Antihypertensive Mechanisms of Chronic Captopril or N-Acetylcysteine Treatment in L-NAME Hypertensive Rats

Research on Experimental Hypertension in Prague (1966-2009)

The study of ontogenetic aspects of water and electrolyte metabolism performed in the Institute of Physiology (Czechoslovak Academy of Sciences) led to the research on the increased susceptibility of immature rats to salt-dependent forms of hypertension since 1966. Hemodynamic studies in developing rats paved the way to the evaluation of hemodynamic mechanisms during the development of genetic hypertension in SHR. A particular attention was focused on altered renal function and kidney damage in both salt and genetic hypertension with a special respect to renin-angiotensin system. Renal damage associated with hypertension progression was in the center of interest of several research groups in Prague. The alterations in ion transport, cell calcium handling and membrane structure as well as their relationship to abnormal lipid metabolism were studied in a close cooperation with laboratories in Munich, Glasgow, Montreal and Paris. The role of NO and oxidative stress in various forms of hypertension was a subject of a joint research with our Slovak colleagues focused mainly on NO-deficient hypertension elicited by chronic L-NAME administration. Finally, we adopted a method enabling us to evaluate the balance of vasoconstrictor and vasodilator mechanisms in BP maintenance. Using this method we demonstrated sympathetic hyperactivity and relative NO deficiency in rats with either salt-dependent or genetic hypertension. At the end of the first decennium of this century we were ready to modify our traditional approach towards modern trends in the research of experimental hypertension. Keywords: Salt-dependent hypertension o Genetic hypertension o Body fluids o Hemodynamics o Ion transport o Cell membrane structure and function o Renal function o Renin-angiotensin systems.

N-Acetylcysteine: more than preventing contrast-induced nephropathy in uremic patients-focus on the antioxidant and anti-inflammatory properties

Oxidative stress (OS) has been recognized as a pathophysiologic mechanism underlying the development and progression of chronic kidney disease (CKD). OS, which results from the disturbance of balance among pro-oxidants and antioxidants favoring the pro-oxidants, is present even in early CKD and increases progressively along with deterioration of kidney function to end-stage kidney disease (ESKD). In ESKD, OS is further exacerbated mainly due to dialysis procedures per se and predisposes to increased cardiovascular morbidity and mortality. Therefore, since OS plays a pivotal role in the pathogenesis and progression of atherosclerosis in uremic patients, several strategies aiming to ameliorate OS in these patients have been proposed. Among those, N-acetylcysteine (NAC), a thiol-containing antioxidant agent, has attracted special attention due to its pleiotropic functions and beneficial effect in various OS-related entities including paracetamol overdose and prevention of contrast-induced nephropathy. In this review, we present the currently available literature on the antioxidant and anti-inflammatory properties of NAC in CKD, including hemodialysis and peritoneal dialysis.

Angiotensin converting enzyme inhibitor potentiates the hypoglycaemic effect of NG-nitro-L-arginine methyl ester (L-NAME) in rats

The inhibition of renin angiotensin system pathway has been largely documented to be effective in the control of cardiovascular events. The present study investigated the effect of angiotensin converting enzyme (ACE) inhibitor on fasting blood glucose level in hypertension induced by the inhibition of nitric oxide synthase (NOS) in male Wistar rats. Hypertension was induced by the inhibition of NOS using a non-selective NOS inhibitor, NG-nitro-L-arginine methyl ester (L-NAME). The blockade of NOS resulted in an increase in blood pressure, ACE, angiotensin II and endothelin-1 levels, and a decrease in fasting blood glucose and nitric oxide (NO) levels. The hypertensive rats treated with ACE inhibitor (ramipril) recorded a decrease in blood pressure, ACE, angiotensin II, endothelin-1, NO and fasting blood glucose levels, and an increase in prostacyclin level. In conclusion, ACE inhibitor potentiated the hypoglycaemic effect of NOS inhibitor and this effect is independent of NO and pancreatic insulin release.

Prophylactic Treatment with Hydrogen Sulphide Can Prevent Renal Ischemia-Reperfusion Injury in L-NAME Induced Hypertensive Rats with Cisplatin-Induced Acute Renal Failure

(Background and Objectives): Renal ischemia perfusion injury is one of the major issues in kidney transplant. The aim of the study was to investigate the hypothesis that prophylactic treatment-with a hydrogen sulphide donor to an acute renal failure case of hypertensive rats-can minimize the ischemia reperfusion injury of the kidney which is beneficial for kidney transplant. To check this hypothesis, the present study was designed to investigate the effect of chronic administration of a hydrogen sulphide (H2S) donor and sodium hydrosulfide (NaHS) on nuclear factor kappa B (NF-kB) and inter cellular adhesion molecule-1 (ICAM-1) concentration in non-renal failure (NRF) and acute renal failure (ARF) rats in the ischemia-reperfusion injury (IRI) model of the kidney in both normotensive WKY and hypertensive rats (L-nitro arginine methyl ester (L-NAME-induced); (Materials and Methods): A total number of 48 Sprague-Dawley rats were recruited into eight groups each consisting of six animals. Each of these eight groups was used to measure systemic and renal parameters, H2S, antioxidant parameters in plasma, plasma concentration of NF-kB and ICAM-1 and renal cortical blood pressure. ARF was induced by single intraperitoneal (i.p.) cisplatin injection (5 mg/kg). Hypertension was induced by oral administration of L-NAME in drinking water for four weeks at 40 mg/kg/day. NaHS was administered (i.p) at 56 µmol/kg for five weeks while dL-propargylglycine (PAG), a H2S generation inhibitor, was administered as a single intra-peritoneal injection (50 mg/kg). An acute surgical experiment was performed for the induction of renal ischemia for 30 min by renal artery clamping followed by reperfusion for three hours; (Results): Chronic administration of NaHS attenuated the severity of ARF in both normotensive and hypertensive animals (L-NAME) along with lowering the blood pressure in hypertensive groups. NaHS improved the oxidative stress parameters such as total superoxide dismutase (T-SOD), glutathione (GSH) and reduced the malondialdehyde (MDA) concentration along with reduction of NF-kB and ICAM-1 following renal IRI; Conclusions: These findings demonstrate that H2S not only reduced the severity of cisplatin induced ARF but also reduced the severity of renal IRI by upregulating antioxidants along with decreased concentrations of NF-kB and ICAM-1 in normotensive and L-NAME induced hypertensive rats.

The effect of the long-term inhibition of hydrogen sulfide production on the reactivity of the cardiovascular system in Wistar rats

In this study, we investigated the blood pressure responses of the peripheral bed in vivo after chronic hydrogen sulphide (H2S) inhibition combined with acute nitric oxide (NO) deficiency. We also evaluated the role of endogenously produced H2S in the vasoactive responses of large- and medium-sized arteries in vitro. Changes in integrated blood pressure responses were measured after chronic inhibition of cystathionine-γ-lyase, an enzyme involved in H2S synthesis, with DL-propargylglycine (PPG), and acute inhibition of NO-synthase with nonspecific L-NG-nitro arginine methyl ester (L-NAME), and vasoactive responses of the thoracic aorta (TA) and mesenteric artery (MA) were investigated after acute incubation with PPG. We confirmed that chronic H2S deficiency had no effect on blood pressure, heart trophycity, noradrenaline and H2S donor vasoactive responses but induced renal hypertrophy and decrease in acetylcholine-induced hypotensive and L-NAME-induced hypertensive responses. Acute H2S deficiency led to an increase in basal tone (MA) or active tone (TA), whereas endothelium-dependent vasorelaxation remained unaffected. Long-term administration of PPG revealed a role of endogenous H2S in the bioavailability of endothelial NO in peripheral arteries. When both H2S and NO were lacking, the activation of H2S-independent compensatory mechanisms plays an important role in maintaining the vasodilator responses of the cardiovascular system.

Hydrogen Sulphide Treatment Prevents Renal Ischemia-Reperfusion Injury by Inhibiting the Expression of ICAM-1 and NF-kB Concentration in Normotensive and Hypertensive Rats

Our main objective was to investigate the effect of chronic administration of hydrogen sulphide donor (sodium hydrosulphide) on the expression of intercellular adhesion molecule-1 (ICAM-1) and concentration of nuclear factor-kappa B (NF-kB) in a renal ischemia-reperfusion injury (IRI) model of WKY and L-nitro-arginine-methyl-ester (L-NAME)-induced hypertensive rats. Sodium hydrosulphide (NaHS) was administered intraperitoneally (i.p.) for 35 days while cystathionine gamma lyase (CSE) inhibitor dL-propargylglycine (PAG) was administered at a single dose of 50 mg/kg. Animals were anesthetised using sodium pentobarbitone (60 mg/kg) and then prepared to induce renal ischemia by clamping the left renal artery for 30 min followed by 3 h of reperfusion. Pre-treatment with NaHS improved the renal functional parameters in both WKY and L-NAME-induced hypertensive rats along with reduction of blood pressure in hypertensive groups. Oxidative stress markers like malondialdehyde (MDA), total superoxide dismutase (T-SOD) and glutathione (GSH) were also improved by NaHS treatment following renal IRI. Levels of ICAM-1 and NF-kB concentration were reduced by chronic treatment with NaHS and increased by PAG administration after renal IRI in plasma and kidney. Treatment with NaHS improved tubular morphology and glomerulus hypertrophy. Pre-treatment with NaHS reduced the degree of renal IRI by potentiating its antioxidant and anti-inflammatory mechanism, as evidenced by decreased NF-kB concentration and downregulation of ICAM-1 expression.

Diosmetin Ameliorates Vascular Dysfunction and Remodeling by Modulation of Nrf2/HO-1 and p-JNK/p-NF-κB Expression in Hypertensive Rats

Diosmetin is a citrus flavonoid that has antioxidant and anti-inflammatory effects. This study examined the effect of diosmetin on blood pressure and vascular alterations and its underlying mechanisms in experimentally hypertensive rats. Male Sprague rats were administered Nω-nitro-l-arginine methyl ester L-NAME for five weeks and were given diosmetin at doses of 20 or 40 mg/kg or captopril (5 mg/kg) for two weeks. Diosmetin alleviated hypertension, improved endothelial dysfunction, and suppressed the overactivity of sympathetic nerve-mediated vasoconstriction in aorta and mesentery hypertensive rats (p < 0.05). Increases in plasma and aortic tissue malondialdehyde (MDA) and carotid superoxide generations and reductions of plasma superoxide dismutase, catalase, and nitric oxide in hypertensive rats were ameliorated by diosmetin (p < 0.05). Diosmetin increased the protein expression of nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1) in hypertensive rats. Furthermore, diosmetin mitigated hypertrophy and collagen accumulation of the aortic wall in L-NAME rats. It exhibited an anti-inflammatory effect by reducing interleukin-6 (IL-6) accumulation and by overexpressing the phospho-c-Jun N-terminal kinases (p-JNK) and the phospho-nuclear factor-kappaB (p-NF-κB) proteins in the aorta (p < 0.05). Captopril was a positive control substance and had similar effects to diosmetin. In summary, diosmetin reduced blood pressure and alleviated vascular abnormalities in L-NAME-treated rats. These effects might be related to antioxidant and anti-inflammatory effects as well as to the modulation of the expression of the Nrf2/HO1 and p-JNK/NF-κB proteins.

Preclinical Evaluation of the Antihypertensive Effect of an Aqueous Extract of Anogeissus leiocarpa (DC) Guill et Perr. Bark of Trunk in L-NAME-Induced Hypertensive Rat

BACKGROUND

The present study investigates the effect of an aqueous extract of Anogeissus leiocarpa (AEAL) on normotensive Wistar rats and its chronic antihypertensive effects in L-NAME-induced hypertensive rats by using a non-invasive tail-cuff model.

METHODS

The effects of AEAL (50mg/kg) and NaCl 0.9% on blood pressure were investigated by daily oral administration in normotensive Wistar rats over four weeks. L-NAME-induced hypertensive rats were produced by L-NAME (40mg/kg) daily oral administration for two weeks. For chronic antihypertensive effects, induced hypertensive rats have received L-NAME in combination with AEAL (10 or 50mg/kg/day) for two following weeks.

RESULTS

In normotensive rats, daily administration of AEAL (50mg/kg) has no significant effect on their blood pressure, which was similar to that of the control group. L-NAME's daily oral administration induces a progressive increase in systolic blood pressure (SBP) from 115.8 ± 7.9mmHg to 153.5 ± 4.6mmHg after two weeks, which was maintained to the end of the treatment. In L-NAME-induced hypertensive rats, AEAL (50mg/kg/day) significantly decreases the SPB from 160.0 ± 5.8 mmHg to 108.8 ± 2.7mmHg after only four days of administration. However, the lower dose of AEAL (10mg/kg) also normalized the SBP of L-NAME-induced hypertensive rats but only evident after seven days of administration. Moreover, AEAL does not effect on the serum biochemical parameters (ALAT, ASAT, CREAT, etc.) and any macroscopic adverse effect was detected on the sensible organs involved during hypertension. In the aorta rings from treated rats, AEAL (50mg/kg/day) alone or in combination with L-NAME has enhanced the vasodilation effect of acetylcholine. However, the vasodilation effect of AEAL alone or in association with L-NAME has enhanced the sodium nitroprusside effect in treated rat aorta rings after autopsy.

CONCLUSION

These findings suggest that AEAL affords significant antihypertensive effects against L-NAME-induced hypertensive rats without modification of serum parameters and deleterious effects.

Hypotensive and antihypertensive effects of an aqueous extract from Guinep fruit (Melicoccus bijugatus Jacq) in rats

Melicoccus bijugatus Jacq (Mb) has been reported to have cardiovascular modulatory effects. In this study, we evaluated the antihypertensive effects and mechanism of action of Mb on N^G-Nitro-l-arginine Methyl Ester (l-NAME) and Deoxycorticosterone Acetate (DOCA) rat models. Aqueous extract of Mb fruit (100 mg/kg) was administered for 6 weeks to rats by gavage and blood pressure was recorded. Effects of the extract on vascular reactivity was evaluated using isolated organ baths, and tissues were collected for biochemical and histological analysis. The systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP) were significantly (P < 0.05) reduced with extract (100 mg/kg) administration and treatment compared to the hypertensive models. Mb (100 µg/mL) reduced the vascular contractility induced by phenylephrine (PE), and caused a dose-dependent relaxation of PE-induced contraction of aortic vascular rings. The vasorelaxation properties seemed to be endothelium dependent, as well as nitric oxide (NO) and guanylyl cyclase, but not prostaglandin dependent. Histomicrograph of transverse sections of the ventricles from the Mb group did not show abnormalities. The extract significantly (P < 0.05) reduced an l-NAME induced elevation of cardiac output and Creatine Kinase Muscle-Brain (CKMB), but had no significant impact on the activities of arylamine N-acetyltransferase. In conclusion, Mb significantly decreased blood pressure in hypertensive models. The extract possesses the ability to induce endothelium dependent vasodilation, which is dependent on guanylyl cyclase but not prostaglandins.

Therapeutic Efficacy of Antioxidants in Ameliorating Obesity Phenotype and Associated Comorbidities

Obesity has been a worldwide epidemic for decades. Despite the abundant increase in knowledge regarding the etiology and pathogenesis of obesity, the prevalence continues to rise with estimates predicting considerably higher numbers by the year 2030. Obesity is characterized by an abnormal lipid accumulation, however, the physiological consequences of obesity are far more concerning. The development of the obesity phenotype constitutes dramatic alterations in adipocytes, along with several other cellular mechanisms which causes substantial increase in systemic oxidative stress mediated by reactive oxygen species (ROS). These alterations promote a chronic state of inflammation in the body caused by the redox imbalance. Together, the systemic oxidative stress and chronic inflammation plays a vital role in maintaining the obese state and exacerbating onset of cardiovascular complications, Type II diabetes mellitus, dyslipidemia, non-alcoholic steatohepatitis, and other conditions where obesity has been linked as a significant risk factor. Because of the apparent role of oxidative stress in the pathogenesis of obesity, there has been a growing interest in attenuating the pro-oxidant state in obesity. Hence, this review aims to highlight the therapeutic role of antioxidants, agents that negate pro-oxidant state of cells, in ameliorating obesity and associated comorbidities. More specifically, this review will explore how various antioxidants target unique and diverse pathways to exhibit an antioxidant defense mechanism.

Ethyl Rosmarinate Prevents the Impairment of Vascular Function and Morphological Changes in L-NAME-Induced Hypertensive Rats

Background and Objectives: The potent, endothelium-independent, vasorelaxant effect of ethyl rosmarinate, an ester derivative of rosmarinic acid, makes it of interest as an alternative therapeutic agent for use in hypertension. This study was designed to investigate the effect of ethyl rosmarinate on Nω-nitro-L-arginine methyl ester (L-NAME)-induced hypertensive rats. Materials and Methods: L-NAME was given orally to male Wistar rats for 6 weeks to induce hypertension concurrently with treatment of ethyl rosmarinate at 5, 15, or 30 mg/kgor enalapril at 10 mg/kg Systolic blood pressure (SBP), heart rate, and body weight of all experimental groups were recorded weekly, while the vascular sensitivity and histological changes of the aorta were evaluated at the end of the experiment. Results: For all treatment groups, the data indicated that ethyl rosmarinate significantly attenuated the SBP in hypertensive rats induced by L-NAME, with no significant differences in heart rate and body weight. In addition, the response of vascular sensitivity to acetylcholine (ACh) was improved but there was no significant difference in the response to sodium nitroprusside (SNP). Furthermore, the sensitivity of the aorta to phenylephrine (PE) was significantly decreased. The thickness of the aortic wall did not differ between groups but the expression of endothelial nitric oxide synthase (eNOS) was increased in ethyl rosmarinate- and enalapril-treated groups compared with the hypertensive group. Conclusions: Ethyl rosmarinate is an interesting candidate as an alternative treatment for hypertension due to its ability to improve vascular function and to increase the expression of eNOS similar to enalapril which is a drug commonly used in hypertension.

Physical training promotes similar effects to the blockade of angiotensin-converting enzyme on the cardiac morphology and function in old female rats subjected to premature ovarian failure

We investigated the effects of angiotensin-converting enzyme (ACE) inhibition and aerobic physical training on the heart of old female rats (82-wk-old) submitted to premature ovarian failure (10-wk.-old). We used different approaches: morphology and function by echocardiography, reactivity of the coronary bed and left ventricular contractibility (Langendorff Technique). Female Wistar ovariectomized (OVX) rats (n=42) were assigned to one of four groups: OVX, vehicle treated only; OVX-EM, Enalapril Maleate only (EM, 10mg·kg^-1·d^-1); OVX-T, aerobic trained only; and OVX-EMT, treated with Enalapril Maleate and aerobic trained. Both Enalapril Maleate treatment and aerobic training were done in the last 20weeks of the experimental protocol. When compared to the OVX group, the OVX-EM group showed lower values of wall thickness and left ventricular (LV) mass, lower values of coronary bed reactivity and reduced maximum response of LV contractility to dobutamine, while the OVX-T group showed lower values of LV wall thickness, increase in end-systolic volume, reduced maximum response of LV contractility to dobutamine, and left intraventricular pressure due to increased flow. The combination of treatments (EM and aerobic physical training) did not promote additional important effects on the parameters evaluated. Our results suggest similar beneficial effects of physical training and EM treatment on the morphology and cardiac function in old female rats submitted to premature ovarian failure. Although the causes of these benefits are still unknown, both treatments have promoted a decrease in cardiac contractility, and the reduced β1-adrenergic sensitivity suggests that both treatments may attenuate the sympathetic effect on the heart.

Blood pressure regulation in stress: focus on nitric oxide-dependent mechanisms

Stress is considered a risk factor associated with the development of various civilization diseases including cardiovascular diseases, malignant tumors and mental disorders. Research investigating mechanisms involved in stress-induced hypertension have attracted much attention of physicians and researchers, however, there are still ambiguous results concerning a causal relationship between stress and long-term elevation of blood pressure (BP). Several studies have observed that mechanisms involved in the development of stress-induced hypertension include increased activity of sympathetic nervous system (SNS), glucocorticoid (GC) overload and altered endothelial function including decreased nitric oxide (NO) bioavailability. Nitric oxide is well known neurotransmitter, neuromodulator and vasodilator involved in regulation of neuroendocrine mechanisms and cardiovascular responses to stressors. Thus NO plays a crucial role in the regulation of the stress systems and thereby in the BP regulation in stress. Elevated NO synthesis, especially in the initial phase of stress, may be considered a stress-limiting mechanism, facilitating the recovery from stress to the resting levels via attenuation of both GC release and SNS activity as well as by increased NO-dependent vasorelaxation. On the other hand, reduced levels of NO were observed in the later phases of stress and in subjects with genetic predisposition to hypertension, irrespectively, in which reduced NO bioavailability may account for disruption of NO-mediated BP regulatory mechanisms and accentuated SNS and GC effects. This review summarizes current knowledge on the role of stress in development of hypertension with a special focus on the interactions among NO and other biological systems affecting blood pressure and vascular function.

Acute and chronic role of nitric oxide, renin-angiotensin system and sympathetic nervous system in the modulation of calcium sensitization in Wistar rats

Principal vasoactive systems - renin-angiotensin system (RAS), sympathetic nervous system (SNS), nitric oxide (NO) and prostanoids - exert their vascular effects through the changes in calcium levels and/or calcium sensitization. To estimate a possible modulation of calcium sensitization by the above vasoactive systems, we studied the influence of acute and chronic blockade of particular vasoactive systems on blood pressure (BP) changes elicited in conscious normotensive rats by acute dose-dependent administration of Rho-kinase inhibitor fasudil. Adult male chronically cannulated Wistar rats were used throughout this study. The acute inhibition of NO synthase (NOS) by L-NAME enhanced BP response to fasudil, the effect being considerably augmented in rats deprived of endogenous SNS. The acute inhibition of prostanoid synthesis by indomethacin modified BP response to fasudil less than the acute NOS inhibition. The chronic NOS inhibition caused moderate BP elevation and a more pronounced augmentation of fasudil-induced BP changes compared to the effect of acute NOS inhibition. This indicates both short-term and long-term NO-dependent attenuation of calcium sensitization. Long-term inhibition of RAS by captopril caused a significant attenuation of BP changes elicited by fasudil. In contrast, a long-term attenuation of SNS by chronic guanethidine treatment (in youth or adulthood) had no effect on BP response to fasudil, suggesting the absence of SNS does not affect calcium sensitization in vascular smooth muscle of normotensive rats. In conclusion, renin-angiotensin system contributes to the long-term increase of calcium sensitization and its effect is counterbalanced by nitric oxide which decreases calcium sensitization in Wistar rats.

Effects of a novel ACE inhibitor, 3-(3-thienyl)-l-alanyl-ornithyl-proline, on endothelial vasodilation and hepatotoxicity in l-NAME-induced hypertensive rats

Nitric oxide (NO) is a widespread biological mediator involved in many physiological and pathological processes, eg, in the regulation of vascular tone and hypertension. Chronic inhibition of NO synthase by N^G-nitro-l-arginine methyl ester (l-NAME) hydrochloride results in the development of hypertension accompanied by an increase in vascular responsiveness to adrenergic stimuli. Recently, we developed a novel sulfur-containing angiotensin-converting enzyme inhibitor: 3-(3-thienyl)-l-alanyl-ornithyl-proline (TOP). Our previous studies indicated a superior nature of the molecule as an antihypertensive agent in spontaneously hypertensive rats (showing the involvement of renin–angiotensin–aldosterone system) in comparison to captopril. The aim of the present study was to investigate the effect of TOP on NO pathway in l-NAME-induced hypertensive rats, and captopril was included as the standard treatment group. Treatment with both TOP (20 mg/kg) and captopril (40 mg/kg) prevented the development of hypertension in l-NAME model, but TOP showed better restoration of NO and normal levels of angiotensin-converting enzyme. In addition, in vitro vasorelaxation assay showed an improvement in endothelium-dependent vasodilation in both the cases. Further, the biochemical (malondialdehyde, alanine aminotransferase, and aspartate aminotransferase) and the histopathological effects of TOP on rat liver tissues revealed a protective nature of TOP in comparison to captopril in the l-NAME model. In conclusion, TOP at 50% lesser dose than captopril was found to be better in the l-NAME model.

Moderate additive effects of endothelin receptor A blockade in Ren-2 transgenic rats subjected to various types of RAS blockade

AIMS

Chronic endothelin receptor A (ETA) blockade lowered blood pressure (BP) by decreasing angiotensin-dependent vasoconstriction and attenuating calcium influx. We tested whether the addition of ETA blockade to renin-angiotensin system (RAS) blockade would have further effects on the principal vasoactive systems contributing to BP maintenance in Ren-2 transgenic rats (TGR).

METHODS

Four-week-old TGR rats were fed with normal-salt diet and given either different renin-angiotensin system (RAS) blockers [angiotensin receptor blocker losartan, angiotensin converting enzyme inhibitor captopril, direct renin inhibitor aliskiren], or ETA blocker (atrasentan) alone, or a combination of atrasentan with RAS blockers for 4weeks. At the end of the study, basal BP and acute BP responses to sequential blockade of renin-angiotensin (RAS), sympathetic nervous (SNS), and nitric oxide (NO) systems were determined in conscious rats. Thereafter, BP responses to acute inhibition of nifedipine-sensitive calcium influx through voltage-dependent calcium channels (L-VDCC) were measured.

KEY FINDINGS

All RAS blockers similarly decreased BP to normotension, their effects being mediated through substantially attenuated RAS-dependent and moderately decreased SNS-dependent vasoconstriction. Atrasentan alone partially lowered BP, while BP was normalized by combination of atrasentan with either RAS blocker. In combination therapies, BP lowering effects resulted from the attenuation of both RAS- and SNS-dependent vasoconstriction. Moreover, atrasentan-treated groups had substantially reduced NO-dependent vasodilation and significantly decreased calcium influx through L-VDCC.

CONCLUSIONS

Although the BP-lowering effect of combined ETA and RAS blockades in TGR is predominantly dependent on the effects exerted by RAS blockade, further effects are attributable to decreased calcium influx due to chronic ETA blockade.

Oral N-acetylcysteine reduces plasma homocysteine concentrations regardless of lipid or smoking status

BACKGROUND

Elevated total plasma homocysteine (tHcy) is considered to be an independent cardiovascular disease risk factor, although tHcy lowering by B-vitamins improves only certain clinical endpoints. N-acetylcysteine (NAC), a thiol-containing antioxidant, acutely lowers tHcy and possibly also blood pressure. However, to our knowledge, at present no conclusive long-term evaluation exists that controls for factors such as hyperlipidemia, smoking, medication, and disease stage, all of which affect the thiol redox state, including tHcy.

OBJECTIVE

We reanalyzed 2 double-blind, placebo-controlled trials in unmedicated middle-aged men, one in a hyperlipidemic group (HYL group; n = 40) and one in a normolipidemic group (NOL group; n = 42), each stratified for smokers and nonsmokers.

DESIGN

We evaluated the effect of 4 wk of oral NAC (1.8 g/d) on tHcy (primary endpoint), plasma thiol (cysteine), and intracellular glutathione concentrations as well as on blood pressure. The HYL group had total cholesterol >220 mg/dL or triglycerides >150 mg/dL.

RESULTS

NAC treatment significantly (P = 0.001, multivariate analysis of variance for repeated measures) lowered postabsorptive plasma concentrations of tHcy by -11.7% ± 3.0% (placebo: 4.1% ± 3.6%) while increasing those of cysteine by 28.1% ± 5.7% (placebo: 4.0% ± 3.4%) with no significant impact of hyperlipidemia or smoking. Moreover, NAC significantly decreased systolic (P = 0.003) and diastolic (P = 0.017) blood pressure within all subjects with a significant reduction in diastolic pressure in the HYL group (P = 0.008) but not in the NOL group. An explorative stepwise multiple regression analysis identified 1) post-treatment cysteine as well as 2) pretreatment tHcy and 3) albumin plasma concentrations as being significant contributors to tHcy reduction.

CONCLUSIONS

Four weeks of oral NAC treatment significantly decreased plasma tHcy concentrations, irrespective of lipid or smoking status, and lowered systolic blood pressure in both normolipidemic and hyperlipidemic men, with significant diastolic blood pressure reductions in the HYL group only. Increased oral intake of cysteine may therefore be considered for primary or secondary prevention of vascular events with regard to the 2 independent risk factors of hyperhomocysteinemia and arterial hypertension.

Nifedipine-Sensitive Blood Pressure Component in Hypertensive Models Characterized by High Activity of Either Sympathetic Nervous System or Renin-Angiotensin System

High blood pressure (BP) of spontaneously hypertensive rats (SHR) is maintained by enhanced activity of sympathetic nervous system (SNS), whereas that of Ren-2 transgenic rats (Ren-2 TGR) by increased activity of renin-angiotensin system (RAS). However, both types of hypertension are effectively attenuated by chronic blockade of L-type voltage-dependent calcium channel (L-VDCC). The aim of our study was to evaluate whether the magnitude of BP response elicited by acute nifedipine administration is proportional to the alterations of particular vasoactive systems (SNS, RAS, NO) known to modulate L-VDCC activity. We therefore studied these relationships not only in SHR, in which mean arterial pressure was modified in a wide range of 100-210 mm Hg by chronic antihypertensive treatment (captopril or hydralazine) or its withdrawal, but also in rats with augmented RAS activity such as homozygous Ren-2 TGR, pertussis toxin-treated SHR or L-NAME-treated SHR. In all studied groups the magnitude of BP response to nifedipine was proportional to actual BP level and it closely correlated with BP changes induced by acute combined blockade of RAS and SNS. BP response to nifedipine is also closely related to the degree of relative NO deficiency. This was true for both SNS- and RAS-dependent forms of genetic hypertension, suggesting common mechanisms responsible for enhanced L-VDCC opening and/or their upregulation in hypertensive animals. In conclusions, BP response to nifedipine is proportional to the vasoconstrictor activity exerted by both SNS and RAS, indicating a key importance of these two pressor systems for actual L-VDCC opening necessary for BP maintenance.

The impact of four different classes of anesthetics on the mechanisms of blood pressure regulation in normotensive and spontaneously hypertensive rats

Most anesthetics induce characteristic hemodynamic changes leading to blood pressure (BP) reduction but the role of renin-angiotensin system (RAS), sympathetic nervous system (SNS) and nitric oxide (NO) synthesis in this BP reduction is unknown. We therefore studied the influence of four widely used anesthetics - pentobarbital (P), isoflurane (ISO), ketamine-xylazine (KX) and chloralose-urethane (CU) - on the participation of these vasoactive systems in BP maintenance. BP effects elicited by the acute sequential blockade of RAS (captopril), SNS (pentolinium) and NO synthase (L-NAME) were compared in conscious and anesthetized Wistar or spontaneously hypertensive rats (SHR). Except for pentobarbital all studied anesthetics evidenced by diminished BP responses to pentolinium. The absolute pentolinium-induced BP changes were always greater in SHR than Wistar rats. KX anesthesia eliminated BP response to pentolinium and considerably enhanced BP response to NO synthase inhibition in SHR. In both rat strains the anesthesia with ISO or CU augmented BP response to captopril, decreased BP response to pentolinium and attenuated BP response to NO synthase inhibition. In conclusion, pentobarbital anesthesia had a modest influence on BP level and its maintenance by the above vasoactive systems. Isoflurane and chloralose-urethane anesthesia may be used in cardiovascular experiments if substantial BP decrease due to altered contribution of RAS, SNS and NO to BP regulation does not interfere with the respective research aim. Major BP reduction (namely in SHR) due to a complete SNS absence is a major drawback of ketamine-xylazine anesthesia.

Chronic antioxidant therapy lowers blood pressure in adult but not in young Dahl salt hypertensive rats: the role of sympathetic nervous system

AIM

It is well-known that salt hypertension is associated with increased oxidative stress. Since the development of salt hypertension is age-dependent, we were interested whether young and adult salt hypertensive Dahl rats differ in oxidative stress level and/or in the effects of chronic antioxidant therapy on blood pressure (BP) level and on the participation of particular vasoconstrictor/vasodilator systems in BP maintenance.

METHODS

Young (5-week-old) and adult (12-week-old) salt-sensitive (Dahl-S) male rats were fed high-salt diet (5% NaCl) and drank tempol solution (2 mm) for 5 weeks. BP was monitored with radiotelemetry and vasoconstrictor/vasodilator balance was evaluated at the end of experiment. Moreover, NO synthase activity, superoxide production and lipoperoxidation were determined in heart, kidney and aorta in separate subgroups of Dahl rats.

RESULTS

Tempol treatment had quite opposite BP effects in young and adult Dahl-S rats. While it tended to increase BP in young salt hypertensive Dahl-S rats, it significantly lowered BP in the adult ones due to reduced sympathetic vasoconstriction. Importantly, high salt intake substantially reduced NO synthase activity in heart and kidney, and markedly increased superoxide production in kidneys and aorta of adult Dahl-S rats in which BP correlated positively with superoxide production in thoracic aorta and lipoperoxidation in kidneys.

CONCLUSION

Chronic antioxidant therapy lowered BP only in adult salt hypertensive Dahl-S rats in which superoxide levels were increased in both kidneys and aorta. Blood pressure reduction induced by chronic tempol treatment is related to attenuated sympathetic vasoconstriction rather than to augmented NO-dependent vasodilatation.

Age-dependent salt hypertension in Dahl rats: fifty years of research

Fifty years ago, Lewis K. Dahl has presented a new model of salt hypertension - salt-sensitive and salt-resistant Dahl rats. Twenty years later, John P. Rapp has published the first and so far the only comprehensive review on this rat model covering numerous aspects of pathophysiology and genetics of salt hypertension. When we summarized 25 years of our own research on Dahl/Rapp rats, we have realized the need to outline principal abnormalities of this model, to show their interactions at different levels of the organism and to highlight the ontogenetic aspects of salt hypertension development. Our attention was focused on some cellular aspects (cell membrane function, ion transport, cell calcium handling), intra- and extrarenal factors affecting renal function and/or renal injury, local and systemic effects of renin-angiotensin-aldosterone system, endothelial and smooth muscle changes responsible for abnormal vascular contraction or relaxation, altered balance between various vasoconstrictor and vasodilator systems in blood pressure maintenance as well as on the central nervous and peripheral mechanisms involved in the regulation of circulatory homeostasis. We also searched for the age-dependent impact of environmental and pharmacological interventions, which modify the development of high blood pressure and/or organ damage, if they influence the salt-sensitive organism in particular critical periods of development (developmental windows). Thus, severe self-sustaining salt hypertension in young Dahl rats is characterized by pronounced dysbalance between augmented sympathetic hyperactivity and relative nitric oxide deficiency, attenuated baroreflex as well as by a major increase of residual blood pressure indicating profound remodeling of resistance vessels. Salt hypertension development in young but not in adult Dahl rats can be attenuated by preventive increase of potassium or calcium intake. On the contrary, moderate salt hypertension in adult Dahl rats is attenuated by superoxide scavenging or endothelin-A receptor blockade which do not affect salt hypertension development in young animals.

Resveratrol and grape juice differentially ameliorate cardiovascular autonomic modulation in L-NAME-treated rats

Polyphenols consumption detected in red wine and grape juice may prevent or help in the treatment of hypertension. However, cardiovascular autonomic effects of polyphenols were poorly studied. Therefore, we evaluated the effects of resveratrol and grape juice treatments in hemodynamics, baroreflex sensitivity, heart rate (HR) and blood pressure (BP) variability and cardiac redox parameters. Male Wistar rats were divided in 3 groups (n=7/each) and treated for 30 days: only L-NAME-treated (60 mg/kg/day by oral gavage), L-NAME+resveratrol (L-NAME+R) and L-NAME+grape juice (L-NAME+G). BP signal was directly recorded and pulse interval (PI) and systolic arterial pressure (SAP) variability were analyzed in time and frequency domains. Baroreflex sensitivity (BRS) was determined by the alpha index. Oxidized and reduced glutathione concentrations were determined in cardiac tissue. L-NAME increased BP with no differences among groups (mean BP: L-NAME=124±4, L-NAME+R=126±3 and L-NAME+G=125±4 mmHg). PI and SAP variability expressed by total variance were also similar among groups. However, normalized low frequency (LF) and high frequency (HF) components of PI variability were lower and higher, respectively, in both R and G-treated groups when compared to only L-NAME group. Interestingly, sympathetic modulation to the vessels (LF from SAP variability) and BRS were decreased and increased, respectively, only in L-NAME+R rats. Additionally, GSH/GSSG ratios were higher in L-NAME+R and L-NAME+G than in L-NAME group. Our results indicate that resveratrol and grape juice treatments can modulate autonomic function and promote cardiac redox benefits even when nitric oxide is decreased. Moreover, resveratrol influences not only cardiac but also vascular autonomic modulation.

Acute and chronic antihypertensive effects of Cinnamomum zeylanicum stem bark methanol extract in L-NAME-induced hypertensive rats

Background

Previous study showed that the aqueous extract of the stem bark of Cinnamomum zeylanicum possesses antihypertensive and vasodilatory properties. The present work investigates the acute and chronic antihypertensive effects of the methanol extract of Cinnamomum zeylanicum stem bark (MECZ) in L-NAME-induced hypertensive rats.

Methods

The acute antihypertensive effects of MECZ (5, 10 and 20 mg/kg) administered intravenously were evaluated in rats in which acute arterial hypertension has been induced by intravenous administration of L-NAME (20 mg/kg). For chronic antihypertensive effects, animals were treated with L-NAME (40 mg/kg/day) plus the vehicle or L-NAME (40 mg/kg/day) in combination with captopril (20 mg/kg/day) or MECZ (300 mg/kg/day) and compared with control group receiving only distilled water. All drugs were administered per os and at the end of the experiment that lasted for four consecutive weeks, blood pressure was measured by invasive method and blood samples were collected for the determination of the lipid profile. The heart and aorta were collected, weighed and used for both histological analysis and determination of NO tissue content.

Results

Acute intravenous administration of C. zeylanicum extract (5, 10 and 20 mg/kg) to L-NAME-induced hypertensive rats provoked a long-lasting decrease in blood pressure. Mean arterial blood pressure decreased by 12.5%, 26.6% and 30.6% at the doses of 5, 10 and 20 mg/kg, respectively. In chronic administration, MECZ and captopril significantly prevented the increase in blood pressure and organs’ weights, as well as tissue histological damages and were able to reverse the depletion in NO tissue’s concentration. The MECZ also significantly lower the plasma level of triglycerides (38.1%), total cholesterol (32.1%) and LDL-cholesterol (75.3%) while increasing that of HDL-cholesterol (58.4%) with a significant low atherogenic index (1.4 versus 5.3 for L-NAME group).

Conclusion

MECZ possesses antihypertensive and organ protective effects that may result from its ability to increase the production of the endogenous NO and/or to regulate dyslipidemia.

The antihypertensive effect of cysteine

Hypertension is a leading cause of morbidity and mortality worldwide. Individuals with hypertension are at an increased risk for stroke, heart disease and kidney failure. Essential hypertension results from a combination of genetic and lifestyle factors. One such lifestyle factor is diet, and its role in the control of blood pressure has come under much scrutiny. Just as increased salt and sugar are known to elevate blood pressure, other dietary factors may have antihypertensive effects. Studies including the Optimal Macronutrient Intake to Prevent Heart Disease (OmniHeart) study, Multiple Risk Factor Intervention Trial (MRFIT), International Study of Salt and Blood Pressure (INTERSALT) and Dietary Approaches to Stop Hypertension (DASH) study have demonstrated an inverse relationship between dietary protein and blood pressure. One component of dietary protein that may partially account for its antihypertensive effect is the nonessential amino acid cysteine. Studies in hypertensive humans and animal models of hypertension have shown that N-acetylcysteine, a stable cysteine analogue, lowers blood pressure, which substantiates this idea. Cysteine may exert its antihypertensive effects directly or through its storage form, glutathione, by decreasing oxidative stress, improving insulin resistance and glucose metabolism, lowering advanced glycation end products, and modulating levels of nitric oxide and other vasoactive molecules. Therefore, adopting a balanced diet containing cysteine-rich proteins may be a beneficial lifestyle choice for individuals with hypertension. An example of such a diet is the DASH diet, which is low in salt and saturated fat; includes whole grains, poultry, fish and nuts; and is rich in vegetables, fruits and low-fat dairy products.

Chronic endothelin A receptor blockade attenuates contribution of sympathetic nervous system to salt hypertension development in adult but not in young Dahl rats

AIM

Endothelin-1 (ET-1) plays an important role in the pathogenesis of salt-dependent forms of hypertension in adult rats, but its participation in salt hypertension elicited in immature rats is still unknown. Therefore, we compared ET-1 role in the development or the maintenance of salt hypertension induced in young (4-week-old) or adult (12-week-old) Dahl rats.

METHODS

The contribution of pressor ET-1 effects to the maintenance of high blood pressure (BP) was studied using acute injection of ET(A) receptor antagonist ambrisentan (BSF 208075, 1 mg kg(-1) iv) to young or adult rats with established salt hypertension. Furthermore, using chronic ambrisentan treatment (30 mg kg(-1) day(-1) in the drinking fluid during 5 weeks of high salt intake), we investigated the age-dependent involvement of ET(A) receptors in salt hypertension development in these two age groups.

RESULTS

Acute ET(A) receptor blockade lowered BP in both age groups of salt hypertensive Dahl rats more than in rats fed a low-salt diet (but without any age-dependent difference). Chronic ET(A) receptor blockade strongly attenuated the development of salt hypertension and cardiac hypertrophy in adult rats, but it had no significant effects on salt hypertension in young animals. Pronounced BP reduction induced in adult salt hypertensive rats by chronic ambrisentan treatment was attributed to attenuated sympathetic BP component, without changes in nitric oxide (NO)-dependent BP regulation. In contrast, chronic ambrisentan treatment of young animals did not modify sympathetic BP component but substantially attenuated NO-dependent vasodilatation.

CONCLUSIONS

ET(A) receptor-mediated ET-1 effects play an important role in salt hypertension of adult but not young Dahl rats.

Preventive dietary potassium supplementation in young salt-sensitive Dahl rats attenuates development of salt hypertension by decreasing sympathetic vasoconstriction

AIM

Increased potassium intake attenuates the development of salt-dependent hypertension, but the detailed mechanisms of blood pressure (BP) reduction are still unclear. The aims of our study were (i) to elucidate these mechanisms, (ii) to compare preventive potassium effects in immature and adult animals and (iii) to evaluate the therapeutic effects of dietary potassium supplementation in rats with established salt hypertension.

METHODS

  Young (4-week-old) and adult (24-week-old) female salt-sensitive Dahl rats were fed a high-salt diet (5% NaCl) or a high-salt diet supplemented with 3% KCl for 5 weeks. The participation of vasoconstrictor (renin-angiotensin and sympathetic nervous systems) and vasodilator systems [prostanoids, Ca(2+) -activated K(+) channels, nitric oxide (NO)] was evaluated using a sequential blockade of these systems.

RESULTS

Preventive potassium supplementation attenuated the development of severe salt hypertension in young rats, whereas it had no effects on BP in adult rats with moderate hypertension. Enhanced sympathetic vasoconstriction was responsible for salt hypertension in young rats and its attenuation for potassium-induced BP reduction. Conversely, neither salt hypertension nor its potassium-induced attenuation were associated with significant changes of the vasodilator systems studied. The relative deficiency of vasodilator action of NO and Ca(2+) -activated K(+) channels in salt hypertensive Dahl rats was not improved by potassium supplementation.

CONCLUSIONS

The attenuation of enhanced sympathetic vasoconstriction is the principal mechanism of antihypertensive action exerted by preventive potassium supplementation in immature Dahl rats. Dietary potassium supplementation has no preventive effects on BP in adult salt-loaded animals or no therapeutic effects on established salt hypertension in young rats.

N-acetylcysteine attenuates leukocytic inflammation and microvascular perfusion failure in critically ischemic random pattern flaps

INTRODUCTION

Microcirculatory dysfunction causes ischemia resulting in tissue necrosis. N-acetylcysteine (NAC) has been shown capable of protecting tissue from ischemic necrosis. However, the mechanism of action of NAC is yet not fully understood.

OBJECTIVE

Herein, we studied whether NAC is capable of attenuating microvascular perfusion failure in critically ischemic musculo-cutaneous tissue.

MATERIAL AND METHODS

A laterally based skin flap was elevated in the dorsum of C57BL/6 mice and fixed into a dorsal skinfold chamber. Arteriolar perfusion, functional capillary density, leukocytic inflammation, apoptotic cell death, and non-perfused tissue area were repetitively analyzed over 10 days by intravital fluorescence microscopy. Treatment with either 100mg/kg NAC or saline (control) was started 30 min before surgery and was continued until day 10 after flap elevation.

RESULTS

Surgery induced leukocytic inflammation, microvascular perfusion failure, apoptosis, and tissue perfusion failure. NAC was capable of significantly attenuating the area of non-perfused tissue. This was associated by a marked arteriolar dilation and an increased capillary perfusion. NAC further reduced the ischemia-associated leukocytic response and significantly attenuated apoptotic cell death in all areas of the flap.

CONCLUSION

NAC is effective to attenuate leukocytic inflammation and microvascular perfusion failure in critically ischemic tissue. Thus, NAC treatment may represent a promising approach to improve the outcome of ischemically endangered flap tissue.

Comparative effects of captopril and l-carnitine on blood pressure and antioxidant enzyme gene expression in the heart of spontaneously hypertensive rats

It has been shown that oxidative stress is involved in the pathogenesis of arterial hypertension. The aim of this work was to study and compare the molecular mechanisms of the antioxidant properties of l-carnitine and captopril in spontaneously hypertensive rats (SHR). Antioxidant enzyme activity/regulation (glutathione peroxidase, glutathione reductase and superoxide dismutase) was measured in the erythrocytes and hearts of SHR. The molecular expression of endothelial nitric oxide synthase (eNOS), NADPH oxidase, angiotensin converting enzyme (ACE), angiotensin II type I receptor (AT(1) receptor) and NF-kappaB/IkappaB system was also measured in the hearts of these animals. Both l-carnitine and captopril augmented the antioxidant defense capacity in SHRs. This effect was mediated by an upregulation of antioxidant enzymes, an increase in the plasma total antioxidant capacity and a reduction of lipid peroxidation and superoxide anion production in the heart. The administration of both compounds to hypertensive animals also produced an upregulation of eNOS and a normalization of ACE, angiotensin AT(1) receptor, and the NF-kappaB/IkappaB system expression. In addition, captopril reduced the arterial blood pressure and the relative heart weights back to control values, whereas l-carnitine caused only a partial reduction of blood pressure values and did not alter the cardiac hypertrophy found in SHRs. In conclusion, we have found that l-carnitine and captopril have a similar antioxidant effect in the hearts of hypertensive rats. The molecular regulation of antioxidant enzymes through an inhibition of the renin-angiotensin system and a modulation of the NF-kappaB/IkappaB system seems to be responsible for this antioxidant effect.

N-acetylcysteine-induced vasodilation involves voltage-gated potassium channels in rat aorta

AIMS

N-acetylcysteine (NAC) has a protective effect against vascular dysfunction by decreasing the level of reactive oxygen species (ROS) in experimental and human hypertension. This study was designed to examine whether NAC would relax vascular rings in vitro via nitric oxide-cyclic guanosine monophosphate (NO-cGMP) pathway, extracellular Ca2+ and/or K+ channels.

MAIN METHODS

Rat aortic arteries were mounted in an organ bath, contracted with 0.1, 0.5 or 1 micromol/L phenylephrine to plateau, and the vasodilatory effect of NAC was examined in the absence or presence of ROS scavengers, inhibitors of NO-cGMP pathway or K+ channels. Vascular smooth muscle cells (VSMCs) were loaded with a calcium sensitive fluorescent dye fluo-3 AM, and [Ca2+](i) was determined with laser-scanning confocal microscopy.

KEY FINDINGS

NAC (0.1-4 mmol/L) dose-dependently relaxed rat aorta pre-contracted with phenylephrine. Endothelium removal, endothelial nitric oxide synthase inhibitor N(omega)-Nitro-l-arginine (L-NNA) (100 micromol/L) or soluble guanylyl cyclase (sGC) inhibitor (ODQ) (10 micromol/L) did not affect NAC-induced vasodilation. In contrast, NAC-induced vasodilation was blunted after extracellular calcium was removed and calcium imaging showed that 4 mmol/L NAC quickly decreased [Ca2+](i) in fluo-3 AM loaded VSMCs. NAC-induced vasodilation was significantly reduced in the presence of voltage-gated K+ channels (Kv) inhibitor 4-aminopyridine (4-AP).

SIGNIFICANCE

The vasodilatory effect of NAC may be explained at least partly by activation of voltage-gated K+ channels.

Role of oxidative stress in elevated blood pressure induced by high free fatty acids

The aim of the study is to investigate the possible mechanism of oxidative stress in the high free fatty acids (FFAs)-induced hypertension. Male Sprague-Dawley rat models were established and classified into three groups, namely the control group (NC group), the FFA group, and the N-acetylcysteine (NAC) group. Blood pressure (BP) was recorded. An organ chamber experiment was performed to determine endothelium-dependent/-independent vasodilation (EDV/EIV). Reactive oxygen species (ROS), nitrotyrosine, reduced glutathione hormone (GSH) and NO(2)(-)/NO(3)(-) levels were measured in plasma. Endothelial nitric oxide synthase (eNOS) mRNA expression in endothelial cells was evaluated by real-time PCR. The following results were observed: (1) In the FFA group, BP increased after 4 h infusion of Intralipid+heparin. In the NAC group, systolic and diastolic BP remained the same. (2) In the FFA group, the aortic rings tended to show impaired EDV in response to acetylcholine (ACh). There was no difference of EDV response in the NAC and NC groups. (3) In the FFA group, NO(2)(-)/NO(3)(-) levels were significantly reduced, and eNOS mRNA expression and activity were significantly decreased compared with the NC group. NAC administration increased eNOS mRNA expression and activity. (4) ROS and nitrotyrosine concentrations in the FFA group were higher than in the NC group, and GSH concentrations in the FFA group were lower than in the NC group. Elevated FFAs can induce elevated BP, potentially through FFA-induced impairment of EDV resulting from decreased eNOS mRNA expression and activity. Oxidative stress may also play an important role in potential mechanisms of this high FFA-induced elevated BP.

Is urethane-chloralose anaesthesia appropriate for pharmacokinetic-pharmacodynamic assessment? Studies with carvedilol

INTRODUCTION

The aim of the work was to establish the impact of urethane-chloralose anaesthesia on pharmacokinetic-pharmacodynamic (PK-PD) properties of carvedilol in control rats and L-NAME hypertensive animals.

METHODS

Male Wistar Rats were randomly divided into: control (n=12) with tap water to drink and L-NAME rats (n=12) with L-NAME solution (40 mg/kg/day) to drink for 2 weeks. Effects of carvedilol (1 mg kg(-1), i.v.) on blood pressure and heart rate were recorded during 3 h in conscious and urethane (500 mg kg(-1), i.p.) - chloralose (50 mg kg(-1), i.p.) anaesthetized rats. Carvedilol plasma pharmacokinetics was studied by means of traditional blood sampling. PK-PD modeling of carvedilol was made by means of an effect compartment model.

RESULTS

Neither urethane-chloralose nor L-NAME modified estimation of pharmacokinetic parameters of carvedilol. Although urethane-chloralose did not modify potency of carvedilol comparing with awake animals in control and hypertensive group, maximal negative chronotropic response was significantly greater in anaesthetized L-NAME rats in comparison to awake animals. Conversely, anaesthesia did not modify maximal chronotropic response to carvedilol in control rats. Whilst no differences were found in the estimated potency of carvedilol hypotensive response comparing control and L-NAME rats in both awake and anaesthetized conditions, maximal hypotensive effect of carvedilol was significantly greater in anaesthetized control and L-NAME animals in comparison to conscious rats. L-NAME rats showed a greater maximal hypotensive response comparing to control group.

DISCUSSION

Urethane-chloralose anaesthesia is an acceptable experimental condition for the evaluation of PK-PD properties of carvedilol, considering that it does not affect the potency of carvedilol for its chronotropic and hypotensive effect. Conclusions obtained from urethane-chloralose anaesthetized animals, regarding the impact of l-NAME treatment on PK-PD properties of carvedilol, did not differ from those obtained from conscious animals. Anaesthesia did not modify pharmacokinetic behaviour of carvedilol in both normotensive and L-NAME hypertensive rats.

The role of inflammatory markers in the cardioprotective effect of L-carnitine in L-NAME-induced hypertension

BACKGROUND

The mechanism(s) underlying the effects of L-carnitine (beta-hydroxy-gamma-N-trimethylammonium-butyrate; LC) in cardiovascular diseases are not well clarified. Previous studies have demonstrated that oxidative stress and inflammation contribute to arterial hypertension, and antioxidant and/or anti-inflammatory therapies have been proposed. We hypothesized that LC might attenuate the hypertensive status through an inhibition of inflammation process.

METHODS

Heart mRNA expression and plasma levels of inflammatory markers, interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha), were measured in rats that were made hypertensive with N(omega)-nitro-L-arginine methyl ester (L-NAME) and subjected to a simultaneous administration of LC. To clarify the role of the renin-angiotensin system (RAS) in this effect of LC, the activity and expression of angiotensin I-converting enzyme (ACE) as well as the expression of angiotensin II type I receptor (AT1R) in the heart were also determined.

RESULTS

LC produced a significant, but not complete, reduction of blood pressure in L-NAME-treated rats. Plasma levels and heart expression of IL-1 beta, IL-6, and TNF-alpha showed an increase in the L-NAME group, which was reversed by LC treatment. The plasma ACE activity was not modified between normotensive and hypertensive rats although LC treatment produced a reduction of these values in the latter. Finally, protein and mRNA expression of ACE and AT1R was enhanced in the heart of L-NAME-treated animals, and LC reversed these values.

CONCLUSIONS

The chronic administration of LC reduces blood pressure and attenuates the inflammatory process associated with arterial hypertension. LC might produce a partial inactivation in the RAS resulting in a reduction in the production and effects of angiotensin II.

Intermittent hypoxia: cause of or therapy for systemic hypertension?

During acute episodes of hypoxia, chemoreceptor-mediated sympathetic activity increases heart rate, cardiac output, peripheral resistance and systemic arterial pressure. However, different intermittent hypoxia paradigms produce remarkably divergent effects on systemic arterial pressure in the post-hypoxic steady state. The hypertensive effects of obstructive sleep apnea (OSA) vs. the depressor effects of therapeutic hypoxia exemplify this divergence. OSA, a condition afflicting 15-25% of American men and 5-10% of women, has been implicated in the pathogenesis of systemic hypertension and is a major risk factor for heart disease and stroke. OSA imposes a series of brief, intense episodes of hypoxia and hypercapnia, leading to persistent, maladaptive chemoreflex-mediated activation of the sympathetic nervous system which culminates in hypertension. Conversely, extensive evidence in animals and humans has shown controlled intermittent hypoxia conditioning programs to be safe, efficacious modalities for prevention and treatment of hypertension. This article reviews the pertinent literature in an attempt to reconcile the divergent effects of intermittent hypoxia therapy and obstructive sleep apnea on hypertension. Special emphasis is placed on research conducted in the nations of the former Soviet Union, where intermittent hypoxia conditioning programs are being applied therapeutically to treat hypertension in patients. Also reviewed is evidence regarding mechanisms of the pro- and anti-hypertensive effects of intermittent hypoxia.