Renal Arachidonic Acid Metabolism Research Articles

Colfibrate attenuates blood pressure and sodium retention in DOCA-salt hypertension

Clofibrate, a peroxisome proliferator-activated receptor-alpha (PPAR alpha) agonist, increases renal tubular cytochrome P450 4a (Cyp4a) expression thereby increasing 20-hydroxyeicosatetraenoic acid (20-HETE) production. To determine if clofibrate affects blood pressure regulation we studied mice with DOCA-salt induced hypertension in wild-type and PPAR alpha knockout mice. Wild-type mice treated with DOCA-salt had higher mean arterial pressures and higher cumulative sodium balance, but lower renal 20-HETE production than did vehicle-treated mice. Treating DOCA-salt mice with clofibrate attenuated the increase in mean arterial pressure and cumulative sodium balance while increasing 20-HETE production and renal Cyp4a expression. In contrast the PPAR alpha knockout mice treated with clofibrate and DOCA-salt showed no attenuation in the increase of blood pressure, cumulative sodium balance, renal 20-HETE production or Cyp4a protein expression. Expression of the PPAR alpha protein was greater in proximal tubules than in renal microvessels. Our results show that PPAR alpha pathway induces renal tubular 20-HETE production which affects sodium retention and blood pressure regulation in DOCA-salt-treated mice.

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

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 +/- 16 vs. 92 +/- 13 and 59 +/- 7 vs. 33 +/- 3 pmol.min(-1).mg protein(-1)). 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 +/- 1.3 to 3.9 +/- 1.0 pg/ml. The effects of ABT in BB rats were attenuated by chronic infusion of oxytocin (0.7 ng.min(-1).100 g(-1)) 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.

Cytochrome P450-Dependent Renal Metabolism of Arachidonic Acid in a Rat Model of Angiotensin II induced Hypertension and End-Organ Damage

Cytochrome P450-Dependent Renal Metabolism of Arachidonic Acid in a Rat Model of Angiotensin II induced Hypertension and End-Organ Damage

Deficiency of 5-Lipoxygenase Accelerates Renal Allograft Rejection in Mice

Acute renal allograft rejection is associated with alterations in renal arachidonic acid metabolism, including enhanced synthesis of leukotrienes (LTs). LTs, the products of the 5-lipoxygenase (5-LO) pathway, are potent lipid mediators with a broad range of biologic activities. Previous studies, using pharmacological agents to inhibit LT synthesis or activity, have implicated these eicosanoids in transplant rejection. To further investigate the role of LTs in acute graft rejection, we transplanted kidneys from CByD2F1 mice into fully allogeneic 129 mice that carry a targeted mutation in the 5lo gene. Unexpectedly, allograft rejection was significantly accelerated in 5-LO-deficient mice compared with wild-type animals. Despite the marked reduction in graft survival, the 5lo mutation had no effect on the hemodynamics or morphology of the allografts. Although LTB4 levels were reduced, renal thromboxane B2 production and cytokine expression were not altered in 5-LO-deficient allograft recipients. These findings suggest that, along with their proinflammatory actions, metabolites of 5-LO can act to enhance allograft survival.

Role of guanylyl cyclase and cytochrome P-450 on renal response to nitric oxide.

The present study evaluated whether inhibition of guanylyl cyclase (GC) with 1H-(1,2,4)oxadiazolo[4,3-a]quinoxaline-1-one (ODQ) and methylene blue (MB) or inhibition of the renal metabolism of arachidonic acid by cytochrome P-450 (CYP450) enzymes with 1-aminobenzotriazole (ABT) and N-hydroxy-N'-(4 butyl-2-methyl phenyl)formamidine (HET0016) alters the renal tubular and vascular effects of a nitric oxide (NO) donor in vivo. Intrarenal infusion of ODQ or MB at a dose of 170 nmol. kg(-1). min(-1) lowered renal blood flow (RBF) by 30 and 15%, respectively; glomerular filtration rate (GFR) by 26 and 18%, respectively; and sodium and water excretion by approximately 35%. In rats pretreated with nitro-L-arginine methyl ester (37 nmol. kg(-1). min(-1)) to block the endogenous production of NO, intrarenal infusion of the NO donor S-nitroso-N-acetylcysteine (S-NO-NAC; 50 nmol. kg(-1). min(-1)) increased RBF (18%), sodium (73%), and water excretion (61%). ODQ or MB administration blocked the effect of S-NO-NAC on RBF but not the diuretic and natriuretic response. Pretreatment of rats with ABT or HET0016 also abolished the renal vasodilatory response to the NO donor and reduced its diuretic and natriuretic effect. These results indicate that both activation of GC and inhibition of CYP450 enzymes contribute to the renal vascular actions of NO, whereas the natriuretic and diuretic actions of NO appear to be largely CYP450 dependent.

Abnormal pressure-natriuresis in hypertension: role of cytochrome P450 metabolites of arachidonic acid

The pressure-natriuresis relationship is shifted to higher pressures in genetic and experimental models of hypertension; however, the factors responsible for altering kidney function remain to be determined. In spontaneously hypertensive (SHR) and Lyon hypertensive rats, the resetting of pressure-natriuresis results from increased preglomerular renal vascular tone, whereas sodium reabsorption is elevated in the thick ascending loop of Henle (TALH) of Dahl S rats. Recently, a new route for the renal metabolism of arachidonic acid (AA) has been described, and there is evidence that this pathway contributes to the resetting of renal function in hypertension. In the kidney, cytochrome P450 (CYP) enzymes metabolize AA primarily to 20-HETE and EETs. 20-HETE is a potent constrictor of renal arterioles that has an important role in autoregulation of renal blood flow and tubuloglomerular feedback. 20-HETE and EETS also inhibit sodium reabsorption in the proximal tubule and TALH. In the SHR, the renal production of 20-HETE is elevated and inhibitors of the formation of 20-HETE decrease arterial pressure. Blockade of 20-HETE formation also reduces blood pressure or improves renal function in deoxycorticosterone acetate (DOCA)-salt, angiotensin II-infused, and Lyon hypertensive rats. In contrast, 20-HETE formation is reduced in the TALH of Dahl S rats and this contributes to elevated sodium reabsorption. Induction of 20-HETE synthesis improves pressure-natriuresis and lowers blood pressure in Dahl S rats, whereas inhibitors of the synthesis of 20-HETE promote the development of hypertension in Lewis rats. These findings indicate that the renal production of CYP metabolites of AA is altered in genetic and experimental models of hypertension and that this system contributes to the resetting of pressure-natriuresis and the development of hypertension in some models.

HET0016, a potent and selective inhibitor of 20-HETE synthesizing enzyme.

The present study examined the inhibitory effects of N-hydroxy-N'-(4-butyl-2-methylphenyl)-formamidine (HET0016) on the renal metabolism of arachidonic acid by cytochrome P450 (CYP) enzymes. HET0016 exhibited a high degree of selectivity in inhibiting the formation of 20-hydroxy-5,8,11,14-eicosatetraenoic acid (20-HETE) in rat renal microsomes. The IC(50) value averaged 35+/-4 nM, whereas the IC(50) value for inhibition of the formation of epoxyeicosatrienoic acids by HET0016 averaged 2800+/-300 nM. In human renal microsomes, HET0016 potently inhibited the formation of 20-HETE with an IC(50) value of 8.9+/-2.7 nM. Higher concentrations of HET0016 also inhibited the CYP2C9, CYP2D6 and CYP3A4-catalysed substrates oxidation with IC(50) values of 3300, 83,900 and 71,000 nM. The IC(50) value for HET0016 on cyclo-oxygenase activity was 2300 nM. These results indicate that HET0016 is a potent and selective inhibitor of CYP enzymes responsible for the formation of 20-HETE in man and rat.

Effects of converting enzyme inhibitors on renal P-450 metabolism of arachidonic acid.

The effects of blockade of the renin-angiotensin system on the renal metabolism of arachidonic acid (AA) were examined. Male Sprague-Dawley rats were treated with vehicle, captopril (25 mg x kg(-1) x day(-1)), enalapril (10 mg x kg(-1) x day(-1)), or candesartan (1 mg x kg(-1) x day(-1)) for 1 wk. The production of 20-hydroxyeicosatetraenoic acid (20-HETE) and epoxyeicosatrienoic acids (EETs) by renal cortical microsomes increased in rats treated with captopril by 59 and 24% and by 90 and 58% in rats treated with enalapril. Captopril and enalapril increased 20-HETE production in the outer medulla by 100 and 143%, respectively. In contrast, blockade of ANG II type 1 receptors with candesartan had no effect on the renal metabolism of AA. Captopril and enalapril increased cytochrome P-450 (CYP450) reductase protein levels in the renal cortex and outer medulla and the expression of CYP450 4A protein in the outer medulla. The effects of captopril on the renal metabolism of AA were prevented by the bradykinin-receptor antagonist, HOE-140, or the nitric oxide (NO) synthase inhibitor, N(G)-nitro-L-arginine methyl ester. These results suggest that angiotensin-converting enzyme inhibitors may increase the formation of 20-HETE and EETs secondary to increases in the intrarenal levels of kinins and NO.

Targeted Disruption of Soluble Epoxide Hydrolase Reveals a Role in Blood Pressure Regulation

Renal microsomal cytochrome P-450 monooxygenase-dependent metabolism of arachidonic acid generates a series of regioisomeric epoxyeicosatrienoic acids that can be further metabolized by soluble epoxide hydrolase to the corresponding dihydroxyeicosatrienoic acids. Evidence exists that these metabolites affect renal function and, in particular, blood pressure regulation. To examine this possibility, blood pressure and renal arachidonic acid metabolism were examined in mice with a targeted disruption of the soluble epoxide hydrolase gene. Systolic blood pressure of male soluble epoxide hydrolase-null mice was lower compared with wild-type mice in both the absence and presence of dietary salt loading. Both female soluble epoxide hydrolase-null and wild-type female mice also had significantly lower systolic blood pressure than male wild-type mice. Renal formation of epoxyeicosatrienoic and dihydroxyeicosatrienoic acids was markedly lower for soluble epoxide hydrolase-null versus wild-type mice of both sexes. Although disruption of soluble epoxide hydrolase in female mice had minimal effects on blood pressure, deletion of this gene feminized male mice by lowering systolic blood pressure and altering arachidonic acid metabolism. These data provide the first direct evidence for a role for soluble epoxide hydrolase in blood pressure regulation and identify this enzyme as a novel and attractive target for therapeutic intervention in hypertension.

Lazaroid and pentoxifylline suppress sepsis-induced increases in renal vascular resistance via altered arachidonic acid metabolism.

Early sepsis leads to renal hypoperfusion, despite a hyperdynamic systemic circulation. It is thought that failure of local control of the renal microcirculation leads to hypoperfusion and organ dysfunction. Of the many mediators implicated in the pathogenesis of microvascular vasoconstriction, arachidonic acid metabolites are thought to be important. Vasoconstriction may be due to excess production of vasoconstrictors or loss of vasodilators. Using the isolated perfused kidney model, we describe a sepsis-induced rise in renal vascular resistance and increased production of key arachidonic acid metabolites, both vasoconstrictors and vasodilators, suggesting excessive production of vasoconstrictors as a cause for microcirculatory hypoperfusion. There is evidence of increased enzymatic production of arachidonic acid metabolites as well as nonenzymatic, free radical, catalyzed conversion of arachidonic acid. Pentoxifylline (a phosphodiesterase inhibitor) and U74389G (an antioxidant) both have a protective effect on the renal microcirculation during sepsis. Both drugs appear to alter the renal microvascular response to sepsis by altering renal arachidonic acid metabolism. This study demonstrates that sepsis leads to increased renal vascular resistance. This response is in part mediated by metabolites produced by metabolism of arachidonic acid within the kidney. The ability of drugs to modulate arachidonic acid metabolism and so alter the renal response to sepsis suggests a possible role for these agents in protecting the renal microcirculation during sepsis.

Cytochrome P-450 arachidonate metabolite inhibition improves renal function in Lyon hypertensive rats

The present study evaluated the effects of miconazole, a selective inhibitor of epoxygenase activity, on renal hemodynamics and the pressure-natriuresis response of saline-drinking, uninephrectomized Lyon hypertensive (LH) and Lyon low blood pressure (LL) rats. Infusion of miconazole (final concentration, 1 μmol/L) into the renal artery had no effect on the renal function of LL rats over a range of renal perfusion pressures (RPP) from 100 to 140 mm Hg. In contrast, miconazole lowered renal vascular resistance (RVR, 17.9 ± 1.1 v 26.3 ± 1.5 mm Hg/mL/min/g, P < .01) and increased urinary sodium excretion (6.4 ± 1.2 v 4.2 ± 0.8 μmol /min/g, P < .05) in LH rats at a RPP of 140 mm Hg. To determine whether the effects of epoxyeicosatrienoic acids were dependent on activation of the thromboxane A2-prostaglandin H2 (TP) receptor, we studied the effects of a TP receptor antagonist, GR 32191B (0.1 mg/kg/min), on the renal response to an infusion of miconazole into the renal artery in LH rats. GR 32191B decreased basal RVR and prevented the dilation induced by miconazole. It did not, however, alter its natriuretic effect. The renal metabolism of arachidonic acid was also compared in LH and LL rats. The production of epoxygenase metabolites was 25% lower in microsomes prepared from the renal cortex of LH versus LL rats. Miconazole (1 μmol /L) reduced epoxygenase activity similarly, by approximately 60%, in both strains. These results suggest that endogenously formed P450 metabolites of arachidonic acid may serve as a substrate for the formation of vasoconstrictor endoperoxides that interact with TP receptors in LH rats and contribute to the enhanced renal vascular tone but not the blunted pressure-natriuresis response.

Cytochrome P-450 arachidonate metabolite inhibition improves renal function in lyon hypertensive rats

The present study evaluated the effects of miconazole, a selective inhibitor of epoxygenase activity, on renal hemodynamics and the pressure-natriuresis response of saline-drinking, uninephrectomized Lyon hypertensive (LH) and Lyon low blood pressure (LL) rats. Infusion of miconazole (final concentration, 1 μmol/L) into the renal artery had no effect on the renal function of LL rats over a range of renal perfusion pressures (RPP) from 100 to 140 mm Hg. In contrast, miconazole lowered renal vascular resistance (RVR, 17.9 ± 1.1 v 26.3 ± 1.5 mm Hg/mL/min/g, P < .01) and increased urinary sodium excretion (6.4 ± 1.2 v 4.2 ± 0.8 μmol /min/g, P < .05) in LH rats at a RPP of 140 mm Hg. To determine whether the effects of epoxyeicosatrienoic acids were dependent on activation of the thromboxane A2- prostaglandin H2 (TP) receptor, we studied the effects of a TP receptor antagonist, GR 32191B (0.1 mg/kg/min), on the renal response to an infusion of miconazole into the renal artery in LH rats. GR 32191B decreased basal RVR and prevented the dilation induced by miconazole. It did not, however, alter its natriuretic effect. The renal metabolism of arachidonic acid was also compared in LH and LL rats. The production of epoxygenase metabolites was 25% lower in microsomes prepared from the renal cortex of LH versus LL rats. Miconazole (1 μmol /L) reduced epoxygenase activity similarly, by approximately 60%, in both strains. These results suggest that endogenously formed P450 metabolites of arachidonic acid may serve as a substrate for the formation of vasoconstrictor endoperoxides that interact with TP receptors in LH rats and contribute to the enhanced renal vascular tone but not the blunted pressure-natriuresis response. Am J Hypertens 1999;12:398–404 © 1999 American Journal of Hypertension, Ltd.

Inhibition of renal arachidonic acid omega-hydroxylase activity with ABT reduces blood pressure in the SHR.

The mechanism-based cytochrome P-450 (CYP) inhibitor 1-aminobenzotriazole (ABT) was characterized as an inhibitor of renal arachidonic acid metabolism and administered to spontaneously hypertensive rats (SHRs) to determine the effect of reduced eicosanoid production on mean arterial pressure (MAP). A single intraperitoneal dose of ABT to Sprague-Dawley rats caused a dose-dependent loss of renal CYP content, arachidonic acid metabolism, and CYP4A protein. In the cortex and outer medulla, ABT showed a high degree of selectivity for the CYP4A enzymes, reflected by the potent inhibition of 19- and 20-hydroxyeicosatetraenoic acid (19- and 20-HETE) formation. A 50 mg/kg dose of ABT reduced cortical 20-HETE formation to 16.1 +/- 0.82% of control and outer medullary 20-HETE formation to 23.8 +/- 0.45% of control. In contrast, there was no inhibition of renal epoxygenase activity at this dose. Renal CYP content, arachidonic acid omega- and (omega-1)-hydroxylase activity, and CYP4A protein levels gradually return to control levels by 72 h after a single dose of ABT. Cortical 20-HETE formation recovered from 17.9 +/- 3.15% of control at 6 h to 84.8 +/- 4.67% of control at 72 h after ABT administration. A single injection of ABT to 7-wk-old SHRs caused an acute reduction in MAP, which remained suppressed for at least 12 h. The effect was maximal within 4 h and averaged 17-23 mmHg during the 4- to 12-h period after administration. 20-HETE formation was inhibited 85% in the cortex and 70-80% in the outer medulla during the period when MAP was reduced. A structurally related ABT analog 1-hydroxybenzotriazole had no effect on blood pressure or renal arachidonic acid metabolism. These results identify ABT as a selective inhibitor of renal CYP4A activity and provide further support for a role for 20-HETE in the regulation of blood pressure.

Renal P450 Metabolites of Arachidonic Acid and the Development of Hypertension in Dahl Salt-Sensitive Rats

Renal transplantation studies indicate that some form of renal dysfunction underlies the development of hypertension in Dahl salt-sensitive (S) rats; however, the factors responsible for altering kidney function remain to be determined. Previous studies have indicated that Dahl S rats require a higher renal perfusion pressure to excrete the same amount of sodium and water as normotensive rats and that this is due largely to an elevation in Cl- transport in the thick ascending limb of the loop of Henle. There are now five lines of evidence that suggest an abnormality in the renal metabolism of arachidonic acid by enzymes of the P4504A family may contribute to the increase in loop Cl- transport and the development of hypertension in Dahl S rats. In this regard, the formation of 20-HETE and the levels of P4504A protein are reduced in the outer medulla of Dahl S rats. Perfusion of the loop of Henle of Dahl S rats with exogenous 20-HETE normalizes the elevated loop Cl- transport. In addition, a genetic marker in the P4504A2 gene, which encodes for the enzyme that makes 20-HETE, cosegregates with the development of hypertension in an F2 cross of Dahl S and Lewis rats. Finally, induction of renal production of 20-HETE with clofibrate prevents the development of hypertension in Dahl S rats and inhibition of renal 20-HETE formation produces hypertension in Lewis rats fed a high salt diet. These results implicate the CYP4A2 locus as a candidate gene that contributes to the alterations in renal function and the development of hypertension in Dahl S rats.

Renal P450 metabolites of arachidonic acid and the development of hypertension in Dahl salt-sensitive rats

Renal transplantation studies indicate that some form of renal dysfunction underlies the development of hypertension in Dahl salt-sensitive (S) rats; however, the factors responsible for altering kidney function remain to be determined. Previous studies have indicated that Dahl S rats require a higher renal perfusion pressure to excrete the same amount of sodium and water as normotensive rats and that this is due largely to an elevation in Cl− transport in the thick ascending limb of the loop of Henle. There are now five lines of evidence that suggest an abnormality in the renal metabolism of arachidonic acid by enzymes of the P4504A family may contribute to the increase in loop Cl− transport and the development of hypertension in Dahl S rats. In this regard, the formation of 20-HETE and the levels of P4504A protein are reduced in the outer medulla of Dahl S rats. Perfusion of the loop of Henle of Dahl S rats with exogenous 20-HETE normalizes the elevated loop Cl− transport. In addition, a genetic marker in the P4504A2 gene, which encodes for the enzyme that makes 20-HETE, cosegregates with the development of hypertension in an F2 cross of Dahl S and Lewis rats. Finally, induction of renal production of 20-HETE with clofibrate prevents the development of hypertension in Dahl S rats and inhibition of renal 20-HETE formation produces hypertension in Lewis rats fed a high salt diet. These results implicate the CYP4A2 locus as a candidate gene that contributes to the alterations in renal function and the development of hypertension in Dahl S rats. Am J Hypertens 1997;10:63S-67S © 1997 American Journal of Hypertension, Ltd.

Inhibition of renal outer medullary 20-HETE production produces hypertension in Lewis rats.

Recent studies have indicated that a deficiency in the production of 20-hydroxyeicosatetraenoic acid (20-HETE) in the outer medulla of the kidney may contribute to the abnormalities in the renal handling of sodium and the development of hypertension in Dahl salt-sensitive rats. To determine whether a reduction in 20-HETE production in the outer medulla is sufficient to induce hypertension, an inhibitor of the renal metabolism of arachidonic acid by P450 enzymes, 17-octadecenoic acid (17-ODYA), was chronically infused directly into the outer medulla of the left kidney of uninephrectomized Lewis rats fed a high salt diet. Renal medullary interstitial infusion of 17-ODYA (400 pmol/min) reduced the formation of 20-HETE in the outer medulla of the infused kidney by 70% compared with values seen in the right kidney collected when the rat was uninephrectomized, but it had no effect on the production of 20-HETE in the renal cortex. After 5 days, mean arterial pressure rose from 115 +/- 2 to 142 +/- 2 mm Hg (n = 6) in the rats infused with 17-ODYA, while mean arterial pressure was not significantly altered in the rats infused with vehicle alone (116 +/- 1 versus 117 +/- 2 mm Hg, n = 6). These results suggest that inhibition of the renal metabolism of arachidonic acid by P450 enzymes in the outer medulla of the kidney is sufficient to induce the development of hypertension in Lewis rats fed a high salt diet and support the view that P450 metabolites of arachidonic acid play an important role in the regulation of renal function and the long-term control of arterial pressure.

Renal Cytochrome P4504A Activity and Salt Sensitivity in Spontaneously Hypertensive Rats

Differences in the renal metabolism of arachidonic acid by cytochrome P450 have been reported in the spontaneously hypertensive rat (SHR) and Wistar-Kyoto rats, but the contribution of this system to the development of hypertension is unclear. The present study compared renal P450 activity and blood pressure in SHR and Brown-Norway rats (BN) under control conditions and in response to an elevation in sodium intake; genetic linkage analysis was performed in an F2 population (n=219) derived from these strains. Basal renal P4504A enzyme activity measured by conversion of [C(14)]arachidonic acid to 20-hydroxyeicosatetraenoic acid (20-HETE) was significantly greater in the kidneys of adult SHR (n=7) than of BN (n=8) (82 +/- 7 versus 60 +/- 5 pmol/min per milligram protein). Renal 20-HETE production fell 45 percent in SHR and 22 percent in BN in which salt intake was elevated by drinking of saline instead of water for 2 weeks. Mean arterial pressure averaged 157 +/- 3mm Hg in SHR (n = 9) and 100 +/- 2 mm Hg in BN fed a normal salt diet, and it rose to 170 +/- 7 mm Hg (P<.05) in SHR and fell to 90 +/- 3 mm Hg (P<.05) in BN (n=8) after sodium intake was elevated. A polymorphic marker, D5Rjr1, that spanned a repeated element in the P4504A gene on chromosome 5, where all three P4504A isoforms are located, was used for genotyping of the F2 population. The P4504A genotype did not cosegregate with baseline mean arterial pressure in the F2 population; however, significant linkage was observed with the change in mean arterial pressure after sodium intake of the rats was elevated. The degree of linkage differed in male and female rats, and the highest LOD score (3.6) was observed in male F2 rats with a BN grandfather. These findings suggest that the difference in renal P450 activity in SHR and BN does not contribute to the development of hypertension in this F2 population, but it may play some role in determining the blood pressure response to an elevation in salt intake.

Role of 20-HETE in Elevating Loop Chloride Reabsorption in Dahl SS/Jr Rats

In vivo tubular perfusion experiments were performed in normotensive Dahl salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) rats maintained from birth on a low salt (0.4% NaCl) diet to examine the role of 20-HETE in elevating loop Cl- transport in SS/Jr rats. Chloride reabsorption in the loop of Henle was significantly greater in SS/Jr than in SR/Jr rats (77 +/- 2% versus 57 +/- 3% of the perfused Cl- load). When the renal metabolism of arachidonic acid by P450 was blocked by the addition of 17-octadecynoic acid (10 micromol/L) to the perfusate, loop Cl- transport increased in SR/Jr rats to 70 +/- 2% of the delivered Cl- load, but it had no effect in SS/Jr rats. Conversely, addition of 20-HETE (10 micromol/L) to the perfusate lowered loop Cl- transport in S rats to 60 +/- 2% of perfused Cl- load, but it had no effect in SR/Jr rats. Addition of another endogenously formed HETE to the perfusate, 15-HETE (20 micromol/L), had no effect on Cl- reabsorption in the loop of Henle of SS/Jr rats. These findings indicate that endogenously produced P450 metabolites of arachidonic acid regulate Cl- transport in the loop of Henle of the rat in vivo and support the view that a diminished production of 20-HETE in the outer medulla of SS/Jr rats contributes to the elevation in loop Cl- transport and the resetting of the pressure-natriuresis relation in these animals.

Role of changes in renal hemodynamics and P-450 metabolites of arachidonic acid in the reversal of one-kidney, one clip hypertension.

To examine the role of changes in renal hemodynamics and P-450 metabolites of arachidonic acid in the reversal of one-kidney, one clip (1-K,1C) hypertension in rats. The stimulus for the release of an antihypertensive lipid from the kidney is not known. This study examined whether cortical or papillary blood flow is altered after removal of the clip from the renal artery of 1-K,1C hypertensive rats, and the effects of blockade of the renal metabolism of arachidonic acid by P-450 with 17-octadecynoic acid (17-ODYA) on the fall in blood pressure. Cortical and medullary blood flows were measured using laser-Doppler flowmetry. 17-ODYA (33 nmol/min) was infused directly into the renal artery to examine the effect of inhibition of renal P-450 activity on reversal of 1-K,1C hypertension. The renal metabolism of arachidonic acid in control and in 1-K,1C hypertensive rats was assessed by incubating microsomes with [14C]-arachidonic acid, the metabolites formed being measured using reverse-phase high-performance liquid chromatography. The antihypertensive effects of these P-450 metabolites of arachidonic acid were compared with those of medullipin I after intravenous administration in conscious spontaneously hypertensive rats (SHR). Cortical and papillary blood flow increased significantly and arterial pressure fell after unclipping the renal artery in the 1-K,1C hypertensive rats. 17-ODYA prevented the fall in blood pressure after unclipping. The production of epoxy- and dihydroxy-eicosatrienoic acids was elevated in microsomes prepared from the renal cortex of the 1-K,1C hypertensive rats. However, intravenous administration of these metabolites did not mimic the effect of medullipin I to lower arterial pressure in SHR. Elevations in renal cortical or papillary blood flow, or both, may stimulate the release of a P-450-derived antihypertensive lipid from the kidney after unclipping of the renal artery in 1-K,1C hypertensive rats. However, it is unlikely that this substance is a P-450 metabolite of arachidonic acid.

Altered renal P-450 metabolism of arachidonic acid in Dahl salt-sensitive rats.

The renal metabolism of arachidonic acid (AA) was compared in male and female prehypertensive Dahl salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) rats maintained on a low- (0.3%) sodium chloride diet. Renal cortical microsomes incubated with AA produced 20-hydroxyeicosatetraenoic acid (20-HETE), 14,15- and 11,12-epoxyeicosatrienoic acids, and a new metabolite of AA, 11,12-epoxy-20-hydroxyeicosatrienoic acid. The production of 20-HETE was similar in cortical microsomes of female SS/Jr and SR/Jr rats maintained on a low-salt diet (72 +/- 5 vs. 66 +/- 3 pmol.min-1.mg protein-1); however, the formation of epoxygenase metabolites was significantly less in SS/Jr than in SR/Jr rats (45 +/- 2 vs. 70 +/- 3 pmol.min-1.mg protein-1). Outer medullary microsomes produced primarily 20-HETE, and the formation of this compound was significantly lower in SS/Jr than in SR/Jr female rats fed a low-salt diet (8 +/- 2 vs. 18 +/- 3 pmol.min-1.mg protein-1). Renal papillary microsomes produced prostaglandin E2 and F2 alpha, and the formation of these compounds was similar in female SS/Jr and SR/Jr rats fed a low-salt diet. Similar differences in the metabolism of AA by P-450 were observed in microsomes prepared from the renal cortex and outer medulla of male SS/Jr and SR/Jr rats. These results indicate that the renal metabolism of AA by P-450 is altered in prehypertensive Dahl SS/Jr rats; however, the functional significance of this system in resetting renal function and in the development of hypertension in this model remains to be established.