19-hydroxy-5-8-11-14-eicosatetraenoic-acid and 14-15-epoxy-5-8-11-eicosatrienoic-acid

The cytochrome P450-dependent monoxygenase pathway represents a major route for the metabolism of arachidonic acid (AA) in the kidney. In turn, AA metabolites have been shown to affect renal electrolyte metabolism, including sodium transport. Specifically AA, 20-HETE and 12-HETE inhibit sodium-dependent (Na+-Pi) uptake into renal culture cells, and both 12-HETE and 14,15 EET have been shown to reduce renin release from renal cortical slices. Since the bulk of Pi transport occurs in the proximal tubule (PT), and the PT is a major site of AA metabolism, we studied the effect of AA and several of its metabolites on Na+-Pi uptake into PT-like opossum kidney (OK) cells. Incubation of OK cells in AA (10(-8) M) resulted in 17% inhibition of Pi uptake. Three metabolites of omega-hydroxylation of AA induced significant decreases in Pi uptake: 19R-HETE (10(-8) M) by 36% (P=0.008), 19S-HETE (10(-8) M) by 24% (P=0.002) and 20-COOH-AA (10(-8) M), a metabolite of 20-HETE, by 25% (P<0.0001). 14,15 EET (10(-8) M), a breakdown product of AA by the epoxygenase pathway, had the greatest effect on Pi uptake in OK cells. It decreased Pi uptake by 47% (P < 0.0001). Addition of the P450 inhibitor, 7-ER (10(-8) M), to OK cells resulted in a significant stimulation (28%) of Pi uptake (P=0.016). These results indicate that these AA metabolites have a significant inhibitory effect on Na+-Pi uptake in OK cells.

Topics: 8,11,14-Eicosatrienoic Acid; Animals; Arachidonic Acid; Biological Transport; Cell Line; Electrolytes; Hydroxyeicosatetraenoic Acids; Ion Transport; Kidney Cortex; Kidney Tubules, Proximal; Opossums; Oxazines; Phosphates; Renin; Sodium

The renovascular effects of cytochrome P450-dependent arachidonic acid (P450-AA) metabolites synthesized by rat and rabbit kidneys were studied in the rabbit isolated kidney under conditions of constant flow and examined for their dependency on cyclooxygenase relative to their expression of vasoactivity. Kidneys were perfused with Krebs-Henseleit solution, and perfusion pressure was raised to levels of 90 to 110 mm Hg with the addition of 2 to 3 microM phenylephrine to the perfusate. Close arterial injection of 1 to 20 micrograms of 5,6-, 8,9- and 11,12-epoxyeicosatrienoic acid (EET) dose-dependently decreased perfusion pressure. The 5,6-EET was the most potent and the only epoxide dependent on cyclooxygenase for expression of vasoactivity, being inhibited by indomethacin (2.8 microM). In contrast, 14,15-EET resulted in dose-dependent increases in perfusion pressure. The vasodilator effects of the omega- and omega-1 oxidation products, 20-hydroxyeicosatetraenoic acid (HETE) and the stereoisomers of 19-HETE, were also inhibited by indomethacin. Furthermore, the renal vasodilator responses to 5,6-EET were not inhibited by either superoxide dismutase (10 U) or catalase (40 U) and, therefore, were unrelated to the formation of oxygen radicals generated during transformation of the epoxide by cyclooxygenase. As 5,6-EET and 19- and 20-HETE are synthesized by the renal tubules and can affect movement of salt and water, expression of vasoactivity by P450-dependent arachidonic acid metabolites, and after release from a nephron segment, may represent a mechanism that couples altered renal tubular function to appropriate changes in local blood flow.

Topics: 8,11,14-Eicosatrienoic Acid; Animals; Arachidonic Acid; Arachidonic Acids; Blood Pressure; Cyclooxygenase Inhibitors; Cytochrome P-450 Enzyme System; Eicosanoids; Free Radicals; Hydroxyeicosatetraenoic Acids; In Vitro Techniques; Kidney; Male; Prostaglandin-Endoperoxide Synthases; Rabbits; Renal Circulation; Vascular Resistance