Localization and properties of NAD⁺-dependent 15-hydroxyprostaglandin dehydrogenase activity in the rat kidney

Abstract

Localization of NAD⁺-dependent (type I) 15-hydroxyprostaglandin dehydrogenase (15PGDH) in the rat kidney was examined using an ultramicro assay of the enzyme activity based on the enzymatic cycling method. The enzyme activities during first 3 weeks of age were 30- to 40-fold higher than the adult and rapidly decreased by 4th week. 15PGDH activities measured with either PGE₂ or PGF_2α as a substrate were five times higher in slices from midcortical or juxtamedullary layers than in slices from the superficial cortex of 3 week-old rat kidney. Little activity was found in inner medulla and papilla. When the enzyme activity was assayed using isolated nephron segments dissected from collagenase treated slices of 3 week-old rat kidneys, the activity was localized only in the proximal convoluted and straight tubules with either PGs (PGE₂: 1.75±0.25 in PCT, 7.70±1.19 in PST, and PGF_2α: 1.63±0.39, 6.18±1.52 pmoles NADH/mm/40 min). The kinetic analysis for renal 15PGDH of 3 week-old rats revealed thatK _m for PGE₂ (8.4 μM) was lower than that for PGF_2α (22.6 μM) with constant NAD⁺, whileV _max for both was similar. In contrast, bothK _m andV _max for NAD⁺ were identical with either PGs. These data suggest that the rate-limiting factor of type I 15PGDH is the concentration of prostaglandins in the kidney rather than the concentration of NAD⁺. It is thought that the enzyme may be physiologically significant in inactivating the prostaglandins reaching the proxial tubule in order to ensure that the classical prostaglandins (PGE₂ and PGF_2α) produced in the medullary interstitium and collecting tubules can effectively regulate the distal nephron function.