed at a PGE2 concentration of 4 X 10(-9) M. This activity was not reversible and was enriched ten-fold in the TALH with 41% of PGE2 transformed to PGF2 alpha after 30 min incubation. PGF2 alpha formation from PGE2 could not be detected in homogenates of cortex, medulla or papilla. PGE-9KR activity, particularly in the thick ascending limb, may be a source of PGF2 alpha in urine.