Nitric oxide inhibition accelerates hypertension and induces perivascular inflammation in rats

Camel (Camelus dromedarius) raw milk’s hypotensive roles within chemical induced hypertension model in rats

Dromedary camels (Camelus dromedarius) inhabit not only arid areas but are among common domestic animals that are normally kept for numerous uses. It’s raw milk (CM) is believed to have exceptional nutraceutical value in addition to it’s other uses similar to camel itself. This study aimed to evaluate hypotensive efficacy of raw CM within context of chemical induced hypertension model in albino rats. Rats received the chemical; L-NAME (50 mg/kg body weight/day, p.o.) and amlodipine (10 mg/kg/day, p.o.) as negative and positive controls for 4 weeks. Rats of treatment group received concurrently L-NAME (50 mg/kg body weight /day, p.o.) and raw milk of camel at (100, 300, and 500 mg/kg body weight/day p.o.) respectively for 4 weeks. Result showed significant decrease (p <  0.001) in treatment relative to negative control in all measured parameters viz systolic, diastolic and mean arterial blood pressures in accordance to the used dosages. Also elevated levels of liver/kidney biomarkers in negative control became reduced compared to normal and positive controls courtesy of CM treatment. In conclusion, obtained data revealed CM to be effective in controlling hypertension. The bioactive constituents present in CM appeared likely to be responsible for the observed effect of antioxidant action and ACE inhibition. Evidence is thus provided from research findings that raw CM can afford efficient hypotensive effect.

Angiotensin II or epinephrine hemodynamic and metabolic responses in the liver of L-NAME induced hypertension and spontaneous hypertensive rats

AIM

To study hepatic vasoconstriction and glucose release induced by angiotensin (Ang)II or Epi in rats with pharmacological hypertension and spontaneously hypertensive rat (SHR).

METHODS

Isolated liver perfusion was performed following portal vein and vena cava cannulation; AngII or epinephrine (Epi) was injected in bolus and portal pressure monitored; glucose release was measured in perfusate aliquots.

RESULTS

The portal hypertensive response (PHR) and the glucose release induced by AngII of L-NAME were similar to normal rats (WIS). On the other hand, the PHR induced by Epi in L-NAME was higher whereas the glucose release was lower compared to WIS. Despite the similar glycogen content, glucose release induced by AngII was lower in SHR compared to Wistar-Kyoto rats although both PHR and glucose release induced by Epi in were similar.

CONCLUSION

AngII and Epi responses are altered in different ways in these hypertension models. Our results suggest that inhibition of NO production seems to be involved in the hepatic effects induced by Epi but not by AngII; the diminished glucose release induced by AngII in SHR is not related to glycogen content.

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.

Damage-associated molecular pattern activated Toll-like receptor 4 signalling modulates blood pressure in L-NAME-induced hypertension

AIMS

Recent publications have shed new light on the role of the adaptive and innate immune system in the pathogenesis of hypertension. However, there are limited data whether receptors of the innate immune system may influence blood pressure. Toll-like receptor 4 (TLR4), a pattern recognition receptor, is a key component of the innate immune system, which is activated by exogenous and endogenous ligands. Hypertension is associated with end-organ damage and thus might lead to the release of damage-associated molecular patterns (DAMPs), which are endogenous activators of TLR4 receptors. The present study aimed to elucidate whether TLR4 signalling is able to modulate vascular contractility in an experimental model of hypertension thus contributing to blood pressure regulation.

METHODS AND RESULTS

NG-nitro-l-arginine methyl ester (l-NAME)-induced hypertension was blunted in TLR4(-/-) when compared with wild-type mice. Treatment with l-NAME was associated with a release of DAMPs, leading to reactive oxygen species production of smooth muscle cells in a TLR4-dependent manner. As oxidative stress leads to an impaired function of the NO-sGC-cyclic GMP (cGMP) pathway, we were able to demonstrate that TLR4(-/-) was protected from sGC inactivation. Consequently, arterial contractility was reduced in TLR4(-/-).

CONCLUSIONS

Cell damage-associated TLR4 signalling might act as a direct mediator of vascular contractility providing a molecular link between inflammation and hypertension.

Female SHR have greater blood pressure sensitivity and renal T cell infiltration following chronic NOS inhibition than males

Nitric oxide is a critical regulator of blood pressure (BP) and inflammation, and female spontaneously hypertensive rats (SHR) have higher renal nitric oxide bioavailability than males. We hypothesize that female SHR will have a greater rise in BP and renal T cell infiltration in response to nitric oxide synthase (NOS) inhibition than males. Both male and female SHR displayed a dose-dependent increase in BP to the nonspecific NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME: 2, 5, and 7 mg·kg(-1)·day(-1) for 4 days each); however, females exhibited a greater increase in BP than males. Treatment of male and female SHR with 7 mg·kg(-1)·day(-1) L-NAME for 2 wk significantly increased BP in both sexes; however, prior exposure to L-NAME only increased BP sensitivity to chronic NOS inhibition in females. L-NAME-induced hypertension increased renal T cell infiltration and indices of renal injury in both sexes, yet female SHR exhibited greater increases in Th17 cells and greater decreases in regulatory T cells than males. Chronic L-NAME was also associated with larger increases in renal cortical adhesion molecule expression in female SHR. The use of triple therapy to block L-NAME-mediated increases in BP attenuated L-NAME-induced increases in renal T cell counts and normalized adhesion molecule expression in SHR, suggesting that L-NAME-induced increases in renal T cells were dependent on both increases in BP and NOS inhibition. Our data suggest that NOS is critical in the ability of SHR, females in particular, to maintain BP and limit a pro-inflammatory renal T cell profile.

Antihypertensive and cardioprotective effects of the Lagenaria siceraria fruit in NG-nitro-L-arginine methyl ester (L-NAME) induced hypertensive rats

CONTEXT

Lagenaria siceraria (Molina) Standl. (Cucurbitacae) (LS) has been reported to possess cardioprotective, antihyperlipidemic, and diuretic activities.

OBJECTIVE

To evaluate antihypertensive and cardioprotective effects of the Lagenaria siceraria fruit powder in N(G)-nitro-L-arginine methyl ester (L-NAME) induced hypertension in rats.

MATERIALS AND METHODS

Male Wistar rats were divided in four groups. Control 2% gum acacia p.o., L-NAME (40 mg/kg p.o.), LS (500 mg/kg p.o.) + L-NAME (40 mg/kg p.o.), L-arginine (100 mg/kg p.o.) + L-NAME (40 mg/kg p.o.). Treatment period was 4 weeks. On day 29 serum marker enzymes, cholesterol and heamodynamic parameters were measured. Histology of heart was performed. LS powder was characterized by HPLC.

RESULT

Systolic blood pressures were increased by L-NAME (p < 0.001). In both drug treated groups systolic and diastolic blood pressures were reduced significantly (p < 0.001) compared to L-NAME. In L-NAME group significantly (p < 0.01) elevated cholesterol which was reduced (p < 0.05) by LS treatment. In L-NAME group inflammation and necrosis (0-35%) was present in heart whereas there was no change in myocardium of LS and L-arginine treated rats. Vitexin, orientin and isoorientin were detected in methanol extract of LS powder.

DISCUSSION AND CONCLUSION

L-NAME induced hypertension in rats was reduced by treatment with LS. The absence of necrosis, inflammation in the heart and significant reduction in serum cholesterol in LS and L-arginine treated rats indicated cardioprotective activity. Antioxidant activity of orientin and isoorientin appears to reduce the L-NAME induced damage. It is concluded that LS fruit possess antihypertensive and cardioprotective activity.

Vascular dysfunction as target organ damage in animal models of hypertension

Endothelial dysfunction is one of the main characteristics of chronic hypertension and it is characterized by impaired nitric oxide (NO) bioactivity determined by increased levels of reactive oxygen species. Endothelial function is usually evaluated by measuring the vasodilation induced by the local NO production stimulated by external mechanical or pharmacological agent. These vascular reactivity tests may be carried out in different models of experimental hypertension such as NO-deficient rats, spontaneously hypertensive rats, salt-sensitive rats, and many others. Wire myograph and pressurized myograph are the principal methods used for vascular studies. Usually, increasing concentrations of the vasodilator acetylcholine are added in cumulative manner to perform endothelium-dependent concentration-response curves. Analysis of vascular mechanics is relevant to identify arterial stiffness. Both endothelial dysfunction and vascular stiffness have been shown to be associated with increased cardiovascular risk.

Short-term ACE inhibition confers long-term protection against target organ damage

Angiotensin converting enzyme (ACE) inhibitors reduce left ventricular (LV) hypertrophy and cardiovascular-renal fibrosis. Experimentally, changes in the LV and kidney persist even after cessation of treatment. The present study investigates whether brief ACE inhibition in spontaneously hypertensive rats (SHR) provides long-term protection against the LV and kidney damage induced by the nitric oxide synthase inhibitor N-ω-nitro-L-arginine-methyl ester (L-NAME). SHR received the ACE inhibitor enalapril (n = 36) or tap water (n = 36). In all, 12 control and treated SHR were sacrificed after 2 weeks and remaining rats were taken off-treatment. After a 2-week washout, 12 controls or previously treated SHR were sacrificed and remaining rats were treated with L-NAME ((control (Con)+L, enalapril (Enal)+L) for 10 days. At sacrifice, blood pressure was recorded via carotid artery cannulation in anesthetized rats, and blood, the kidney and LV were isolated for analysis. LV mass and arterial pressure were significantly reduced by enalapril. LV mass showed a persistent reduction throughout the study. In LV, prior enalapril treatment provided significant (P<0.05) protection against L-NAME-induced increases in proliferating cells (Con+L: 11 ± 10.0 mm(2) vs. Enal+L: 4 ± 4.4 mm(2)), interstitial fibrosis (Con+L: 3 ± 2.5% vs. Enal+L: 1 ± 1.0%) and tissue macrophages (Con+L: 12 ± 9 mm(2) vs. Enal+L: 5 ± 3.6 mm(2)). In the kidney, prior enalapril treatment protected against L-NAME-induced interstitial fibrosis and vascular injury. There was no difference in glomerular size or glomerulosclerosis regardless of prior treatment. Plasma creatinine and urea were significantly increased in L-NAME treated rats. This study suggests that brief ACE inhibition confers protection against future heart and kidney injury, even in the absence of continued antihypertensive treatment.

Effects of freeze-dried cranberry powder on serum lipids and inflammatory markers in lipopolysaccharide treated rats fed an atherogenic diet

This study investigated the effects of freeze-dried cranberry powder on anti-inflammation and lipid profiles of lipopolysaccharide (LPS)-treated rats fed an atherogenic diet for 6 weeks. Forty Sprague-Dawley male rats (6-weeks-old) were equally divided into the following five groups: 1) normal diet group + saline (NC); 2) atherogenic diet + saline (HFC); 3) atherogenic diet + LPS (HL); 4) atherogenic diet with 5% cranberry power + LPS (C5); 5) atherogenic diet with 10% cranberry power + LPS (C10). LPS (0.5 mg/kg) was injected into the abdominal cavities of rats 18 hours prior to sacrifice. At the end of the experimental period, we measured serum lipid profiles as well as levels of serum C-reactive protein (CRP), nitric oxide (NO), and pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, IL-6, and IL-10 as an anti-inflammatory cytokine. The mean serum high density lipoprotein (HDL)-cholesterol level in C5 rats was significantly higher than that in NC and HL rats (P < 0.05). The mean serum levels of CRP and IL-1β were significantly lower (P < 0.05) in the cranberry powder groups compared to those in HL rats. Additionally, mean serum IL-6 levels tended to be lower in the cranberry groups than that in the HL group, whereas serum IL-10 and NO showed 29% and 88% higher mean values in the C5 group and 49% and 24% higher in the C10 group than those in the HL group, respectively. These results suggest that freeze-dried cranberry powder may have beneficial effects on cardiovascular diseases by modifying serum lipids and the early inflammatory response.

Effects of nitric oxide donor and nitric oxide synthase inhibitor on the resistance, exchange and capacitance functions of the canine intestinal vasculature

In the present study, we determined the vascular functions using a canine model of isolated intestinal segment perfused with constant flow. The effects of an NO donor, S-nitroso-N-acetylpenicillamine (SNAP) and an NO synthase inhibitor, N(omega)-nitro-l-arginine methyl ester (l-NAME) on the vascular factors (resistance, exchange and capacitance) were evaluated. In condition of venous pressure at 0 mmHg, we determined and calculated arterial pressure (Pa) and capillary pressure (Pc). Vascular factors including total, pre- and post-capillary resistance (R(T), Ra and Rv), vascular compliance (VC) and capillary filtration coefficient (K(fc)) were obtained. SNAP at doses 10(-6) to 10(-4) mol/l produced vasodilatory effects. It dose-dependently reduced the Pa, Pc, R(T) and Ra, as well as the Ra/Rv ratio. The Rv was slightly decreased. This agent increased the vascular capacity, VC and K(fc). NO inhibition with l-NAME (10(-6) to 10(-4) mol/l) produced the opposite effects. The vasoconstrictory effects of l-NAME increased Pa, Pc, R(T) and Ra as well as the Ra/Rv ratio. It slightly raised the Rv. l-NAME reduced the vascular capacity, VC and K(fc). The effects of l-NAME were also dose-dependent. This study has provided a detailed data of the vasodilatory and vasoconstrictory effects NO donation and inhibition on vascular factors in the intestinal vasculature.

Blood pressure variability, cardiac baroreflex sensitivity and organ damage in experimentally hypertensive rats

1. The present study was designed to investigate the haemodynamic features and morphological changes in experimentally hypertensive rat models. 2. Sprague-Dawley rats were used to prepare the experimentally hypertensive models, including two-kidney, one-clip renovascular hypertensive (2K1C) rats, deoxycorticosterone acetate salt hypertensive (DOCA) rats and N(G)-nitro-l-arginine methyl ester-induced hypertensive (l-NAME) rats. Six weeks after the induction of hypertension, 24 h blood pressure was recorded and blood pressure variability (BPV) expressed by 24 h (or 12 h in the daytime and night-time study) standard deviation of the variables was calculated. Then, cardiac baroreflex sensitivity (BRS) was determined and four endogenous factors (tumour necrosis factor-alpha, interleukin-1beta, angiotensin II and endothelin-1) were measured. Finally, morphological changes were examined. 3. It was found that an increase in BPV and a decrease in BRS were accompanied by an elevation of blood pressure in all three hypertensive models. The DOCA rats had the highest BPV, whereas the l-NAME rats had the lowest BRS. 4. Morphological changes were similar in DOCA and l-NAME rats and the cardiac changes were relatively slight in 2K1C rats. Tumour necrosis factor-alpha was increased in all the three models, especially in DOCA rats. Endothelin-1 was higher in DOCA rats and angiotensin II was increased in 2K1C rats and decreased in DOCA rats. 5. In conclusion, increased BPV and decreased BRS accompanied the elevation of blood pressure in all three hypertensive models. The DOCA rats had the highest BPV and the l-NAME rats had the lowest BRS. Obvious organ damage was seen in all three hypertensive models 6 weeks after the induction of hypertension.