Renal cytochrome P450 omega-hydroxylase and epoxygenase activity are differentially modified by nitric oxide and sodium chloride

Renal function is perturbed by inhibition of nitric oxide synthase (NOS). T o probe the basis of this effect, we characterized the effects of nitric ox ide (NO), a known suppressor of cytochrome P450 (CYP) enzymes, on metabolis m of arachidonic acid (AA), the expression of omega-hydroxylase, and the ef flux of 20-hydroxyeicosatetraenoic acid (20-HETE) from the isolated kidney. The capacity to convert [C-14]AA to HETEs and epoxides (EETs) was greater in cortical microsomes than in medullary microsomes. Sodium nitroprusside ( 10-100 mu M), an NO donor, inhibited renal microsomal conversion of [C-14]A A to HETEs and EETs in a dose-dependent manner. 8-bromo cGMP (100 mu M), th e cell-permeable analogue of cGMP, did not affect conversion of [C-14]AA. I nhibition of NOS with N-omega-nitro-L-arginine-methyl ester (L-NAME) signif icantly increased conversion of [C-14]AA to HETE and greatly increased the expression of omega-hydroxylase protein, but this treatment had only a mode st effect on epoxygenase activity. L-NAME induced a 4-fold increase in rena l efflux of 20-HETE, as did L-nitroarginine, Oral treatment with 2% sodium chloride (NaCl) for 7 days increased renal epoxygenase activity, both in th e cortex and the medulla. In contrast, cortical omega-hydroxylase activity was reduced by treatment with 2% NaCl. Coadministration of L-NAME and 2% Na Cl decreased conversion of [C-14]AA to HETEs without affecting epoxygenase activity. Thus, inhibition of NOS increased omega-hydroxylase activity, CYP 4A expression, and renal efflux of 20-HETE, whereas 2% NaCl stimulated epox ygenase activity.