Polyphenols restore endothelial function in DOCA-salt hypertension: role of endothelin-1 and NADPH oxidase

Red wine polyphenols (RWPs) have been reported to exert beneficial effects in preventing cardiovascular diseases, such as hypertension. We studied the effects of chronic treatment with RWPs and apocynin, an inhibitor of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, on blood pressure, endothelial function, and oxidative status in deoxycorticosterone acetate (DOCA)-salt-induced hypertension. Rats were administered RWPs (40 mg/kg) or apocynin (33 microg/kg) daily by gavage for 5 weeks. Plasma catechin levels were detected only after RWP treatment. RWPs and apocynin prevented both the increase in systolic blood pressure and the proteinuria induced by DOCA-salt. Plasma malonyldialdehyde levels, urinary iso-prostaglandin F(2alpha) excretion, aortic superoxide production, and aortic NADPH oxidase activity were found to be increased in animals of the DOCA group. RWP and apocynin treatments reduced these parameters in DOCA-salt rats, having no effect on control rats. However, only RWPs reduced the increase in plasma endothelin-1 (ET-1) levels and aortic p22(phox) gene overexpression found in DOCA-salt animals. RWPs and apocynin also improved the blunted endothelium-dependent relaxation response to acetylcholine in noradrenaline-precontracted aortic rings. All these results suggest that chronic treatment with RWPs prevents hypertension and vascular dysfunction. RWPs prevent vascular oxidative stress by inhibiting NADPH oxidase activity and/or by reducing ET-1 release.     

DOCA-salt treatment enhances responses to endothelin-1 in murine corpus cavernosum

The penis is kept in the flaccid state mainly via a tonic activity of norepinephrine and endothelins (ETs). ET-1 is important in salt-sensitive forms of hypertension. We hypothesized that cavernosal responses to ET-1 are enhanced in deoxycorticosterone acetate (DOCA)-salt mice and that blockade of ETA receptors prevents abnormal responses of the corpus cavernosum in DOCA-salt hypertension. Male C57BL/6 mice were unilaterally nephrectomized and treated for 5 weeks with both DOCA and water containing 1% NaCl and 0.2% KCl. Control mice were uninephrectomized and received tap water with no added salt. Animals received either the ETA antagonist atrasentan (5 mg x day(-1) x kg(-1) body weight) or vehicle. DOCA-salt mice displayed increased systolic blood pressure (SBP), and treatment with atrasentan decreased SBP in DOCA-salt mice. Contractile responses in cavernosal strips from DOCA-salt mice were enhanced by ET-1, phenylephrine, and electrical field stimulation (EFS) of adrenergic nerves, whereas relaxations were not altered by IRL-1620 (an ETB agonist), acetylcholine, sodium nitroprusside, and EFS of nonadrenergic noncholinergic nerves. PD59089 (an ERK1/2 inhibitor), but not Y-27632 (a Rho-kinase inhibitor), abolished enhanced contractions to ET-1 in cavernosum from DOCA-salt mice. Treatment of DOCA-salt mice with atrasentan did not normalize cavernosal responses. In summary, DOCA-salt treatment in mice enhances cavernosal reactivity to contractile, but not to relaxant, stimuli, via ET-1/ETA receptor-independent mechanisms.     

Role of ET-1 receptor binding and [Ca(2+)](i) in contraction of coronary arteries from DOCA-salt hypertensive rats

Hypertension is associated with an increase in coronary artery disease, but little is known about the regulation of coronary vascular tone by endothelin-1 (ET-1) in hypertension. The present study evaluated the mechanisms mediating altered contraction to ET-1 in coronary small arteries from deoxycorticosterone acetate (DOCA)-salt hypertensive rats. DOCA-salt rats exhibited an increase in systolic blood pressure and plasma ET-1 levels compared with placebo rats. Contraction to ET-1 (1 x 10(-11) to 3 x 10(-8) M), measured in isolated coronary small arteries maintained at a constant intraluminal pressure of 40 mmHg, was largely reduced in vessels from DOCA-salt rats compared with placebo rats. To determine the role of endothelin receptor binding in the impaired contraction to ET-1, (125)I-labeled ET-1 receptor binding was measured in membranes isolated from coronary small arteries. Maximum binding (fmol/mg protein) and binding affinity were similar in coronary membranes from DOCA-salt rats compared with placebo rats. Changes in intracellular Ca(2+) concentration ([Ca(2+)](i)) were measured in freshly dissociated coronary small artery smooth muscle cells loaded with fura 2. ET-1 (10(-9) M) produced a 30 +/- 9% increase in [Ca(2+)](i) in smooth muscle cells from placebo rats, but had no effect on cells from DOCA-salt rats (2 +/- 2%). In summary, the ET-1-induced coronary artery contraction and increase in [Ca(2+)](i) are impaired in DOCA-salt hypertensive rats, whereas endothelin receptor binding is not altered. These results suggest endothelin receptor uncoupling from signaling mechanisms and indicate that impaired [Ca(2+)](i) signaling contributes to the decrease in ET-1-induced contraction of coronary small arteries in DOCA-salt hypertensive rats.     

Increased reactive oxygen species contributes to kidney injury in mineralocorticoid hypertensive rats.

Hypertension is associated with increased reactive oxygen species (ROS). Renal ROS production and their effects on renal function have never been investigated in mineralocorticoid hypertensive rats. In this study we hypothesized that increased ROS production in kidneys from deoxycorticosterone (DOCA)-salt rats contributes to adverse renal morphological changes and impaired renal function in DOCA-salt hypertensive rats. We also determined whether ROS-induced renal injury was dependent on blood pressure. DOCA-salt hypertensive rats exhibited a marked increase in blood pressure, renal ROS production, glomerular and tubular lesions, and microalbuminuria compared to sham rats. Treatment of DOCA-salt hypertensive rats with apocynin for 28 days resulted in attenuation of systolic blood pressure and improvement of renal morphology. Renal superoxide level in DOCA-salt rats was 215% of sham-operated rats and it was significantly decreased to 140% with apocynin treatment. Urinary protein level was decreased from 27 +/- 3 mg/day in DOCA-salt hypertensive rats to 9 +/- 2 mg/day. 28 days of Vitamin E treatment also reduced renal injury in regard to urinary protein level and renal morphology but had no effect on blood pressure in DOCA-salt rats. Increased urinary 8-isoprostane, a marker for oxidative stress, in DOCA-salt hypertensive rats (55 +/- 8 ng/day) was diminished by vitamin E treatment (24 +/- 6 ng/day). These data suggest that renal injury characteristic of mineralocorticoid hypertension is associated with oxidative stress and is partly independent of blood pressure.     

α-MSH Analogue Attenuates Blood Pressure Elevation in DOCA-Salt Hypertensive Mice

Melanocyte-stimulating hormones, α-, β- and γ-MSH, regulate important physiological functions including energy homeostasis, inflammation and sodium metabolism. Previous studies have shown that α-MSH increases sodium excretion and promotes vascular function in rodents, but it is unexplored whether these characteristics of α-MSH could translate into therapeutic benefits in the treatment of hypertension. Therefore, we first assessed the diuretic and natriuretic properties of the stable α-MSH analogue [Nle⁴, D-Phe⁷]-α-MSH (NDP-α-MSH) and investigated whether it has protective effects in deoxycorticosterone acetate (DOCA)-salt hypertensive mice. Adult male C57Bl/6N mice were subjected to DOCA-salt treatment and randomized to receive intraperitoneal injections of either saline as vehicle or NDP-α-MSH (0.3 mg/kg/day for 14 days) starting 7 days after the DOCA-salt treatment. Systemic hemodynamics, serum and urine electrolytes, and oxidative stress markers were assessed in control sham-operated and DOCA-salt mice. NDP-α-MSH elicited marked diuretic and natriuretic responses that were reversible with the MC3/4 receptor antagonist SHU9119. Chronic NDP-α-MSH treatment attenuated blood pressure elevation in DOCA-salt mice without affecting the blood pressure of normotensive control animals. Owing to the enhanced sodium excretion, NDP-α-MSH-treated mice were protected from DOCA-salt-induced hypernatremia. DOCA-salt treatment mildly increased oxidative stress at the tissue level, but NDP-α-MSH had no significant effects on the oxidative stress markers. In conclusion, treatment with NDP-α-MSH increases urinary sodium excretion and protects against DOCA-salt-induced hypertension. These findings point to the potential future use of α-MSH analogues in the treatment of hypertension.     

TNF-alpha inhibition reduces renal injury in DOCA-salt hypertensive rats

Studies suggest that the inflammatory cytokine TNF-alpha plays a role in the prognosis of end-stage renal diseases. We previously showed that TNF-alpha inhibition slowed the progression of hypertension and renal damage in angiotensin II salt-sensitive hypertension. Thus, we hypothesize that TNF-alpha contributes to renal inflammation in a model of mineralocorticoid-induced hypertension. Four groups of rats (n = 5 or 6) were studied for 3 wk with the following treatments: 1) placebo, 2) placebo + TNF-alpha inhibitor etanercept (1.25 mg.kg(-1).day(-1) sc), 3) deoxycorticosterone acetate + 0.9% NaCl to drink (DOCA-salt), or 4) DOCA-salt + etanercept. Mean arterial blood pressure (MAP) measured by telemetry increased in DOCA-salt rats compared with baseline (177 +/- 4 vs. 107 +/- 3 mmHg; P < 0.05), and TNF-alpha inhibition had no effect in the elevation of MAP in these rats (177 +/- 8 mmHg). Urinary protein excretion significantly increased in DOCA-salt rats compared with placebo (703 +/- 76 vs. 198 +/- 5 mg/day); etanercept lowered the proteinuria (514 +/- 64 mg/day; P < 0.05 vs. DOCA-salt alone). Urinary albumin excretion followed a similar pattern in each group. Urinary monocyte chemoattractant protein (MCP)-1 and endothelin (ET)-1 excretion were also increased in DOCA-salt rats compared with placebo (MCP-1: 939 +/- 104 vs. 43 +/- 7 ng/day, ET-1: 3.30 +/- 0.29 vs. 1.07 +/- 0.03 fmol/day; both P < 0.05); TNF-alpha inhibition significantly decreased both MCP-1 and ET-1 excretion (409 +/- 138 ng/day and 2.42 +/- 0.22 fmol/day, respectively; both P < 0.05 vs. DOCA-salt alone). Renal cortical NF-kappaB activity also increased in DOCA-salt hypertensive rats, and etanercept treatment significantly reduced this effect. These data support the hypothesis that TNF-alpha contributes to the increase in renal inflammation in DOCA-salt rats.     

An analysis of the DOCA-salt model of hypertension in HO-1-/- mice and the Gunn rat

Heme oxygenase-1 (HO-1) is induced in the vasculature in the DOCA-salt model of hypertension in rats. Whereas the HO system and its products may exert vasodilator effects, recent studies have suggested that the HO system may predispose to hypertension. The present study examined the effects of selected components of the HO system, specifically, the HO-1 isozyme and the product bilirubin in the DOCA-salt model of systemic hypertension; the experimental approach employed mutant rodent models, namely, the HO-1(-/-) mouse and the hyperbilirubinemic Gunn rat. DOCA-salt induced HO-1 protein in the aorta in HO-1(+/+) mice and provoked a significant rise in systolic arterial pressure in HO-1(-/-) mice but not in HO-1(+/+) mice; this effect could not be ascribed to impaired urinary sodium excretion or impaired glomerular filtration rate in the DOCA-salt-treated HO-1(-/-) mice. The administration of DOCA salt to uninephrectomized rats significantly increased systolic arterial pressure in wild-type rats, an effect that was attenuated in the mutant Gunn rat; this reduction in systemic hypertension in the DOCA-salt-treated Gunn rat was not due to a greater induction of HO-1 in the vasculature or to a more avid urinary sodium excretion. DOCA-salt impaired endothelium-dependent and endothelium-independent vasorelaxation in wild-type rats but not in Gunn rats; prior exposure to bilirubin repaired the defect in endothelium-dependent vasorelaxation in aortic rings in DOCA-salt-treated rats. DOCA salt stimulated vascular production of superoxide anion in wild-type but not in Gunn rats. We suggest that HO-1 and the product bilirubin may exert a countervailing effect in the DOCA-salt model of systemic hypertension.     

Mechanism of the anti-hypertensive property of the naturally occurring phenolic,malabaricone C in DOCA-salt rats

In this study, we studied whether chronic oral administration of the natural antioxidant, malabaricone C (mal C) can reduce blood pressure (BP) and attenuate cardio-vascular remodeling in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. The dose of mal C for its anti-hypertensive action was optimized by measuring the systolic BP (SBP). DOCA-salt rats showed very high SBP, associated with organ hypertrophy, collagen depositions, and inflammatory infiltrations in cardiac and aortic sections, reduced plasma total antioxidant status and NO level, and increased levels of TBARS, PGI2 as well as vasoconstrictors (AVP, Big ET, and ET-1). DOCA-salt also reduced smooth muscle- and endothelium-dependent vascular relaxation in rats. Mal C reversed all these changes of the DOCA-salt rats and improved their vascular reactivity. Mal C exerts anti-hypertensive property in DOCA-salt rats by reducing oxidative stress and organ hypertrophy, and improving endothelial and vascular functions. Given that mal C has appreciable natural abundance and is non-toxic to rodents, further studies would help in establishing its medicinal potential against hypertension.     

Endothelin in the splanchnic vascular bed of DOCA-salt hypertensive rats

Vascular capacitance is reduced by endothelin-1 (ET-1) in deoxycorticosterone (DOCA)-salt hypertensive rats. This may contribute to hypertension development. Because the splanchnic blood vessels (especially veins) are important in determining vascular capacitance, we tested the hypothesis that ET-1 levels in the splanchnic vasculature are elevated in hypertensive DOCA-salt compared with normotensive rats. Tissue ET-1 content was measured by ELISA in aorta, vena cava, superior mesenteric artery and vein, and small mesenteric arteries and veins from normotensive sham-operated (sham) and 4-wk DOCA-salt rats. We also determined ET-1 concentration in aortic and portal venous blood (draining the nonhepatic splanchnic organs) in anesthetized and conscious sham and DOCA-salt rats before and after acute blockade of ETB receptor-mediated plasma clearance of ET-1. Results showed a higher ET-1 content in veins than in arteries of similar size. However, ET-1 content was similar in vessels from sham and DOCA-salt rats, except in aorta and superior mesenteric artery, where ET-1 content was greater in DOCA-salt rats. ET-1 concentration was significantly higher in portal venous than in aortic blood, indicating net nonhepatic splanchnic release (nNHSR) of ET-1. However, nNHSR of ET-1 was similar in sham and DOCA-salt rats. Although nNHSR of ET-1 increased significantly after ETB receptor blockade in sham rats, it was completely unchanged in DOCA-salt rats. These data suggest that, despite the absence of ETB receptor-mediated plasma clearance of ET-1, neither the venous peptide content nor the net release of ET-1 is increased in the splanchnic vasculature of DOCA-salt rats. These results argue against the hypothesis that increased venomotor tone in DOCA-salt hypertension is caused by increased ET-1 concentration around splanchnic venous smooth muscle cells.     

ETA receptor-mediated role of endothelin in the kidney of doca-salt hypertensive rats

Renal effects of FR139317, an endothelin ET_A receptor antagonist, were examined using anesthetized normotensive and deoxycorticosterone acetate (DOCA)-salt hypertensive rats. The intravenous bolus injection of FR139317 (10 mg/kg) produced a slight decrease in mean blood pressure (MAP; −13%) in the control rats and this hypotension was accompanied by a moderate renal vasodilation (renal vascular resistance: RVR; −12%). In the DOCA-salt hypertensive rat, FR139317 had a more pronounced hypotensive effect (MAP; −26%) accompanied by a potent renal vasodilation (RVR; −33%). FR 139317 significantly increased renal blood flow only in the DOCAsalt rats. In contrast, FR139317 produced a significant decrease in urine flow and urinary sodium excretion only in control rats. Northern blot analysis revealed that the renal prepro endothelin-1 (ET-1) mRNA level was significantly increased in DOCA-salt hypertensive rats. Thus, it seems likely that endogenous ET-1 is responsible for the maintenance of DOCA-salt-induced hypertension. We also suggest that at least in part, ET-1 and £ta receptors are involved in renal hemodynamic abnormalities in DOCA-salt-induced hypertension. The augmentation of renal ET-1 production may possibly have a function in the development and maintenance of DOCA-salt-induced hypertension.     

Reactive oxygen species contribute to sleep apnea-induced hypertension in rats

In clinical studies, sleep apnea is associated with hypertension, oxidative stress, and increased circulating endothelin-1 (ET-1). We previously developed a model of sleep apnea by exposing rats to eucapnic intermittent hypoxia (IH-C) during sleep, which increases both blood pressure and plasma levels of ET-1. Because similar protocols in mice increase tissue and plasma markers of oxidative stress, we hypothesized that IH-C generation of reactive oxygen species (ROS) contributes to the development of ET-1-dependent hypertension in IH-C rats. To test this, male Sprague-Dawley rats were instrumented with indwelling blood pressure telemeters and drank either plain water or water containing the superoxide dismutase mimetic, Tempol (4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl, 1 mM). Mean arterial pressure (MAP) and heart rate (HR) were recorded for 3 control days and 14 treatment days with rats exposed 7 h/day to IH-C or air/air cycling (Sham). On day 14, MAP in IH-C rats treated with Tempol (107 +/- 2.29 mmHg) was significantly lower than in untreated IH-C rats (118 +/- 9 mmHg, P < 0.05). Tempol did not affect blood pressure in sham-operated rats (Tempol = 101 +/- 3, water = 101 +/- 2 mmHg). Immunoreactive ET-1 was greater in plasma from IH-C rats compared with plasma from sham-operated rats but was not different from Sham in Tempol-treated IH-C rats. Small mesenteric arteries from IH-C rats but not Tempol-treated IH-C rats had increased superoxide levels as measured by ferric cytochrome c reduction, lucigenin signaling, and dihydroethidium fluorescence. The data show that IH-C increases ET-1 production and vascular ROS levels and that scavenging superoxide prevents both. Thus oxidative stress appears to contribute to increases in ET-1 production and elevated arterial pressure in this rat model of sleep apnea-induced hypertension.     

Morphological and biochemical characterization of remodeling in aorta and vena cava of DOCA-salt hypertensive rats

Arterial remodeling occurs in response to mechanical and neurohumoral stimuli. We hypothesized that veins, which are not exposed to higher pressures in hypertension, would demonstrate less active remodeling than arteries. We assessed remodeling with two standard measures of arterial remodeling: vessel morphometry and the expression/function of matrix metalloproteinases (MMPs). Thoracic aorta and vena cava from sham normotensive and DOCA-salt hypertensive rats (110 +/- 4 and 188 +/- 8 mmHg systolic blood pressure, respectively) were used. Wall thickness was increased in DOCA-salt vs. sham aorta (301 +/- 23 vs. 218 +/- 14 mum, P < 0.05), as was medial area, but neither measure was altered in the vena cava. The aorta and vena cava expressed the gelatinases MMP-2, MMP-9, transmembrane proteinase MT1-MMP, and tissue inhibitor of metalloproteinase-2 (TIMP-2). Immunohistochemically, MMP-2 localized to smooth muscle in the aorta and densely in endothelium/smooth muscle of the vena cava. Western and zymographic analyses verified that MMP-2 was active in all vessels and less active in the vena cava than aorta. In hypertension, MMP-2 expression and activity in the aorta were increased (59.1 +/- 3.7 and 74.5 +/- 6.1 units in sham and DOCA, respectively, P < 0.05); similar elevations were not observed in the vena cava. MMP-9 was weakly expressed in all vessels. MT1-MMP was expressed by the aorta and vena cava and elevated in the vena cava from DOCA-salt rats. TIMP-2 expression was significantly increased in the aorta of DOCA rats compared with sham but was barely detectable in the vena cava of sham or DOCA-salt hypertensive rats. These findings suggest that large veins may not undergo vascular remodeling in DOCA-salt hypertension.     

Preserved expression of GLUT4 prevents enhanced agonist-induced vascular reactivity and MYPT1 phosphorylation in hypertensive mouse aorta

We previously showed that GLUT4 expression is decreased in arterial smooth muscle of deoxycorticosterone acetate (DOCA)-salt hypertensive rats and that GLUT4-knockout mice have enhanced arterial reactivity. Therefore, we hypothesized that increased GLUT4 expression in vascular smooth muscle in vivo would prevent enhanced arterial reactivity and possibly reduce blood pressure in DOCA-salt hypertensive mice. Adult wild-type (WT) and GLUT4 transgenic (TG) mice were subjected to DOCA-salt hypertension with uninephrectomy or underwent uninephrectomy and remained normotensive. GLUT4 expression was increased more than twofold in the aortas of GLUT4 TG mice compared with WT aortas. Eight weeks after implantation of the DOCA pellets, GLUT4 expression decreased by 75% in aortas of WT hypertensive mice, but not in GLUT4 TG hypertensive aortas. Systolic blood pressure was significantly and similarly increased in WT and GLUT4 TG DOCA-salt mice compared with their respective sham-treated controls (159 vs. 111 mmHg). Responsiveness to the contractile agonist 5-HT was significantly increased in aortic rings from WT DOCA-salt mice but remained normal in GLUT4 TG DOCA mice. Phosphorylation of the myosin phosphatase targeting subunit MYPT1 was significantly enhanced in aortas of WT DOCA-salt mice, and this increase was prevented in GLUT4 TG mice. MYPT1 phosphorylation was also increased in nonhypertensive GLUT4-knockout mice. Myosin phosphatase, a major negative regulator of calcium sensitivity, is itself negatively regulated by phosphorylation of MYPT1. Therefore, our results show that preservation of GLUT4 expression prevents enhanced arterial reactivity in hypertension, possibly via effects on myosin phosphatase activity.     

NAD(P)H oxidase/nitric oxide interactions in peroxisome proliferator activated receptor (PPAR)alpha-mediated cardiovascular effects

Activation of peroxisome proliferator activated receptor (PPAR)alpha and its protective role in cardiovascular function has been reported but the exact mechanism(s) involved is not clear. As we have shown that PPARalpha ligands increased nitric oxide (NO) production and cardiovascular function is controlled by a balance between NO and free radicals, we hypothesize that PPARalpha activation tilts the balance between NO and free radicals and that this mechanism defines the protective effects of PPARalpha ligands on cardiovascular system. Systolic blood pressure (SBP) was greater in PPARalpha knockout (KO) mice compared with its wild type (WT) litter mates (130+/-10 mmHg versus 107+/-4 mmHg). L-NAME (100mg/L p.o.), the inhibitor of NO production abolished the difference between PPARalpha KO and WT mice. In kidney homogenates, tissue lipid hydroperoxide generation was greater in KO mice (11.8+/-1.4 pM/mg versus 8.3+/-0.6 pM/mg protein). This was accompanied by a higher total NOS activity (46+/-6%, p<0.05) and a approximately 3 fold greater Ca2+-dependent NOS activity in kidney homogenates of untreated PPARalpha WT compared with the KO mice. Clofibrate, a PPARalpha ligand, increased NOS activity in WT but not KO mice. Bezafibrate (30 mg/kg) reduced SBP in conscious rats (19+/-4%, p<0.05), increased urinary NO excretion (4.06+/-0.53-7.07+/-1.59 microM/24 h; p<0.05) and reduced plasma 8-isoprostane level (45.8+/-15 microM versus 31.4+/-8 microM), and NADP(H) oxidase activity (16+/-5%). Implantation of DOCA pellet (20mg s.c.) in uninephrectomized mice placed on 1% NaCl drinking water increased SBP by a margin that was markedly greater in KO mice (193+/-13 mmHg versus 130+/-12 mmHg). In the rat, DOCA increased SBP and NAD(P)H oxidase activity and both effects were diminished by clofibrate. In addition, clofibrate reduced ET-1 production in DOCA/salt hypertensive rats. Thus, apart from inhibition of ET-1 production, PPARalpha activation exerts protective actions in hypertension via a mechanism that involves NO production and/or inhibition of NAD(P)H oxidase activity.     

Endothelin-1 contributes to the sexual differences in renal damage in DOCA-salt rats

We investigated whether gender differences in renal damage in DOCA-salt hypertension are associated with effects of ovarian hormones and/or endothelin-1 (ET-1). Renal injuries and renal pre-pro-ET-1 mRNA expression were enhanced in male and female ovariectomized (OVX) DOCA rats versus female DOCA rats. Treatment with estrogen plus progesterone or progesterone, but not estrogen alone, attenuated renal damage and pre-pro-ET-1 mRNA expression in OVX DOCA rats. The ETA antagonist BMS182874 greatly ameliorated renal damage in male and OVX DOCA rats. In conclusion, the ovarian hormones have a protective role on the renal structural alterations in female DOCA rats by modulating effects of ET-1, via ETA receptors.     

Plasma concentrations of endothelin-1 in spontaneously hypertensive rats and DOCA-salt hypertensive rats

To investigate the possible involvement of endothelin-1 (ET-1), an endothelium-derived potent vasoconstrictor peptide, in the pathophysiology of hypertension, plasma ET-1 levels in 15-week-old spontaneously hypertensive rats (SHR) and DOCA-salt hypertensive rats were measured with a sandwich-type enzyme immunoassay. The vasocontractile effect of ET-1 in aortic helical preparations was significantly more sensitive in DOCA-salt hypertensive rats than in control sham-operated rats, but plasma levels of ET-1 did not differ between them. Plasma ET-1 levels in genetically hypertensive rats (SHR and stroke-prone SHR) were significantly lower than those in age-matched normotensive Wistar-Kyoto (WKY) rats. The plasma concentrations of big ET-1, a precursor of ET-1, in both SHR and SHR-SP were significantly lower than those of WKY, suggesting that the production of ET-1 is decreased in rats of genetic hypertension. Although the vascular reactivity to ET-1 increased in both DOCA-salt hypertensive and genetically hypertensive rats, present findings of the plasma ET-1 levels suggest that the role of ET-1 in the vascular control system may be different in DOCA-salt hypertensive rats and genetically hypertensive rats.     

Increased sympathetic venoconstriction and reactivity to norepinephrine in mesenteric veins in anesthetized DOCA-salt hypertensive rats

Increased sympathetic nervous activity (SNA) elevates venomotor tone in deoxycorticosterone acetate (DOCA)-salt hypertension. We studied the mechanisms by which the SNA increases venomotor tone in DOCA-salt hypertension by making in situ intracellular recordings of venous smooth muscle cell (VSMC) membrane potential (E(m)) and measurement of outside diameter (OD) in mesenteric veins (MV) and mesenteric arteries (MA) of anesthetized rats. We also studied norepinephrine (NE)- and endothelin-1 (ET-1)-induced increases in MA or MV perfusion pressure (PP) in vitro. E(m) in DOCA-salt MV was depolarized compared with sham MV. Prazosin hyperpolarized VSMC E(m) in DOCA-salt but not in sham MV. NE concentration-response curves (CRCs) for OD decreases in MV from DOCA-salt rats were left-shifted with an increased maximum response (E(max)) compared with sham MV. NE CRCs for OD decreases in MA were right-shifted with reduced E(max) in DOCA-salt compared with sham rats. ET-1 CRCs were similar in DOCA-salt and sham MV but were right-shifted with reduced E(max) in DOCA-salt MA. NE CRCs for MAPP increases were left-shifted without a change in E(max) in DOCA-salt rats. NE did not change MVPP. MAPP and MVPP for ET-1 CRCs were similar in sham and DOCA-salt rats, but E(max) for MAPP was reduced in DOCA-salt rats. Hematoxylin staining revealed hypertrophy in DOCA-salt MA but not in MV. We conclude that there is increased reactivity to NE released from the sympathetic nervous system in DOCA-salt MV that causes VSMC depolarization and increased venomotor tone. In DOCA-salt rats, in vivo ET-1 reactivity is maintained in MV, but reduced in MA.     

Contribution of cytochrome P450 1B1 to hypertension and associated pathophysiology: a novel target for antihypertensive agents

The aim of this review is to discuss the contribution of cytochrome P450 (CYP) 1B1 in vascular smooth muscle cell growth, hypertension, and associated pathophysiology. CYP1B1 is expressed in cardiovascular and renal tissues, and mediates angiotensin II (Ang II)-induced activation of NADPH oxidase and generation of reactive oxygen species (ROS), and vascular smooth muscle cell migration, proliferation, and hypertrophy. Moreover, CYP1B1 contributes to the development and/or maintenance of hypertension produced by Ang II-, deoxycorticosterone (DOCA)-salt-, and N(ω)-nitro-L-arginine methyl ester-induced hypertension and in spontaneously hypertensive rats. The pathophysiological changes, including cardiovascular hypertrophy, increased vascular reactivity, endothelial and renal dysfunction, injury and inflammation associated with Ang II- and/or DOCA-salt induced hypertension in rats, and Ang II-induced hypertension in mice are minimized by inhibition of CYP1B1 activity with 2,4,3',5'-tetramethoxystilbene or by Cyp1b1 gene disruption in mice. These pathophysiological changes appear to be mediated by increased production of ROS via CYP1B1-dependent NADPH oxidase activity and extracellular signal-regulated kinase 1/2, p38 mitogen-activated protein kinase, and c-Src.     

Role of renal nerves in development of hypertension in DOCA-salt model in rats: a telemetric approach

Centrally mediated hyperactivity of the autonomic nervous system contributes to DOCA hypertension; however, the targeted peripheral vascular bed(s) remain unclear. We propose that if renal sympathetic activity is a factor in the development of DOCA-salt hypertension, then renal denervation (RDNX) should attenuate the hypertensive response. In protocol 1, uninephrectomized RDNX (n = 9) and sham-denervated (n = 6) Sprague-Dawley rats were allowed free access to 0.9% NaCl solution and 0.1% NaCl diet. Mean arterial pressure (MAP) and heart rate were telemetrically recorded for 4 days before and 36 days after DOCA (100 mg/rat) implantation; sodium and water balances were recorded daily. Protocol 2 was similar except that saline intake in sham rats (n = 7) was matched to that observed in RDNX rats of protocol 1 for 30 days; for the last 10 days, the rats were allowed free access to saline. Before DOCA in protocol 1, MAP was lower (P < 0.05) in RDNX rats (99 +/- 1 mmHg) compared with sham rats (111 +/- 3 mmHg); however, heart rate and sodium and water balances were similar between groups. RDNX attenuated the MAP response to DOCA by approximately 50% (DeltaMAP = 22 +/- 3 mmHg, where Delta is change in MAP) when compared with sham rats (DeltaMAP = 38 +/- 6). RDNX rats consumed significantly less saline than sham rats, and cumulative sodium and water balances were reduced by 33% and 23%, respectively. In protocol 2, a similar pattern in MAP elevation was observed in RDNX and saline-restricted, sham-denervated rats even when saline restriction was removed. These results indicate that the renal sympathetic nerves are important in hypertension development but that other factors are also involved.