RENAL IDENTIFICATION OF CYCLOOXYGENASE-2 IN A SUBSET OF THICK ASCENDING LIMB CELLS

The prostaglandin G2/H2 synthase (cyclooxygenase, COX) is a key regula tory enzyme of prostanoid synthesis pathway. The message-encoding COX isoenzymes (constitutive COX-1 and inducible COX-2) have been describe d in the rat kidney. However, there is scarce information on the local ization of COX-2 in the kidney, although it has been recently reported to be localized in the macula densa. The present study was designed t o evaluate the localization of COX-2 in adult rat kidneys. Normal rat kidneys (n=10) were fixed in Bouin and were immunostained with specifi c antibodies against COX-2 by the peroxidase method. The cellular orig in of COX-2 was assessed by the immunostaining of serial consecutive s ections with antibodies against Na-K-ATPase, Tamm-Horsfall glycoprotei n, H-K-ATPase, kallikrein, and macrophages. COX-2 was consistently obs erved in a subset of tubular cells located in the cortex and in the ou ter medulla. The staining of serial sections showed that the COX-2+ ce lls contained both Na-K-ATPase and Tamm-Horsfall, indicating that they corresponded to thick ascending limb (TAL) cells. They were observed at a considerable distance from the corresponding macula densa, althou gh occasionally they were observed close to glomeruli. The COX-2 stain ing in the TAL cells was not abolished by dexamethasone treatment (1 t o 20 mg/kg), suggesting its constitutive expression in normal kidneys. The presence of COX-2 in TAL (a tubular segment postulated to be devo id of COX-1) may contribute to the handling of ions through local prod uction of prostaglandins.