Vascular structure and expression of endothelin-1 gene in L-NAME-treated spontaneously hypertensive rats

Beneficial effects of swimming and pomegranate juice in rats with hypertension: A possible role of serum adropin

Hypertension, characterized by persistent and uncontrolled high blood pressure, is one of the most common significant causes of mortality worldwide. Lifestyle modifications such as exercise and antioxidant intake have showed beneficial effects on hypertensive conditions. Adropin and endothelin-1 (ET-1) have important vasoregulatory functions in the endothelium. However, the underlying mechanisms linking exercise- and/or antioxidant intake-mediated improvement of hypertension are not fully understood. In this study, it was hypothesized that swimming exercise and pomegranate juice (PJ) (as an antioxidant) administration might have protective effects on hypertension development and possible involvements of serum adropin and ET-1. To test the hypothesis, the rats with hypertension, induced by Nω-nitro-L-arginine methyl ester hydrochloride, were subjected to swimming exercise and received PJ for 8 weeks. Weekly systolic and diastolic pressures, serum concentrations of adropin and ET-1, and oxidant/antioxidant parameters in various tissues were measured. The obtained data show that swimming exercise leads to complete protection against hypertension within the 8-week duration, whereas the PJ administration causes an ameliorative effect. In addition, the combination of swimming exercise and PJ administration do not have additive effects in protection against hypertension. Notably, the 8-week swimming exercise restores the diminished serum adropin concentration in rats with hypertension to the control level. Serum adropin significantly correlated with systolic and diastolic pressures, depending on swimming exercise, but not PJ administration. Serum ET-1 concentration inconsistently fluctuates in response to Nω-nitro-L-arginine methyl ester hydrochloride, swimming exercise, and PJ intake. In addition, swimming exercise and/or PJ administration lead to a complete normalization in liver malondialdehyde concentrations of rats with hypertension, whereas these interventions cause slight or no improvements in superoxide dismutase, catalase, and glutathione in the heart, liver, and kidney. In conclusion, 8-week swimming exercise modulates hypertension, possibly by influencing adropin concentration and oxidative stress.

Resveratrol Protects Cardiac Tissue in Experimental Malignant Hypertension Due to Antioxidant, Anti-Inflammatory, and Anti-Apoptotic Properties

Hypertension is one of the most prevalent and powerful contributors of cardiovascular diseases. Malignant hypertension is a relatively rare but extremely severe form of hypertension accompanied with heart, brain, and renal impairment. Resveratrol, a recently described grape-derived, polyphenolic antioxidant molecule, has been proposed as an effective agent in the prevention of cardiovascular diseases. This study was designed to examine chronic resveratrol administration on blood pressure, oxidative stress, and inflammation, with special emphasis on cardiac structure and function in two models of experimental hypertension. The experiments were performed in spontaneously (SHRs) and malignantly hypertensive rats (MHRs). The chronic administration of resveratrol significantly decreased blood pressure in both spontaneously and malignant hypertensive animals. The resveratrol treatment ameliorated morphological changes in the heart tissue. The immunohistochemistry of the heart tissue after resveratrol treatment showed that both TGF-β and Bax were not present in the myocytes of SHRs and were present mainly in the myocytes of MHRs. Resveratrol suppressed lipid peroxidation and significantly improved oxidative status and release of NO. These results suggest that resveratrol prevents hypertrophic and apoptotic consequences induced by high blood pressure with more pronounced effects in malignant hypertension.

Thick Ascending Limb Sodium Transport in the Pathogenesis of Hypertension

The thick ascending limb plays a key role in maintaining water and electrolyte balance. The importance of this segment in regulating blood pressure is evidenced by the effect of loop diuretics or local genetic defects on this parameter. Hormones and factors produced by thick ascending limbs have both autocrine and paracrine effects, which can extend prohypertensive signaling to other structures of the nephron. In this review, we discuss the role of the thick ascending limb in the development of hypertension, not as a sole participant, but one that works within the rich biological context of the renal medulla. We first provide an overview of the basic physiology of the segment and the anatomical considerations necessary to understand its relationship with other renal structures. We explore the physiopathological changes in thick ascending limbs occurring in both genetic and induced animal models of hypertension. We then discuss the racial differences and genetic defects that affect blood pressure in humans through changes in thick ascending limb transport rates. Throughout the text, we scrutinize methodologies and discuss the limitations of research techniques that, when overlooked, can lead investigators to make erroneous conclusions. Thus, in addition to advancing an understanding of the basic mechanisms of physiology, the ultimate goal of this work is to understand our research tools, to make better use of them, and to contextualize research data. Future advances in renal hypertension research will require not only collection of new experimental data, but also integration of our current knowledge.

Candesartan prevents L-NAME-induced cardio-renal injury in spontaneously hypertensive rats beyond hypotensive effects

Our goal was to assess the cardiovascular and renal protection afforded by angiotensin II type 1-receptor blockade against NG-nitro-L-arginine methyl ester (L-NAME)-exacerbated hypertension in young spontaneously hypertensive rats (SHR), in comparison with the antihypertensive drug, hydralazine. Male SHR were assigned to four groups (n=8 per group): no treatment (controls); L-NAME-treated group (20 mg/kg/day, 10 days, orally); co-treatment with L-NAME and hydralazine (15 mg/kg/day, by gavage); co-treatment with L-NAME and candesartan cilexetil (10 mg/kg/day, by gavage), i.e. at a dose that inhibited acute pressor responses to 5—20 ng angiotensin II. One animal died in the L-NAME group, and tail-cuff systolic blood pressure (SBP) increased significantly compared with controls to 201±5 mmHg. Albumin excretion increased 235-fold in L-NAME-treated rats. Heart weight index averaged 3.5±0.1 and 3.8±0.1 mg/g body weight (p<0.05) in control and L-NAME rats, respectively, indicating moderate cardiac hypertrophy induced by L-NAME. Preglomerular vascular lesions affected 63±6% of interlobular arteries and 10±2% of afferent arterioles (vs. 8±3 and 0.8±0.4% in controls, respectively). Hydralazine and candesartan cilexetil treatment similarly reduced SBP to 153±7, and 165±6 mmHg, respectively. However, candesartan provided more protection, in terms of no significant change in albuminuria (vs. 25-fold increase with hydralazine), regression of cardiac hypertrophy, frequency of vascular lesions and histological indices of renal injury maintained within control values. In conclusion, candesartan cilexetil prevented L-NAME-exacerbated hypertension and associated cardio-renal injury in young SHR, the beneficial effects exceeding those of hydralazine.

Endothelin Receptor A Antagonism and Fetal Growth in Endothelial Nitric Oxide Synthase Gene Knockout Maternal and Fetal Mice

Fetal growth restriction (FGR) is commonly associated with perinatal morbidity and mortality. Nitric oxide (NO) deficiency increases endothelin-1 (ET-1) production, and this increased ET-1 may contribute to the pathophysiology of NO deficiency-induced FGR. Using an endothelial NO synthase knockout mouse model of FGR, we sought to determine (a) the relative importance of maternal versus conceptus (fetal and placental) NO deficiency and (b) the contribution of ET-1 to the pathogenesis of FGR in this model. Fetal growth restriction occurred both with NO-deficient conceptuses in the setting of maternal NO production and with maternal NO deficiency in the setting of NO-producing conceptuses. Placental ET-1 expression was increased in NO-deficient dams, ET receptor A (ETA) production increased in endothelial nitric oxide synthase(+/-) placentas, and antagonism of ETA prevented FGR. These results demonstrate that both maternal and conceptus NO deficiency can contribute to FGR and suggest a role for ETA antagonists as therapeutic agents in FGR.

Biochemical changes of the endothelium in the murine model of NO-deficient hypertension

Alterations in the α-helix and β-sheet content and the lipid-to-protein ratio are the most striking features of hypertension development in the vascular endothelium.

L-NAME in the cardiovascular system - nitric oxide synthase activator?

L-arginine analogues are widely used inhibitors of nitric oxide synthase (NOS) activity both in vitro and in vivo, with N(ω)-nitro-L-arginine methyl ester (L-NAME) being at the head. On the one hand, acute and chronic L-NAME treatment leads to changes in blood pressure and vascular reactivity due to decreased nitric oxide (NO) bioavailability. However, lower doses of L-NAME may also activate NO production via feedback regulatory mechanisms if administered for longer time. Such L-NAME-induced activation has been observed in both NOS expression and activity and revealed considerable differences in regulatory mechanisms of NO production between particular tissues depending on the amount of L-NAME. Moreover, feedback activation of NO production by L-NAME seems to be regulated diversely under conditions of hypertension. This review summarizes the mechanisms of NOS regulation in order to better understand the apparent discrepancies found in the current literature.

Regression of left ventricular hypertrophy and aortic remodelling in NO-deficient hypertensive rats: effect of L-arginine and spironolactone

AIM

We investigated, whether the substrate for nitric oxide (NO) formation -L-arginine - and the aldosterone receptor antagonist - spironolactone - are able to reverse alterations of the left ventricle (LV) and aorta in N(omega)-nitro-L-arginine methyl ester (L-NAME)-induced hypertension.

METHODS

Six groups of male adult Wistar rats were investigated: controls after 4 and 7 weeks of experiment, rats treated with L-NAME for 4 weeks and three recovery groups: spontaneous-reversion (4 weeks L-NAME + 3 weeks placebo), spironolactone-induced reversion (4 weeks L-NAME + 3 weeks spironolactone) and L-arginine-induced reversion (4 weeks L-NAME+ 3 weeks L-arginine). Blood pressure was measured by tail-cuff plethysmography. Relative weight of the LV, myocardial fibrosis (based upon histomorphometry and hydroxyproline determination) and conjugated dienes in the LV and aortic cross-sectional area, inner diameter and wall thickness were determined. NO-synthase activity was investigated in the LV and aorta.

RESULTS

L-NAME administration induced hypertension, left ventricular hypertrophy (LVH), LV fibrosis, aortic thickening and diminution of NO-synthase activity in the LV and aorta. Reduction in blood pressure and regression of LVH were observed in all recovery groups, yet reduction in LV fibrosis and aortic thickening were not. NO-synthase activity was restored only in the L-arginine and spironolactone group.

CONCLUSION

In our study, the reversion of hypertension and LVH was not dependent on the restoration of NO-synthase activity. Moreover, LV fibrosis and aortic remodelling seem to be more resistant to conditions resulting in regression of LVH. Preserved level of fibrosis in the initial period of LVH regression might result in loss of structural homogeneity and possible functional alterations of the LV.

Altered endothelin receptor binding in response to nitric oxide synthase inhibition in the pregnant rat

The authors evaluate the expression of endothelin-1 (ET-1) and its receptors in the uterus and placenta during maternal nitric oxide synthase (NOS) inhibition. Timed-pregnant rats received L-NAME (2.5 mg/kg/h) or saline from day 14 to 21 of gestation. Uterine and placental tissues collected on day 21 were assayed for preproET-1, ET( A), and ET(B) mRNA expression; localization and expression of ET-1 and receptor proteins; and receptor activity. NOS inhibition did not affect preproET-1 mRNA expression in the placenta or uterus. ET(A) expression decreased in the uterine free wall, but no other changes in receptor mRNA expression were observed in the uterus or placenta. ET-1 and receptor proteins were unchanged. Placental ET(A) and ET(B) receptor binding decreased. Uterine ET(A) receptor binding decreased in the placental bed. ET-1, a prominent mediator during NOS inhibition, is not of uterine or placental origin. Reduced receptor binding activity is the primary means by which these tissues regulate their response to ET-1 in the setting of NOS inhibition.

Dietary isoflavones during pregnancy and lactation provide cardioprotection to offspring rats in adulthood

In adult rats, elongation of cardiac myocytes (CMs) correlates with dilatation (and sometimes dysfunction) of cardiac ventricles. Although sex steroids may constitute one possible factor that affects the dimensions of CMs, studies on their effects in rodents is complicated by the fact that most commercial soy-based diets also contain abundant phytoestrogens. We report that feeding Wistar-Kyoto rat dams during gestation and lactation with a phytoestrogen-rich soy-based diet caused the CMs of their adult offspring to be shorter than in counterparts originating from mothers fed with a phytoestrogen-free casein-based diet. The soy-based diet had no such effects when given to rats after 6 wk of age, and its effects were replicated when supplementing the maternal casein-based diet with the isoflavones daidzein and genistein (the most abundant phytoestrogens in soy-based diets). In contrast to rats whose mothers had been fed with a soy-based diet, the hearts of adult rats raised with a casein-based diet only featured dilated eccentric hypertrophy and progressed toward congestive heart failure when further challenged. Thus the presence of isoflavones in the maternal diet provides cardioprotection to the hearts of their offspring during adulthood.

L-arginine fails to protect against myocardial remodelling in L-NAME-induced hypertension

BACKGROUND

We investigated whether the substrate for nitric oxide synthesis L-arginine is able to modify hypertension and left ventricular hypertrophy development induced by chronic blockade of nitric oxide synthase activity by NG-nitro-L-arginine-methyl ester (L-NAME).

MATERIAL AND METHODS

Four groups of rats were investigated: control, L-arginine 1.5 g kg-1, L-NAME 40 mg kg-1, and L-NAME +L-arginine in corresponding doses. Systolic blood pressure was measured by non-invasive tail-cuff plethysmography each week. After 4 weeks, the animals were sacrificed and hydroxyproline and coenzyme Q9 and Q10 concentrations in the left ventricle, and nitric oxide synthase activity in the left ventricle, kidney and brain were investigated.

RESULTS

In the L-NAME group, nitric oxide synthase activity was decreased in the left ventricle, kidney and brain, and hypertension, left ventricular hypertrophy and fibrosis developed. Heart remodelling was associated with the decrease of coenzyme Q9 and Q10 concentrations in the left ventricle. Simultaneous treatment with L-NAME and L-arginine prevented nitric oxide synthase activity diminution in the left ventricle but not in the kidney and brain, and completely failed to prevent hypertension, left ventricular hypertrophy and fibrosis. Nevertheless, l-arginine prevented the diminution of coenzyme Q9 and Q10 concentrations in the left ventricle.

CONCLUSIONS

We conclude that L-arginine failed to prevent hypertension, left ventricular hypertrophy and fibrosis development despite restoration of nitric oxide synthase activity in the left ventricle. However, L-arginine prevented the diminution of coenzyme Q levels in the left ventricle.

Attenuation of iNOS mRNA exacerbates hypoperfusion and upregulates endothelin-1 expression in hippocampus and cortex after brain trauma

Nitric oxide (NO, a vasodilator) and endothelin-1 (ET-1, a powerful vasoconstrictor) participate in the regulation of brain's microcirculation influencing each other's expression and synthesis. Following injury to the brain, NO is derived largely from the inducible form of nitric oxide synthase (iNOS). We used Marmarou's model of traumatic brain injury (TBI) to study the cerebral blood flow and expression (mRNA) of ET-1 in rats that were pretreated with antisense iNOS oligodeoxynucleotides (ODNs). Intracerebroventricular application of iNOS ODNs resulted in reduced synthesis of iNOS as detected by Western blot analysis. The cerebral blood flow (measured by laser Doppler flowmetry), generally decreased after TBI, was further markedly reduced in the treated animals and remained at low levels up to 48 h post-TBI. The expression of ET-1 (detected by in situ hybridization in cortex and hippocampus) was increased 2-3-fold following TBI alone and this increase reached 5-6-fold in animals pretreated with antisense iNOS ODNs. The results indicate that most likely, NO, generated primarily by iNOS, suppresses ET-1 production and that a decrease of NO results in upregulation of ET-1 via transcriptional and translational mechanisms. Increased availability of ET-1 at the vascular bed and the neuropil may contribute to the altered microvascular reactivity and reduced perfusion of the brain following TBI.

In-vivo interaction of nitric oxide and endothelin

OBJECTIVE AND METHODS

Endothelin-1 (ET-1) was initially characterized as a potent vasoconstrictor. However, the expected role of ET-1 as a major blood pressure controlling peptide could not be clearly established. Moreover, ET-1 transgenic mice are not hypertensive. We assume that counter-regulating mechanisms such as the nitric oxide (NO) system or an altered expression of endothelin receptors might cause this finding.

RESULTS

An intravenous (i.v.) bolus injection of N(omega)-nitro-L-arginine methyl ester (L-NAME) resulted in a significantly higher blood pressure increase in ET-1 transgenic mice, as compared to non-transgenic littermates. On the other hand, blood pressure increased similarly after an i.v. injection of ET-1 in ET-1 transgenic mice and non-transgenic littermates. Pretreatment with dexamethasone abolished the higher blood pressure increase after L-NAME in ET-1 transgenic mice. Urinary excretion of NO metabolites was elevated in ET-1 transgenic mice and decreased significantly after dexamethasone treatment. Immunohistochemistry revealed that the inducible NO synthase (iNOS) was highly expressed in intrarenal arteries in these mice. Dexamethasone pretreatment abolished vascular iNOS expression. No vascular iNOS expression was detectable in non-transgenic littermates. Furthermore, immunohistochemistry revealed that ET-1 transgenic mice are characterized by an increased tissue density of CD4-positive lymphocytes and macrophages. Analysis of endothelin receptor expression and function revealed that the endothelin subtype A (ETA) receptor was not differently expressed in ET-1 transgenic mice as compared to age-matched littermates. The blood pressure response to an ETA receptor antagonist was likewise similar in ET-1 transgenic mice and age-matched littermates. The endothelin subtype B (ETB) receptor density was decreased in ET-1 transgenic mice. Treatment with an ETB receptor antagonist led to a non-significant slightly higher blood pressure increase in ET-1 transgenic mice as compared to controls.

CONCLUSION

The endothelin receptor expression pattern and the blood pressure responses to ETA and ETB receptor antagonists could not explain the lack of hypertension in ET-1 transgenic mice. Overexpression of the human ET-1 gene causes chronic kidney inflammation with an induction of vascular iNOS expression. The induction of iNOS expression might cause a new local balance between vascular ET-1 and nitric oxide, resulting in no alterations of blood pressure.

Intracellular coexpression of endothelin-1 and inducible nitric oxide synthase underlies hypoperfusion after traumatic brain injury in the rat

We used Marmarou's rat model of traumatic brain injury to demonstrate colocalization of mRNAs for endothelin-1 (ET-1, a powerful vasoconstrictor) and inducible nitric oxide synthase (iNOS, generator of NO, a vasodilator) in individual cells that form the brain's microvascular wall. The results were confirmed with double immunocytochemistry. After trauma endothelial, smooth muscle cells and macrophages contributed to the abnormal synthesis of ET-1 and iNOS which may underlie a dysfunctional brain microcirculation. This is the first in vivo single cell demonstration of ET-1 and iNOS colocalization, suggesting reciprocal regulation of each other's expression both at the transcriptional and translational levels. The results further indicate that interaction between ET-1 and iNOS occurs at the cytosol and possibly the nuclear membranes, implicating mediation via endothelin receptors.

Effect of simvastatin on remodeling of the left ventricle and aorta in L-NAME-induced hypertension

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors have been shown to prevent or reverse hypertrophy of the LV in several models of left ventricular hypertrophy. The aim of the present study was to determine whether treatment with simvastatin can prevent hypertension, reduction of tissue nitric oxide synthase activity and left ventricular (LV) remodeling in NG-nitro-L-arginine methyl ester(L-NAME)-induced hypertension. Four groups of rats were investigated: control, simvastatin (10 mg/kg), L-NAME (40 mg/kg) and L-NAME + simvastatin (in corresponding doses). Animals were sacrificed and studied after 6 weeks of treatment. The decrease of NO-synthase activity in the LV, kidney and brain was associated with hypertension, LV hypertrophy and fibrosis development and remodeling of the aorta in the L-NAME group. Simvastatin attenuated the inhibition of NO-synthase activity in kidney and brain, partly prevented hypertension development and reduced the concentration of coenzyme Q in the LV. Nevertheless, myocardial hypertrophy, fibrosis and enhancement of DNA concentration in the LV, and remodeling of the aorta were not prevented by simultaneous simvastatin treatment in the L-NAME treated animals. We conclude that the HMG-CoA reductase inhibitor simvastatin improved nitric oxide production and partially prevented hypertension development, without preventing remodeling of the left ventricle and aorta in NO-deficient hypertension.

Combination of low-dose valsartan and enalapril improves endothelial dysfunction and coronary reserve in Nomega-nitro-L-arginine methyl ester-treated spontaneously hypertensive rats

Combination of nonhypotensive doses of valsartan and enalapril markedly improved survival (+87%) compared with untreated animals (37%) in spontaneously hypertensive rats (SHRs) with endothelial dysfunction. However, the combination had no effect on kidney function, and proteinuria persisted over the 12 weeks of the study. It was hypothesized that the greater survival was due to improvement in endothelial function or coronary vasculature despite blockade of nitric oxide synthase and high blood pressure. Therefore, endothelial function was evaluated in isolated aortic ring and maximal coronary blood flow was studied in isolated perfused SHR hearts (20-24 weeks) treated with -nitro-l-arginine methyl ester (L-NAME) (50 mg/l) for 4 weeks. The animals received vehicle, valsartan 5 mg/kg/d, enalapril 1 mg/kg/d, valsartan 50 mg/kg/d, or the combination valsartan 5 mg/kg/d with enalapril 1 mg/kg/d in drinking water. Normotensive Wistar-Kyoto (WKY) rats were used as control. Blood pressure was measured by telemetry. Histopathology was performed on heart, kidney (hematoxylin-eosin), and aorta (Masson trichrome). L-NAME elevated blood pressure by 50 mm Hg after vehicle (199 +/- 5 mm Hg). Valsartan 50 mg/kg/d completely abolished this increase (150 +/- 4 mm Hg) whereas the valsartan-enalapril combination synergistically decreased blood pressure (-37 mm Hg at 162 +/- 7 mm Hg) compared with monotherapy (valsartan 5 mg/kg/d -10 mm Hg; enalapril 1 mg/kg/d -15 mm Hg). All treatments improved the histopathology, most markedly in those receiving the valsartan-enalapril combination. The severity mean grades for lesions were 2.1, 1.9, 1.7, 1.1, and 0.9 in vehicle-treated SHRs, enalapril 1 mg/kg/d, valsartan 5 mg/kg/d, valsartan 5 or 50 mg/kg/d, and the valsartan-enalapril combination, respectively, compared with 0.02 in WKY rats. Acetylcholine-induced relaxation was significantly greater in treated SHRs than after vehicle (-40% at 0.1 mmol acetylcholine) but the combination induced the maximal relaxation (-85%). The ratio of maximal tension induced by serotonin in rings with and without endothelium was 1.4 and 1.3 in vehicle and valsartan 5 mg/kg/d-treated rats whereas it did not differ from 1 in WKY rats and all other treated groups. The cardiac hypertrophy (+27%) was prevented by valsartan 50 mg/kg/d and the valsartan-enalapril combination. Coronary reserve was significantly increased by valsartan 50 mg/kg/d (+85% at 7.8 +/- 0.7 ml/min/g) and the valsartan-enalapril combination (+42% at 6.0 +/- 0.4 ml/min/g) compared with 4.2 +/- 0.5 (vehicle). This was not different of 8.8 +/- 0.5 (WKYs). Despite the maintenance of a high blood pressure, low-dose valsartan-enalapril significantly improved endothelial function and histopathology and increased coronary reserve in SHRs chronically receiving L-NAME.

Angiotensin II and nitric oxide interaction

Nitric oxide degradation linked to endothelial dysfunction plays a central role in cardiovascular diseases. Superoxide producing enzymes such as NADPH oxidase and xanthine oxidase are responsible for NO degradation as they generate a variety of reactive oxygen species (ROS). Moreover, superoxide is rapidly degraded by superoxide dismutase to produce hydrogen peroxide leading to the uncoupling of NO synthase and production of increased amount of superoxide. Angiotensin II is an important stimulus of NADPH oxidase. Through its AT(1) receptor, Ang II stimulates the long-term increase of several membrane component of NADPH oxidase such as P(22) phox or nox-1 and causes an increased activity of NADPH oxidase with inactivation of NO leading to impaired endothelium-dependent vasorelaxation, vascular smooth muscle cell hypertrophy, proliferation and migration, extracellular matrix formation, thrombosis, cellular infiltration and inflammatory reaction. Several preclinical and clinical studies have now confirmed the involvement of the AT(1) receptor in endothelial dysfunction. It is proposed that the AT(2) receptor counterbalances the deleterious effect of the Ang II-induced AT(1) receptor stimulation through bradykinin and NOS stimulation. This mechanism could be especially relevant in pathological cases when the NADPH oxidase activity is blocked with an AT(1) receptor antagonist.

Hypertensive emergencies: diagnosis and management

The treatment of hypertension is preventive medicine. This principle applies in the emergency room as well as the clinic. However, there are crucial contrasts between these two care settings related to specific goals of management for real emergencies and nonemergency conditions. In the emergency room, rapid triage is necessary to separate those who can safely be sent home for future clinic assessment from those who require immediate interventions including short stays in 24-hour observation units or hospitalization for more serious problems. This review focuses on decisions related to hypertension management in the emergency room and over brief periods of observation and treatment. Strategy is supported by evidence-based considerations whenever possible. Where outcome studies are not available, we rely on the rationale derived from relevant clinical research.

Characterization of myocardium, isolated cardiomyocytes, and blood pressure in WKHA and WKY rats

We previously reported that the left ventricular (LV) mass of Wistar-Kyoto (WKY)-derived hyperactive (WKHA) rats was higher than that of WKY rats in the absence of a difference in systolic blood pressure. To extend these earlier observations, we conducted a series of functional and morphological investigations on both strains. Analysis of tissue sections revealed that the surface of ventricular tissue from WKHA rats was higher than that of WKY rats, without any enlargement of the cavity area. Analysis of isolated adult cells showed that cell width (as well as cell volume) of ventricular cardiomyocytes was significantly higher in WKHA than WKY rats. However, LV of WKHA rats contained approximately 33% less cardiomyocytes than those from WKY rats. Mean intracellular free calcium concentration of cardiomyocytes was also higher in WKHA than WKY rats. Hemodynamic measurements revealed that the values of the maximum rates of pressure change (dP/dt) were higher in LV from WKHA rats. However, these differences were reduced (-dP/dt) or abolished (+dP/dt) when the values were normalized for both the number and mean cross-sectional area of ventricular cardiomyocytes. Mean levels of systolic and diastolic blood pressure (corresponding to the 24-h average of measurements obtained continuously in conscious unrestrained animals using radiotelemetric implants) were not different between strains. However, circadian rhythm was more evident in WKY rats, because the difference between morning and night values of systolic and diastolic blood pressure was greater (by 3 mmHg) in WKY rats. Altogether, our data validate the use of WKHA rats as models of predominantly concentric LV hypertrophy developing in the absence of increased mean levels of hemodynamic cardiac load and show that the hypertrophy phenotype is more pronounced in isolated cardiomyocytes than at the level of the whole ventricle.

Vasopeptidase inhibition and endothelial function in hypertension

Vasopeptidase inhibitors are a new class of drugs capable of inhibiting both angiotensin-converting enzyme and neutral endopeptidase 24.11. This involves simultaneous inhibition with a single molecule of two key enzymes, ACE and NEP, which are both involved in the regulation of cardiovascular homeostasis in many ways. This includes metabolism of several vasoactive peptides and their clearance from the circulation, therefore contributing to neurohumoral modulation, which might have therapeutic advantages in the prevention of endothelial dysfunction in hypertension.

Enhancement of phenylephrine-induced contraction in the isolated rat aorta with endothelium by H2O-extract from an Oriental medicinal plant Leonuri herba

Leonuri herba (I-mu-ts'ao, the Chinese motherwort) is an ancient Chinese traditional herb. Although the pharmacological effects of extracts of Leonuri herba have been shown in platelets and uteri, the effect on the vascular system has not been determined. In the present study, we investigated the effects of extracts of Leonuri herba on the contraction of the isolated rat aorta. Although the H20-extract (0.3-3 mg/ml) by itself showed a limited effect, the extract enhanced phenylephrine-induced contraction of the aorta with endothelium, but not without endothelium. The H20-extract, like N(G)-nitro-L-arginine methyl ester (L-NAME, an inhibitor of nitric oxide synthase), significantly inhibited the relaxation induced by acetylcholine in the aorta with endothelium. The inhibitory effect of H20-extract on the relaxation decreased by co-addition with 1 mM L-arginine. The vasoconstrictive effect of H20-extract was not due to leonurine, which is a constituent in Leonuri herba and shows uterotonic activity. Intravenous injection of the H20-extract (1.5 mg/kg) to rats caused an increase in blood pressure for 5 min, like L-NAME (1.35 mg/kg). These findings suggest that there is a component(s) in Leonuri herba, which shows a vasoconstrictive activity in rat aorta in vitro and in vivo and has similar pharmacological profile to that of L-NAME.

Inhibition of nitric oxide synthesis increases erythrocyte membrane fluidity and unsaturated fatty acid content

Changes in the lipid composition of the membrane affect its fluidity and function. These variables are altered in various forms of hypertension. Our hypothesis was that the rapid increase in blood pressure (BP) caused by inhibition of nitric oxide production would lead to alterations in membrane fluidity similar to those observed in genetic hypertension. We used Nomega-nitro L-arginine methyl ester (L-NAME) and vehicle-treated (3 weeks) Wistar-Kyoto rats to study the effects of nitric oxide synthase (NOS) inhibition on membrane fluidity and lipid composition. Erythrocyte membrane fluidity was measured by fluorescence anisotropy. Membrane lipids were separated using Sep-Pak and thin-layer chromatography. Fatty acid methyl esters were produced and analyzed by gas chromatography-mass spectrometry. Nomega-nitro L-arginine methyl ester treatment increased BP and erythrocyte membrane fluidity. The phospholipid and unsaturated fatty acid levels in the membranes from the L-NAME-treated rats were consistent with the increase in fluidity (ie, more unsaturated fatty acid, in particular, arachidonic and docosahexaenoic acid) and a reduction in membrane sphingomyelin content. Fatty acid analysis of individual lipid groups suggested the changes in membrane fatty acid composition may be asymmetric, with the majority of the changes occurring in the outer leaflet. Inhibition of NOS results in changes in membrane composition that may explain the concurrent changes in fluidity. The increased membrane fluidity observed here contrasts with the reduced fluidity observed in genetic hypertension or unchanged fluidity in secondary hypertension. The effects could be related to NOS inhibition or may be a direct effect of L-NAME.

Regional hemodynamics after chronic nitric oxide inhibition in spontaneously hypertensive rats

BACKGROUND

Inhibition of nitric oxide (NO) synthase by L-arginine analogs is associated with elevation of blood pressure in rats. Because endothelium-dependent vasomotion in different vascular beds is not homogenous, the aim of this study was to characterize and compare regional hemodynamic responses in carotid, femoral, and renal vascular beds after chronic NO inhibition in spontaneously hypertensive rats. The possible role of circulating endothelin and renin angiotensin systems in mediating the effects of chronic NO inhibition was also studied.

METHODS

Systemic and regional hemodynamics, left ventricular mass, plasma renin activity, and plasma endothelin-1 were determined in control and Nomega-nitro-Larginine methyl ester (L-NAME)-treated (10 mg/kg/day, 4 weeks) spontaneously hypertensive rats.

RESULTS

L-NAME treatment increased arterial pressure and total peripheral and regional vascular resistance and decreased cardiac output, stroke volume, and regional blood flow. An increase in blood flow ratio and a decrease in vascular resistance ratio between carotid and renal as well as femoral and renal vascular beds in rats treated with L-NAME was found. Blood flow and vascular resistance ratios between femoral and carotid vascular beds remained unchanged. L-NAME increased plasma renin activity and left ventricular weight/body weight ratio, whereas plasma endothelin-1 was not modified.

CONCLUSIONS

The results of this study showed that the renal circulation seemed to be more sensitive to the effects of chronic NO inhibition than carotid and femoral vascular beds. Simultaneous activation of the renin angiotensin system may further potentiate cardiovascular effects of chronic NO inhibition. No evidence that circulating endothelin-1 plays a role in this model of hypertension was found.

Glomerular basement membrane polyanion distribution and nitric oxide in spontaneous hypertensive rats: effects of salt loading and antihypertensive therapy with propranolol

Cationic colloidal gold (CCG), a polycationic histochemical probe, was used to analyze the distribution of glomerular basement membrane (GBM) polyanions, mainly heparan sulfate proteoglycan in spontaneous hypertensive rats (SHR) with or without salt loading and antihypertensive treatment with propranolol. The changes of mean GBM width and anionic sites distribution were assessed by electron microscopy. Plasma and urinary nitrates (NO(x)) were measured by nitrite (NO2) + nitrate (NO3), stable metabolites of NO. SHR had decreased NO production and increased GBM width (27%) compared with the control Wistar-Kyoto (WKY) rats. The chronic high dietary salt intake resulted in a significant increase in blood pressure, proteinuria, and renal function in the SHR rats. The chronic high salt dietary intake resulted in a decrease in NO in the WKY and a further reduction in NO production in the SHR. The GBM anionic sites count was similar in the SHR and WKY nonsalt-loaded groups, 13.5 +/- 0.5 and 12.8 +/- 0.4 CCG counts/microm GBM, respectively, but significantly lower in both salt-loaded SHR and WKY, 9.9 +/- 0.55 (P < .01) and 9.6 +/- 0.55 (P < .01) CCG counts/microm GBM, respectively. Antihypertensive treatment with propranolol in the salt-loaded SHR group resulted in lower blood pressure, a further decrease in NO production, but no significant changes in GBM width and anionic sites count. It is concluded that chronic high salt intake may be deleterious to the permselectivity of the GBM. A low NO production state that results from chronic salt loading in already hypertensive rats will result in more severe organ (renal) damage, most probably by the addition of the loss of GBM permselectivity to the existing pathomorphologic changes.

Combination of non-hypotensive doses of valsartan and enalapril improves survival of spontaneously hypertensive rats with endothelial dysfunction

There is increasing evidence to suggest endothelial dysfunction as a critical factor in vascular diseases. Genetically predisposed spontaneously hypertensive rats (SHR) treated with inhibitors of nitric oxide (NO) synthase, develop a severe hypertensive nephrosclerosis without the necessity for surgical reduction in renal mass, nephrectomy, renal infarction or nephrotoxic drugs. In these animals, endothelial dysfunction is considered a valid model for assessment of the efficacy of cardiovascular therapy. SHR were treated with either the angiotensin-converting enzyme inhibitor enalapril or the angiotensin II (Ang II) AT(1)-receptor antagonist (AIIA) valsartan at sub-hypotensive doses and the effects on survival rates, cardiac and renal changes were monitored. Rats treated with valsartan, alone or in combination with enalapril, showed markedly higher survival rates (67-85%, respectively) than untreated animals (37%) or those treated with enalapril alone (55%). Valsartan at a dose which attenuated blood pressure increase led to even greater survival rates (95%). Despite these improved survival rates, at non-hypotensive doses the drugs had no effect on histological appearance, nor was kidney function improved. Plasma creatinine levels were reduced by valsartan, alone or in combination with enalapril, but proteinuria persisted with all treatments over the 12 weeks of the study. Aldosterone levels were significantly reduced by all treatments. The results suggest a beneficial role for endothelium in hypertension. Reduced renal perfusion pressure probably underlies the beneficial renal effects of high-dose valsartan.

Dysfunctional renal nitric oxide synthase as a determinant of salt-sensitive hypertension: mechanisms of renal artery endothelial dysfunction and role of endothelin for vascular hypertrophy and Glomerulosclerosis

This study investigated the role of renal nitric oxide synthase (NOS), endothelin, and possible mechanisms of renovascular dysfunction in salt-sensitive hypertension. Salt-sensitive (DS) and salt-resistant (DR) Dahl rats were treated for 8 wk with high salt diet (4% NaCl) alone or in combination with the ET(A) receptor antagonist LU135252 (60 mg/kg per d). Salt loading markedly increased NOS activity (pmol citrulline/mg protein per min) in renal cortex and medulla in DR but not in DS rats by 270 and 246%, respectively. Hypertension in DS rats was associated with renal artery hypertrophy, increased vascular and renal endothelin-1 (ET-1) protein content, and glomerulosclerosis. In the renal artery but not in the aorta of hypertensive DS rats, endothelium-dependent relaxation to acetylcholine was unchanged; however, endothelial dysfunction due to enhanced prostanoid-mediated, endothelium-dependent contractions and attenuation of basal nitric oxide release was present. Treatment with LU135252 reduced hypertension in part, but completely prevented activation of tissue ET-1 without affecting ET-3 levels. This was associated with a slight increase of renal NOS activity, normalization of endothelial dysfunction and renal artery hypertrophy, and marked attenuation of glomerulosclerosis. Thus, DS rats fail to increase NOS activity in response to salt loading. This abnormality may predispose to activation of the tissue ET-1 system, abnormal renal vasoconstriction, and renal injury. Chronic ET(A) receptor blockade normalized salt-induced changes in the renal artery and reduced glomerular injury, suggesting therapeutic potential for ET antagonists in salt-sensitive forms of hypertension.

Nitric oxide and preglomerular vascular lesions in lyon spontaneously hypertensive rats

Accumulation of Sudan black-stainable (SB+) lipids is a hallmark of the focal inflammato-proliferative lesions that develop along preglomerular vessels in N G-nitro-L-arginine methyl ester (L-NAME) and angiotensin II hypertensive rats. We extended our findings to genetically hypertensive Lyon (LH) rats aged 14 and 30 weeks and to age-matched normotensive (LN) rats. Vessels were isolated by HCl maceration. Despite high systolic blood pressure (SBP), hypercholesterolaemia, albuminuria and increased interlobular and afferent arteriolar media thickness, SB+ lesions were rarely found in LH rats, regardless of age. To probe nitric oxide as a potential source of vascular protection, 14-week-old LN and LH rats received L-NAME for 10 days (20 mg kg-1 day-1, per os), which increased SBP to 174 +/- 5 and to >200 mmHg, respectively. It induced formation of focal SB+ lesions less frequently in LN than LH rats, in which they affected 39 +/- 7, 44 +/- 5 and 15 +/- 5% of arcuate arterial branches, interlobular arteries and afferent arterioles, respectively. Immunoreactive endothelin-1 was found to accumulate at the level of SB+ lesions. Co-administered with L-NAME, hydralazine (15 mg kg-1 day-1, per os) limited SBP rise to approximately 10 mmHg in both LN and LH rats. As a result, SB+ lesions were rare in LN rats, but were frequent in LH rats. In conclusion, preglomerular SB+ lesions are spontaneously lacking in LH rats. Endogenous nitric oxide production provides protection against vascular barotrauma. Endothelin-1 likely plays an autocrine/paracrine role in vascular lesion formation.

Nitric oxide and endothelin-1 in coronary and pulmonary circulation

Since the discovery of the vasorelaxant properties of nitric oxide and the vasoconstrictor effect of endothelin-1, there have been many studies of the distribution and functional significance of these agents in various vascular beds. In the coronary and pulmonary circulation nitric oxide and endothelin-1 actions have been largely investigated in terms of an imbalance between the opposing effects of these vasoactive agents leading to pathophysiological conditions. This article review functional and immunocytochemical studies with emphasis on the ultrastructural localization of nitric oxide synthase and endothelin-1 in the coronary and pulmonary vascular beds. Localization of nitric oxide synthase (type III or I or II) has been shown in endothelial cells, smooth muscle, and perivascular nerves of the coronary and pulmonary vascular beds and in the neurons, nerve fibers, and the small granule-containing cells within cardiac ganglia. Endothelin-1 was mainly localized in subpopulations of coronary and pulmonary endothelial cells. These immunocytochemical studies provide information about the sources of nitric oxide and endothelin-1 that contribute to the vasomotor control of cardiac and pulmonary circulation under normal and pathophysiological conditions.

Endothelin receptor antagonists influence cardiovascular morphology in uremic rats

BACKGROUND

In is generally held that renal failure results in blood pressure (BP)-independent structural changes of the myocardium and the vasculature. The contribution, if any, of endothelin (ET) to these changes has been unknown.

METHODS

We morphometrically studied random samples of the left ventricle myocardium and small intramyocardial arteries in subtotally (5/6) nephrectomized (SNx) male Sprague-Dawley rats treated with either the selective ETA receptor antagonist BMS182874 (30 mg/kg/day) or the nonselective ETA/ETB receptor antagonist Ro46-2005 (30 mg/kg/day) in comparison with either sham-operated rats, untreated SNx, or SNx rats treated with the angiotensin-converting enzyme inhibitor trandolapril (0.1 mg/kg/day).

RESULTS

Eight weeks later, systolic BP was lower in trandolapril-treated SNx compared with untreated SNx animals. No decrease in BP was seen following either ET receptor antagonist at the dose used. A significantly increased volume density of the myocardial interstitium was found in untreated SNx rats as compared with sham-operated controls. Such interstitial expansion was prevented by trandolapril and either ET receptor antagonist. SNx caused a substantial increase in the wall thickness of small intramyocardial arteries. The increase was prevented by trandolapril or BMS182874 treatment. The arteriolar wall:lumen ratio was significantly lower in all treated groups when compared with untreated SNx. In contrast, only trandolapril, but not the ET receptor antagonists, attenuated thickening of the aortic media in SNx animals.

CONCLUSIONS

The ETA-selective and ETA/ETB-nonselective receptor antagonists appear to prevent development of myocardial fibrosis and structural changes of small intramyocardial arteries in experimental chronic renal failure. This effect is independent of systemic BP.

Role of nitric oxide in the control of renin secretion

Because of the significant constitutive expression of NO synthases in the juxtaglomerular apparatus, nitric oxide (NO) is considered as a likely modulator of renin secretion. In most instances, NO appears as a tonic enhancer of renin secretion, acting via inhibition of cAMP degradation through the action of cGMP. Depending on as yet unknown factors, the stimulatory effect of NO on renin secretion may also switch to an inhibitory one that is compatible with the inhibition of renin secretion by cGMP-dependent protein kinase activity. Whether NO plays a direct regulatory role or a more permissive role in the control of renin secretion remains to be answered.

Role of nitric oxide in vascular hyper-responsiveness to norepinephrine in hypertensive Dahl rats

OBJECTIVE

To determine whether the abnormal vascular responses observed in salt-sensitive hypertension are caused by an impairment in vascular nitric oxide function.

DESIGN

Isometric tension was measured in aortic rings isolated from Dahl salt-sensitive and salt-resistant rats fed a regular-salt (0.4% NaCl) or a high-salt (8% NaCl) diet, with and without inhibition of endogenous nitric oxide synthesis.

METHODS AND RESULTS

Systolic arterial pressure, measured weekly by the tail-cuff method, increased markedly in DS rats with a high-salt diet but did not increase in the other groups. In aortic rings, norepinephrine evoked dose-dependent contractions which were significantly increased in rings from DS rats with a high-salt diet Pretreatment with Nomega-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, increased the norepinephrine-induced contraction in all groups and abolished differences in contractile responses between high-salt DS rats and the other groups. Acetylcholine induced endothelium-dependent relaxation, which was significantly depressed in high-salt DS rats. L-NAME attenuated the acetylcholine-induced relaxation in all groups and abolished the difference in relaxation response between high-salt DS rats and the other groups. Sodium nitroprusside-induced relaxation was significantly depressed in high-salt DS rats.

CONCLUSIONS

Vascular hypercontractile responses to norepinephrine in DS hypertensive rats can, in part, be explained by an impairment in endothelial nitric oxide production.

The endothelin system in cardiovascular physiology and pathophysiology

Endothelin-1, a member of a novel family of regulatory peptides, is the most potent vasoconstrictor and pressor substance known. Endothelin-1 is a 21-amino-acid endothelium-derived peptide causing uniquely sustained vasoconstriction. In addition, endothelin-1 has pronounced effects on the coronary, renal and cerebral circulations, enhances responses to other vasoconstrictors, and is comitogenic. Recent studies have shown that the endothelins are essential for normal fetal development, and that endothelin-1 plays an important physiological role in the regulation of basal vascular tone and blood pressure in healthy humans. There is now also a wealth of evidence suggesting that endothelin-1 is a key mediator in a range of cardiovascular diseases associated with sustained vasoconstriction, such as chronic heart failure, and with vasospasm, such as subarachnoid haemorrhage. In addition, endothelin-1 appears to act in opposition to nitric oxide to promote the atherosclerotic process. There are a large number of oral and intravenously active endothelin antagonists entering clinical development and a number of clinical studies, particularly with endothelin receptor antagonists, are now under way. Such studies are beginning to define the role of the endothelins in cardiovascular disease and to confirm the potential of the endothelin system as an important new therapeutic target.

Left ventricular hypertrophy and arterial blood pressure in experimental models of hypertension

Cardiac hypertrophy in essential and experimental (genetic) hypertension have been initially attributed to increased pressure load. However, the level of blood pressure does not parallel the degree of cardiac hypertrophy, i.e., a complex relationship rather than a simple dose-response effect has to be suggested. Several non-haemodynamic factors which influence LV mass have been identified with genetic and neuro-hormonal influences playing a major role. The experimental strategies which have been used to highlight one or more of these influences include pharmacological studies of regression or prevention of LVH and studies designed to produce LVH de-novo in normotensive strains. All these studies while confirming an important role of haemodynamic factors also stress the major influence of the renin-angiotensin system and the inter-relationship between angiotensin II and nitric oxide. In contrast, genetic strategies, from simple co-segregation analysis to most complex genome scan studies, suggest the existence of "susceptibility genes" for LV hypertrophy, a finding which deserves further study in large collections of siblings and family groups with essential hypertension.

The vasoconstriction induced by endothelin-1 is mediated only by ET(A) receptors in mesenteric small resistance arteries of spontaneously hypertensive rats and Wistar Kyoto rats

OBJECTIVE

To evaluate the functional responses of mesenteric small resistance arteries of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rat controls to endothelin-1 (ET-1), in the presence and absence of an ET(A) receptor antagonist drug as well as to an ET(B) receptor agonist.

METHODS

Twenty rats aged 12 weeks were studied. They were 10 SHR and 10 WKY rats. Mesenteric small resistance arteries (relaxed diameter 100-180 microm) were dissected and mounted on a micromyograph (Mulvany's technique). A dose-response curve for response to ET-1 was plotted for cumulative concentrations (from 10(-11) to 10(-8) mol/l) in the presence and absence of 10(-6) mol/l FR 139317 (a selective antagonist of ET(A) receptors). In addition, the effects of 10(-7) mol/l N-succinyl-[Glu9, Ala11,15]-endothelin 1 fragment 8-21 (IRL 1620, a selective agonist of ET(B) receptors) were evaluated.

RESULTS

The response of ET-1 was greater in WKY rats than it was in SHR. Almost all the vasoconstrictor effect of ET-1 could be prevented by addition of FR 139317, whereas the agonist of ET(B) receptors had no effect (no change in active force).

CONCLUSIONS

The contractile effects of ET-1 on mesenteric small resistance arteries of SHR and WKY rats are mediated mostly by ET(A) receptors, whereas ET(B) receptors play a minor role, if any. It is possible, however, that a vasoconstrictor effect of ET(B) receptors on the smooth muscle could be masked by the concomitant stimulation of endothelial ET(B) vasodilator receptors.

Inhibition of nitric oxide in rats. Regulation of cardiovascular structure and expression of insulin-like growth factor I and its receptor messenger RNA

OBJECTIVE

To determine whether 12 days' treatment with NG-nitro-L-arginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, in spite of the increased arterial load, resulted in a growth-inhibitory response in the heart, aorta and skeletal muscle vascular bed, and whether the presence of L-NAME affected the expression of insulin-like growth factor-I and its receptor messenger RNA (mRNA).

METHODS

Wistar rats were treated orally either with 100 mg/kg L-NAME or with tap water. On days 2, 4, 7 and 12 after initiation of treatment, the systolic blood pressure/mean arterial blood pressure and heart rate were measured, rats were killed and their heart and aorta were excised. Insulin-like growth factor-I and its receptor mRNA were quantitated by solution hybridization assay. On day 12 resistance properties in the skeletal muscle vascular bed were measured by using an in-vivo constant-flow preparation.

RESULTS

The blood pressure in L-NAME-treated rats was increased immediately after initiation of treatment and it continued to increase throughout the experimental period. No hypertrophy was noted in the heart. Moreover, a 21% (P < 0.05) decrease in the right: left ventricular weight ratio indicated that attenuation of growth of the right ventricle had occurred. Increased expression of insulin-like growth factor-I and its receptor mRNA was observed neither in the heart nor in the aorta. The skeletal muscle vascular bed showed a 26% increased resistance at maximal vasodilatation (P < 0.05), which was indicative of a reduced average lumen size. A lower than expected perfusion pressure at maximal vasoconstriction was observed (17% above control, P < 0.05), implicating only modest medial thickening.

CONCLUSION

L-NAME hypertension caused a prompt increase in blood pressure, which led neither to left ventricular hypertrophy nor to the expected overexpression of left ventricular/aortic insulin-like growth factor-I mRNA and only to partial structural adaptation in the skeletal muscle vasculature. These findings suggest that augmented expression of insulin-like growth factor-I and its receptor could be mandatory for conveying an appropriate adaptive hypertrophic response, at least in the heart.

Effect of chronic ETA-selective endothelin receptor antagonism on blood pressure in experimental and genetic hypertension in rats

1. Chronic treatment with a combined ETA/ETB endothelin receptor antagonist has been shown to reduce blood pressure in experimental rat models of hypertension in which endothelin-1 gene overexpression occurs in the walls of blood vessels, particularly small, resistance-sized arteries, but not in those genetic or experimental models of hypertension in which there is no overexpression of vascular endothelin-1. Failure of some experimental models of hypertension to respond to treatment with the combined ETA/ETB endothelin antagonist may be due in part to blockade of vasorelaxant endothelial ETB receptors which could in theory reduce the efficacy of endothelin antagonism. 2. In this study the orally active ETA-selective endothelin antagonists A-127722.5 and LU 135252 were used in chronic experiments on deoxycorticosterone acetate (DOCA)-salt hypertensive rats (which overexpress vascular endothelin-1 and respond with blood pressure lowering to combined ETA/ETB endothelin receptor antagonism), on spontaneously hypertensive rats (SHR) (which do not overexpress vascular endothelin-1 and do not respond with blood pressure lowering to the combined ETA/ETB receptor antagonist), and in 1-kidney 1 clip Goldblatt (1-K IC) hypertensive rats (which present mild overexpression of vascular endothelin-1 but do not respond with blood pressure lowering to the combined ETA/ETB receptor antagonist). Additionally, it has been suggested that interruption of the renin-angiotensin system may sensitize responses to endothelin antagonism. Accordingly, SHR were treated with an angiotensin converting enzyme inhibitor, cilazapril, in addition to the ETA receptor antagonist. 3. Blood pressure of DOCA-salt hypertensive rats was lowered by a mean of 24 and of 27 mmHg (P < 0.01) by A-127722.5 after 4 weeks of treatment, when given orally at two different doses (10 and 30 mg kg-1 day-1), and by 18 mmHg by LU 135252 50 mg kg-1 day-1. 4. SHR treated with A-127722.5 for 8 weeks starting at 12 weeks of age exhibited the same progressive rise in blood pressure as untreated SHR. Addition of cilazapril resulted in similar reduction of blood pressure in A-127722.5-treated and untreated SHR. 5. Treatment of 1-K IC hypertensive rats with the dose of LU 135252 which lowered blood pressure in DOCA-salt hypertensive rats did not cause any reduction in blood pressure relative to untreated rats. 6. These results demonstrate that treatment with either dose of the selective ETA receptor antagonists A-127722.5 or LU 135252 caused reductions in blood pressure similar to those obtained for a combined ETA/ETB endothelin antagonist. Blood pressure was lowered only in hypertensive rats known to overexpress vascular endothelin-1 (DOCA-salt hypertensive rats) but not in those which do not (SHR) or only have mild vascular overexpression of endothelin-1 gene (1-K 1C hypertensive rats). Reduction in activity of the renin-angiotensin system in SHR did not sensitize blood pressure to potential hypotensive effects of an ETA-selective receptor antagonist.

Nitric oxide synthase inhibition with N omega-nitro-L-arginine methyl ester affects blood pressure and cardiovascular structure in the genetically hypertensive rat strain

1. Inhibition of nitric oxide (NO) synthesis with the nitric oxide synthase (NOS) inhibitor N omega-nitro-L-arginine methyl ester (L-NAME) was used as a tool to investigate further a possible endothelial defect in the New Zealand genetically hypertensive (GH) rat strain compared with its normotensive (N) control strain. 2. N omega-nitro-L-arginine methyl ester was given to GH and N groups in their drinking water from age 7-10 weeks (10 mg/kg per day for week 1 and 2 and then 5 mg/kg per day for week 3). Tailcuff blood pressure (BP) was measured weekly and at the end of the experiment the mesentery was fixed by perfusion, second order branches of the mesenteric artery were embedded in Technovit and stained sections were used to quantify the structure of the mesenteric resistance arteries (MRA). The heart was removed and weighed for determination of left ventricular (LV) mass. 3. In GH rats, BP and LV mass were significantly raised by L-NAME, while in N rats L-NAME treatment significantly elevated BP, but had no effect on LV mass. 4. In GH rats, the media width was significantly increased by L-NAME treatment (P < 0.01); lumen diameter remained unchanged. Thus, the ratio of media width/lumen diameter (M/L) was significantly increased by exacerbation of the hypertrophic outward remodelling characteristic of the GH strain. There were no significant changes in the M/L ratio in L-NAME-treated N rats. 5. Thus, in the GH strain, cardiovascular structure is more sensitive to NOS inhibition than either its N control strain or (on evidence from the literature) the spontaneously hypertensive rat strain.

Endothelin, vascular hypertrophy, and hypertension

The endothelins (ET-1, 2, and 3) constitute a family of 21 amino-acid peptides with potent biological activities. They are synthesized in several tissues, including the vascular endothelium (ET-1 exclusively) and smooth muscle cells. The production and release of endothelin is stimulated by many factors, hormonal and metabolic, and by growth factors, hypoxia, and shear stress. Released endothelin binds to the endothelin receptors ETA and ETB, the ETA receptors on vascular smooth muscle cells mediating vasoconstriction, and the ETB receptors on the endothelium linked to nitric oxide (NO) and prostacyclin release. The ETA receptors activate the PLC-IP3-DAG transduction pathway, which through an increase in cytosolic Ca2+ and protein kinase C (PKC) causes vasoconstriction and stimulation of vascular smooth muscle cell growth and proliferation. In the pathogenesis of vascular hypertrophy in hypertension, there is a complex interaction between endothelin, angiotensin II, alpha-adrenergic agonists, Ca2+, and other growth factors. In animal models of hypertension, endothelin causes vascular hypertrophy, more pronounced in deoxycorticosterone acetate (DOCA)-salt hypertension in the rat than in the spontaneously hypertensive rate. In humans there is an increase in the plasma concentration of endothelin in severe atherosclerotic disease, but not consistently in hypertension. Evidence for the role of endothelin in the vascular hypertrophy of human hypertension is scanty, but the development of nonpeptide and receptor subtype-selective antagonists will permit meaningful studies, including clinical trials of a new class of antihypertensive agents.