Antihypertensive therapy prevents endothelial dysfunction in chronic nitric oxide deficiency. Effect of verapamil and trandolapril

Dilation of Pregnant Rat Uterine Arteries with Phenols from Extra Virgin Olive Oil Is Endothelium-Dependent and Involves Calcium and Potassium Channels

During pregnancy, uterine vasculature undergoes significant circumferential growth to increase uterine blood flow, vital for the growing feto-placental unit. However, this process is often compromised in conditions like maternal high blood pressure, particularly in preeclampsia (PE), leading to fetal growth impairment. Currently, there is no cure for PE, partly due to the adverse effects of anti-hypertensive drugs on maternal and fetal health. This study aimed to investigate the vasodilator effect of extra virgin olive oil (EVOO) phenols on the reproductive vasculature, potentially benefiting both mother and fetus. Isolated uterine arteries (UAs) from pregnant rats were tested with EVOO phenols in a pressurized myograph. To elucidate the underlying mechanisms, additional experiments were conducted with specific inhibitors: L-NAME/L-NNA (10-4 M) for nitric oxide synthases, ODQ (10-5 M) for guanylate cyclase, Verapamil (10-5 M) for the L-type calcium channel, Ryanodine (10-5 M) + 2-APB (3 × 10-5 M) for ryanodine and the inositol triphosphate receptors, respectively, and Paxilline (10-5 M) for the large-conductance calcium-activated potassium channel. The results indicated that EVOO-phenols activate Ca2+ signaling pathways, generating nitric oxide, inducing vasodilation via cGMP and BKCa2+ signals in smooth muscle cells. This study suggests the potential use of EVOO phenols to prevent utero-placental blood flow restriction, offering a promising avenue for managing PE.

Extra Virgin Olive Oil Phenols Vasodilate Rat MesentericResistance Artery via Phospholipase C (PLC)-CalciumMicrodomains-Potassium Channels (BKCa) Signals

Recent evidence suggests that the reason Extra Virgin Olive Oil (EVOO) lowers blood pressure and reduces the risk of developing hypertension is partly due to minor components of EVOO, such as phenols. However, little is still known about the mechanism(s) through which EVOO phenols mediate anti-hypertensive effects. The aim of the present study was to investigate the mechanisms of action of EVOO phenols on mesenteric resistance arteries. A pressure myograph was used to test the effect of EVOO phenols on isolated mesenteric arteries in the presence of specific inhibitors of: 1) BKca channels (Paxillin, 10^-5 M); 2) L-type calcium channels (Verapamil, 10^-5 M); 3) Ryanodine receptor, RyR (Ryanodine, 10^-5 M); 4) inositol 1,4,5-triphosphate receptor, IP3R, (2-Aminoethyl diphenylborinate, 2-APB, 3 × 10^-3 M); 5) phospholipase C, PLC, (U73122, 10^-5 M), and 6) GPCR-G_αi signaling, (Pertussis Toxin, 10^-5 M). EVOO phenols induced vasodilation of mesenteric arteries in a dose-dependent manner, and this effect was reduced by pre-incubation with Paxillin, Verapamil, Ryanodine, 2-APB, U73122, and Pertussis Toxin. Our data suggest that EVOO phenol-mediated vasodilation requires activation of BKca channels potentially through a local increase of subcellular calcium microdomains, a pivotal mechanism on the base of artery vasodilation. These findings provide novel mechanistic insights for understanding the vasodilatory properties of EVOO phenols on resistance arteries.

In Silico identification of angiotensin-converting enzyme inhibitory peptides from MRJP1

Hypertension is considered as one of the most common diseases that affect human beings (both male and female) due to its high prevalence and also extending widely to both industrialize and developing countries. Angiotensin-converting enzyme (ACE) has a significant role in the regulation of blood pressure and ACE inhibition with inhibitory peptides is considered as a major target to prevent hypertension. In the current study, a blood pressure regulating honey protein (MRJP1) was examined to identify the ACE inhibitory peptides. The 3D structure of MRJP1 was predicted by utilizing the threading approach and further optimized by performing molecular dynamics simulation for 30 nanoseconds (ns) to improve the quality factor up to 92.43%. Root mean square deviation and root mean square fluctuations were calculated to evaluate the structural features and observed the fluctuations in the timescale of 30 ns. AHTpin server based on scoring vector machine of regression models, proteolysis and structural characterization approaches were implemented to identify the potential inhibitory peptides. The anti-hypertensive peptides were scrutinized based on the QSAR models of anti-hypertensive activity and the molecular docking analyses were performed to explore the binding affinities and potential interacting residues. The peptide "EALPHVPIFDR" showed the strong binding affinity and higher anti-hypertensive activity along with the global energy of -58.29 and docking score of 9590. The aromatic amino acids especially Tyr was observed as the key residue to design the dietary peptides and drugs like ACE inhibitors.

Practicality and importance of selected endothelial dysfunction measurement techniques: review

The measurement of endothelial dysfunction (ED) has importance in that it indicates the presence of coronary artery disease (Kuvin et al. in J Am Coll Cardiol 38(7):1843-1849, 2001) in addition to acting as a predictor of future adverse events (Halcox et al. in Circulation 106:653-658, 2002). Various tools, methods, and metrics exist that can provide an indicator of endothelial dysfunction. Given the significance of ED, it is of utmost importance to find a measurement technique that is reliable, while defining a metric providing a framework for an overall system that is practical, accurate, and repeatable. Success would provide a tool for the early detection of cardiovascular disease not only moving patients that are currently classified as asymptomatic to symptomatic, but also providing a method to monitor the efficacy of treatments.

Gal-geun-dang-gwi-tang improves diabetic vascular complication in apolipoprotein E KO mice fed a western diet

BACKGROUND

Gal-geun-dang-gwi-tang (GGDGT), an herbal medicine, is used to treat hypertension, stroke, and other inflammatory disorders in the clinical setting. Recently, GGDGT was recognized by the Korea Institute of Oriental Medicine. This study aimed to evaluate the effects of GGDGT in a diabetic atherosclerosis model using apolipoprotein E knockout (ApoE-/-) mice fed a Western diet.

METHODS

The mice were divided into four groups: control group, C57BL6J mice receiving a regular diet (RD); ApoE-/- group, ApoE-/- mice receiving a Western diet (WD); rosiglitazone group, ApoE-/- mice receiving rosiglitazone (WD + 10 mg · kg(-1) · day(-1)); GGDGT group, ApoE-/- mice receiving GGDGT (WD + 200 mg · kg(-1) · day(-1)).

RESULTS

Treatment with GGDGT significantly improved glucose tolerance and plasma lipid levels. In addition, GGDGT ameliorated acetylcholine-induced vascular relaxation of the aortic rings. Immunohistochemical staining showed that GGDGT suppressed intercellular adhesion molecule (ICAM)-1 expression; however, expression of endothelial nitric oxide synthase (eNOS) and insulin receptor substrate (IRS)-1 were restored in the thoracic aorta and skeletal muscle, respectively.

CONCLUSIONS

These findings suggest that GGDGT attenuates endothelial dysfunction via improvement of the nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) signalling pathway and improves insulin sensitivity in diabetic atherosclerosis.

Endothelium-derived Relaxing Factors of Small Resistance Arteries in Hypertension

Endothelium-derived relaxing factors (EDRFs), including nitric oxide (NO), prostacyclin (PGI₂), and endothelium-derived hyperpolarizing factor (EDHF), play pivotal roles in regulating vascular tone. Reduced EDRFs cause impaired endothelium-dependent vasorelaxation, or endothelial dysfunction. Impaired endothelium-dependent vasorelaxation in response to acetylcholine (ACh) is consistently observed in conduit vessels in human patients and experimental animal models of hypertension. Because small resistance arteries are known to produce more than one type of EDRF, the mechanism(s) mediating endothelium-dependent vasorelaxation in small resistance arteries may be different from that observed in conduit vessels under hypertensive conditions, where vasorelaxation is mainly dependent on NO. EDHF has been described as one of the principal mediators of endothelium-dependent vasorelaxation in small resistance arteries in normotensive animals. Furthermore, EDHF appears to become the predominant endothelium-dependent vasorelaxation pathway when the endothelial NO synthase (NOS3)/NO pathway is absent, as in NOS3-knockout mice, whereas some studies have shown that the EDHF pathway is dysfunctional in experimental models of hypertension. This article reviews our current knowledge regarding EDRFs in small arteries under normotensive and hypertensive conditions.

Alagebrium (ALT-711) improves the anti-hypertensive efficacy of nifedipine in diabetic-hypertensive rats

Combining drugs with complementary mechanisms of action may contribute to improved hypertension control in diabetic patients. Advanced glycation end-product (AGE) breakers, a new class of candidate drugs targeting aging-related cardiovascular dysfunction, may be useful as novel adjuvant agents to improve the efficacy of diabetic hypertension (DH) treatment. This study evaluated the effects of alagebrium (ALT-711), an AGE breaker, combined with nifedipine, a Ca(2+) channel blocker, in a rat model of streptozotocin-induced DH. Compared with monotherapy, combination treatment significantly decreased systolic and diastolic blood pressure values, increased the pulse pressure, and decreased the coefficient of variation of the systolic blood pressure. Plasma biochemistry indicated that the concentrations of prostacyclin and nitric oxide were increased. Gene expression analysis showed significantly decreased prepro-endothelin-1expression in the aorta. These results reveal that alagebrium significantly improves the anti-hypertensive actions of nifedipine in a rat model of DH and suggest its potential use in the successful control of clinical DH.

Doinseunggitang ameliorates endothelial dysfunction in diabetic atherosclerosis

Atherosclerosis, a chronic and progressive disease characterized by vascular inflammation, is a leading cause of death in diabetes patients. Doinseunggitang (DYSGT), traditional prescription, has been used for promoting blood circulation to remove blood stasis. The aim of this study was to investigate the beneficial effects of DYSGT on endothelial dysfunction in diabetic atherosclerosis animal model. Apolipoprotein E knockout (ApoE KO) mice fed on a Western diet were treated with DYSGT (200 mg/kg/day). DYSGT significantly lowered blood glucose level and glucose tolerance as well as systolic blood pressure. Metabolic parameter showed that DYSGT markedly decreased triglyceride and LDL-cholesterol levels. In the thoracic aorta, the impairment of vasorelaxation response to acetylcholine and atherosclerotic lesion was attenuated by DYSGT. Furthermore, DYSGT restored the reduction of endothelial nitric oxide synthase (eNOS) expression, leading to the inhibition of intracellular adhesion molecule-1 (ICAM-1) and endothelin-1 (ET-1) expression. In conclusion, DYSGT improved the development of diabetic atherosclerosis via attenuation of the endothelial dysfunction, possibly by inhibiting ET-1, cell adhesion molecules, and lesion formation. Therefore, these results suggest that Korean traditional prescription Doinseunggitang may be useful in the treatment and prevention of diabetic vascular complications.

Arctium lappa ameliorates endothelial dysfunction in rats fed with high fat/cholesterol diets

Background

Arctium lappa L. (Asteraceae), burdock, is a medicinal plant that is popularly used for treating hypertension, gout, hepatitis, and other inflammatory disorders. This study was performed to test the effect of ethanol extract of Arctium lappa L. (EAL) seeds on vascular reactivity and inflammatory factors in rats fed a high fat/cholesterol diet (HFCD).

Method

EAL-I (100 mg·kg⁻¹/day), EAL-II (200 mg·kg⁻¹/day), and fluvastatin (3 mg·kg⁻¹/day) groups initially received HFCD alone for 8 weeks, with EAL supplementation provided during the final 6 weeks.

Results

Treatment with low or high doses of EAL markedly attenuated plasma levels of triglycerides and augmented plasma levels of high-density lipoprotein (HDL) in HFCD-fed rats. Chronic treatment with EAL markedly reduced impairments of acetylcholine (ACh)-induced relaxation of aortic rings. Furthermore, chronic treatment with EAL significantly lowered systolic blood pressure (SBP) and maintained smooth and flexible intimal endothelial layers in HFCD-fed rats. Chronic treatment with EAL suppressed upregulation of intercellular adhesion molecule (ICAM)-1, vascular cell adhesion molecule (VCAM)-1, and E-selectin in the aorta. Chronic treatment with EAL also suppressed increases in matrix metalloproteinase (MMP)-2 expression. These results suggested that EAL can inhibit HFCD-induced vascular inflammation in the rat model.

Conclusion

The present study provides evidence that EAL ameliorates HFCD-induced vascular dysfunction through protection of vascular relaxation and suppression of vascular inflammation.

Hypotensive, Hypolipidemic, and Vascular Protective Effects of Morus alba L. in Rats Fed an Atherogenic Diet

Morus alba L. has been used in traditional Chinese medicine and almost all parts of this plant are useful in cardiovascular, liver and spleen disorders. The present study was designed to investigate the inhibitory effect of a water extract from Morus alba L. (WMA) on vascular dysfunction in rat models fed a high fat and high cholesterol diet. Male rats were fed an atherogenic diet consisting of food with 7.5% cocoa butter and 1.25% cholesterol, with or without 100 or 200 mg/day/kg WMA, for 14 weeks. Chronic treatment with low (100 mg/kg/day) or high (200 mg/day/kg) doses of WMA markedly attenuated hypertension and the impairments of acetylcholine-induced relaxation of aortic rings in rats fed an atherogenic diet. WMA reduced intima/media thickness in rats fed an atherogenic diet. WMA improved plasma levels of triglyceride (TG) and augmented plasma levels of high-density lipoprotein (HDL) and plasma low-density lipoprotein (LDL), but did not affect blood glucose levels. Interestingly, WMA suppressed increased cell adhesion molecules such as E-selectin, vascular cell adhesion molecule-1 (VCAM-1), and intracellular adhesion molecule-1 (ICAM-1) expression in the aorta. Taken together, these results suggested that Morus alba L. could improve an atherogenic diet-induced hypertension, hyperlipidemia, and vascular dysfunction through inhibition of cell adhesion molecules expression and induction of vascular relaxation.

Sex differences in primary hypertension

Men have higher blood pressure than women through much of life regardless of race and ethnicity. This is a robust and highly conserved sex difference that it is also observed across species including dogs, rats, mice and chickens and it is found in induced, genetic and transgenic animal models of hypertension. Not only do the differences between the ovarian and testicular hormonal milieu contribute to this sexual dimorphism in blood pressure, the sex chromosomes also play a role in and of themselves. This review primarily focuses on epidemiological studies of blood pressure in men and women and experimental models of hypertension in both sexes. Gaps in current knowledge regarding what underlie male-female differences in blood pressure control are discussed. Elucidating the mechanisms underlying sex differences in hypertension may lead to the development of anti-hypertensives tailored to one's sex and ultimately to improved therapeutic strategies for treating this disease and preventing its devastating consequences.

Improved endothelial dysfunction by Cynanchum wilfordii in apolipoprotein E(-/-) mice fed a high fat/cholesterol diet

Cynanchum wilfordii is used in traditional Chinese medicine with almost all parts of this plant considered beneficial for various vascular diseases. This study was performed to evaluate the effect of an ethanol extract of C. wilfordii (ECW) on vascular dysfunction in apolipoprotein E (apoE)(-/-) mice fed with high fat/cholesterol diets (HFCDs). The apoE(-/-) mice were fed HFCD consisting of 7.5% cocoa butter and 1.25% cholesterol, with or without 100 or 200 mg/day/kg ECW. Chronic ECW treatment significantly lessened the level of low-density lipoprotein (P<.05) and elevated that of high-density lipoprotein-cholesterol (P<.01). Chronic ECW treatment normalized the HFCD-induced increase in systolic blood pressure, maintained smooth and soft intimal endothelial layers, and decreased intima-media thickness in aortic sections of HFCD-fed apoE(-/-) mice. ECW significantly restored the diet-induced decrease in vasorelaxation response to acetylcholine; however, the response to sodium nitroprusside did not change. ECW clearly restored the HFCD-induced reduction in endothelial nitric oxide synthase expression levels in aortic tissue, leading to decreased vascular inflammation through an inhibition of cellular adhesion molecules such as E-selectin, vascular cell adhesion molecule-1, and intracellular adhesion molecule-1 as well as endothelin-1 (ET-1) expression. In conclusion, ECW ameliorates endothelial dysfunction via improvement of the nitric oxide/cyclic GMP signaling pathway in a diet/genetic model of hyperlipidemia. ECW also substantially inhibited the development of atherosclerosis, possibly by inhibiting ET-1, cell adhesion molecules, and lesion formation, suggesting a vascular protective role for this herb in the treatment and prevention of atherosclerotic vascular disease.

Effects of hyperglycemia on the modulation of vascular function by perivascular adipose tissue

OBJECTIVE

To study the acute and chronic effect of hyperglycemia on perivascular adipose tissue (PVAT) function in rat aorta.

METHOD

Alterations in PVAT function in rat aorta incubated with 22 mmol/l D-glucose for 30 min and in aorta from streptozotocin (STZ)-induced diabetic rats were studied.

RESULTS

Incubation with D-glucose caused an attenuation of contraction in response to phenylephrine, both in the presence and absence of endothelium, whereas removal of PVAT eliminated this attenuation effect. The presence of PVAT did not affect concentration-related relaxation response of the aorta to carbamylcholine in STZ rats. There was also no difference in the relaxation response of the aorta to carbamylcholine between STZ and control rats. The presence of PVAT, however, caused a higher attenuation of the concentration-dependent contraction to phenylephrine in aorta from STZ rats with intact endothelium as compared with that from control rats. Incubation of the aorta from control rats with Nomega-nitro-L-arginine or carboxy-2-phenyl-4,4,5,5-tetra-methyl-imidazoline-1-oxyl-3-oxide potentiated the contraction of the vessels to phenylephrine, and this potentiation effect was higher in the vessels from STZ rats than control rats when N-nitro-L-arginine was used. Removal of PVAT reduced this potentiation effect and eliminated the difference between the vessels from control and STZ rats.

CONCLUSION

Under both acute and chronic conditions, hyperglycemia enhanced the relaxation response of the vessels mediated by PVAT. These new findings provide important information on the mechanism underlying the postprandial effect of hyperglycemia on blood pressure control and the presence of hypotension under chronic hyperglycemia in a type-1 model of diabetes.

Impact of diet and stress on the development of preeclampsia-like symptoms in p57kip2 mice

The cyclin-dependent kinase inhibitor p57kip2 regulates the cell cycle of trophoblastic cells. It has been established by a Japanese group that the heterozygous p57kip2 knockout (p57−/+) mice are a good model of preeclampsia as they develop hypertension, proteinuria, and placental pathology. However, apart from the placental pathology, we could not observe these symptoms in our laboratory. Hence, we investigated the impact of diet and stress on this model. To do so, we compared the effects of the Japanese diet to that of the North American diet used by our animal facility. Furthermore, the impact of stress was determined by placing the mice in a restraining device before and at the end of gestation. Although the Japanese diet did not have any impact on blood pressure or proteinuria, the mice did develop endothelial dysfunction, left ventricular hypertrophy, as well as increased placental pathology. Also, all mice had smaller litters when fed the Japanese diet. However, stress response of these mice was not increased during gestation; in fact, a decrease was observed in the p57−/+ mice, suggesting that this was probably not a player in the development of the pathology. Taken together, these results suggest that other environmental factors may have been implicated in the development of preeclampsia-like symptoms in this animal model. Moreover, we demonstrated that placental pathology and genetic factors are not sufficient to trigger preeclampsia-like symptoms in this model and that the diet might play an important part in the development of this multifactorial disease.

Different effects of angiotensin converting enzyme inhibitors on endothelin-1 and nitric oxide balance in human vascular endothelial cells: evidence of an oxidant-sensitive pathway

Angiotensin converting enzyme inhibitors (ACE-I) are able to reduce the formation of the potent vasoconstrictor endothelin-1 and increase nitric oxide bioavailability in human vascular endothelial cells (HUVECs). We tested the effects of two sulfhydryl-containing ACE-I, zofenoprilat, and captopril, and two nonsulfhydryl containing ACE-I, enalaprilat and lisinopril, on endothelin-1/nitric oxide balance and oxidative stress in HUVECs. All the four tested ACE-I reduced endothelin-1 secretion and increased nitric oxide metabolite production by HUVECs. However, zofenoprilat (−42% after 8 hours of incubation) was more effective (P < .05) than enalaprilat (−25%), lisinopril (−21%), and captopril (−30%) in reducing endothelin-1 secretion. Similarly, zofenoprilat (+110% after 8 hours of incubation) was more effective (P < .05) than enalaprilat (+64%), lisinopril (+63%), and captopril (+65%) in increasing nitric oxide metabolite production. The effect of ACE-I on endothelin-1 and nitric oxide metabolite production is mediated by the activation of bradykinin B₂ receptor being counteracted, at least in part, by a specific antagonist. Zofenoprilat and, to a lesser extent, captopril also reduced oxidative stress in HUVECs. In conclusion, among the four tested ACE-I, zofenoprilat was more effective in improving endothelin-1/nitric oxide balance in HUVECs likely because of its greater antioxidant properties.

Anti-hypertensive effects of the methanol/methylene chloride stem bark extract of Mammea africana in l-NAME-induced hypertensive rats

AIM OF THE STUDY

The methanol/methylene chloride (CH(3)OH/CH(2)Cl(2)) extract from the stem bark of Mammea africana was showed to possess vasodilating effect in the presence and the absence of N(omega)-nitro-l-arginine methyl ester (l-NAME). The present study was designed to evaluate the effects of the methanol/methylene chloride from the stem bark of Mammea africana.

MATERIALS AND METHODS

The extract (200 mg/(kg day)) was administered orally in rats treated concurrently with l-NAME (40 mg/(kg day)). l-Arginine (100 mg/(kg day)) and captopril (20 mg/(kg day))were used as positive controls. Bodyweight, systolic arterial blood pressure and heart rate were measured weekly throughout the experiment period (28 days). At the end of treatment, animals were killed and the cardiac mass index evaluated. The aorta was used to evaluate the endothelium-dependant relaxation to carbachol. The aorta contraction induced by noradrenalin was also examined and expressed as a percentage of that induced by KCl.

RESULTS

The extract neither affected the body weight nor the heart rate. The extract as captopril completely prevented the development of arterial hypertension. Both the substances failed to restore the endothelium-dependent vascular relaxation and increased the vascular contraction to norepinephrine in relation to KCl contraction. They also significantly reduced the left ventricular hypertrophy induced by l-NAME.

CONCLUSION

These findings are in agreement with the traditional use of Mammea africana in the treatment of arterial hypertension and indicate that it may have a beneficial effect in patients with NO deficiency but will be unable to improve their endothelium-dependent vasorelaxation.

The vascular endothelium in hypertension

The vascular endothelium plays a fundamental role in the basal and dynamic regulation of the circulation. Thus, it has a crucial role in the pathogenesis of hypertension. A spectrum of vasoactive substances is synthesised in the endothelium; of these, nitric oxide (NO), prostacyclin (PGI2) and endothelin (ET)-1 are the most important. There is a continuous basal release of NO determining the tone of peripheral blood vessels. Systemic inhibition of NO synthesis or scavenging of NO through oxidative stress causes an increase in arterial blood pressure. Also, the renin-angiotensin-aldosterone system has a major role in hypertension as it has a direct vasoconstrictor effect and important interactions with oxygen free radicals and NO. Prostacyclin, in contrast to NO, does not contribute to the maintenance of basal vascular tone of conduit arteries, but its effect on platelets is most important. ET acts as the natural counterpart to endothelium-derived NO and has an arterial blood pressure-raising effect in man. Anti-hypertensive therapy lowers blood pressure and may influence these different mediators, thus influencing endothelial function. In summary, due to its position between the blood pressure and smooth muscle cells responsible for peripheral resistance, the endothelium is thought to be both victim and offender in arterial hypertension. The delicate balance of endothelium-derived factors is disturbed in hypertension. Specific anti-hypertensive and anti-oxidant treatment is able to restore this balance.

Angiotensin II type 1 receptor antagonism improves endothelial vasodilator function in L-NAME-induced hypertensive rats by a kinin-dependent mechanism

OBJECTIVE

This study was designed to investigate the ability of a chronic blockade of angiotensin II type 1 receptors with losartan to reverse the endothelial dysfunction present in N-nitro-L-arginine methyl ester (L-NAME)-treated hypertensive rats and the possible dependence of this effect on bradykinin B2-receptor activation.

METHODS

Rats treated with L-NAME alone (60 mg/kg per day for 8 weeks) or with L-NAME + losartan, L-NAME + icatibant (a bradykinin B2-receptor antagonist) and L-NAME + losartan + icatibant were studied. Losartan, icatibant or losartan + icatibant were co-administered with L-NAME during the last 4 weeks of the experiment. Endothelial nitric oxide synthase gene expression in aortic tissues, plasma nitrite/nitrate concentrations, the relaxant effect of acetylcholine on norepinephrine-precontracted aortic rings and 6-keto-PGF1alpha release from aortic rings were used as markers of the endothelial function.

RESULTS

Rats treated with L-NAME alone and L-NAME + icatibant showed, as compared with untreated animals, a clear-cut increase in systolic blood pressure and a decrease of all the markers of endothelial function evaluated. In L-NAME-rats, administration of losartan reduced the systolic blood pressure and restored endothelial nitric oxide synthase gene expression, plasma nitrite/nitrate levels, the relaxant activity of acetylcholine on aortic rings and the generation of 6-keto-PGF1alpha from the aortic tissues. Co-administration of icatibant with losartan blunted the stimulatory effect of losartan on the markers of endothelial function evaluated.

CONCLUSION

These results demonstrated that losartan is capable of reversing the endothelial vasodilator dysfunction in L-NAME-induced hypertensive rats, and that the beneficial effect of losartan is mediated by bradykinin B2-receptor activation.

New methods to evaluate endothelial function: Evaluation of endothelial function by hemoglobin-nitric oxide complex using electron paramagnetic resonance spectroscopy

This minireview describes the practical use of assay systems to detect nitric oxide (NO) by electron paramagnetic resonance (EPR) spectroscopy for evaluation of endothelial functions. The iron(II)-dithiocarbamate complexes, such as iron(II)-(N-methyl-D-glucamine dithiocarbamate), are commonly used in EPR detection of NO both in vivo and in vitro. However, due to their redox activity, these complexes have some drawbacks that limit their usefulness for the detection of NO. On the other hand, the measurement of hemoglobin-NO adduct (HbNO) in whole blood by the EPR method seems relevant for the assessment of systemic NO levels. However, ceruloplasmin and an unknown radical species overlapping the same magnetic field as that of HbNO, which makes it physically impossible to measure small amounts of HbNO. Thus, to reveal the EPR spectrum of HbNO, we developed the EPR signal subtraction method, which is based on the computer-assisted subtraction of the digitized EPR spectrum of HbNO-depleted blood from that of the sample blood using software. Using this technique, we succeeded in measuring the steady blood HbNO level as an index of NO by the EPR HbNO signal subtraction method. We also demonstrated that temocapril reduces abnormalities of NO dynamics in the L-NAME (N(omega)-nitro-L-arginine-methylester)-induced endothelial dysfunction of rats using the EPR HbNO signal subtraction method.

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.

Prostacyclin and thromboxane A2 production in nitric oxide-deficient hypertension in vivo. Effects of high calcium diet and angiotensin receptor blockade

The effects of chronic nitric oxide deficiency on prostacyclin and thromboxane A(2) production in vivo are unknown. Therefore, we treated rats with N(G)-nitro-L-arginine methyl ester (L-NAME), and used losartan and high calcium diet as antihypertensive treatments. Forty eight Wistar rats were divided into six groups: control; losartan (20mgkg(-1)day(-1)); high calcium diet (dietary calcium elevated from 1.1% to 3%); L-NAME (20mgkg(-1)day(-1)); losartan+L-NAME and high calcium diet+L-NAME. Prostacyclin and thromboxane A(2) production were measured after eight weeks as urinary 2,3-dinor-6-keto-PGF(1alpha) and 11-dehydro-TXB(2), respectively. Both the high calcium diet and losartan reduced blood pressure in L-NAME hypertension. Chronic nitric oxide deficiency did not modulate prostacyclin production but it nearly doubled thromboxane A(2) production in vivo. This effect was not influenced by lowering of blood pressure by blockade of angiotensin II type 1 receptors. Independent of the level of blood pressure and blockade of nitric oxide synthesis the high calcium diet decreased prostacyclin production by one third and increased thromboxane A(2) production almost two-fold in vivo.

ERK1/2-mediated vasoconstriction normalizes wall stress in small mesenteric arteries during NOS inhibition in vivo

As in essential hypertension, chronic nitric-oxide synthase (NOS) inhibition leads to hypertrophic remodeling in conduit and muscular arteries and inward eutrophic remodeling in small resistance arteries with activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) in both vessel types. The authors tested the hypothesis that this remodeling heterogeneity could be related to distinct vasoreactivity patterns in small and larger arteries, with a vessel-specific function of ERK1/2 signaling. Using intravital microscopy in rats we have demonstrated that acute NOS inhibition (l-NA injection, 100 mg/kg) produced vasoconstriction of small mesenteric arteries. Consequently, the calculated in vivo wall stress was not significantly modified, despite the local rise in pressure. This could explain the lack of vascular protein synthesis elevation in vivo, an early index of hypertrophy. Inhibition of ERK1/2 activation with PD98059 blunted mesenteric artery contractions. Femoral arteries did not contract and were thus submitted to an enhanced wall stress and underwent hypertrophic remodeling in chronic conditions. In conclusion, the heterogeneous vascular remodeling in the l-NAME model is associated with a heterogeneous vasoconstriction response to acute NOS inhibition. Indeed, in contrast to larger arteries, l-NA-induced vasoconstriction in small arteries normalized wall stress and prevented early signs of hypertrophy. The results also suggest that ERK1/2 is a signaling element in NOS inhibition-induced vasoconstriction of small arteries in vivo.

Evaluation of systemic blood NO dynamics by EPR spectroscopy: HbNO as an endogenous index of NO

The measurement of hemoglobin-nitric oxide (NO) adduct (HbNO) in whole blood by the electron paramagnetic resonance (EPR) method seems relevant for the assessment of systemic NO levels. However, ceruloplasmin and unknown radical species overlap the same magnetic field as that of HbNO. To reveal the EPR spectrum of HbNO, we then introduced the EPR signal subtraction method, which is based on the computer-assisted subtraction of the digitized EPR spectrum of HbNO-depleted blood from that of sample blood using the software. Rats were treated with N(omega)-nitro-L-arginine methyl ester (L-NAME; 120 mg. kg-1. day-1) for 1 wk to obtain HbNO-depleted blood. When this method was applied to the analysis of untreated fresh whole blood, the five-coordinate state of HbNO was observed. HbNO concentration in pentobarbital-anesthetized rats was augmented (change in [HbNO] = 1.6-5.5 microM) by infusion of L-arginine (0.2-0.6 g/kg) but not D-arginine. Using this method, we attempted to evaluate the effects of temocapril on HbNO dynamics in an L-NAME-induced rat endothelial dysfunction model. The oral administration of L-NAME for 2 wk induced a serious hypertension, and the HbNO concentration was reduced (change in [HbNO] = 5.7 microM). Coadministration of temocapril dose dependently improved both changes in blood pressure and the systemic HbNO concentration. In this study, we succeeded in measuring the blood HbNO level as an index of NO by the EPR HbNO signal subtraction method. We also demonstrated that temocapril improves abnormalities of NO dynamics in L-NAME-induced endothelial dysfunction rats using the EPR HbNO signal subtraction method.

[Endothelium-derived factors in hypertensive blood vessels, especially nitric oxide and hypertension]

Endothelium-dependent relaxation (EDR) in the blood vessels of spontaneously hypertensive rats (SHR) and the role of nitric oxide (NO) in the initiation of hypertension are reviewed. EDR was impaired in blood vessels of SHR depending on age and degree of hypertension when compared with those of normotensive rats. The cause of the impairment varied among the type of blood vessels: a decrease in the production of NO and endothelium-derived relaxing factor (EDRF) and an increase in the production of endothelium-derived contracting factor (EDCF) are the main causes of the impairment in large arteries, while a decrease in endothelium-dependent hyperpolarization and increased release of EDCF are the main causes of the impairment in small arteries. Interactions among these endothelium-derived factors and changes in the interactions are also causes of impairment. Superoxide may be involved in the impairment of EDR by destroying NO. The endothelium depresses smooth muscle contraction, including spontaneous tone developed in vascular smooth muscle, and the depressing effect of the endothelium is impaired in the preparations from SHR. The endothelium of blood vessels of SHR are structurally injured as demonstrated by scanning electron microscopy. Antihypertensive treatment prevented these functional and structural changes. Chronic treatment with inhibitors of NO production in normotensive rats impaired EDR and elevated blood pressure. The impairment of EDR is a secondary change due to continued hypertension, and early initiation of antihypertensive therapy is recommended.

Chronic inhibition of nitric oxide synthase induces hypertension and cardiomyocyte mitochondrial and myocardial collagen remodelling in the absence of hypertrophy

OBJECTIVES

To evaluate the morphometric and ultrastructural alterations of the heart produced by long-term inhibition of nitric oxide (NO) synthase with N(omega)-nitro-l-arginine methyl ester (l-NAME) and to examine whether the changes are caused by l-NAME-induced hypertension or a lack of NO.

METHODS

Male Wistar rats were divided randomly into three sets: control group, standard diet/l-NAME-treated group, and standard diet/l-NAME + captopril-treated group.

RESULTS

Chronic inhibition of NO synthesis with l-NAME given for 4 weeks promoted a time-dependent hypertensive response which was not accompanied by an increase in cardiac mass, myocellular hypertrophy or other evidence of myocyte damage. However, this response was associated with left ventricular cardiomyocyte mitochondrial remodelling and discrete interstitial fibrosis in both the left and right ventricles. The remodelling was characterized by an increase in the number and size of mitochondria. Importantly, systolic pressure overload did not result in left ventricle decompensation. The concomitant treatment with l-NAME and captopril abolished the development of hypertension and left ventricular cardiomyocyte subcellular remodelling, but not the discrete interstitial fibrosis in the left and right ventricle.

CONCLUSIONS

The present study suggests that, in the l-NAME model of hypertension, decreased NO production could be an important means of controlling cardiovascular hypertensive stress by regulating mitochondrial biogenesis and function in the tissue. On the other hand, discrete interstitial ventricular myocardial fibrosis observed in l-NAME-treated rats, either hypertensive or rendered normotensive with captopril, clearly indicates that this response depends on a process associated with NO insufficiency.

Endothelium-dependent relaxation in pulmonary arteries of L-NAME-treated Wistar and stroke-prone spontaneously hypertensive rats

To evaluate whether the elevated blood pressure induced by chronic treatment with N(omega)-nitro-L-arginine methyl ester (L-NAME) contributes to an impairment of endothelium-dependent relaxation (EDR), the effects of chronic treatment of Wistar rats with L-NAME on systolic blood pressure, pulmonary arterial blood pressure and EDR of the pulmonary arteries were studied and compared with those of stroke-prone spontaneously hypertensive rats (SHRSP). While the systolic blood pressure (SBP) of Wistar rats was increased above that of controls by chronic treatment with L-NAME, it was still significantly lower than that of SHRSP. Chronic treatment with L-NAME did not affect pulmonary arterial blood pressure. On the other hand, the pulmonary arterial blood pressure of SHRSP was slightly but significantly higher than that of the control normotensive Wistar Kyoto rats (WKY). EDR in response to acetylcholine in the pulmonary artery of L-NAME-treated rats was significantly smaller than that in control Wistar rats. The EDR markedly increased in the presence of L-arginine and completely disappeared in the presence of N(omega)-nitro-L-arginine. Indomethacin hardly affected EDR. In preparations from SHRSP, the EDR was not different from that in those from WKY. Relaxation induced by sodium nitroprusside was identical in all preparations. Elevation of SBP and the impairment of EDR observed in L-NAME-treated rats recovered two weeks following cessation of treatment. These results suggest that the impaired EDR in the pulmonary artery of L-NAME-treated rats is not due to an L-NAME-induced increase in blood pressure but due to the inhibition of nitric oxide synthase by the drug remaining in the endothelium.

Verapamil improves the pacing-induced vasodilatation in symptomatic patients with hypertrophic cardiomyopathy

The purpose of the study was to assess the effect of verapamil on the response of diastolic coronary flow velocity and coronary vascular resistance to pacing in symptomatic patients with hypertrophic cardiomyopathy. In 14 patients with hypertrophic cardiomyopathy, the coronary flow velocity was detected in the left anterior descending coronary artery using transthoracic Doppler echocardiography. The peak diastolic coronary flow velocity and coronary vascular resistance was measured at baseline and during pacing. Changes of these parameters induced by the pacing (expressed as the percentage of baseline values) were compared on verapamil treatment and after verapamil withdrawal. The same measurements were obtained in ten control subjects. The results show that, in hypertrophic cardiomyopathy patients, increase in coronary flow velocity during pacing was significantly higher on than off verapamil therapy (64.8+/-32.5 vs. 41.1+/-21.3%, P<0.05). In control subjects, pacing-induced increase in coronary flow velocity was comparable to changes in coronary flow velocity in hypertrophic cardiomyopathy patients receiving verapamil (80.2+/-18.4 vs. 64.8+/-32.5%, P>0.05). After verapamil withdrawal in hypertrophic cardiomyopathy patients, coronary flow velocity increase during pacing was significantly lower than in control subjects (41.1+/-21.3 vs. 80.2+/-18.4%, P<0.05). During pacing the coronary vascular resistance decreased more on verapamil than after drug withdrawal (-34.7+/-11.7 vs. -24.6+/-12.9%, P<0.05). In control subjects the coronary vascular resistance decreased during pacing -38.6+/-6.3% to similar extent as in hypertrophic cardiomyopathy patients on verapamil. We can conclude that endothelium-dependent vasodilatation during pacing was impaired in symptomatic patients with hypertrophic cardiomyopathy. Verapamil treatment was able to restore adequate vasodilator response to pacing stress.

Effects of antihypertensive drugs on endothelial dysfunction: clinical implications

Essential hypertension is associated with endothelial dysfunction, which is caused mainly by the production of oxygen-free radicals that can destroy nitric oxide (NO), and impair its beneficial and protective effects on the vessel wall. In prospective studies, endothelial dysfunction is associated with increased incidence of cardiovascular events. Antihypertensive drugs show contrasting effects in terms of improvement or restoration of endothelial function. Little evidence is available with beta-blockers. Whereas treatment with atenolol has a negative effect in peripheral subcutaneous and muscle microcirculation, insufficient evidence is available to establish whether new compounds such as nebivolol, which activates the L-Arginine--NO pathway, and carvedilol, which has strong antioxidant activity, can improve endothelial function in patients with hypertension. Calcium channel antagonists, particularly the dihydropyridines, can reverse impaired endothelium-dependent vasodilation in different vascular districts, including the subcutaneous, epicardial, renal and forearm circulation. However, conflicting results are found in the brachial artery. In the forearm circulation, nifedipine and lacidipine can improve endothelial dysfunction by restoring NO availability through a mechanism probably related to an antioxidant effect. ACE inhibitors, on the other hand, seem to improve endothelial function in subcutaneous, epicardial, brachial and renal circulation, whereas they are ineffective in potentiating the blunted response to acetylcholine in the forearm of patients with essential hypertension. They can also selectively improve endothelium-dependent vasodilation to bradykinin, an effect not mediated by restoring NO availability but probably related to hyperpolarisation. Recent evidence suggests angiotensin II AT(1)-receptor antagonists can restore endothelium-dependent vasodilation to acetylcholine in subcutaneous microcirculation but not in that of the forearm muscle. Evidence concerning the effect of these drugs on the brachial artery in patients with atherosclerosis is positive. However, treatment with an AT(1)-receptor antagonist can improve basal NO release and decrease the vasoconstrictor effect of endogenous endothelin-1. In conclusion, despite the considerable evidence that impaired endothelium-dependent vasodilation can be improved by appropriate antihypertensive treatment, no clinical data exist demonstrating that the reversal of endothelial dysfunction is associated with a reduction in cardiovascular events. In the near future, large scale clinical trials are required to demonstrate that treatment of endothelial dysfunction can lead to better prognosis in patients with essential hypertension.

Reciprocal regulation of endothelin-1 and nitric oxide: relevance in the physiology and pathology of the cardiovascular system

The endothelium plays a crucial role in the regulation of cardiovascular structure and function by releasing several mediators in response to biochemical and physical stimuli. These mediators are grouped into two classes: (1) endothelium-derived constricting factors (EDCFs) and (2) endothelium-derived relaxing factors (EDRFs), the roles of which are considered to be detrimental and beneficial, respectively. Endothelin-1 (ET-1) and nitric oxide (NO) are the prototypes of EDCFs and EDRFs, respectively, and their effects on the cardiovascular system have been studied in depth. Numerous conditions characterized by an impaired availability of NO have been found to be associated with enhanced synthesis of ET-1, and vice versa, thereby suggesting that these two factors have a reciprocal regulation. Experimental studies have provided evidence that ET-1 may exert a bidirectional effect by either enhancing NO production via ETB receptors located in endothelial cells or blunting it via ETA receptors prevalently located in the vascular smooth muscle cells. Conversely, NO was found to inhibit ET-1 synthesis in different cell types. In vitro and in vivo studies have started to unravel the molecular mechanisms involved in this complex interaction. It has been clarified that several factors affect in opposite directions the transcription of preproET-1 and NO-synthase genes, nuclear factor-KB and peroxisome proliferator-activated receptors playing a key role in these regulatory mechanisms. ET-1 and NO interplay seems to have a great relevance in the physiological regulation of vascular tone and blood pressure, as well as in vascular remodeling. Moreover, an imbalance between ET-1 and NO systems may underly the mechanisms involved in the pathogenesis of systemic and pulmonary hypertension and atherosclerosis.

Gastrointestinal enzyme production of bioactive peptides from royal jelly protein and their antihypertensive ability in SHR

In order to clarify the potential physiological function of royal jelly (RJ), we report here the gastrointestinal enzyme production of antihypertensive peptides from RJ. Intact RJ and its protein fraction did not retard the action of angiotensin I-converting enzyme (ACE) activity at all. However, development of ACE inhibition power of RJ was newly observed by pepsin hydrolysis (IC(50)=0.358 mg protein/mL), and the subsequent trypsin and chymotrypsin hydrolyses (IC(50)=0.099 mg protein/mL). Single oral administration of this gastrointestinal RJ hydrolysate (1 g/kg dose) in 10-week spontaneously hypertensive rat resulted in a significant reduction of systolic blood pressure of 22.7 plus minus 3.6 mmHg at 2 hr (P<0.05 vs. 0 hr by one-way ANOVA, n=7). Then, the RJ hydrolysate was fractionated with gel permeation chromatography to obtain the di- and tri-peptides (DTP) fraction. As a result of isolation from the DTP fraction by reversed phase-high performance liquid chromatography, eleven ACE inhibitory peptides were isolated from the DTP-RJ hydrolysate. Some of the ACE inhibitors were derived from the RJ-glycoprotein; eight peptides with the IC(50) value of <10 &mgr;M were identified from natural resources for the first time. Consequently, RJ protein was thought to be a good resource of ACE inhibitory peptides produced by the gastrointestinal enzyme hydrolyses.

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.

Effects of cilnidipine on nitric oxide and endothelin-1 expression and extracellular signal-regulated kinase in hypertensive rats

We evaluated the effects of cilnidipine, a long-acting Ca(2+) channel antagonist, on endothelial nitric oxide synthase (eNOS), preproendothelin-1 and endothelin ETA receptor expression in the left ventricle, and evaluated the relations between these effects and coronary microvascular remodeling and extracellular signal-regulated kinases belonging to one subfamily of mitogen-activated protein kinases in deoxycorticosterone acetate (DOCA)-salt hypertensive rats. Cilnidipine (DOCA-cilnidipine, 1 mg/kg/day, subdepressor dose) or vehicle (DOCA-vehicle) was given after induction of DOCA-salt hypertension for 5 weeks. The eNOS mRNA and protein expression in the left ventricle was significantly lower in DOCA-vehicle than in control rats and significantly higher in DOCA-cilnidipine than in DOCA-vehicle rats. Preproendothelin-1 and endothelin ETA receptor expression levels and phospho-p42/p44 extracellular signal-regulated kinase activities were significantly increased in DOCA-vehicle compared with control rats and significantly suppressed in DOCA-cilnidipine compared with DOCA-vehicle rats. DOCA-vehicle rats showed a significant increase in the wall-to-lumen ratio, perivascular fibrosis and myocardial fibrosis, with all these parameters being significantly improved by cilnidipine. These results led us to conclude that phospho-p42/p44 extracellular signal-regulated kinase activities may contribute to the coronary microvascular remodeling of DOCA rats and that protective effects of cilnidipine on cardiovascular remodeling may be at least in part mediated by an increased eNOS expression and a decreased endothelin-1 and endothelin ETA receptor expression in the left ventricle.

Hypertension and impairment of endothelium-dependent relaxation of arteries from spontaneously hypertensive and L-NAME-treated Wistar rats

Effects of chronic treatment of normotensive Wistar rats with N(omega)-nitro-L-arginine methyl ester (L-NAME) on blood pressure and on endothelium-dependent relaxation of the aorta, carotid and iliac arteries were studied. The endothelium-dependent relaxation was compared in arteries from normotensive Wistar Kyoto rats (WKY) and genetically hypertensive rats (stroke-prone spontaneously hypertensive rats, SHRSP). Chronic treatment of normotensive Wistar rats with L-NAME caused an elevation of blood pressure. The elevated blood pressure at 15 weeks of age was significantly higher in these animals than that of untreated Wistar rats, but lower than that of SHRSP. Endothelium-dependent relaxation of the arteries induced by acetylcholine (ACh) was almost abolished by chronic treatment with L-NAME. The remaining small relaxation in arteries from L-NAME-treated rats was completely inhibited by application of L-NAME (10(-4) M). In such preparations, higher concentrations of ACh induced a contraction, which was abolished by removal of the endothelium or by an application of indomethacin (10(-5) M). Endothelium-independent relaxation induced by sodium nitroprusside was similar between preparations from untreated and L-NAME-treated Wistar rats. Endothelium-dependent relaxation was significantly impaired in preparations from SHRSP, when compared with that in those from WKY. However, the impairment was less prominent in preparations from SHRSP than in those from L-NAME-treated rats. These results suggest that the impairment of endothelium-dependent relaxation in the arteries from L-NAME-treated rats is not due to the elevated blood pressure resulting from the chronic treatment, and that impairment of NO synthesis by the endothelium does not play a major role in the initiation of hypertension in SHRSP.

Celiprolol stimulates endothelial nitric oxide synthase expression and improves myocardial remodeling in deoxycorticosterone acetate-salt hypertensive rats

OBJECTIVE

Endothelium-dependent vasodilation is attenuated in humans and experimental hypertension models, and this phenomenon may be largely due to decreased release or activity of nitric oxide (NO). However, very few studies have evaluated whether beta-adrenoceptor antagonists increase endothelial NO synthase (eNOS) expression in the left ventricle. We examined the effects of long-term treatment with celiprolol, a specific beta1-antagonist with a weak beta2-agonist action, on eNOS expression in the left ventricle and evaluated its relationship to myocardial remodeling in the left ventricle of deoxycorticosterone acetate (DOCA)-salt hypertensive rats.

METHODS

DOCA-salt rats (n = 18) were induced with weekly injections of DOCA (30 mg/kg) and 1% saline in their drinking water after right nephrectomy. Celiprolol (DOCA-CEL, n = 9, 10 mg/kg per day, subdepressor dose) or a vehicle (DOCA-V, n = 9) were given after induction of DOCA-salt hypertension for 5 weeks, and age-matched sham-operated rats (ShC, n = 9) served as a control group.

RESULTS

Blood pressure levels in DOCA-V and DOCA-CEL were similar and significantly higher than that in ShC. The eNOS mRNA and protein levels, and NOS activity in the left ventricle significantly decreased in DOCA-V compared with ShC, and significantly increased in DOCA-CEL compared with DOCA-V. DOCA-V showed a significant increase in the wall-to-lumen ratio, perivascular fibrosis, myocardial fibrosis, and type I collagen mRNA, with all these parameters being significantly improved by celiprolol.

CONCLUSIONS

Myocardial remodeling of DOCA-salt hypertensive rats was significantly ameliorated by subdepressor doses of celiprolol, which may be due to increased eNOS expression in the left ventricle.

Unaltered endothelium-dependent modulation of contraction in the pulmonary artery of hypertensive rats

Involvement of endothelium-derived nitric oxide (EDNO) in alpha-adrenoceptor agonist-induced contractile responses was studied in isolated pulmonary arteries from Wistar Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP). In the presence of propranolol, noradrenaline-induced contraction was potentiated by endothelium removal or by N(G)-nitro-L-arginine (L-NOARG). The magnitude of the potentiation was independent of the noradrenaline concentration. L-NOARG also shifted the concentration-response curves for phenylephrine and methoxamine to the left and upward. Contractile responses to 2-amino-5,6,7,8, -tetrahydro-6-ethyl-4H-oxazolo-(5,4-d)-azepine-dihydrochloride (BHT-933) and 5-bromo-6-(2-imidazolin-2-ylamino)-quinoxaline (UK-14304) were augmented by L-NOARG in a concentration-dependent manner. There were no differences in the effects of L-NOARG on the contractile responses to alpha-adrenoceptor agonists between the preparations from WKY and SHRSP. Endothelium-dependent relaxation in response to acetylcholine was not impaired in the preparations from SHRSP when compared with those from WKY. These observations suggest that the contractile responses to the alpha(1)-adrenoceptor agonists were depressed mainly by basally released EDNO, while the responses to the alpha(2)-adrenoceptor agonists were depressed mainly by EDNO released in response to alpha(2)-adrenoceptor stimulation. The comparable influence of the endothelium on the alpha-adrenoceptor agonist-induced contractions in the pulmonary arteries from WKY and SHRSP, which were markedly different from other arteries, could be explained by the unaltered endothelium-dependent relaxation in the preparations from SHRSP.

Effect of verapamil on systolic and diastolic coronary blood flow velocity in asymptomatic and mildly symptomatic patients with hypertrophic cardiomyopathy

OBJECTIVE

To assess non-invasively the effect of verapamil treatment on coronary blood flow velocity in asymptomatic and mildly symptomatic patients with hypertrophic cardiomyopathy.

DESIGN

High frequency transthoracic Doppler echocardiography was used to compare resting phasic coronary blood flow velocity before and after a one month period of verapamil treatment in 17 patients (14 men and three women) with non-obstructive hypertrophic cardiomyopathy. Eighteen healthy subjects formed an age and sex matched control group. Systolic and diastolic coronary blood flow velocity was measured in the distal portion of left anterior descending coronary artery using high frequency transthoracic Doppler echocardiography. Blood flow velocity before and after verapamil was compared in the patients with cardiomyopathy and with the results in the control group.

RESULTS

Compared with the controls, patients with hypertrophic cardiomyopathy had increased diastolic coronary blood flow velocity (41.8 (8.1) v 59.9 (21.9) cm/s, p < 0.01) and a lower mean systolic coronary blood flow velocity (18.7 (10.8) v -11.2 (27.5) cm/s, p < 0. 01) before verapamil treatment. A backward pattern of systolic flow, manifested by negative values of coronary blood flow velocity, was recorded in eight of the patients, while no negative values were found in the controls. After verapamil treatment the retrograde systolic blood flow was restored to an anterograde pattern in only one patient. The mean value of systolic coronary blood flow velocity did not change significantly and remained lower than the systolic forward flow velocity in the controls (-3.6 (31.8) v 18.7 (10.8) cm/s, p < 0.05). However, diastolic coronary blood flow velocity decreased significantly after verapamil (59.9 (21.9) v 50.7 (19.5) cm/s p < 0.05), reaching a level comparable with that in the controls (50.7 (19.5) v 41.8 (8.1) cm/s, p > 0.05).

CONCLUSIONS

In contrast to healthy subjects, in non-obstructive hypertrophic cardiomyopathy the systolic pattern of coronary blood flow was heterogeneous (both retrograde and anterograde), and diastolic coronary blood flow velocity was abnormally increased, despite a lack of significant symptoms. Verapamil treatment did not restore the forward pattern of systolic blood flow but decreased diastolic blood flow velocity to a level comparable with that in healthy subjects.

Cyclooxygenase inhibition reduces blood pressure elevation and vascular reactivity dysfunction caused by inhibition of nitric oxide synthase in rats

In the present study we investigated the role of cyclooxygenase (COX)-dependent vasoconstrictors in the hypertension and altered vascular reactivity following prolonged nitric oxide (NO) synthase inhibition. Male Wistar rats (250-270 g) were divided into four groups and treated for 7 days with Placebo (control), L-NAME (48 mg/kg/day), indomethacin (4 mg/kg/day) and L-NAME in combination with indomethacin. L-NAME treatment induced arterial hypertension, in vitro aortic hyperresponsiveness to phenylephrine, impaired vasodilatory response to acetylcholine and no significant change in response to sodium nitroprusside. Indomethacin co-treatment partially prevented blood pressure elevation, restored responsiveness to phenylephrine and improved sensitivity to acetylcholine. Indomethacin treatment alone did not modify blood pressure and aortic vascular reactivity. Both enhanced phenylphrine-induced contraction and impaired acetylcholine-evoked vasodilation induced by acute NO synthase inhibition with L-NAME (10(-4) M) in normal rat aortas were not modified by indomethacin (10(-5) M). These results are consistent with the hypothesis that constricting factors, which arise from the COX pathway, contribute to hypertension and altered vascular reactivity following continued inhibition of NO synthase.

Antihypertensive drugs and reversing of endothelial dysfunction in hypertension

Essential hypertension is associated with impaired endothelium-dependent vasodilation and is caused mainly by production of oxygen free radicals that can destroy nitric oxide (NO), impairing its beneficial and protective effects on the vessel wall. Antihypertensive drugs can improve or restore endothelium-dependent vasodilation depending on their ability to counteract the mechanisms that impair endothelial function. Although treatment with atenolol gives negative results in peripheral subcutaneous and muscle microcirculation, acute nebivolol exerts a modest vasodilating effect in the forearm circulation. Whether this compound can activate NO production in essential hypertensive patients is controversial. Calcium entry blockers, particularly the dihydropyridine-like drugs, can reverse impaired endothelium-dependent vasodilation in different vascular districts, including the subcutaneous, epicardial, and peripheral arteries and forearm circulation. In the forearm circulation, nifedipine and lacidipine can improve endothelial dysfunction by restoring NO availability. Angiotensin-converting enzyme (ACE) inhibitors, however, seem to improve endothelial function in subcutaneous, epicardial, and renal circulation, but are ineffective in potentiating the blunted response to acetylcholine in the forearm of patients with essential hypertension. Finally, recent evidence suggests angiotensin II receptor antagonists can restore endothelium-dependent vasodilation to acetylcholine in subcutaneous, but not in the forearm muscle, microcirculation. However, treatment with an angiotensin II receptor antagonist can improve basal NO release and decrease the vasoconstrictor effect of endogenous endothelin-1.

Effect of imidapril on myocardial remodeling in L-NAME-induced hypertensive rats is associated with gene expression of NOS and ACE mRNA

Chronically administered N(omega)nitro-L-arginine methyl ester (L-NAME) produces vascular structural changes and fibrosis of the left ventricle (LV). However, very few studies have evaluated whether the beneficial effects of angiotensin-converting enzyme (ACE) inhibitors on these myocardial remodelings are associated with local gene expression of nitric oxide synthase (NOS) and ACE mRNA in the LV. Effects of long term treatment with imidapril, an ACE inhibitor, on gene expression of endothelial-cell NOS (eNOS) and ACE mRNA in the LV and its relation to myocardial remodeling in L-NAME-induced hypertensive rats were evaluated. Fifteen male Sprague-Dawley rats were given L-NAME (60 mg/ kg/day) in drinking water for 6 weeks to induce hypertension, and then treated with imidapril (L-NAME-I, n = 8, 1 mg/kg/day, subdepressor dose), or a vehicle (L-NAME-V, n = 7) for 4 weeks. Age-matched rats (C, n = 7) served as a control group. Blood pressure in L-NAME-V and L-NAME-I was similar and significantly higher than that in C. The level of eNOS mRNA in the LV was significantly decreased in L-NAME-V compared with C, and was significantly increased in L-NAME-I compared with C and L-NAME-V. The ACE mRNA and type I collagen mRNA expression levels were significantly increased in L-NAME-V compared with C, and significantly suppressed in L-NAME-I compared with L-NAME-V. L-NAME-V demonstrated a significant increase in wall-to-lumen ratio, perivascular fibrosis, and myocardial fibrosis. These changes in the microvasculature were improved significantly by imidapril. Myocardial remodeling in L-NAME-induced hypertensive rats was significantly ameliorated by a subdepressor dose of imidapril, which may be due to an increase in local eNOS mRNA expression and a decrease in angiotensin II in the LV.

Dual mode of action of dihydropyridine calcium antagonists: a role for nitric oxide

Dihydropyridine calcium antagonists have been used for many years in the treatment of angina pectoris and hypertension. According to the common view, their mechanism of action is based on an inhibition of the smooth muscle L-type calcium current, thus decreasing intracellular calcium concentration and inducing smooth muscular relaxation. However, in recent years evidence has accumulated that besides the smooth muscle effects of these agents, their effect on the endothelium must also to be taken into account. It was shown that dihydropyridines can induce the release of nitric oxide (NO) from the vascular endothelium of various vessels and in different species. This was first shown by Günther and colleagues by assaying the methaemoglobin formation in the presence of intact endothelium (in porcine coronary arteries) with and without treatment with nitrendipine. These findings were later confirmed by direct measurement of NO or of nitrite production. In addition, in several preparations, including micro- and macrovasculature, the sensitivity of the vasorelaxing effect of the dihydropyridines to inhibitors of NO-synthase, such as L-N(G)-nitroarginine (LNNA) or L-N-nitro-arginine-methyl-ester (L-NAME), has been shown. With these studies it became evident that the NO-releasing effect was not unique to nitrendipine but was a group phenomenon shared by the dihydropyridines and several nondihydropyridine calcium antagonists. In addition to their action on vascular endothelium, NO release by nifedipine has also been detected in platelets. There are also studies showing long term effects of calcium antagonists involving NO release. Regarding the underlying mechanism of NO release, nitrendipine was shown, not to decrease but to increase intracellular Ca2+ in cultured endothelial cells. This increase was sensitive to both Ca2+-free extracellular superfusion and to gadolinium, a lanthanide known to inhibit shear-stress activated cation channels. This increase in intracellular calcium can activate endothelial NO-synthase, thus inducing the release of NO. These findings on a dual mode of action, i.e. the direct relaxing effect by inhibition of the smooth muscle L-type calcium current and indirect relaxing effect by release of NO from vascular endothelium may help to understand the beneficial antihypertensive effects of the dihydropyridine calcium antagonists and the preferential effect of certain drugs in certain vascular regions (resistance versus conductive vessels). In addition, NO release from both vascular endothelium and platelets may contribute to the antiatherosclerotic and antithrombotic effects described for certain dihydropyridines.

Angiotensin converting enzyme inhibitors and vascular protection in hypertension

Strategically located between the circulating blood and the vascular smooth muscle, endothelial cells release numerous vasoactive substances regulating the function of vascular smooth muscle and circulating blood cells. Endothelium-derived vasodilators include prostacyclin, nitric oxide and endothelium-derived hyperpolarizing factor. In particular, nitric oxide inhibits cellular growth and migration. In concert with prostacyclin, nitric oxide exerts potent antiatherogenic and thromboresistant properties by preventing platelet aggregation and cell adhesion. These effects are counterbalanced by vasoconstrictors, such as angiotensin II and endothelin (ET)-1, both of which exert prothrombotic and growth-promoting properties. In hypertension, elevated blood pressure causes vascular disease by inducing endothelial dysfunction. Hence, modern therapeutic strategies in human hypertension focus on preserving or restoring endothelial integrity. Beyond inhibiting the renin-angiotensin system, angiotensin-converting enzyme (ACE) inhibitors diminish the inactivation of bradykinin, thus leading to an augmentation of nitric oxide release. In addition, the compounds stabilize the B2-receptor, and reduce oxidative stress and tissue ET-1 levels. In patients with coronary artery disease, chronic ACE inhibition improves endothelial function. Further clinical studies are already under way which will prove whether these beneficial vascular effects of ACE inhibitors on endothelial dysfunction result in a clinical benefit for patients with hypertension.

Losartan-sensitive renal damage caused by chronic NOS inhibition does not involve increased renal angiotensin II concentrations

BACKGROUND

Chronic nitric oxide synthase (NOS) inhibition results in hypertension, proteinuria, and renal morphological changes. Continuous angiotensin II (Ang II) blockade prevents these effects, suggesting an essential role of Ang II. However, it is not known whether renal Ang II concentrations are primarily increased or whether the scarcity of NO allows normal concentrations of Ang II to cause these detrimental effects. Therefore, we measured renal Ang II concentrations before and during the development of renal damage.

METHODS

Group 1 served as controls. Groups 2 through 5 received the NOS inhibitor Nomega-nitro-L-arginine (L-NNA; 40 mg/kg/day) for 4, 7, 14, and 21 days, respectively. Systolic blood pressure (SBP), proteinuria, glomerular filtration rate (GFR), and renal and blood Ang II were measured. In a separate experiment, rats were treated with L-NNA + the Ang II AT1 receptor blocker losartan to determine the functional effects of endogenous Ang II during chronic NOS inhibition.

RESULTS

L-NNA treatment resulted in an increase in SBP from day 4 (161 +/- 4 vs. 135 +/- 4 mm Hg in control, P < 0.05) to day 21 (230 +/- 9 mm Hg). GFR was decreased from day 4 (1.9 +/- 0.2 vs. 2.5 +/- 0.2 ml/min in control, P < 0.05) to day 21 (1.2 +/- 0.2 ml/min). Proteinuria was increased from day 14 (85 +/- 14 vs. 6 +/- 1 mg/day in control, P < 0.05) to day 21 (226 +/- 30 mg/day). L-NNA treatment during four days resulted in a significant decrease in renal Ang II (183 +/- 32 vs. 454 +/- 40 fmol/g in control, P < 0.05). On day 7, 14, and 21, renal Ang II was not significantly different from the control. Blood Ang II was not significantly different from the control on days 4, 7, and 14 but was significantly increased after 21 days of L-NNA treatment (215 +/- 35 vs. 78 +/- 13 fmol/ml in control, P < 0.05). Ang II type-1 (AT1) receptor blockade prevented the severe renal injury and hypertension induced by chronic NOS inhibition.

CONCLUSIONS

Losartan-sensitive renal damage caused by chronic NOS inhibition does not involve increased renal Ang II concentrations. This suggests that the detrimental effects of endogenous Ang II are increased during chronic NOS inhibition. Thus, when NO levels are low, normal Ang II concentrations can cause renal injury and hypertension.

Effect of Ca2+ channel blockers on arterial hypertension and heart ischaemic lesions induced by chronic blockade of nitric oxide in the rat

The effects of the Ca2+ channel blockers diltiazem, nifedipine and amlodipine were investigated on both arterial hypertension and myocardial changes induced by chronic blockade of nitric oxide synthesis. Control male Wistar rats received Nomega-nitro-L-arginine methyl ester (L-NAME; 20 mg rat(-1) day(-1)) in the drinking water for 8 weeks; blood pressure and body weight were monitored weekly. The Ca2+ channel blockers were given concomitantly to L-NAME, as follows: diltiazem (13.5 mg rat(-1) day(-1)) and amlodipine (6.25 mg rat(-1) day(-1)) were administered in the drinking water whereas nifedipine (6.25 mg rat(-1) day(-1)) was given in the chow. Nomega-nitro-L-arginine methyl ester induced a time-dependent increase in blood pressure which was significantly attenuated by diltiazem (154+/-1.6 vs. 139+/-1.6 mm Hg, p < 0.05), nifedipine (166+/-2.7 vs. 150+/-2.1 mm Hg, p < 0.05) and amlodipine (208+/-5.8 vs. 158+/-1.8 mm Hg, p < 0.05) at the last week of the treatment. Rats treated with the L-NAME also developed myocardial ischaemia, as indicated by the increased percentage of fibrous tissue found in the left ventricles of these animals (10.9+/-0.1%, p < 0.01) when compared to control ones (6.3+/-0.1%). Neither diltiazem (14.9+/-1.2%) nor nifedipine (11.1+/-1.5%) prevented this effect whereas amlodipine (6.9+/-1.1%, p < 0.01) virtually abolished the increase in fibrous tissue induced by L-NAME. The plasma concentration of the Ca2+ channel blockers was measured by liquid chromatography coupled to mass spectrometry at two different time points (morning and afternoon). Only amlodipine treatment was able to maintain constant levels (186+/-46 ng ml(-1) in the morning and 110+/-19 ng ml(-1) in the evening) compared to nifedipine (3003+/-578 ng ml(-1) in the morning and 436+/-100 ng ml(-1) in the evening) and diltiazem (77+/-51 ng ml(-1) in the morning and not detectable in the evening). In conclusion, our results indicate that amlodipine (but not diltiazem and nifedipine) can efficiently control myocardial ischaemia in nitric oxide deficient rats, probably due to its intrinsically long half-life.

High flaxseed (linseed) diet restores endothelial function in the mesenteric arterial bed of spontaneously hypertensive rats

The effect of high flaxseed diet (HFD) on blood pressure (BP) and mesenteric arterial bed (MAB) reactivity was studied in spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats. HFD did not affect BP in either SHR (control, 157 +/- 3; HFD, 153 +/- 3 mmHg) or WKY (control, 114 +/- 2; HFD, 117 +/- 2 mmHg) rats. Increases in perfusion pressure of the endothelium-intact MAB to phenylephrine and norepinephrine were higher (p < 0.05) in SHR than in WKY rats and the HFD failed to alter these responses. Vasorelaxant responses to acetylcholine (ACh) and bradykinin (BK) were greater (p < 0.05) in SHR maintained on HFD compared to SHR on control diet. While HFD also enhanced ACh responses in WKY, the effect was less than in SHR. Responses to sodium nitroprusside (SNP), were similar in all groups. Since ACh and BK-induced responses of the MAB were augmented in SHR on HFD, with no changes in BP, it is suggested that HFD improves endothelial vasorelaxant function through a pressure-independent mechanism.