ARACHIDONIC-ACID PROTECTS AGAINST HYPOXIC INJURY IN RAT PROXIMAL TUBULES

Free fatty acids (FFA) and lysophospholipids accumulate during hypoxia (H) in rat proximal tubular epithelial cells partly as a result of in creased phospholipase A(2) (PLA(2)) activity. The role of FFA in media ting hypoxic injury and modulating PLA(2) activity is not dear. In the present study, the effect of several FFA including arachidonic acid ( AA, 20:4) on hypoxia-induced injury and PLA(2) activity was assessed i n freshly isolated rat proximal tubules. Hypoxia (H) was induced in th e presence of either an unsaturated free fatty acid (uFFA) [AA or lino leic acid (LA, 18:2)] or a saturated FFA (sFFA) [palmitic (PA, 16:0) o r myristic acid (MA, 14:0)]. Cell membrane injury was assessed by meas uring lactate dehydrogenase release (LDH). AA markedly reduced LDH rel ease during hypoxia in a dose dependent manner, while sFFA had no prot ective effect. LA showed similar protection to that observed with AA. AA did not affect buffer calcium concentration, buffer pH, intracellul ar pH or intracellular calcium concentration. Neither inhibiting the c yclooxygenase pathway with indomethacin, nor the lipoxygenase pathway with nordihydroguaiaretic acid (NDGA) had any effect on the AA observe d cytoprotection. In vitro PLA(2) activity in the control tubular extr acts was compared to that following addition of AA or PA. PLA, activit y decreased significantly with AA but not with PA in a dose dependent manner. These data suggest that: (1) AA protects against hypoxic injur y in rat proximal tubules. (2) This cytoprotection is not specific for AA and other uFFA have a similar effect. (3) AA significantly inhibit s PLA(2) activity. (4) AA induced cytoprotection may be related to a n egative feedback inhibition of PLA(2) activity.