Considerable evidence has accumulated over the last decade implicating a role of cytochrome P450 (CYP)-dependent metabolites of arachidonic acid (AA) in the pathogenesis of hypertension. Indeed, 20-hydroxyeicosatetraenoic acid (20-HETE) is produced by vascular smooth muscle (VSM) cells and is a potent vasoconstrictor that depolarizes VSM by blocking large conductance Ca+-activated K2+ channels. In contrast, epoxyeicosatrienoic acids (EETs) are synthesized by the vascular endothelium and have opposite effects on VSM (hyperpolarization and vasodilatation). Inhibition of the synthesis of 20-HETE attenuates myogenic tone and autoregulation of blood flow and modulates vascular responses to vasodilators (NO and CO) and vasoconstrictors (angiotensin II, endothelin). In the kidney, 20-HETE inhibits sodium transport in the proximal tubule by blocking Na+-K+-ATPase activity. In the thick ascending limb of the loop of Henle, 20-HETE inhibits Na+-K+-2Cl- transport, in part, by blocking a 70 pS apical K+ channel. EETs are produced in the proximal tubule where they inhibit Na+-H+ exchange and in the collecting duct where they inhibit sodium and water transport. Numerous studies have established that the formation of EETs and 20-HETE and the expression of CYP enzymes are altered in the kidney in many genetic and experimental animal models of hypertension and in some forms of human hypertension. However, the functional significance of these changes remains to be determined. Given the importance of this pathway in the control of renal function and vascular tone, it is likely that alterations in the renal formation of CYP-dependent metabolites of AA will be shown to participate in the development of hypertension in many of these models.

This study examined the effect of transfer of overlapping regions of chromosome 5 that includes (4A(+)) or excludes (4A(-)) the cytochrome P-450 4A (CYP4A) genes from the Lewis rat on the renal production of 20-hydroxyeicosatetraenoic acid (20-HETE) and the development of hypertension-induced renal disease in congenic strains of Dahl salt-sensitive (Dahl S) rats. The production of 20-HETE was higher in the outer medulla of 4A(+) than in Dahl S or 4A(-) rats. Mean arterial pressure (MAP) rose to 190 +/- 7 and 185 +/- 3 mmHg in Dahl S and 4A(-) rats fed a high-salt (HS) diet for 21 days but only to 150 +/- 5 mmHg in the 4A(+) strain. Protein excretion increased to 423 +/- 40 and 481 +/- 37 mg/day in Dahl S and 4A(-) rats vs. 125 +/- 15 mg/day in the 4A(+) strain. Baseline glomerular capillary pressure (Pgc) was lower in 4A(+) rats (38 +/- 1 mmHg) than in Dahl S rats (42 +/- 1 mmHg). Pgc increased to 50 +/- 1 mmHg in Dahl S rats fed a HS diet, whereas it remained unaltered in 4A(+) rats (39 +/- 1 mmHg). Baseline glomerular permeability to albumin (P(alb)) was lower in 4A(+) rats (0.19 +/- 0.05) than in Dahl S or 4A(-) rats (0.39 +/- 0.02). P(alb) rose to approximately 0.61 +/- 0.03 in 4A(-) and Dahl S rats fed a HS diet for 7 days, but it remained unaltered in the 4A(+) rats. The expression of transforming growth factor-beta2 was higher in glomeruli of Dahl S rats than in 4A(+) rats fed either a low-salt (LS) or HS diet. Chronic administration of a 20-HETE synthesis inhibitor (HET0016; 10 mg.kg(-1).day(-1) sc) reversed the fall in MAP and renoprotection seen in 4A(+) rats. These results indicate that the introgression of the CYP4A genes from Lewis rats into the Dahl S rats increases the renal formation of 20-HETE and attenuates the development of hypertension and renal disease.

Abstract-This study examined the role of changes in renal interstitial pressure on the renal levels of cytochrome P450 metabolites of arachidonic acid and compared the effects of inhibition of the formation of 20-hydroxyeicosatetraenoic acid (20-HETE) and epoxyeicosatrienoic acids with 1-aminobenzotriazole on the pressure-natriuretic response versus that seen after administration of HET0016, a more selective inhibitor of the formation of 20-HETE. Renal interstitial pressure rose by 3.4Ϯ0.3 mm Hg, and the levels of 20-HETE in renal cortical tissue doubled when renal perfusion pressure was increased from 100 to 160 mm Hg. Removal of the renal capsule prevented the increase in renal interstitial pressure and 20-HETE levels after an elevation in renal perfusion pressure. Urine flow and sodium excretion increased 5-fold when renal perfusion pressure was increased from 106 to 160 mm Hg. The administration of 1-aminobenzotriazole (50 mg/kg, IP) or HET0016 (10 mg/kg IV bolus plus 1 mg/kg per hour of infusion) decreased the pressure-natriuretic response by 50% and inhibited the renal formation of 20-HETE and epoxyeicosatrienoic acids by 90% and 50%, respectively. Administration of a lower dose of HET0016 (1 mg/kg per hour, IV) selectively reduced the formation of 20-HETE by 80% without inhibiting renal epoxygenase activity and blunted the pressure-natriuretic response by 42%. These results indicate that elevations in renal perfusion pressure increase 20-HETE levels in the kidney secondary to a rise in renal interstitial pressure. They also suggest that 20-HETE, rather than epoxyeicosatrienoic acids, modulates the pressure-natriuretic response, because selective blockade of the formation of 20-HETE with HET0016 blunts the response to the same extent as that seen after inhibition of the formation of 20-HETE and epoxyeicosatrienoic acids with 1-aminobenzotriazole. T he concept that the kidney plays an essential role in the long-term control of arterial pressure is based on the pressure-natriuretic response; however, the mechanism by which this occurs is unknown. 1,2 Previous studies have indicated that pressure natriuresis is associated with elevations in medullary blood flow 3-6 and renal interstitial hydrostatic pressure (RIHP) 7-13 and a fall in sodium transport in the proximal tubule. 14 -18 The fall in sodium transport is associated with inhibition of Na ϩ K ϩ -ATPase activity and internalization of sodium/hydrogen exchanger from the brush border. 19,20 The rise in RIHP seems to be important in triggering pressure natriuresis, because removal of the renal capsule blocks the fall in proximal tubular reabsorption and attenuates the natriuretic response after an elevation in renal perfusion pressure (RPP). 7-13 However, the mechanism by which elevations in RPP and/or RIHP inhibits sodium transport in the proximal tubule remains to be determined.Recent studies have indicated that cytochrome P450 (CYP) metabolites of arachidonic acid (AA) may be involved. 19,20 In this regard, chronic blockade of the formation of epoxyeico...

This review summarizes recent findings that address the issue of whether cytochrome P-450 metabolites of arachidonic acid play an important role in the regulation of renal tubular and peripheral vascular function and contribute to the pathogenesis of hypertension.

The present study examined whether transfer of overlapping regions of chromosome 5 that include (4A ϩ ) or exclude the cytochrome P-450 (CYP) 4A genes from the Lewis rat alters the renal production of 20-hydroxyeicosatetraenoic acid (20-HETE) and/or the development of hypertension in congenic strains of Dahl salt-sensitive (S) rats. The expression of CYP4A protein and the production of 20-HETE in the renal outer medulla was greater in the 4A ϩ congenic strain than the levels seen in S rats or in overlapping control congenic strains that exclude the CYP4A region. Mean arterial pressure (MAP) rose from 122 Ϯ 2 to 190 Ϯ 7 mmHg in S rats and from 119 Ϯ 2 and 123 Ϯ 2 to 189 Ϯ 7 and 187 Ϯ 3 mmHg in the two control congenic strains fed an 8.0% NaCl diet for 3 wk. In contrast, MAP only increased from 112 Ϯ 2 to 150 Ϯ 5 mmHg in the 4A ϩ congenic strain. Chronic blockade of the formation of phenyl-NЈ-hydroxyimido formamide (TS-011; 1 mg/kg bid) restored the salt-sensitive phenotype in the 4A ϩ congenic strain and MAP rose to 181 Ϯ 6 mmHg after an 8.0% NaCl dietary challenge. TS-011 had no effect on the development of hypertension in S rats or the two control congenic strains. The pressure-natriuretic and diuretic responses were fivefold greater in the 4A ϩ congenic strain than in S rats. These results indicate that transfer of the region of chromosome 5 between markers D5Rat108 to D5Rat31 from the Lewis rat into the Dahl S genetic background increases the renal production of 20-HETE, improves pressure-natriuresis and opposes the development of salt-induced hypertension.cytochrome P-450; kidney; 20-HETE RENAL TRANSPLANTATION STUDIES have indicated that some form of renal dysfunction underlies the development of hypertension in humans and in experimental animal models (4, 9, 10, 21). However, the factors responsible for altering kidney function and the genes involved remain to be determined. Several lines of evidence suggest that a deficiency in the renal formation of 20-hydroxyeicosatetraenoic acid (20-HETE) contributes to the development of hypertension in Dahl salt-sensitive (S) rats. In this regard, 1) the formation of 20-HETE and the expression of cytochrome P-450 (CYP) enzymes of the 4A family is reduced in the outer medulla and the thick ascending limb of the loop of Henle (TALH) of S rats (13, 17); 2) 20-HETE is an endogenously-formed inhibitor of Cl Ϫ transport in the TALH and Na ϩ and Cl Ϫ reabsorption is elevated in this segment of the nephron in S rats (13,15,31); 3) 20-HETE modulates tubuloglomerular feedback (TGF) responses (32) and glomerular hemodynamics is altered in S rats (14, 26, 28); 4) increasing the renal formation of 20-HETE with fibrates or the SOD mimetic Tempol, lowers blood pressure (BP) and improves renal function in S rats (12, 29); and 5) inhibitors of the formation of 20-HETE blunts the pressure-natriuretic response (5) and promotes the development of salt-sensitive hypertension in normotensive strains of rats (11,25).These studies suggest that the renal formation of 20-HETE is reduced in S ...

The present study evaluated whether the impairment in autoregulation of renal blood flow (RBF) in the fawn-hooded Hypertensive (FHH) rat colocalizes with the Rf-1 region on chromosome 1 that has been previously linked to the development of proteinuria in this strain. Autoregulation of RBF was measured in FHH and a consomic strain (FHH.1 BN ) in which chromosome 1 from the Brown-Norway (BN) rat was introgressed into the FHH genetic background. The autoregulation indexes (AI) averaged 0.80 Ϯ 0.08 in the FHH and 0.19 Ϯ 0.05 in the FHH.1 BN rats. We next performed a genetic linkage analysis for autoregulation of RBF in 85 F2 rats generated from a backcross of FHH.1 BN consomic and FHH rats. The results revealed a significant quantitative trait locus (QTL) with a peak logarithm of the odds score of 6.3 near marker D1Rat376. To confirm the existence of this QTL, five overlapping congenic strains were created that spanned the region from markers D1Rat234 to D1Mit14. Transfer of a region of BN chromosome 1 from markers D1Mgh13 to D1Rat89 into the FHH genetic background improved autoregulation of RBF (AI ϭ 0.23 Ϯ 0.04) and reduced protein excretion. In contrast, RBF was poorly autoregulated and the rats were not protected from proteinuria in congenic strains in which other regions of chromosome 1 that exclude the D1Rat376 marker were transferred. These results indicate that there is a gene(s) that influences autoregulation of RBF and proteinuria between markers D1Mgh13 and D1Rat89 on chromosome 1 that lies within the confidence interval of the Rf-1 QTL previously linked to the development of proteinuria in FHH rats. renal disease; Rf-1; consomic and congenic rats; quantitative trait locus END-STAGE RENAL DISEASE (ESRD) is a major health problem in the United States and the incidence of the disease is expected to increase over the next decade (35). Hypertension and diabetes account for Ͼ67% of the newly diagnosed cases of ESRD (34). However, not all patients with diabetes or hypertension develop ESRD and little is known about the genes that determine the genetic susceptibility to develop diabetic-or hypertension-induced nephropathy.The fawn-hooded hypertensive (FHH) rat is a genetic model of hypertension-induced renal disease (26,27). These animals gradually develop systolic hypertension, followed by progressive proteinuria, focal glomerulosclerosis, and, eventually, ESRD (16,17). Previous genetic studies identified two quantitative trait loci (QTL) on chromosome 1 (Rf-1 and Rf-2) that are associated with the development of proteinuria (3, 32). Rf-1 QTL is homologous to a region on human chromosome 10 that has been linked to the development of hypertension-and diabetic-induced glomerulosclerosis in humans (12, 13). A more recent study has identified an functional mutation in the Rab38 gene in the FHH rat as the likely candidate gene for Rf-2 (29). This gene influences the intracellular trafficking of proteins. The mutation in Rab38 was postulated to alter the reabsorption of filtered protein in FHH rats (29). On the other...

The present study evaluated the acute effects of ANG II (5-480 ng/kg iv) and phenylephrine (PE; 0.2-146 microg/kg iv) on total renal (RBF) and medullary blood flow (MBF) in anesthetized Lyon hypertensive (LH) and low-blood-pressure (LL) rats. ANG II and PE induced dose-dependent decreases in both RBF and MBF, which were greater in LH than in LL rats. Interestingly, after ANG II, but not after PE, the initial medullary vasoconstriction was followed by a long-lasting and dose-dependent vasodilation that was significantly blunted in LH compared with LL rats. The mechanisms of the MBF effects of ANG II were studied in LL rats only. Blockade of AT(1) receptors with losartan (10 mg/kg) abolished all the effects of ANG II, whereas AT(2) receptor blockade with PD-123319 (50 microg x kg(-1) x min(-1) iv) did not change these effects. Indomethacin (5 mg/kg) decreased by approximately 90% the medullary vasodilation induced by the lowest doses of ANG II (from 15 ng/kg). In contrast, N(G)-nitro-l-arginine methyl ester (10 mg/kg and 0.1 mg. kg(-1). min(-1) iv) and the bradykinin B(2)-receptor antagonist HOE-140 (20 microg/kg and 10 microg x kg(-1) x min(-1) iv) markedly lowered the medullary vasodilation at the highest doses of ANG II only. In conclusion, this study shows that LH rats exhibit an altered MBF response to ANG II compared with LL rats and indicates that the AT(1) receptor-mediated medullary vasodilator response to low doses of ANG II is mainly due to the release of PGs, whereas the dilator response to high doses of ANG II has additional nitric oxide- and kinin-dependent components.

The present work studied renal medullary blood flow (MBF) and its response to salt load in Lyon hypertensive (LH) rats to understand the mechanisms underlying the abnormal renal sodium excretion exhibited by LH rats. Experiments were conducted in uninephrectomized, anesthetized, and volume-expanded 15-week-old male LH and their normotensive (LL) controls. Under standard diet, LH rats exhibited a blunted pressure diuresis and natriuresis associated with an absence of pressure-induced increase in MBF compared to LL rats. One week of salt load (2% NaCl as drinking water) induced a significant increase in blood pressure (BP) in LH (+11 mm Hg) than in LL (+6 mm Hg) rats associated with a decrease in MBF in LH rats only (from 182 +/- 25 to 122 +/- 20 perfusion units, P < .001). Finally, despite the salt load-induced increase in pressure natriuresis, it remained significantly lower in LH than in LL rats. The results show an alteration in MBF regulation in LH rats and suggest that this abnormality may be involved in their blunted pressure natriuresis and their enhanced salt sensitivity.