CytochromeP-450-dependent metabolism of arachidonic acid in the kidney of rats with diabetes insipidus

Abstract

. Cytochrome P-450-dependent metabolism of arachidonic acid in the kidney of rats with diabetes insipidus. Am J Physiol Renal Physiol 289: F1333-F1340, 2005. First published July 12, 2005 doi:10.1152/ajprenal.00188.2005.-This study compared the renal metabolism of arachidonic acid in Brattleboro (BB) (vasopressin deficient) and Long-Evans (LE) control rats and the effects of a cytochrome P-450 (CYP) inhibitor 1-aminobenzotriazole (ABT) on renal function in these animals. The production of 20-hydroxyeicosatetraenoic acid (20-HETE) by renal cortical and outer medullary microsomes was significantly greater in BB than in LE rats (155 Ϯ 16 vs. 92 Ϯ 13 and 59 Ϯ 7 vs. 33 Ϯ 3 pmol ⅐ min Ϫ1 ⅐ mg protein Ϫ1 ). Renal cortical epoxygenase activity was not different in these strains. The expression of CYP4A proteins was 58 and 78% higher in the renal cortex and outer medulla of BB than in LE rats. Chronic treatment of BB rats with a vasopressin type 2 receptor agonist for 1 wk normalized the renal production of 20-HETE. Chronic blockade of the formation of 20-HETE and EETs with ABT had little effect on renal function in LE rats. However, urine flow increased by 54% and urine osmolarity decreased by 33% in BB rats treated with ABT. Plasma levels of oxytocin fell significantly from 7.2 Ϯ 1.3 to 3.9 Ϯ 1.0 pg/ml. The effects of ABT in BB rats were attenuated by chronic infusion of oxytocin (0.7 ng ⅐ min Ϫ1 ⅐ 100 g Ϫ1 ) to maintain fixed high plasma levels of this hormone. These results indicate that the expression of CYP4A protein and the renal formation of 20-HETE are elevated in the kidney of BB rats due to a lack of vasopressin and that chronic blockade of the formation of 20-HETE and EETs with ABT promotes water excretion in vasopressin-deficient BB rats by reducing the circulating levels of oxytocin, which is a weak vasopressin agonist. Brattleboro rats; 20-hydroxyeicosatetraenoic acid; cytochrome P-450; epoxyeicosatrienoic acid; renal hemodynamics ARACHIDONIC ACID (AA) is metabolized by cytochrome P-450 (CYP) enzymes in the kidney to produce epoxyeicosatrienoic acids (EETs), 20-hydroxyeicosatetraenoic acid (20-HETE), and dihydroxyeicosatrienoic acids (DiHETEs). These compounds have been reported to play an important role in the control of both renal tubular and vascular function (26). EETs are potent endothelial-derived vasodilators in the renal circulation (17, 47). They also inhibit sodium and water reabsorption in the collecting duct (40). In contrast, 20-HETE is produced by vascular smooth muscle cells and is a potent constrictor of renal arterioles (5,19,23). Inhibition of the synthesis of 20-HETE attenuates the vasoconstrictor response of renal arterioles to elevations in transmural pressure in vitro (16, 18) and autoregulation of renal blood flow and tubuloglomerular feedback responses in vivo (8,48). At the level of the renal tubules, 20-HETE inhibits sodium reabsorption in the proximal tubule and thick ascending limb of the loop of Henle (6,32,34,39).Previous studies indicated that the renal production of EETs an...

Group VIA phospholipase A2is a target for vasopressin signaling in the thick ascending limb

“…The observed reduction of outer medullary iPLA 2 ␤ levels in dDAVP-treated DI rats as well as the pharmacologically induced inhibition of iPLA 2 ␤ in mTAL cells are therefore likely to result in a decrease in 20-HETE, which in turn may cause an activation of NKCC2. In line with this assumption, earlier studies have shown an increased capacity for 20-HETE synthesis in outer medullary tissue preparations from DI rats that was reduced by dDAVP treatment (36).…”

Mechanisms of Podocyte Injury in Diabetes

“…The predominant CYP450 in the kidney cortex that synthesizes 20-HETE is cytochrome P450 of the 4A family (CYP4A) ( 19 – 21 ). 20-HETE has multiple and opposing functions depending on the site of production and target cells/tissues ( 19 , 22 – 24 ).…”

Chronic activation of vasopressin V2 receptor signalling lowers renal medullary oxygen levels in rats

“…Other vasoactive mediators that have been implicated in the regulation of AVP signalling in the renal medulla include angiotensin 2, endothelin, ATP, adenosin and eicosanoids such as 20‐HETE and EETs (Sarkis et al . , Stricklett et al . , Dobrowolski et al .…”