Transduction of physical force by the vascular wall Role of phospholipase C and cytochrome P450 metabolites of arachidonic acid

The blood vessel wall responds actively to an elevation in transmural pressure. This pressure-induced myogenic response is thought to set the basal level of vascular tone upon which metabolic and neural influences operate in concert to regulate organ blood flow. The cellular mechanisms that mediate the vascular muscle response to mechanical deformation via a changing transmural pressure include membrane depolarization, activation of phospholipase C, and a rise in intracellular [Ca(2+)](i), which appear to be nonadapting-remaining active as long as the pressure stimulus is applied. This brief review addresses some of the cellular events mediating transduction of transmural pressure by the vessel wall. Two possible mechanisms that are responsible for the nonadapting nature of pressure-induced myogenic tone are also explored, namely, formation of a P450 metabolite of arachidonic acid, which acts to buffer activation of K(+) channels as intracellular Ca(2+) rises, and direct activation of Ca(2+) channels by diacylglycerol. Evidence is provided suggesting that activation of phospholipase C is responsible for both the release of the arachidonic acid substrate for P450 enzymes and for the formation of diacylglycerol via its action on membrane-bound phospholipids.

Role of 20-hydroxyeicosatetraenoic acid in altering vascular reactivity in diabetes

1 This study examined the role of 20-hydroxyeicosatetraenoic (20-HETE) in altering vascular function in streptozotocin (STZ)-induced diabetic rats. 2 The expression of CYP4A protein and the formation of 20-HETE were elevated in the kidney, but not in the renal or mesenteric vasculature, of diabetic animals. The vasoconstrictor responses to norepinephrine (NE), endothelin-1 (ET-1), and angiotensin II (Ang II) were significantly enhanced in the isolated perfused mesenteric vascular bed and renal artery segments of diabetic rats. Chronic treatment of the diabetic rats with 1-aminobenzotriazole (ABT, 50 mg kg(-1) alt(-1) diem) or N-hydroxy-N'-(4-butyl-2-methylphenyl) formamidine (HET0016, 2.5 mg kg(-1) day(-1)) attenuated the responses to these vasoconstrictors in both vascular beds. 3 The synthesis of 20-HETE in renal microsomes was reduced by >80% confirming that the doses of ABT and HET0016 were sufficient to achieve system blockade. Addition of HET0016 (1 microM) in vitro also normalized the enhanced vascular responsiveness of renal and mesenteric vessels obtained from diabetic animals to NE and inhibited the formation of 20-HETE by >90% while having no effect on the formation of epoxides. Vasodilator responses to carbachol and histamine were reduced in the mesenteric vasculature, but not in renal arteries, of diabetic rats. Treatment of the diabetic animals with HET0016 improved vasodilator responses in both vascular beds. Vascular sensitivity to exogenous 20-HETE was elevated in the mesenteric bed of diabetic animals compared to controls. 4 These results suggest that 20-HETE contributes to the elevation in vascular reactivity in diabetic animals. This effect is not due to increased vascular expression of CYP4A but may be related to either enhanced agonist-induced release of substrate (arachidonic acid) by the CaMKII/Ras-GTPase system and/or elevated vascular responsiveness to 20-HETE by the CaMKII/Ras-GTPase system and/or elevated vascular responsiveness to 20-HETE.

Cytochrome P450 metabolites of arachidonic acid play a role in the enhanced cardiac dysfunction in diabetic rats following ischaemic reperfusion injury

1 This study examined the contribution of cytochrome P450 metabolites of arachidonic acid in mediating ischaemia/reperfusion (I/R)-induced cardiac dysfunction in normal and diabetic rats. 2 We first compared the metabolism of arachidonic acid in microsomes prepared from the hearts of control rats and rats treated with streptozotocin (55 mg kg(-1)) to induce diabetes. The production of dihydroxyeicosatrienoic acids and epoxyeicosatrienoic acids (EETs) were similar in microsomes prepared from the hearts of control and diabetic rats, but the production of 20-hydroxyeicosatetraenoic acid (20-HETE) was two-fold higher in diabetic hearts than in control animals. 3 We then compared the change in left ventricular pressure (P(max)), left ventricular end-diastolic pressure, coronary flow and coronary vascular resistance in isolated perfused hearts obtained from control and diabetic animals after 40 min of global ischaemia (I) followed by 30 min of reperfusion (R). The decline in cardiac function was three- to five-fold greater in the hearts obtained from diabetic vs. control animals. 4 Pretreatment of the hearts with N-hydroxy-N'-(4-butyl-2-methyl-phenyl)-formamidine (HET0016, 1 microm), a selective inhibitor of the synthesis of 20-HETE, for 30 min before I/R resulted in significant improvement in the recovery of cardiac function in the hearts obtained from diabetic but not in control rats. Perfusion with an inhibitor of soluble epoxide hydrolase, 1-cyclohexyl-3-dodecyl urea (CDU), before I/R improved the recovery of cardiac function in hearts obtained from both control and diabetic animals. Perfusion with both HET0016 and CDU resulted in significantly better recovery of cardiac function of diabetic hearts following I/R than that seen using either drug alone. Pretreatment of the hearts with glibenclamide (1 microm), an inhibitor of ATP-sensitive potassium channels, attenuated the cardioprotective effects of both CDU and HET0016. 5 This is the first study to suggest that acute blockade of the formation of 20-HETE and/or reduced inactivation of EETs could be an important strategy to reduce cardiac dysfunction following I/R events in diabetes.

Rat survival to anthrax lethal toxin is likely controlled by a single gene

We examined whether survival of different rat strains administered anthrax lethal toxin is genetically determined. A reproducible test population of first filial generation hybrid rats was bred based on the susceptibility of progenitors to anthrax lethal toxin and to maximize genetic diversity across the strains. These rats were then tested with varying doses of anthrax lethal toxin. We found that all 'sensitive' strains died within 2 h following systemic administration of 240 mug/kg lethal toxin, while one strain survived following a five times higher dose (1.4 mg/kg). The ability of lethal toxin to lyse macrophage cultures derived from the bone marrow of these strains corresponded with in vivo results. We conclude that a rat test population can detect strain differences in response to anthrax lethal toxin. Survival is influenced by the host genome background and is likely due to a single gene with a recessive mode of inheritance.

Reversal of delayed vasospasm by TS-011 in the dual hemorrhage dog model of subarachnoid hemorrhage

PURPOSE

Arachidonic acid is avidly metabolized to a potent vasoconstrictor, 20-hydroxyeicosatetraenoic acid (20-HETE), in the cerebral circulation. 20-HETE has been reported to contribute to the acute fall in cerebral blood flow following subarachnoid hemorrhage (SAH), but its role in the development of delayed vasospasm is unknown. The present study examined whether delayed vasospasm is associated with elevations in 20-HETE in CSF in the dual hemorrhage model of SAH in dogs and if blockade of the synthesis of 20-HETE with N-(3-chloro-4-morpholin-4-yl)phenyl-N'-hydroxyimido formamide (TS-011) can reverse delayed vasospasm in this model.

MATERIALS AND METHODS

Delayed vasospasm was induced in 22 adult beagle dogs by dual injection of blood (0.5 mL/kg) into the cisterna magna on days 1 and 4. Sequential samples of CSF were collected before intracisternal injections of blood on days 1 and 4 and after the development of delayed vasospasm on day 7. Sequential angiograms were obtained before and after intracisternal injection of blood on days 1 and 4 and before and 1 hour after administration of TS-011 (1 mg/kg IV) on day 7.

RESULTS

The dogs consistently developed delayed vasospasm, and the diameter of the basilar artery fell to 68 +/- 3% (n = 15), 3 days after the second intracisternal injection of blood. The levels of 20-HETE in CSF increased from 4 +/- 2 to 39 +/- 16 pg/mL. In 9 dogs with delayed vasospasm, acute blockade of the synthesis of 20-HETE with TS011 (1 mg/kg IV) significantly increased the diameter of the basilar artery by 39%. Chronic administration of TS-011 (1 mg/kg per day) attenuated the development of delayed vasospasm, and the diameter of the basilar artery fell by 17 +/- 1% versus the 33 +/- 3% decrease in diameter seen in control animals 3 days following the second injection of blood into the cisterna magna.

CONCLUSIONS

These results indicate that the development of delayed vasospasm in dogs is associated with an increase in 20-HETE levels in CSF, and acute blockade of the synthesis of 20-HETE with TS-011 reverses delayed vasospasm in this model.

Consomic rat model systems for physiological genomics

A consomic rat strain is one in which an entire chromosome is introgressed into the isogenic background of another inbred strain using marker-assisted selection. The development and physiological screening of two inbred consomic rat panels on two genetic backgrounds (44 strains) is well underway. Consomic strains enable one to assign traits and quantitative trait loci (QTL) to chromosomes by surveying the panel of strains with substituted chromosomes. They enable the rapid development of congenic strains over a narrow region and enable one to perform F2 linkage studies to positionally locate QTL on a single chromosome with a fixed genetic background. These rodent model systems overcome many of the problems encountered with segregating crosses where even if linkage is found, each individual in the cross is genetically unique and the combination of genes cannot be reproduced or studied in detail. For physiologists, consomics enable studies to be performed in a replicative or longitudinal manner to elucidate in greater detail the sequential expression of genes responsible for the observed phenotypes of these animals. They often provide the best available inbred control strains for physiological comparisons with the parental strains and they enable one to assess the impact of a causal gene region in a genome by allowing comparisons of the effect of replacement of a specific chromosome on a disease susceptible or a resistant genomic background. Consomic rat strains are proving to be a unique scientific resource that can greatly extend our understanding of genes and their role in the regulation of complex function and disease.

Role of Cytochrome P450 Metabolites of Arachidonic Acid in Hypertension

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.

Differential effect of cytochrome P-450 omega-hydroxylase inhibition on O2-induced constriction of arterioles in SHR with early and established hypertension

OBJECTIVE

To determine whether two structurally and mechanistically different inhibitors of cytochrome P-450 omega-hydroxylase would alter the enhanced vasoconstrictor response to elevated PO2 in arterioles of spontaneously hypertensive rats (SHR). Cytochrome P-450 omega-hydroxylases, which catalyze the formation of the vasoconstrictor 20-hydroxyeicosatetraenoic acid from arachidonic acid, have been proposed to serve as microvascular O2 sensors.

METHODS

Arteriolar diameters were measured in the in situ cremaster muscle of 4- to 6- and 12- to 16-week-old SHR and normotensive Wistar-Kyoto (WKY) controls during superfusion with physiological salt solution (PSS) equilibrated with 0% O2 and 21% O2 before and after P-450 enzyme inhibition.

RESULTS

The P-450 omega-hydroxylase inhibitors 17-octadecynoic acid (17-ODYA) and N-methylsulfonyl-12, 12-dibromododec-11-enamide (DDMS) significantly reduced O2-induced constriction of arterioles of 12- to 16-week-old SHR and WKY and eliminated the difference in the response between the two groups. In contrast, both enzyme inhibitors attenuated the O2-induced constriction of arterioles in the younger WKY, but not in the 4- to 6-week-old SHR.

CONCLUSIONS

These results support the hypothesis that cytochrome P-450 4A may act as an O2 sensor in the skeletal muscle microcirculation and suggest that 20-hydroxyeicosatetraenoic acid plays an important role in the enhanced response to elevated PO2 in the SHR with established hypertension. Other mechanisms seem to contribute to the enhanced sensitivity of arterioles to elevated PO2 in young SHR during the early development of hypertension.

A genomic-systems biology map for cardiovascular function

With the draft sequence of the human genome available, there is a need to better define gene function in the context of systems biology. We studied 239 cardiovascular and renal phenotypes in 113 male rats derived from an F2 intercross and mapped 81 of these traits onto the genome. Aggregates of traits were identified on chromosomes 1, 2, 7, and 18. Systems biology was assessed by examining patterns of correlations ("physiological profiles") that can be used for gene hunting, mechanism-based physiological studies, and, with comparative genomics, translating these data to the human genome.

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.

Relative contributions of cyclooxygenase- and cytochrome P450 omega-hydroxylase-dependent pathways to hypoxic dilation of skeletal muscle resistance arteries

This study determined the contribution of prostanoids, cytochrome P450 (CP450) 4A enzyme metabolites of arachidonic acid, and other potential mediators of hypoxic dilation of isolated rat skeletal muscle resistance arteries. Gracilis arteries (GA) were viewed via television microscopy and dilator responses to hypoxia (reduction in superfusate and perfusate PO2 from approximately 145 to approximately 40 mm Hg) were measured with a video micrometer. Hypoxic dilation of gracilis arteries was severely impaired by either endothelium removal or cyclooxygenase inhibition with indomethacin, but not by nitric oxide synthase inhibition with L-NAME. Treatment of GA with 17-octadecynoic acid (17-ODYA) alone to inhibit CP450 4A enzymes significantly reduced hypoxic dilation from control levels. Treatment of vessels with N-methylsulfonyl-6-(2-proparglyoxyphenyl)hexanoic acid (MS-PPOH) to inhibit the production of epoxyeicosatrienoic acids (EETs) did not alter hypoxic dilation, although treatment with dibromo-dodecenyl-methylsulfimide (DDMS) to inhibit 20-hydroxyeicosatetraenoic acid (20-HETE) production had similar effects as 17-ODYA. Treatment of GA with 6(Z),15(Z)-20-HEDE, a competitive antagonist of the actions of 20-HETE, mimicked the effects of 17-ODYA and DDMS treatment on hypoxic dilation. These results suggest that hypoxic dilation of skeletal muscle resistance arteries primarily represents the effects of enhanced prostanoid release from vascular endothelium, although a contribution of reduced 20-HETE production via CP450 omega-hydroxylase enzymes also regulates hypoxic dilation of these vessels.

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.

Cytochrome P-450 omega-hydroxylase: a potential O(2) sensor in rat arterioles and skeletal muscle cells

The purposes of this study were to 1) further evaluate the possible role that vasoconstrictor metabolites of cytochrome P-450 (CYP) omega-hydroxylase plays in O(2)-induced constriction of arterioles in the rat skeletal muscle microcirculation, 2) determine whether omega-hydroxylases are expressed in rat cremaster muscle, and 3) determine whether the enzyme is located in the parenchyma or the arterioles. O(2)-induced constriction of third-order arterioles in the in situ cremaster muscle of Sprague-Dawley rats was significantly inhibited by the CYP inhibitors N-methyl-sulfonyl-12,12-dibromododec-11-enamide (DDMS; 50 microM) and 17-octadecynoic acid (ODYA; 10 microM). Immunoblot analysis with antibody raised against CYP4A protein indicated the presence of immunoreactive proteins in the cremaster muscle and in isolated arterioles and muscle fibers from this tissue. However, the molecular mass of the immunoreactive proteins was 85 kDa instead of the expected 50--52 kDa for CYP4A omega-hydroxylase isolated from rat liver or kidney. Treatment of the cremaster muscle with deglycosidases shifted the bands to the expected range which indicates that these proteins are likely glycosylated in skeletal muscle. Immunohistochemistry revealed intense staining of both muscle fibers and microvessels in the cremaster muscle. The results of this study indicate that O(2) sensing in the skeletal muscle microcirculation may be mediated by CYP4A omega-hydroxylases in both arterioles and parenchymal cells.

Altered mechanisms underlying hypoxic dilation of skeletal muscle resistance arteries of hypertensive versus normotensive Dahl rats

OBJECTIVE

To determine mechanisms underlying hypoxic dilation of skeletal muscle resistance arteries from normotensive (NT) and hypertensive (HT) Dahl salt-sensitive (SS) rats.

METHODS

Isolated gracilis arteries (GA) from both rat groups were viewed via television microscopy and vascular responses to a reduction in PO2 from 145 mm Hg to 40 mm Hg were measured with a video micrometer. Responses were determined following endothelium removal and following inhibition of specific biochemical pathways regulating vascular tone.

RESULTS

Hypoxic dilation was impaired in HT rats versus NT controls. Endothelium removal abolished hypoxic dilation in NT rats, although a significant dilation to hypoxia remained in vessels from HT animals. Inhibition of cytochrome P450 (CP450) 4A enzymes blunted hypoxic dilation in both groups, while inhibition of epoxyeicosatrienoic acid (EET) production impaired responses in NT rats only. Inhibition of 20-hydroxyeicosatetraenoic acid (20-HETE) production or blockade of membrane receptors for 20-HETE reduced hypoxic dilation in HT rats, with minimal effects in NT animals. Nitric oxide synthase inhibition had no effect on hypoxic dilation in either group, while cyclooxygenase inhibition significantly reduced this response in both groups.

CONCLUSIONS

These results suggest that the mechanisms of hypoxic dilation in GA from NT Dahl-SS rats are altered with HT, impairing the response to reduced PO2. While hypoxia induces substantial prostanoid release in both groups, the role of CP450 4A enzymes is shifted from EET production in NT rats toward inhibition of 20-HETE production in HT rats.

20-HETE modulates myogenic response of skeletal muscle resistance arteries from hypertensive Dahl-SS rats

The present study determined the role of 20-hydroxyeicosatetraenoic acid [20-HETE; produced by omega-hydroxylation of arachidonic acid via cytochrome P-450 (CP450) 4A enzymes] in regulating myogenic activation of skeletal muscle resistance arteries from normotensive (NT) and hypertensive (HT) Dahl salt-sensitive (SS) rats. Gracilis arteries (GA) were isolated from each rat and viewed via television microscopy, and changes in vessel diameter with altered transmural pressure were measured with a video micrometer. Under control conditions, GA from both groups exhibited strong, endothelium-independent myogenic activation. Treatment of GA with 17-octadecynoic acid (17-ODYA; inhibitor of CP450 4A enzymes) did not alter myogenic activation in NT rats, but impaired this response in HT animals. Treatment of GA from HT rats with dibromo-dodecynyl-methylsulfimide (DDMS; inhibitor of 20-HETE production) impaired myogenic activation, as did application of 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid, an antagonist for 20-HETE receptors. Application of iberiotoxin, a Ca(2+)-activated potassium (K(Ca)) channel inhibitor, restored myogenic activation from HT rats treated with DDMS. These results suggest that myogenic activation of skeletal muscle resistance arteries from NT Dahl-SS rats does not depend on CP450, whereas myogenic activation of these vessels in HT Dahl-SS rats is partly a function of 20-HETE production, inhibiting K(Ca) channels through a receptor-mediated process.

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.

Renin gene transfer restores angiogenesis and vascular endothelial growth factor expression in Dahl S rats

In a previous study, we demonstrated that Dahl S rats (SS group) have low plasma renin activity, whereas transfer of a region of chromosome 13 containing the renin gene from Dahl R onto a congenic strain of Dahl SS/Jr/Hsd/MCW rats (S/ren(RR) group) restores renin secretory responses. In the present study, we compared the angiogenic responses to electrical stimulation in the SS and S/ren(RR) groups to explore the hypotheses that the renin-angiotensin system is involved in vascular endothelial growth factor (VEGF) expression and angiogenesis in skeletal muscle. Congenic SS and S/ren(RR) rats fed a 0.4% or 4% salt diet were surgically prepared by chronic implantation of an electrical stimulator. Another group of S/ren(RR) rats was treated with lisinopril 2 days before the surgery and throughout the stimulation protocol. The right tibialis anterior (TA) and extensor digitorum longus (EDL) were stimulated for 8 hours per day for 7 days. The contralateral muscles served as controls. Western blot analysis was performed to identify VEGF protein expression in these muscles. Electrical stimulation produced no change in vessel density of the SS group fed a 0.4% salt diet (change 5.50% and 8.14% for EDL and TA, respectively). Transfer of a region containing the renin gene restored the angiogenic response (change 16% and 30% for EDL and TA, respectively) despite a significantly higher blood pressure. Blockade of the renin-angiotensin system by lisinopril or high salt restored the responses observed in the SS group fed a low salt diet. In addition, increases in VEGF expression to electrical stimulation were observed only in the S/ren(RR) group fed a low salt diet. These results suggest that renin gene transfer restores angiogenesis and VEGF expression in the skeletal muscle of Dahl S rats.

Brown Norway chromosome 13 confers protection from high salt to consomic Dahl S rat

Consomic rats (SS.BN13), in which chromosome 13 from normotensive inbred Brown Norway rats from a colony maintained at the Medical College of Wisconsin (BN/Mcw) was introgressed into the background of Dahl salt-sensitive (SS/Mcw) rats, also maintained in a colony at the Medical College of Wisconsin, were bred. The present studies determined the mean arterial pressure (MAP) responses to salt and renal and peripheral vascular responses to norepinephrine and angiotensin II; 24-hour protein excretion and histological analyses were used to assess renal pathology in rats that received a high salt (4% NaCl) diet for 4 weeks. MAP of rats measured daily during the fourth week averaged 170+/-3.3 mm Hg in SS/Mcw rats, 119+/-2.1 mm Hg in SS.BN13 rats, and 103+/-1.3 mm Hg in BN/Mcw rats. After salt depletion, MAP fell an average of 27+/-4.5 mm Hg in SS/Mcw rats, 9+/-2.6 mm Hg in SS.BN13 rats, and 11+/-3.0 mm Hg in BN/Mcw rats. Protein excretion of SS/Mcw rats on a high salt diet averaged 189+/-30 mg/24 h, 63+/-18 mg/24 h in SS.BN13 rats, and 40+/-6.4 mg/24 h in BN/Mcw rats. Compared with SS.BN13 and BN/Mcw rats, SS/Mcw rats exhibited significantly greater increases of renal vascular resistance in response to intravenous norepinephrine and angiotensin II. Severe medullary interstitial fibrosis and tubular necrosis after a high salt diet were found consistently in SS/Mcw rat kidneys but were largely absent in the SS.BN13 and BN/Mcw rat kidneys. A similar degree of glomerular sclerosis was found in both SS/Mcw and SS.BN13 rats. In rats fed a 0.4% salt diet, the glomerular filtration rate of SS/Mcw rats was significantly less than that of BN/Mcw and SS.BN13 rats. These results reveal a powerful gene, or set of genes, within chromosome 13 of BN/Mcw rats that confers protection from the detrimental effects of high salt to the SS/Mcw rats.

20-HETE contributes to myogenic activation of skeletal muscle resistance arteries in Brown Norway and Sprague-Dawley rats

OBJECTIVE

To evaluate the role of 20-hydroxyeicosatetraenoic acid (20-HETE), a product of arachidonic acid omega-hydroxylation via cytochrome P450 (CP450) 4A enzymes, in regulating myogenic activation of skeletal muscle resistance arteries from normotensive Brown Norway (BN) and Sprague-Dawley (SD) rats.

METHODS

Gracilis arteries (GA) were isolated from each animal, viewed via television microscopy, and vessel diameter responses to elevated transmural pressure were measured with a video micrometer under control conditions and following pharmacological inhibition of the CP450 4A enzyme system.

RESULTS

Under control conditions, GA from both rat groups exhibited strong, endothelium-independent myogenic activation, which was impaired following treatment with either 17-octadecynoic acid (17-ODYA) or dibromo-dodecenylmethylsulfimide (DDMS), two mechanistically different inhibitors of 20-HETE production. The addition of tetraethylammonium (KCa channel inhibitor) to 17-ODYA-treated GA restored myogenic reactivity to levels comparable to those under control conditions. Treatment of GA from BN and SD rats with 6(Z),15(Z)-20-HEDE, a selective antagonist for 20-HETE receptors, mimicked the effects of 17-ODYA and DDMS treatment on myogenic reactivity.

CONCLUSIONS

These results suggest that the production of 20-HETE via CP450 4A enzymes contributes to the myogenic activation of skeletal muscle resistance arteries from normotensive BN and SD rats. 20-HETE may act through a receptor-mediated process to block vascular smooth muscle KCa channels in response to the elevated transmural pressure.

Cytochrome P450 metabolites of arachidonic acid in the control of renal function

Recent studies indicate that arachidonic acid is primarily metabolized by cytochrome P450 enzymes of the 4A and 2C families in the kidney to 20-hydroxyeicosatetraenoic acid (HETE), epoxyeicosatrienoic acids (EETs) and dihydroxyeicosatrienoic acids. These compounds play central roles in the regulation of renal tubular and vascular function. 20-HETE is produced by renal vascular smooth muscle (VSM) cells and is a potent constrictor that depolarizes VSM cells by blocking the calcium-activated potassium channel. Inhibition of the formation of 20-HETE blocks the myogenic response of isolated renal arterioles in vitro, and autoregulation of renal blood flow and tubuloglomerular feedback responses in vivo. EETs are products formed in the endothelium and are potent dilators that activate the calcium-activated potassium channel in renal VSM. Endothelial-dependent vasodilators stimulate the release of EETs, and these compounds appear to serve as an endothelial-derived hyperpolarizing factor. EETs and 20-HETE are produced in the proximal tubule. There, they regulate sodium/potassium-ATPase activity and serve as second messengers for the natriuretic effects of dopamine, parathyroid hormone and angiotensin II. 20-HETE is also produced in the thick ascending loop of Henle. It regulates sodium-potassium-chloride transport in this nephron segment. The renal production of cytochrome P450 metabolites of arachidonic acid is altered in hypertension, diabetes, toxemia of pregnancy, and hepatorenal syndrome. Given the importance of cytochrome P450 metabolites of arachidonic acid in the control of renal function, it is likely that changes in this system contribute to the abnormalities in renal function that are associated with many of these conditions.

Renal and cardiovascular actions of 20-hydroxyeicosatetraenoic acid and epoxyeicosatrienoic acids

1. Arachidonic acid (AA) is metabolized by cytochrome P450 (CYP)-dependent pathways to epoxyeicosatrienoic acids (EET) and 20-hydroxyeicosatetraenoic acid (20-HETE) in the kidney and the peripheral vasculature. 2. The present short review summarizes the renal and cardiovascular actions of these important mediators. 3. Epoxyeicosatrienoic acids are vasodilators produced by the endothelium that hyperpolarize vascular smooth muscle (VSM) cells by opening Ca2+-activated K+ (KCa) channels. 20-Hydroxyeicosatetraenoic acid is a vasoconstrictor that inhibits the opening of KCa channels in VSM cells. Cytochrome P450 4A inhibitors block the myogenic response of small arterioles to elevations in transmural pressure and autoregulation of renal and cerebral blood flow in vivo. Cytochrome P450 4A blockers also attenuate the vasoconstrictor response to elevations in tissue PO2, suggesting that this system may serve as a vascular oxygen sensor. Nitric oxide and carbon monoxide inhibit the formation of 20-HETE and a fall in 20-HETE levels contributes to the activation of KCa channels in VSM cells and the vasodilator response to these gaseous mediators. 20-Hydroxyeicosatetraenoic acid also mediates the inhibitory actions of peptide hormones on sodium transport in the kidney and the mitogenic effects of growth factors in VSM and mesangial cells. A deficiency in the renal production of 20-HETE is associated with the development of hypertension in Dahl salt-sensitive rats. 4. In summary, the available evidence indicates that CYP metabolites of AA play a central role in the regulation of renal, pulmonary and vascular function and that abnormalities in this system may contribute to the pathogenesis of cardiovascular diseases.

Microvascular flow and tissue PO(2) in skeletal muscle of chronic reduced renal mass hypertensive rats

This study determined whether arteriolar blood flow, capillary red blood cell (RBC) velocity, capillary hematocrit (Hct(cap)), and tissue PO(2) are altered in cremaster muscles of rats with chronic reduced renal mass hypertension (RRM-HT) relative to normotensive rats on high- or low-salt (NT-HS vs. NT-LS) diet. The blood flow in first- through third-order arterioles was not different between NT and HT rats, either at rest or during maximal relaxation of the vessels with 10(-4) M adenosine. Capillary RBC velocity was similar between the groups at rest but was elevated in RRM-HT and NT-HS rats during adenosine superfusion. Hct(cap) was reduced at rest in RRM-HT and NT-HS rats compared with NT-LS and was reduced in RRM-HT rats during adenosine-induced dilation. Tissue PO(2) was reduced in RRM-HT and NT-HS rats compared with NT-LS rats during control conditions and was lower in RRM-HT than in NT-LS rats during adenosine-induced dilation. These results indicate that both RRM-HT and chronic exposure of normotensive rats to a high-salt diet lead to reduced tissue oxygenation, despite the maintenance of normal arteriolar blood flow.

Hypoxic pulmonary vasoconstriction is modified by P-450 metabolites

20-Hydroxyeicosatetraenoic acid (20-HETE) is a cytochrome P-450 4A (CYP4A) metabolite of arachidonic acid (AA) in human and rabbit lung microsomes and is a dilator of isolated human pulmonary arteries (PA). However, little is known regarding the contribution of P-450 metabolites to pulmonary vascular tone. We examined 1) the effect of two mechanistically distinct omega- and omega1-hydroxylase inhibitors on perfusion pressures in isolated rabbit lungs ventilated with normoxic or hypoxic gases, 2) changes in rabbit PA ring tone elicited by 20-HETE or omega- and omega1-hydroxylase inhibitors, and 3) expression of CYP4A protein in lung tissue. A modest increase in perfusion pressure (55 +/- 11% above normoxic conditions) was observed in isolated perfused lungs during ventilation with hypoxic gas (FI(O(2)) = 0.05). Inhibitors of 20-HETE synthesis, 17-oxydecanoic acid (17-ODYA) or N-methylsulfonyl-12,12-dibromododec-11-enamide (DDMS), increased baseline perfusion pressure above that of vehicle and amplified hypoxia-induced increases in perfusion pressures by 92 +/- 11% and 105 +/- 11% over baseline pressures, respectively. 20-HETE relaxed phenylephrine (PE)-constricted PA rings. Treatment with 17-ODYA enhanced PE-induced contraction of PA rings, consistent with inhibition of a product that promotes arterial relaxation, whereas 6-(20-propargyloxyphenyl)hexanoic acid (PPOH), an epoxygenase inhibitor, blunted contraction to PE. Conversion of AA into 20-HETE was blocked by 17-ODYA, DDMS, and hypoxia. CYP4A immunospecific protein confirms expression of CYP4A in male rabbit lung tissue. Our data suggest that endogenously produced 20-HETE could modify rabbit pulmonary vascular tone, particularly under hypoxic conditions.

Endotoxin augments cerebral hyperemic response to halothane by inducing nitric oxide synthase and cyclooxygenase

We examined the cerebral hyperemic response to halothane after treatment with bacterial lipopolysaccharide (LPS). To determine the involvement of inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX-2), we tested whether the effect of LPS on halothane-induced hyperemia was altered by pretreatment with the selective iNOS inhibitor, aminoguanidine (100 mg/kg), COX-2 inhibitor, NS-398 (5 mg/kg), or enzyme expression inhibitor, dexamethasone (4 mg/kg). Further, we examined whether the administration of a nitric oxide donor, diethylamine NONOate, would change the cerebral hyperemic response of halothane. Sprague-Dawley rats were anesthetized with 0.5 minimum alveolar anesthetic concentration of halothane and artificially ventilated. Regional cerebrocortical blood flow (rCBF) was assessed by laser-Doppler flowmetry. LPS (1 mg/kg) was administered intracerebroventricularly; artificial cerebrospinal fluid was used in controls. Four hours after LPS infusion, iNOS and COX-2 messenger ribonucleic acid (mRNA) levels (reverse transcription-polymerase chain reaction) and enzyme activities (arginine-citrulline conversion and prostaglandin E(2) enzyme immunoassay) were significantly increased. LPS enhanced halothane-induced 3.9 and 1.6-fold increases in rCBF at 1.0 and 1.5 minimum alveolar concentration, respectively. Co-treatment with NS-398 attenuated, but aminoguanidine or dexamethasone abolished the effect of LPS on halothane-induced rCBF increase. Diethylamine NONOate mimicked the enhanced rCBF response to halothane. These results suggest that LPS augmented halothane-induced cerebrocortical hyperemia by induction of iNOS and COX-2.

Fluorescent HPLC assay for 20-HETE and other P-450 metabolites of arachidonic acid

This study describes a fluorescent HPLC assay for measuring 20-hydroxyeicosatetraenoic acid (20-HETE) and other cytochrome P-450 metabolites of arachidonic acid in urine, tissue, and interstitial fluid. An internal standard, 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid, was added to samples, and the lipids were extracted and labeled with 2-(2,3-naphthalimino)ethyl trifluoromethanesulfonate. P-450 metabolites were separated on a C18 reverse-phase HPLC column. Coelution and gas chromatography-mass spectrometry studies confirmed the identity of the 20-HETE peak. The 20-HETE peak can be separated from those for dihydroxyeicosatrienoic acids, other HETEs, and epoxyeicosatrienoic acids. Known amounts of 20-HETE were used to generate a standard curve (range 1-10 ng, r(2) = 0.98). Recovery of 20-HETE from urine averaged 95%, and the intra-assay variation was <5%. Levels of 20-HETE were measured in 100 microliter of urine and renal interstitial fluid or 0.1 mg of renal tissue. The assay was evaluated by studying the effects of 1-aminobenzotriazole (ABT) on the excretion of 20-HETE in rats. ABT reduced excretion of 20-HETE by >65% and inhibited the formation of 20-HETE by renal microsomes. The availability of this assay should facilitate work in this field.

Production of 20-HETE and its role in autoregulation of cerebral blood flow

In the brain, pressure-induced myogenic constriction of cerebral arteriolar muscle contributes to autoregulation of cerebral blood flow (CBF). This study examined the role of 20-HETE in autoregulation of CBF in anesthetized rats. The expression of P-450 4A protein and mRNA was localized in isolated cerebral arteriolar muscle of rat by immunocytochemistry and in situ hybridization. The results of reverse transcriptase-polymerase chain reaction studies revealed that rat cerebral microvessels express cytochrome P-450 4A1, 4A2, 4A3, and 4A8 isoforms, some of which catalyze the formation of 20-HETE from arachidonic acid. Cerebral arterial microsomes incubated with [(14)C]arachidonic acid produced 20-HETE. An elevation in transmural pressure from 20 to 140 mm Hg increased 20-HETE concentration by 6-fold in cerebral arteries as measured by gas chromatography/mass spectrometry. In vivo, inhibition of vascular 20-HETE formation with N-methylsulfonyl-12, 12-dibromododec-11-enamide (DDMS), or its vasoconstrictor actions using 15-HETE or 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid (20-HEDE), attenuated autoregulation of CBF to elevations of arterial pressure. In vitro application of DDMS, 15-HETE, or 20-HEDE eliminated pressure-induced constriction of rat middle cerebral arteries, and 20-HEDE and 15-HETE blocked the vasoconstriction action of 20-HETE. Taken together, these data suggest an important role for 20-HETE in the autoregulation of CBF.

Impairment of flow-induced dilation of skeletal muscle arterioles with elevated oxygen in normotensive and hypertensive rats

The effects of elevated PO(2) on flow-induced dilation of in situ skeletal muscle arterioles was assessed in cremaster muscle preparations from spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. Blood flow increases in selected arterioles were initiated by occlusion of a parallel daughter branch from a parent arteriole. Changes in the diameter of the perfused arteriole were measured with a video micrometer and erythrocyte velocity was measured using optical Doppler velocimetry. Superfusate PO(2) was controlled by changing the O(2) concentration (0% O(2) or 21% O(2)) of the equilibration gas mixture. The increase in arteriolar diameter during occlusion was reduced in SHR compared to WKY rats, resulting in an elevated wall shear rate in SHR. Elevated PO(2) decreased flow-induced dilation in both groups and increased wall shear rate during parallel occlusion. An inhibitor of the formation of 20-HETE via cytochrome P450-4A enzymes (P450), dibromododecenyl methylsulfimide, minimized O(2)-induced constriction of arterioles and prevented the O(2)-induced decrease in flow-induced dilation and the increase in wall shear rate in both SHR and WKY rats. These results suggest that: (1) flow-induced dilation of in situ skeletal muscle arterioles is impaired in SHR compared to WKY, (2) elevated O(2) compromises flow-induced dilation in both groups, (3) 20-HETE contributes to both the O(2)-induced increases in resting tone and the reduced flow-induced dilation of cremasteric arterioles with elevated PO(2).

Role of cGMP versus 20-HETE in the vasodilator response to nitric oxide in rat cerebral arteries

This study examined the response to nitric oxide (NO) in rat middle cerebral arteries (MCA). NO donors increased the activity of a 205-pS K(+) channel recorded from vascular smooth muscle (VSM) cells isolated from MCA 10-fold. Blockade of guanylyl cyclase activity with 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (ODQ, 10(-5) M) did not alter the effect of NO on this channel. In contrast, adding 20-hydroxyeicosatetraenoic acid (20-HETE) to the bath (10(-7) M) abolished the response to NO. NO donors also increased the diameter of serotonin-preconstricted MCA to 85% of control. Blockade of K(+) channels with iberiotoxin or a high-K(+) medium reduced this response by 50%. ODQ (10(-5) M) reduced this response by 47 +/- 3%, whereas preventing the fall of 20-HETE levels reduced the response by 59 +/- 2% (n = 5). Blockade of both pathways eliminated the response to NO donors. These results indicate that activation of K(+) channels contributes 50% to vasodilator response to NO in rat MCA. This is mediated by a fall in 20-HETE levels rather than a rise in cGMP levels or a direct effect of NO.

Genetically defined risk of salt sensitivity in an intercross of Brown Norway and Dahl S rats

A genetic segregation analysis was performed to identify genes that cosegregate with arterial blood pressure traits reflective of salt sensitivity. A population of 113 F2 male rats was derived from an intercross of inbred SS/JrHsd/Mcw (Dahl salt-sensitive) and BN/SsN/Mcw (Brown Norway) rats. Rats were maintained on an 8% salt diet from the age of 9 to 13 wk, and arterial pressure was measured for 3 h daily during the 4th wk of high salt intake in unanesthetized rats using implanted arterial catheters. At the end of the 3rd day of high-salt pressure recordings, the arterial pressure response to salt depletion was determined 1.5 days following treatment with Lasix and a low-sodium (0. 4%) diet. A genome-wide scan using 265 polymorphic simple sequence length polymorphism (SSLP) markers found that seven arterial pressure phenotypes determined at different times and circumstances, and representing two distinct indexes of salt sensitivity, mapped to the same region of rat chromosome 18. The trait of salt sensitivity was strongly influenced by the presence of SS alleles in this region of chromosome 18, and those rats which were homozygote SS/SS exhibited a significantly greater reduction of mean arterial pressure following sodium depletion (29 +/- 2 mmHg) than homozygote BN/BN (17 +/- 3 mmHg) or heterozygotic (22 +/- 2 mmHg) rats. This region of rat chromosome 18 corresponds to the long arm of human chromosome 5 and a region of human chromosome 18 that has been linked to hypertension in humans. Given the unlikely chance of these different blood pressure traits mapping to the same region, we believe these data provide evidence that this region of rat chromosome 18 plays an important role in salt-induced hypertension.

Molecular mechanisms controlling nutritive blood flow: role of cytochrome P450 enzymes

This short review summarizes the potential role of cytochrome P450 (P450) in regulating blood flow in the brain tissue and in the skeletal muscle. We provide data showing that pressure-induced myogenic activity in the brain is largely responsible for autoregulation of CBF. This myogenic response to pressure is maintained, in part, by 20-HETE formation in arterial muscle cells through a P450 omega-hydroxylase coded for by a P450 4A cDNA. Autoregulation of CBF is a hallmark of the cerebral circulation and provides adequate nutritive blood flow despite large fluctuations in arterial pressure. Given the importance of oxidative metabolism in the brain, support of neuronal activity is mediated by functional hyperaemia to active neurones providing adequate delivery of oxidative substrate. We provide data demonstrating that this functional hyperaemia in the brain is regulated by astrocytes which sense neural activity and release dilator metabolites which shunt blood flow to active neurones. One of the metabolites released by astrocytes in this regard are epoxygenated products of arachidonic acid (AA) formed by P450 enzymes. These AA metabolites of P450 enzymes are epoxyeicosatrienoic acid (EETs). One of these P450 enzymes is coded by a 2C11 cDNA present in astrocytes. Furthermore, astrocytes are capable of inducing capillary angiogenesis which appears to be mediated, in part, by P450-derived EETs.

Glomerular hyperfiltration in hypertensive African Americans

The incidence of end-stage renal disease attributable to hypertension is 5-fold greater in African Americans than in whites. To determine whether glomerular hyperfiltration is an antecedent to renal failure, we compared responses of renal blood flow and glomerular filtration rate to graded infusions of norepinephrine (0. 01, 0.025, and 0.05 microg. kg(-1). min(-1) for 30 minutes each) in 29 African Americans and 33 age-matched French Canadian whites with essential hypertension. Renal blood flow and glomerular filtration rate were measured by using a constant-infusion technique of PAH and inulin, respectively. Studies were conducted on an inpatient clinical research center, and antihypertensive medications had been discontinued for at least 1 week. Based on 24-hour blood pressure monitoring, nighttime blood pressures decreased (P<0.01) in the French Canadians but not in the African Americans. Baseline renal blood flow was higher (P<0.05) in the African Americans (1310+/-127 mL. min(-1) per 1.73 m(2)) than in the French Canadians (1024+/-42 mL. min(-1) per 1.73 m(2)); baseline glomerular filtration rate was also higher (P<0.01) in the African Americans (140+/-4 versus 121+/-4 mL. min(-1) per 1.73 m(2)). In response to norepinephrine-induced blood pressure increases, renal blood flow was autoregulated and did not change in either patient group. In the African Americans, glomerular filtration rate increased (P<0.01) to 167 mL. min(-1) per 1.73 m(2) during the first norepinephrine infusion, without subsequent change. In contrast, glomerular filtration rate did not change with norepinephrine-induced increases of blood pressure in the French Canadians. In the African Americans, the elevation of baseline glomerular filtration rate, with a further increase in response to norepinephrine, may be indicative of glomerular hyperfiltration. Glomerular hyperfiltration and lack of nocturnal blood pressure decline may contribute to the higher incidence of end-stage renal disease in hypertensive African Americans.

Epoxyeicosatrienoic acids constrict isolated pressurized rabbit pulmonary arteries

Little information is available regarding the vasoactive effects of epoxyeicosatrienoic acids (EETs) in the lung. We demonstrate that 5, 6-, 8,9-, 11,12-, and 14,15-EETs contract pressurized rabbit pulmonary arteries in a concentration-dependent manner. Constriction to 5,6-EET methyl ester or 14,15-EET is blocked by indomethacin or ibuprofen (10(-5) M), SQ-29548, endothelial denuding, or submaximal preconstriction with the thromboxane mimetic U-46619. Constriction of pulmonary artery rings to phenylephrine is blunted by treatment with the epoxygenase inhibitor N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide. Pulmonary arteries and peripheral lung microsomes metabolize arachidonate to products that comigrate on reverse-phrase HPLC with authentic regioisomers of 5,6-, 8,9-, 11,12-, and 14,15-EETs, but no cyclooxygenase products of EETs could be demonstrated. Proteins of the CYP2B, CYP2E, CYP2J, CYP1A, and CYP2C subfamilies are present in pulmonary artery and peripheral lung microsomes. Constriction of isolated rabbit pulmonary arteries to EETs is nonregioselective and depends on intact endothelium and cyclooxygenase, consistent with the formation of a pressor prostanoid compound. These data raise the possibility that EETs may contribute to regulation of pulmonary vascular tone.

Contribution of 20-HETE to vasodilator actions of nitric oxide in the cerebral microcirculation

BACKGROUND AND PURPOSE

The present study examined the contributions of a rise in cGMP versus a fall in 20-HETE levels to the vasodilator response to nitric oxide (NO) in the cerebral circulation of the rat.

METHODS

Intact rat middle cerebral and basilar arteries were bathed in physiological saline solution containing indomethacin (5 micromol/L) and baicalein (0.5 micromol/L) and pressurized at 90 mm Hg. Relaxations to sodium nitroprusside (SNP) were studied before and after addition of [1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one] (ODQ, a guanylyl cyclase blocker), 8R,9S, 11S-(-)-9-methoxy-carbamyl-8-methyl-2,3,9,10-tetrahydro-8, 11-epoxy-1H,8H,11H-2,7b,11a-trizadibenzo-(a,g)-cycloocta-(c, d, e)-trinden-1-one (KT5823, a protein kinase G blocker), and 20-hydroxyeicosatetraenoic acid (20-HETE). Cerebral blood flow was measured by using a laser Doppler flow probe over a thin cranial window in anesthetized rats, and the effects of intracerebroventricular infusion of 1-hexamine, 6-(2-hydroxy-1-methyl-2-nitrosohydrazino)N-methyl (MAHMA nonoate) and dibromododecenyl methylsulfimide (DDMS) were determined.

RESULTS

SNP-induced dilation of serotonin-preconstricted (0.2 micromol/L) middle cerebral arteries (10(-7) to 10(-3) mol/L) was attenuated in arteries treated with ODQ (10 micromol/L) or KT5823 (1 micromol/L) by 52% and 27%, respectively. Preventing the NO-induced fall in intracellular 20-HETE, by adding 20-HETE (100 nmol/L) to the bath, reduced the dilation to SNP by 62%. Simultaneous administration of ODQ and 20-HETE markedly attenuated the SNP-induced dilation by 90%. In basilar arteries, ODQ (10 micromol/L) alone completely blocked the response to SNP. Infusion of MAHMA nonoate (10 nmol/min ICV) in anesthetized rats increased cerebral blood flow by 52% before and 8% after blockade of the endogenous production of 20-HETE with DDMS (50 pmol/min).

CONCLUSIONS

These results suggest that NO dilates cerebral arteries through both cGMP-dependent and cGMP-independent pathways and that inhibition of 20-HETE formation contributes to the cerebral vasodilator response to NO both in vitro and in vivo.

20-HETE agonists and antagonists in the renal circulation

The present study examined the effects of a series of 20-hydroxyeicosatetraenoic acid (20-HETE) derivatives on the diameter of renal arterioles to determine the structural requirements of the vasoconstrictor response to 20-HETE. The vascular responses to 5-, 8-, 12-, 15-, 19-, 20-, 21-HETEs, arachidonic acid (AA), and saturated, partially saturated, dimethyl, carboxyl, and 19-carbon derivatives of 20-HETE (10(-8) to 10(-6) M) were assessed in rat renal interlobular arteries (65-125 micrometer). 20-HETE, 21-HETE, dimethyl-20-HETE, and a partially saturated derivative of 20-HETE, 20-hydroxyeicosa-5(Z),14(Z)-dienoic acid, reduced vessel diameter by 19 +/- 3, 17 +/- 3, 16 +/- 2, and 28 +/- 2%, respectively. In contrast, 5-, 8-, 12-, 15-, and 19-HETE, AA, saturated, partially saturated, carboxyl, and the 19-carbon derivatives of 20-HETE had no effect on vessel diameter. Pretreatment with 5-, 15-, and 19-HETE, the 19-carbon derivative or 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid (1 microM) completely blocked the vasoconstrictor response to 20-HETE in renal arterioles. Pretreatment with AA, carboxyl, saturated 19-carbon, and saturated 20-HETE derivatives (1 microM) partially blocked the response, whereas 8- and 12-HETE (1 microM) had no effect on the vasoconstrictor response to 20-HETE. These findings suggest that 20-HETE agonists and antagonists require a carboxyl or an ionizable group on carbon 1 and a double bond near the 14 or 15 carbon. 20-HETE agonists also require a functional group capable of hydrogen bonding on carbon 20 or 21, whereas antagonists lack this reactive group.

Altered expression and activity of G-proteins, mitogen activated protein kinases, and tyrosine kinases in aging kidney cortex

BACKGROUND

Renal function declines with age and this may be related to changes in the expression or activity of various signal transduction proteins in the kidney.

METHODS

The present study compared the expression and activity of G alpha i(1-3) and G alpha s phosphorylation of mitogen activated protein kinases (MAP-K) (44 and 42 kd) and the activity of tyrosine kinase in renal cortical homogenates of young (4-month-old) and aging (14-month-old) rats.

RESULTS

The GTP/(GTP + GDP) binding ratio of G alpha s was significantly decreased in the kidney cortex of aging rats compared to young rats, while the GTP/(GTP + GDP) binding ratio of G alpha i(1-3) increased significantly in kidney cortex of aging rats. Tyrosine kinase activity and phosphorylation of MAP-K (44 and 42 kd) were also reduced in the kidney cortex of aging rats compared to young rats.

CONCLUSIONS

These results suggest that diminished phosphorylation of MAP-K and tyrosine kinase activity as well as changes in the binding of GTP/(GTP + GDP) to G alpha i(1-3) and G alpha s may contribute to the age-related decline in renal tubular and vascular function seen in aging animals.

20-Hydroxyeicosatetraenoic acid and renal function in Lyon hypertensive rats

To evaluate the contribution of cytochrome P450 (CYP450) metabolites of arachidonic acid in the increased renal vascular resistance and blunted pressure-natriuresis response exhibited by Lyon hypertensive (LH) rats, the effects of an intrarenal infusion of 17-octadecynoic acid (3 microM), an inhibitor of the formation of epoxyeicosatrienoic and 20-hydroxyeicosatetraenoic acids, were compared in 8-week-old LH and low blood pressure (LL) control rats. 17-Octadecynoic acid failed to affect renal function in LL rats. In contrast, it reduced renal vascular resistance and shifted the pressure-natriuresis relationship to lower pressures in LH rats. Blockade of thromboxane-endoperoxide (TP) receptors with GR 32191B prevented the renal vasodilator response to 17-octadecynoic acid but not its natriuretic action. Miconazole (1 microM), an inhibitor of epoxygenase activity, had no effect on renal function in LH rats. These results indicate that CYP450 metabolites of arachidonic acid, likely 20-hydroxyeicosatetraenoic acid, contribute to the resetting of the pressure-natriuresis relation in LH rats and that the renal vasoconstrictor effects of 20-hydroxyeicosatetraenoic acid in LH rats may be related to activation of TP receptors.

Regulation of P-450 4A activity in the glomerulus of the rat

We recently reported that an enzyme of the cytochrome P-450 4A family is expressed in the glomerulus, but there is no evidence that 20-hydroxyeicosatetraenoic acid (20-HETE) can be produced by this tissue. The purpose of present study was to determine whether glomeruli isolated from the kidney of rats can produce 20-HETE and whether the production of this metabolite is regulated by nitric oxide (NO) and dietary salt intake. Isolated glomeruli produced 20-HETE, dihydroxyeicosatrienoic acids, and 12-hydroxyeicosatetraenoic acid (4.13 +/- 0.38, 4.20 +/- 0.38, and 2. 10 +/- 0.20 pmol. min-1. mg protein-1, respectively) when incubated with arachidonic acid (10 microM). The formation of 20-HETE was dependent on the availability of NADPH and the PO2 of the incubation medium. The formation of 20-HETE was inhibited by NO donors in a concentration-dependent manner. The production of 20-HETE was greater in glomeruli isolated from the kidneys of rats fed a low-salt diet than in kidneys of rats fed a high-salt diet (5.67 +/- 0.32 vs. 2.83 +/- 0.32 pmol. min-1. mg protein-1). Immunoblot experiments indicated that the expression of P-450 4A protein in glomeruli from the kidneys of rats fed a low-salt diet was sixfold higher than in kidneys of rats fed a high-salt diet. These results indicate that arachidonic acid is primarily metabolized to 20-HETE and dihydroxyeicosatrienoic acids in glomeruli and that glomerular P-450 activity is modulated by NO and dietary salt intake.

Acute and chronic renal effects of recombinant human TGF-beta2 in the rat

The expression of transforming growth factor-beta (TGF-beta) correlates with the incidence of renal glomerular and interstitial injury, however, nothing is known of the effect of these proteins on renal hemodynamics. This study examines the renal hemodynamic and morphologic effects of recombinant human TGF-beta2 in normal male Sprague Dawley rats. Acute infusion of TGF-beta (1.2 microg/kg per min) induced no hemodynamic changes, except for a modest though significant fall in mean arterial pressure. Administering TGF-beta2 at varying doses (20, 100, and 400 microg/kg) for 9 wk caused modest increases in systolic BP and proteinuria and minimal tubular interstitial fibrosis, however, renal hemodynamic end points were not significantly altered. TGF-beta2 (800 microg/kg) was also administered to volume-depleted rats for 7 consecutive days. In contrast to the findings in volume-replete animals, administration of TGF-beta2 to volume-depleted rats caused a marked reduction in GFR and medullary blood flow. Histologic fibrosis of the medullary vasa recta and cortical interstitium was seen, but glomeruli were unaffected. Thus, acute and short-term chronic TGF-beta2 administration did not induce major renal changes in the volume-replete state, however, TGF-beta2 combined with volume depletion caused medullary hypoperfusion and reduced GFR.

Inflammatory modulation of calcium-activated potassium channels in canine colonic circular smooth muscle cells

BACKGROUND & AIMS

The characteristics of colonic circular smooth muscle slow waves are altered during inflammation. The aim of this study was to examine whether inflammation modulates the open-state probability of Ca2+-activated K+ (KCa) channels in these cells to contribute to these alterations.

METHODS

The experiments were performed on freshly dissociated single smooth muscle cells from the canine colon using standard patch clamp methods. Inflammation was induced by mucosal exposure to ethanol and acetic acid.

RESULTS

Inflammation decreased the open-state probability of large-conductance KCa (BK) channels in the cell-attached and excised inside-out configurations. The voltage sensitivity of the channels was also reduced during inflammation. Inflammation had no significant effect on the large, medium, and small conductances or the unitary current levels of channel openings. However, it decreased the maximum number of simultaneous channel openings. The channels were Ca2+-dependent and were blocked by tetraethylammonium and charybdotoxin in normal and inflamed cells.

CONCLUSIONS

Inflammation decreases the open-state probability of BK channels. This may partially reverse the decrease in duration and amplitude of slow waves and depolarization of membrane potential seen in inflammation.

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 micromol/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 micromol/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 micromol/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.

Altered renal hemodynamics and impaired myogenic responses in the fawn-hooded rat

The present study examined whether an abnormality in the myogenic response of renal arterioles that impairs autoregulation of renal blood flow (RBF) and glomerular capillary pressure (PGC) contributes to the development of renal damage in fawn-hooded hypertensive (FHH) rats. Autoregulation of whole kidney, cortical, and medullary blood flow and PGC were compared in young (12 wk old) FHH and fawn-hooded low blood pressure (FHL) rats in volume-replete and volume-expanded conditions. Baseline RBF, cortical and medullary blood flow, and PGC were significantly greater in FHH than in FHL rats. Autoregulation of renal and cortical blood flow was significantly impaired in FHH rats compared with results obtained in FHL rats. Myogenically mediated autoregulation of PGC was significantly greater in FHL than in FHH rats. PGC rose from 46 +/- 1 to 71 +/- 2 mmHg in response to an increase in renal perfusion pressure from 100 to 150 mmHg in FHH rats, whereas it only increased from 39 +/- 2 to 53 +/- 1 mmHg in FHL rats. Isolated perfused renal interlobular arteries from FHL rats constricted by 10% in response to elevations in transmural pressure from 70 to 120 mmHg. In contrast, the diameter of vessels from FHH rats increased by 15%. These results indicate that the myogenic response of small renal arteries is altered in FHH rats, and this contributes to an impaired autoregulation of renal blood flow and elevations in PGC in this strain.

Cytochrome P-450 omega-hydroxylase senses O2 in hamster muscle, but not cheek pouch epithelium, microcirculation

The goal of this study was to investigate the role of cytochrome P-450 omega-hydroxylase in mediating O2-induced constriction of arterioles in the microcirculation of the hamster. Male Golden hamsters were anesthetized with pentobarbital sodium, and the cremaster muscle or cheek pouch was prepared for observation by intravital microscopy. Arteriolar diameters were measured during elevations of superfusate PO2 from approximately 5 to 150 mmHg. Arteriolar responses to elevated PO2 were determined in the cremaster muscle, in the retractor muscle where it inserts on the cheek pouch, and in the epithelial portion of the cheek pouch. Elevation of superfusion solution PO2 caused a vigorous constriction of arterioles in the cremaster and retractor muscles and in the epithelial portion of the cheek pouch. Superfusion with 10 microM 17-octadecynoic acid, a suicide substrate inhibitor of cytochrome P-450 omega-hydroxylase, and intravenous infusion of N-methylsulfonyl-12,12-dibromododec-11-enamide, a mechanistically different and highly selective inhibitor of cytochrome P-450 omega-hydroxylase, caused a significant reduction in the magnitude of O2-induced constriction of arterioles in the cremaster and retractor muscles. However, arteriolar constriction in response to elevated PO2 was unaffected by 17-octadecynoic acid or N-methylsulfonyl-12,12-dibromododec-11-enamide in the epithelial portion of the cheek pouch. These data confirm that there are regional differences in the mechanism of action of O2 on the microcirculation and indicate that cytochrome P-450 omega-hydroxylase senses O2 in the microcirculation of hamster skeletal muscle, but not in the cheek pouch epithelium.

Electrical and mechanical responses of rat middle cerebral arteries to reduced PO2 and prostacyclin

Isolated rat middle cerebral arteries were perfused and superfused with physiological salt solution equilibrated with a control (approximately 140 mmHg) or reduced (approximately 35-40 mmHg) PO2. In other experiments, cerebral arteries were isolated and prostacyclin release was determined by radioimmunoassay for 6-ketoprostaglandin F1alpha. Equilibration of the vessels with reduced PO2 (35 mmHg) solution caused a significant increase in prostacyclin release relative to control PO2 (140 mmHg) conditions. Exposure of middle cerebral arteries to reduced PO2 caused vascular smooth muscle (VSM) hyperpolarization and vessel relaxation, which could be blocked by 1 microM glibenclamide, an inhibitor of the ATP-sensitive K+ channel, but not by 1 mM tetraethylammonium (TEA), an inhibitor of the Ca2+-activated K+ channel. Glibenclamide also inhibited VSM hyperpolarization and vasodilation in response to the stable prostacyclin analog iloprost, but TEA did not affect iloprost-induced dilation of the vessel. Endothelial removal eliminated the electrical and mechanical responses of the arteries to reduced PO2, but vessel responses to iloprost were similar to those of intact vessels. The results of this study are consistent with the hypothesis that hypoxic dilation of rat middle cerebral arteries is due to VSM hyperpolarization mediated by prostacyclin-induced activation of glibenclamide-sensitive K+ channels.

Role of 20-HETE in elevating chloride transport in the thick ascending limb of Dahl SS/Jr rats

This study examined the role of endogenous 20 hydroxyeicosatetraenoic acid (20-HETE) in elevating Cl- transport in the medullary thick ascending loop of Henle (MTAL) of 9-week-old male Dahl salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) rats perfused in vitro. Basal transepithelial voltage (Vte; 14.9+/-0.9 versus 10.1+/-0.5 mV) and net lumen-to-bath Cl- flux (JCl) (155+/-6 versus 127+/-5 pEq. min-1. mm-1) were significantly greater in MTAL isolated from SS/Jr rats (n=16) than in those obtained from SR/Jr rats (n=16). Blockade of the synthesis of 20-HETE with 17-octadecynoic acid (17-ODYA; 10 micromol/L) increased Vte from 9. 9+/-0.8 to 13.1+/-1.0 mV and JCl from 127+/-7 to 152+/-8 pEq. min-1. mm-1 in the MTAL of SR/Jr rats (n=8), but it had no significant effect on Vte or JCl in the MTAL of SS/Jr rats (n=8). Exogenous 20-HETE (1 micromol/L) decreased Vte from 14.8+/-0.6 to 10.5+/-0.6 mV and JCl from 155+/-10 to 116+/-6 pEq. min-1. mm-1 in MTAL of SS/Jr rats (n=8), but it had no effect on Vte or JCl in the MTAL of SR/Jr rats (n=8). The expression of P4504A2 protein in the MTAL of SS/Jr rats was approximately half of that seen in the MTAL of SR/Jr rats. These results indicate that endogenously formed 20-HETE regulates transepithelial voltage and Cl- transport in the MTAL and that a diminished production of 20-HETE contributes to an elevation in Cl- transport in the MTAL of SS/Jr rats.

Role of tyrosine kinase and PKC in the vasoconstrictor response to 20-HETE in renal arterioles

The present study examined the hypothesis that activation of protein kinase C (PKC), components of the mitogen-activated protein (MAP) kinase pathway, or both contributes to the inhibitory effects of 20-hydroxyeicosatetraenoic acid (20-HETE) on K+-channel activity and its vasoconstrictor response in renal arterioles. 20-HETE (0.1 to 50 micromol/L) dose-dependently produced a 30% increase in PKC activity and a fivefold rise in the expression of active extracellular signal-regulated kinase 1 (ERK1) and ERK2 proteins in renal microvessels. 20-HETE (0.01 to 1 micromol/L) reduced the diameter of isolated perfused renal interlobular arterioles by 33+/-2%. Blockade of PKC activity with an N-myristoylated PKC pseudosubstrate inhibitor (Myr-PKCi, 100 micromol/L) or calphostin C (0.5 micromol/L) had no significant effect on the vasoconstrictor response to 20-HETE. In contrast, the tyrosine kinase inhibitors genistein (30 micromol/L) and tyrphostin 25 (10 micromol/L) reduced the response to 20-HETE by 76.5+/-2.1% and 67.5+/-1.8%, respectively. A specific inhibitor of mitogen-activated extracellular signal-regulated kinase (MEK), PD98059, had no effect on the vasoconstrictor response to 20-HETE. In cell-attached patches on renal vascular smooth muscle cells, 20-HETE reduced the open state probability of a large-conductance K+ channel (from 0.0026+/-0.0004 to 0.0006+/-0.0001). The Myr-PKCi (100 micromol/L) did not alter the inhibitory effects of 20-HETE on this channel. In contrast, the tyrosine kinase inhibitor genistein (30 micromol/L) blocked the inhibitory effects of 20-HETE on the large-conductance K+ channel. These data suggest that 20-HETE activates the MAP kinase system in renal arterioles and that the activation of a tyrosine kinase, which is proximal to MEK in this cascade, contributes to the inhibitory effects of 20-HETE on K+-channel activity and its vasoconstrictor effects in the renal arterioles.

Impaired autoregulation of renal blood flow in the fawn-hooded rat

The responses to changes in renal perfusion pressure (RPP) were compared in 12-wk-old fawn-hooded hypertensive (FHH), fawn-hooded low blood pressure (FHL), and August Copenhagen Irish (ACI) rats to determine whether autoregulation of renal blood flow (RBF) is altered in the FHH rat. Mean arterial pressure was significantly higher in conscious, chronically instrumented FHH rats than in FHL rats (121 +/- 4 vs. 109 +/- 6 mmHg). Baseline arterial pressures measured in ketamine-Inactin-anesthetized rats averaged 147 +/- 2 mmHg (n = 9) in FHH, 132 +/- 2 mmHg (n = 10) in FHL, and 123 +/- 4 mmHg (n = 9) in ACI rats. Baseline RBF was significantly higher in FHH than in FHL and ACI rats and averaged 9.6 +/- 0.7, 7.4 +/- 0.5, and 7.8 +/- 0.9 ml. min-1. g kidney wt-1, respectively. RBF was autoregulated in ACI and FHL but not in FHH rats. Autoregulatory indexes in the range of RPPs from 100 to 150 mmHg averaged 0.96 +/- 0.12 in FHH vs. 0.42 +/- 0.04 in FHL and 0.30 +/- 0.02 in ACI rats. Glomerular filtration rate was 20-30% higher in FHH than in FHL and ACI rats. Elevations in RPP from 100 to 150 mmHg increased urinary protein excretion in FHH rats from 27 +/- 2 to 87 +/- 3 microg/min, whereas it was not significantly altered in FHL or ACI rats. The percentage of glomeruli exhibiting histological evidence of injury was not significantly different in the three strains of rats. These results indicate that autoregulation of RBF is impaired in FHH rats before the development of glomerulosclerosis and suggest that an abnormality in the control of renal vascular resistance may contribute to the development of proteinuria and renal failure in this strain of rats.

A common pathway for regulation of nutritive blood flow to the brain: arterial muscle membrane potential and cytochrome P450 metabolites

Perfusion pressure to the brain must remain relatively constant to provide rapid and efficient distribution of blood to metabolically active neurones. Both of these processes are regulated by the level of activation and tone of cerebral arterioles. The active state of cerebral arterial muscle is regulated, to a large extent, by the level of membrane potential. At physiological levels of arterial pressure, cerebral arterial muscle is maintained in an active state owing to membrane depolarization, compared with zero pressure load. As arterial pressure changes, so does membrane potential. The membrane is maintained in a relatively depolarized state because of, in part, inhibition of K+ channel activity. The activity of K+ channels, especially the large conductance Ca(2+)-activated K+ channel (KCa) is dependent upon the level of 20-HETE produced by arterial muscle. As arterial pressure increases, so does cytochrome P450 (P4504A) activity. P4504A enzymes catalyse omega-hydroxylation of arachidonic acid and formation of 20-hydroxyeicosatetraenoic acid (20-HETE). 20-HETE is a potent inhibitor of KCa which maintains membrane depolarization and muscle cell activation. Astrocytes also metabolize AA via P450 enzymes of the 2C11 gene family to produce epoxyeicosatrienoic acids (EETs). Epoxyeicosatrienoic acids are released from astrocytes by glutamate which 'spills over' during neuronal activity. These locally released EETs shunt blood to metabolically active neurones providing substrate to support neuronal function. This short paper will discuss the findings which support the above scenario, the purpose of which is to provide a basis for future studies on the molecular mechanisms through which cerebral blood flow matches metabolism.