Correction of arterial structure and endothelial dysfunction in human essential hypertension by the angiotensin receptor antagonist losartan

Inhibition of mitogen-activated protein/extracellular signal-regulated kinase improves endothelial function and attenuates Ang II-induced contractility of mesenteric resistance arteries from spontaneously hypertensive rats

OBJECTIVES

Extracellular signal-regulated kinases (ERK1/2) modulate vascular smooth muscle cell (VSMC) growth and contractility, important factors in blood pressure regulation. In the present in vivo study, we investigated whether short-term inhibition of ERK1/2-dependent signaling pathways influences vascular function and blood pressure (BP) in spontaneously hypertensive rats (SHR).

METHODS

SHR and Wistar-Kyoto (WKY) rats were injected subcutaneously with either PD98059, selective MEK1/2 inhibitor (20 mg/kg), or vehicle. BP was measured by telemetry. Rats were killed 24 h after injection and small mesenteric arteries mounted as pressurized systems for morphometric analysis and assessment of endothelial function and angiotensin II (Ang II)-induced contractility. ERK1/2 phosphorylation was measured by Western blots, using protein extracts from mesenteric arteries, aorta, heart and kidneys.

RESULTS

BP was higher (P < 0.01) in SHR than in WKY rats. PD98059 did not influence BP in either group. Endothelial-dependent relaxation (acetylcholine-induced), which was impaired in SHR, was improved by PD98059 (P < 0.05). Ang II increased contraction, with greater responses in SHR (Emax = 25 +/- 4%) than WKY (Emax = 9 +/- 3%) (P < 0.01). PD98059 reduced Ang II-induced contraction in SHR (Emax = 5.8 +/- 0.4%) and WKY (Emax = 4 +/- 0.4%). Vascular structure was unaltered by PD98059. Vascular and renal ERK1/2 phosphorylation, which was higher in SHR than WKY, was decreased by PD98059 in SHR.

CONCLUSION

Short-term treatment with PD98059 improves endothelial function and vascular contractility without influencing BP in SHR. These findings provide evidence that vascular ERK1/2 activity is upregulated and that MEK1/2-sensitive signaling pathways play an important role in the regulation of vascular function in SHR. Acute inhibition of MEK1/2 does not alter blood pressure despite improved endothelial function and reduced arterial reactivity to Ang II.

Comparison of nitric oxide production in response to carbachol between macrovascular and microvascular cardiac endothelial cells

Cardiac microvascular endothelial cells (EC) play an important role in the physiological regulation of coronary blood flow, but their function has not been rigorously examined, because suitable in vitro models have not been available. Cardiac macrovascular and microvascular EC were isolated and cultured from 14-16-week-old Sprague-Dawley rats to examine the pharmacological responses of carbachol-induced nitric oxide (NO) production using a Griess method. Carbachol-induced NO production was only detected in cardiac macrovascular EC, which suggests that endothelial production of NO differs between macrovascular and microvascular EC. Next, cardiac microvascular EC was treated with either vehicle, angiotensin-converting enzyme (ACE) inhibitor (captopril, 10 micromol/L) or angiotensin II type 1 (AT1) receptor antagonist (CV11974, 10 micromol/L) for 4 days. Carbachol-induced NO production was improved by captopril (136+/-45nmol, p<0.01 vs vehicle) and CV11974 (146+/-30nmol, p<0.01 vs vehicle). Angiotensin II concentration in the culture medium and protein expressions of endothelial nitric oxide synthase and AT1 receptor in the EC were similar among the 3 groups. Interestingly, the level of muscarinic subtype 3 (M3) receptor was significantly increased in the EC treated with captopril (214%, p<0.01) and CV11974 (296%, p<0.01). When cardiac microvascular EC were treated with neomycin (non-selective phospholipase C inhibitor), carbachol-induced NO production was also improved (146+/-35nmol, p<0.01, neomycin I mmol/L) together with increased expression of M3 receptor (p<0.01). These data suggest that the upregulation of the M3 receptor by captopril or CV11974 occurs via a phospholipase C-dependent pathway. Cardiac microvascular EC also produced NO constitutively, as did the macrovascular EC, but carbachol-induced NO production was decreased. The present data suggest that the upregulation of the M3 receptor by the ACE inhibitor and AT1 receptor antagonist is a new beneficial effect of these drugs on microvascular endothelial function.

Severity of hypertension affects improved resistance artery endothelial function by angiotensin-converting enzyme inhibition

The purpose of this study was to determine whether there are differences in the restoration of endothelial function by angiotensin-converting enzyme inhibition based on the severity of hypertension. Forearm blood flow (FBF) was measured in 69 patients with essential hypertension (mild, n = 23; moderate, n = 29; and severe, n = 17 randomly assigned to treatment with either imidapril or amlodipine for 24 weeks in a double-blind fashion during reactive hyperemia and after sublingual administration of nitroglycerin. Imidapril augmented the FBF response to reactive hyperemia after 24 weeks of treatment in the mild and moderate hypertensive groups, but not in the severe hypertensive group. The augmentation of the FBF response to reactive hyperemia induced by imidapril was significantly greater in the moderate hypertensive group than in the mild hypertensive group. Amlodipine did not alter the FBF response to reactive hyperemia. The increase in FBF after the sublingually administered nitroglycerin was similar in all groups. The infusion of NG-monomethyl-l-arginine, a nitric oxide synthase inhibitor, abolished the enhancement of reactive hyperemia in the mild and moderate hypertensive groups treated with imidapril. These findings suggest that the effects of imidapril on endothelial function are affected by the severity of hypertension and that angiotensin-converting enzyme inhibitor-induced augmentation of reactive hyperemia may be due to increased nitric oxide production.

Comparative antihypertensive efficacy of olmesartan: comparison with other angiotensin II receptor antagonists

Hypertension is a major risk factor for cardiovascular morbidity and mortality. Effective control of elevated blood pressure (BP) has been shown to reduce this risk. Early studies of risk reduction assumed that the mechanism by which BP was lowered had little impact on the benefit obtained. Recent evidence, however, suggests that agents that inhibit the renin-angiotensin system may be particularly beneficial. The results of the recent Heart Outcomes Prevention Evaluation (HOPE) trial suggest that angiotensin-converting enzyme (ACE) inhibitors have a greater impact on cardiovascular morbidity and mortality than would be anticipated from their antihypertensive effects alone. Angiotensin receptor blockers, the other major class of antihypertensive drugs that inhibit the renin-angiotensin system, have not been widely tested in outcomes trials, but early results suggest that they are beneficial for controlling target organ damage that is related to hypertension. Furthermore, unlike ACE inhibitors, these agents have a side-effect profile that is similar to that of placebo. Based on their efficacy in controlling hypertension and their wider health benefits, together with minimal side effects, angiotensin II (A II) receptor blockers should be considered as first-line agents for the treatment of hypertension, particularly in patients with other cardiovascular risk factors. Preliminary evidence suggests that olmesartan, an A II receptor blocker currently being evaluated for approval for clinical use, may provide antihypertensive efficacy that is superior to other members of the class.

Vascular signaling pathways in the metabolic syndrome

There are several potential cellular and molecular pathways whereby cardiovascular risk factors act through very specific signal transduction pathways in the formation of atherosclerosis, as seen often in the metabolic syndrome. Many examples point to multiple postreceptor defects in the insulin signaling pathway in vascular tissue, however, there are differences in the insulin receptor pathway in vascular tissue compared with skeletal muscle or fat. In addition to insulin receptors, insulin may affect atherosclerotic changes in the vascular cells via stimulation of insulin-like growth factor-1 receptors and their signaling pathway. Insulin also causes activation of the vascular renin-angiotensin system in both vascular smooth muscle cells and endothelial cells. Insulin-activated tissue renin-angiotensin system leads to increased cell growth and contributes to the cause of atherosclerosis. The fact that agents that inhibit the renin-angiotensin system also block insulin-mediated renin-angiotensin system expression and cell growth reinforces the potential implication of a vascular insulin-renin-angiotensin system pathway. Finally, novel substances such as the adipokines, factors produced from fat cells, reveal new risk factors in the metabolic syndrome and offer further evidence for a link between insulin resistance and accelerated atherosclerosis.

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.

Nitric oxide synthase and hypertension

Nitric oxide, the metabolic product of L-arginine by the enzyme nitric oxide synthase, plays a pivotal role in the regulation of vascular homeostasis. Its complex interaction with the autocrine and paracrine systems, particularly angiotensin II, modulates vasoconstriction and vasodilatation as well as the architectural remodeling of the vascular bed. The major vascular hormones known to be involved are angiotensin II and endothelin-1. Upregulation of endothelin-1, a potent molecule, appears to be a consequence of the nitric oxide-angiotensin II imbalance that contributes to end-organ injury. Increased oxidative stress, common to different diseases including diabetes mellitus and hypertension, is also a determinant player in the interaction between angiotensin II and nitric oxide. The influence of a relative malfunction of the nitric oxide system on the vascular tone and vascular structure, and the effects of hypertension on this system, are discussed.

Angiotensin II receptor antagonist improves age-related endothelial dysfunction

BACKGROUND

We previously demonstrated that the angiotensin converting enzyme (ACE) inhibitor, enalapril, prevents the age-related impairment of endothelium-dependent hyperpolarization and relaxation mediated by endothelium-derived hyperpolarizing factor (EDHF).

OBJECTIVE

To test whether angiotensin II type 1 (AT1) receptor antagonists would also improve age-related endothelial dysfunction.

METHODS

Normotensive Wistar-Kyoto (WKY) rats were treated for 3 months with either the AT1 receptor antagonist, candesartan cilexetil (3.5 mg/kg per day; candesartan group), or the ACE inhibitor, enalapril (20 mg/kg per day; enalapril group), from 9 to 12 months of age. Untreated 12-month-old WKY rats (old group) served as controls (n = 7-12).

RESULTS

The two treatments decreased systolic blood pressure comparably. EDHF-mediated hyperpolarization in response to acetylcholine (ACh; 10(-5) mol/l) in the presence of norepinephrine in mesenteric arteries was improved in both the candesartan and enalapril groups to a similar extent compared with the old group (candesartan group, -24 +/- 3 mV; enalapril group, -21 +/- 2 mV; old group, -13 +/- 2 mV). EDHF-mediated relaxation was similarly improved in the candesartan and enalapril groups (maximum relaxation: candesartan group, 70 +/- 7%; enalapril group, 63 +/- 8%; old group, 33 +/- 9%). Hyperpolarization and relaxation responses to levcromakalim, an ATP-sensitive K+-channel opener, were similar in all groups.

CONCLUSIONS

These findings suggest that the AT1 receptor antagonist is as effective as the ACE inhibitor in improving the age-related decline in EDHF-mediated hyperpolarization and relaxation in normotensive rats. Thus AT1 receptor antagonists might serve as novel tools with which to prevent endothelial dysfunction associated with aging.

Reduction of the soluble cyclic GMP vasorelaxing system in the vascular wall of stroke-prone spontaneously hypertensive rats: effect of the alpha1 -receptor blocker doxazosin

OBJECTIVE

The aim of the present study was to analyse the nitric oxide (NO)/cyclic GMP (cGMP) relaxing system in spontaneously hypertensive rats of the stroke-prone substrain (SHRSP).

DESIGN

The study was performed in 20-week-old SHRSP rats. A group of normotensive Wistar-Kyoto (WKY) rats was used as control.

RESULTS

The endothelium-dependent relaxation to acetylcholine was reduced in SHRSP rats (n = 15). No modifications in the expression of the endothelial nitric oxide synthase were found in the vascular wall of WKY rats (n = 15) and SHRSP rats. SHRSP rats demonstrated an impaired relaxing response to the NO-donor sodium nitroprusside that was accompanied by a reduction in the level of the main second messenger of NO, cyclic GMP. The expression of the soluble guanylate cyclase (sGC) beta1-subunit was markedly reduced in the vascular wall of SHRSP rats. In the experimental model of SHRSP, an increased concentration of catecholamines has been reported. Therefore, we evaluated the effect of an alpha1-receptor blocker, doxazosin, on the NO/cGMP system. Doxazosin [10 mg/kg body weight (bw) per day for 15 days, n = 15] reduced mean arterial pressure (MAP) in SHRSP rats. Treatment with doxazosin preserved the endothelium-independent relaxation response to sodium nitroprusside in aortic segments from SHRSP rats which was associated with an increased expression of the sGC beta1-subunit. A dose of doxazosin (1 mg/kg bw per day, n = 15) that did not modify MAP partially prevented sGC protein expression in the vascular wall.

CONCLUSIONS

Independently of the endothelial NO-generating system, impaired vasorelaxation could also result from vascular smooth muscle cell layer dysfunction. Doxazosin treatment improved the endothelial-independent relaxation and preserved the cGMP generating system in the vascular wall of SHRSP rats.

The effect of a losartan-based treatment regimen on isolated systolic hypertension

This study was conducted to compare the antihypertensive efficacy and tolerability, over 12 weeks, of a losartan-based treatment regimen and placebo in patients with isolated systolic hypertension. Three hundred eight patients > or =35 years of age with isolated systolic hypertension, defined as trough sitting blood pressure between 140 and 200 mm Hg systolic and between 70 and 89 mm Hg diastolic, were randomized to losartan 50 mg (n=157) or placebo (n=151) once daily, with titration as necessary to achieve a goal trough sitting systolic blood pressure (SBP) <140 mm Hg. At baseline, mean trough sitting SBP was 140-159 mm Hg in 20.5% of patients, 160-179 mm Hg in 62.7%, and 180-200 mm Hg in 16.9%, and was similar in the two groups (losartan, 165.3 mm Hg; placebo, 166.1 mm Hg). At 12 weeks, mean trough sitting SBP decreased significantly (p<0.001) in both the losartan-based treatment group (by 19.2 mm Hg) and in the placebo group (by 7.6 mm Hg). The reduction in sitting SBP was significantly greater for losartan than placebo (-11.6 mm Hg; 95% confidence interval, -14.8 to -8.4). In patients with isolated systolic hypertension, a once-daily losartan-based treatment regimen significantly lowered SBP. The losartan-based regimen exhibited antihypertensive efficacy that was superior to that of placebo, with a similar tolerability profile.

The regulation of human vascular smooth muscle extracellular matrix protein production by alpha- and beta-adrenoceptor stimulation

OBJECTIVE

The sympathetic nervous system (SNS) is commonly activated in hypertension; however, the role of SNS activation in the pathogenesis of cardiovascular structural changes remains poorly defined. In particular, the effect of adrenergic stimulation on extracellular matrix (ECM) protein production by human cardiovascular cells is unknown. The present study thus investigated the direct effect of adrenergic stimulation on ECM protein production by cultured human vascular smooth muscle (VSM) cells.

METHODS AND RESULTS

Exposing human VSM cells to norepinephrine increased collagen protein production by 42%, P < 0.01, when compared to control (unstimulated) cells. This effect was mediated by the alpha1-adrenoceptor, since it was inhibited by the selective alpha1-adrenoceptor antagonist; prazosin (2 micromol/l) and reproduced by the selective alpha1-adrenoceptor agonist; phenylephrine (10 micromol/l). In contrast, beta-adrenoceptor stimulation - isoprenaline (1 micromol/l) or norepinephrine (10 micromol/l) + prazosin (2 micromol/l) - inhibited collagen production by 12%, P < 0.01. This inhibitory effect was mediated via the beta1-adrenoceptor, since it was blocked by atenolol (beta1-adrenoceptor antagonist) but not butoxamine (beta2-adrenoceptor antagonist). Fibronectin, another ECM protein, was similarly regulated by alpha- and beta-adrenoceptor stimulation. Transforming growth factor beta1 (TGFbeta1) mRNA expression by human VSM cells was also significantly influenced by adrenergic stimulation, being increased by phenylephrine (alpha-agonist) and inhibited by isoprenaline (beta-agonist).

CONCLUSIONS

These results uniquely demonstrate the capacity for adrenergic stimulation to directly modulate TGFbeta1 expression and ECM protein synthesis by the human cardiovascular system.

Small artery remodeling in hypertension

Hypertension is associated with altered structure of the resistance vessels, a process known as remodeling. This review summarizes current concepts concerning the structure of a subgroup of the resistance vessels, the small arteries, and the modes of remodeling, some of the determinants of remodeling, and some signaling pathways for remodeling. It is shown that the available evidence points to important roles for blood flow and growth factors, in addition to blood pressure, as causes of resistance artery remodeling. Finally, the relationship between vascular structure and blood pressure is discussed, in particular with regard to the effects of antihypertensive therapy. Here again, it appears that blood flow plays an important role in allowing the correction of the abnormal resistance vessel structure seen in hypertension.

Effect of amlodipine compared to atenolol on small arteries of previously untreated essential hypertensive patients

In a previous retrospective study, long-term treatment of essential hypertensive patients with a slow-release calcium channel blocker resulted in normal resistance artery structure and endothelial function, which did not occur with a beta-blocker. In the present prospective study, 19 previously untreated essential hypertensive patients (aged 47 +/- 2 years, 75% male) were treated for 1 year in a double-blind randomized study with the long-acting calcium channel blocker amlodipine or the beta-blocker atenolol. Resistance arteries (lumen diameter, 150 to 350 microm) dissected from gluteal subcutaneous biopsies were studied on a pressurized myograph. Blood pressure (BP) control (129 +/- 2/85 +/- 2 mm Hg) was identical in both groups for the last 6 months of the study. After 1 year of treatment with amlodipine, the media-to-lumen ratio (M/L) of resistance arteries decreased from 7.89% +/- 0.40% to 6.81% +/- 0.41% (P < .05). Acetylcholine-induced endothelium-dependent relaxation tended to improve from 84.3% +/- 5.5% to 90.5% +/- 4.8% (P = .06), whereas sodium nitroprusside-induced relaxation was unchanged in the patients treated with amlodipine. In the beta-blocker-treated group there was no significant change in M/L or acetylcholine-induced relaxation. In conclusion, treatment with the calcium channel blocker amlodipine corrected altered resistance artery structure and tended to improve endothelial function in essential hypertensive patients, whereas similar good control of BP with the beta-blocker atenolol did not. Whether the vascular protective effect of amlodipine will result in improved outcomes in hypertension remains to be demonstrated.

Angiotensin and cytoskeletal proteins: role in vascular remodeling

Vascular remodeling occurs during normal development and is involved in various physiologic events. However, the adaptive structural changes of the vasculature can also be pathologic, leading to vascular disease such as hypertension, atherosclerosis, and vein graft disease. Pre-eclampsia may develop as a consequence of inappropriate vascular remodeling during pregnancy. Angiotensin II contributes to vascular remodeling by activating signal transduction cascades that promote vasoconstriction, growth, and inflammation. The cytoskeleton also participates in structural adaptation responses of the vasculature; cytoskeletal filaments may mediate vasoactive responses, transduce mechanical stimuli, and are involved in pharmacologic signal transduction. It has become clear that many of the cytoskeletal changes during vascular remodeling can be induced by angiotensin II. Recently, the small G-protein Rho has attracted much attention. The Rho/Rho-kinase system is activated by angiotensin II, is a prominent regulator of the cytoskeleton, and is involved in pathologic vascular remodeling.

Assessment of effect of angiotensin II receptor antagonist losartan on aortic distensibility in patients with essential hypertension by echocardiography

The effects of angiotensin II receptor antagonist losartan on elastic properties of aorta in patients with mild to moderate essential hypertension were assessed. The ascending aortic distensibility in 26 patients (48 +/- 3 years) with mild to moderate essential hypertension before and after 12 weeks of treatment with losartan (50 mg/day) was evaluated by using two-dimensional echocardiography. M-mode measurements of aortic systolic (Ds) and diastolic diameter (Dd) were taken at a level approximately 3 cm above the aortic valve. Simultaneously, cuff brachial artery systolic (SBP) and diastolic (DBP) pressures were measured. Aortic pressure-strain elastic modulus (Ep) was calculated as Dd x (SBP-DBP)/(Ds-Dd) x 1333 and stiffness index beta (beta) was defined as Dd x Ln (SBP/DBP)/(Ds-Dd). Blood pressure significantly decreased from 148 +/- 13/95 +/- 9 mmHg to 138 +/- 12/88 +/- 8 mmHg (systolic blood pressure, P = 0.001; diastolic blood pressure, P = 0.003). There was no significant difference in pulse pressure before and after treatment with losartan (53 +/- 10 mmHg vs 50 +/- 7 mmHg). The distensibility of ascending aorta increased significantly as showed by the significant decrease in pressure-strain elastic modulus from 4.42 +/- 5.79 x 10(6) dynes/cm2 to 1.99 +/- 1.49 x 10(6) dynes/cm2 (P = 0.02) and stiffness index beta from 27.4 +/- 32.9 to 13.3 +/- 9.9 (P = 0.02). Although there was a weak correlation between the percent changes in pressure-strain elastic modulus and stiffness index beta and that in diastolic blood pressure after losartan treatment (r = 0.40, P = 0.04 and r = 0.55, P = 0.004, respectively), no correlation was found between the percent changes in pressure-strain elastic modulus and stiffness index beta and that in systolic blood pressure (r = 0.04, P = 0.8 and r = 0.24, P = 0.2, respectively). Our study demonstrated that angiotensin II receptor antagonist losartan has a beneficial effect on aortic distensibility in patients with mild to moderate essential hypertension and this effect is partly independent of blood pressure reduction.

Effect of crossing over hypertensive patients from a beta-blocker to an angiotensin receptor antagonist on resistance artery structure and on endothelial function

BACKGROUND

Treatment of essential hypertensive patients with an AT1 angiotensin receptor antagonist has previously resulted in correction of resistance artery structure and endothelial function, whereas in a parallel group treated with the beta-blocker atenolol there was no improvement of altered vascular structure and function. To test the hypothesis that patients previously treated with atenolol could present improvement of vascular structure and endothelial function if they were subjected to blockade of the renin-angiotensin system, we crossed over hypertensive patients that had been randomized to treatment with the beta-blocker atenolol to treatment with the AT1 antagonist irbesartan, and studied small artery structure and endothelial function before and after treatment.

METHODS

Eleven essential hypertensive patients (51 +/- 2 years, range 38-65; 75% male) that had previously been randomized to treatment with atenolol and treated for 1 year with good blood pressure control, were crossed over to treatment with the AT1 antagonist irbesartan for 1 year. Small resistance arteries were dissected from gluteal subcutaneous biopsies that were performed before and after 1 year of treatment. The structure and endothelial function of the resistance arteries were studied on a pressurized myograph.

RESULTS

Blood pressure control (129 +/- 3.3/85 +/- 1.8 mmHg) was identical to that achieved previously with atenolol (131 +/- 3.3/84 +/- 1.1 mmHg). Following 1 year of treatment, the arterial media width to lumen ratio (M/L) of resistance arteries (lumen diameter, 150-350 microm), which had remained unchanged under atenolol treatment, decreased from 8.44 +/- 0.45% when patients were on atenolol, to 6.46 +/- 0.30%, P < 0.01, when patients received irbesartan. Maximal acetylcholine-induced endothelium-dependent relaxation was 81.1 +/- 4.1% when patients were on atenolol, unchanged from before starting treatment with the beta-blocker, and was normalized by irbesartan (to 94.8 +/- 2.0%, P < 0.01).

CONCLUSION

Crossing over essential hypertensive patients with well-controlled blood pressure from the beta-blocker atenolol to the AT1 receptor antagonist irbesartan resulted in correction of previously persistently altered vascular structure and endothelial function, suggesting a structural and endothelial vascular protective effect of antihypertensive treatment with the AT1 receptor antagonist.

Effects of candesartan on cardiac and arterial structure and function in hypertensive subjects

OBJECTIVES

To study the effect of candesartan cilexetil on left ventricular mass index (LVMI), left ventricular systolic and diastolic function, arterial structure and function and blood pressure (BP) in hypertensive patients.

DESIGN AND METHODS

Patients (n=35), aged >20 years, with hypertension and average baseline LVMI of 89 g/m2 were treated for 24 weeks with candesartan, 16 mg o.d., following a four-week placebo run-in period. If diastolic BP remained above 95 mmHg, hydrochlorothiazide, 12.5 mg o.d.,was added. Left ventricular structure and function were assessed using transthoracic echocardiography. Arterial function and structure were assessed using pulse wave analysis to calculate augmentation index (AIx) and forearm plethysmography to calculate minimum vascular resistance. BP was measured in the office and by 24-hour ambulatory BP monitoring (ABPM).

RESULTS

The mean reduction in LVMI was 4.4 g/m2(p=0.022). Left ventricular systolic function was not significantly altered from baseline, but diastolic function significantly improved: the mean change in diastolic time was 54 ms (p=0.037), in peak velocity filling 6.3 cm/s (p=0.023); E:A ratio improved by 0.08 (p=0.049). The mean reduction in forearm vascular resistance was 15 units at rest (p=0.001) and 1.3 units after limb ischaemia (p=0.006). AIx decreased significantly, with a mean reduction of 9% (p<0.001). Central BP also significantly reduced(systolic blood pressure/diastolic blood pressure 31/20 mmHg; p<0.001). BP was significantly reduced, both in the office (22/16 mmHg; p<0.001) and by 24-hourABPM (18/12 mmHg; p<0.001).

CONCLUSIONS

Treatment with candesartan, 16 mg o.d., with or without hydrochlorothiazide, for 24 weeks, significantly reduced left ventricular mass and arterial hypertrophy in patients with hypertension. In parallel, there were significant improvements in left ventricular diastolic function and arterial function.

Endothelial factors and microvascular hypertensive disease

This paper discusses the role of endothelial dysfunction in human hypertension, especially in relation to small resistance artery structure, as well as the effects of anti-hypertensive drugs on endothelial function of small arteries in human and experimental hypertension. A significant impairment of endothelial function was observed in human essential hypertension as well as in secondary forms of hypertension. No correlation was observed with vascular structure. In animal models of genetic hypertension there is substantial evidence for a beneficial effect of anti-hypertensive treatment with angiotensin converting enzyme (ACE) inhibitors, calcium entry blockers and angiotensin II receptor blockers on endothelial function in small resistance arteries. A significant improvement in endothelial dysfunction may be observed in hypertensive patients after prolonged treatment with ACE inhibitors (cilazapril, lisinopril), calcium entry blockers (nifedipine), and angiotensin II receptor blockers (losartan), while atenolol and hydrochlorotiazide proved to be ineffective in this regard despite similar blood pressure reductions. We conclude that: (i) the development of hypertension is usually associated with the presence of endothelial dysfunction in small resistance arteries of essential hypertensive patients; (ii) vascular structure does not seem to be the major determinant of endothelial function, at least in subcutaneous small resistance arteries; (iii) anti-hypertensive therapy with ACE inhibitors, angiotensin II receptor blockers and calcium entry blockers may improve endothelial function; (iv) a decrease in blood pressure seems to be necessary but not sufficient to obtain a beneficial effect on the endothelium in humans.

Repeated thermal therapy improves impaired vascular endothelial function in patients with coronary risk factors

OBJECTIVES

We sought to determine whether sauna therapy, a thermal vasodilation therapy, improves endothelial function in patients with coronary risk factors such as hypercholesterolemia, hypertension, diabetes mellitus and smoking.

BACKGROUND

Exposure to heat is widely used as a traditional therapy in many different cultures. We have recently found that repeated sauna therapy improves endothelial and cardiac function in patients with chronic heart failure.

METHODS

Twenty-five men with at least one coronary risk factor (risk group: 38 +/- 7 years) and 10 healthy men without coronary risk factors (control group: 35 +/- 8 years) were enrolled. Patients in the risk group were treated with a 60 degrees C far infrared-ray dry sauna bath for 15 min and then kept in a bed covered with blankets for 30 min once a day for two weeks. To assess endothelial function, brachial artery diameter was measured at rest, during reactive hyperemia (flow-mediated endothelium-dependent dilation [%FMD]), again at rest and after sublingual nitroglycerin administration (endothelium-independent vasodilation [%NTG]) using high-resolution ultrasound.

RESULTS

The %FMD was significantly impaired in the risk group compared with the control group (4.0 +/- 1.7% vs. 8.2 +/- 2.7%, p < 0.0001), while %NTG was similar (18.7 +/- 4.2% vs. 20.4 +/- 5.1%). Two weeks of sauna therapy significantly improved %FMD in the risk group (4.0 +/- 1.7% to 5.8 +/- 1.3%, p < 0.001). In contrast, %NTG did not change after two weeks of sauna therapy (18.7 +/- 4.2% to 18.1 +/- 4.1%).

CONCLUSIONS

Repeated sauna treatment improves impaired vascular endothelial function in the setting of coronary risk factors, suggesting a therapeutic role for sauna treatment in patients with risk factors for atherosclerosis.

Treatment with irbesartan or atenolol improves endothelial function in essential hypertension

OBJECTIVES

To investigate if antihypertensive treatment could improve endothelium-dependent vasodilatation in hypertensive patients, and whether the angiotensin II subtype-1 (AT1)-receptor antagonist irbesartan and the beta1-receptor antagonist atenolol would differ in this respect.

SUBJECTS AND METHODS

Thirty-four patients (28 men and six women) with mild-to-moderate essential hypertension (diastolic blood pressure 90-120 mmHg) were randomized to once daily 150-300 mg irbesartan or 50-100 mg atenolol in a double-blind fashion, preceded by a placebo run-in period. Forearm blood flow (FBF) was assessed by venous occlusion plethysmography during local intra-arterial infusions of methacholine and sodium nitroprusside, to evaluate endothelium-dependent and endothelium-independent vasodilatation, respectively. Measurements of FBF were undertaken at the end of the run-in placebo period and repeated after 3 months of active antihypertensive treatment.

RESULTS

Irbesartan and atenolol induced a similar decline in blood pressure (from 171/107 to 158/98 mmHg, P < 0.05), and improved endothelium-dependent vasodilatation (e.g. an increase in FBF response to 4 microg/min methacholine from 325 +/- 29% to 411 +/- 41%, P < 0.05), with no difference between the two study drugs. No significant changes in endothelium-independent vasodilatation were induced by irbesartan or by atenolol.

CONCLUSIONS

The present study shows that 3 months of antihypertensive therapy with irbesartan or atenolol improves endothelium-dependent vasodilatation.

Renin-angiotensin system is involved in the mechanism of increased serum asymmetric dimethylarginine in essential hypertension

Endothelium-dependent/nitric oxide (NO)-mediated vasodilation is impaired in hypertensive individuals. Asymmetric dimethylarginine (ADMA), an endogenous inhibitor of NO synthase, is synthesized by many types of cells including vascular endothelial cells. The serum level of ADMA is elevated in patients with essential hypertension, but the mechanism for this increase is unknown. Therefore, the present study examined whether the renin-angiotensin system (RAS) is involved. Patients with essential hypertension [systolic blood pressure (BP) > 160 mmHg and/or diastolic BP > 95 mmHg] were randomized to an angiotensin-converting enzyme (ACE) inhibitor treatment group (perindopril, 4mg/day for 4 weeks, n = 7), an angiotensin II type 1 (AT1) receptor antagonist treatment group (losartan, 50 mg/day for 4 weeks, n = 7) or a beta-blocker treatment group (bisoprolol, 5 mg/day for 4 weeks, n = 7). Before and after the treatment, BP, serum concentration of ADMA and plasma concentration of von Willebrand factor (vWF, a biological marker of endothelial injury) were measured. Perindopril, losartan and bisoprolol decreased BP to a similar extent, and either perindopril or losartan, but not bisoprolol, significantly decreased serum ADMA and plasma vWF. These findings suggest that the RAS may contribute to the mechanism of increased serum ADMA as well as to the endothelial injury observed in hypertensive patients. The vasculoprotective actions of ACE inhibitors or AT1 receptor antagonists may be explained at least in part by amelioration of the endothelial injury through a decrease in the serum ADMA concentration.

Therapeutic potential of angiotensin II receptor antagonists

The circulating renin-angiotensin system plays an important role in cardiovascular homeostasis. More importantly, the local tissue renin angiotensin plays a pivotal role in cell growth and remodelling of cardiomyocytes and on the peripheral arterial vasculature. In addition, the renin angiotensin system is related to apoptosis, control of baroreflex and autonomic responses, vascular remodelling and regulation of coagulation, inflammation and oxidation. The cardioprotective and vascular protective effects of the angiotensin receptive blockade appears to be related to selective blockade of the angiotensin II (A-II) Type I (AT(1)) receptors. However, there is now growing evidence showing that some of the effects of AT-II receptor blockers (ARBs) are related to the activation of the kinin pathways. This paper will review some of the recent mechanisms related to the cardiovascular effects of angiotensin and more specifically of ARBs. This paper will present the novel data on the role of ARB in the development of atherosclerosis, vascular remodelling, coagulation balance and autonomic regulation. Finally, the role of ARBs, used alone or in combination with ACE inhibitor in patients with heart failure, will be discussed.

Effects of antihypertensive drugs on vascular remodeling: do they predict outcome in response to antihypertensive therapy?

Remodeling of large and small arteries in hypertension contributes to elevation of blood pressure, and may participate in the complications of hypertension. Large arteries exhibit increased lumen size, thickened media with increased collagen deposition, and decreased compliance, which contributes to raised systolic blood pressure and pulse pressure. In small (resistance) arteries smooth muscle cells are restructured around a smaller lumen, without true hypertrophy, particularly in milder forms of hypertension, whereas in severe forms and in secondary hypertension hypertrophic remodeling has been reported. Endothelial dysfunction occurs in many patients, with prevalence similar to that of left ventricular hypertrophy. Treatment with angiotensin-converting enzyme inhibitors, angiotensin receptor subtype 1 antagonists and long-acting calcium channel blockers has corrected changes in large and small arteries in hypertensive patients. Treatment with beta-blockers did not modify either structure or function of small arteries. Improved outcomes were reported in clinical trials with drugs that exert vascular protective effects, such as angiotensin-converting enzyme inhibitors and angiotensin receptor subtype 1 antagonists, as well as with those that do not appear to improve vascular structure or function. Recent trials suggest that these different drugs may provide similar benefits essentially through blood pressure lowering, although some minor differences between drugs have been noted. For example, the alpha-blocker doxasozin has been associated with worse outcomes (heart failure) than have diuretics. That hard end-point clinical trials have not demonstrated any advantages of agents with vasculoprotective properties may relate in part to the relatively short duration of some of these multicenter trials (3-5 years). Another contributing factor may be the low number of events with each drug class in the longer trials. Thus, current evidence does not support the rational expectation that vasculoprotective antihypertensive agents will be associated with better outcomes in hypertensive patients, possibly because of limitations of these trials.

The effect of antihypertensive drugs on vascular compliance

Measurement of vascular compliance has assumed increasing importance as a marker of early disease of the vascular wall, a predictor of future vascular disease, and a way to monitor the effects of vasoactive agents on arterial wall stiffness. Vascular compliance can be estimated by several methods: measurement of the pulse pressure, or pulse pressure-stroke volume ratio; analysis of the systolic pulse wave augmentation index and the diastolic pulse wave contour; ultrasonic echo-tracking; and MRI. Because few comparative studies have been done, the physiologic significance of the measures of compliance obtained by each method is uncertain. Antihypertensive drugs may improve vascular compliance by reducing blood pressure, relaxing vascular smooth muscle, or promoting long-term effects on vascular smooth muscle and cardiomyocyte growth and remodeling. Angiotensin converting enzyme (ACE) inhibitors have been reported to improve vascular compliance in nearly all studies, suggesting a beneficial class effect independent of blood pressure reduction. Favorable changes in the vascular wall-lumen ratio of small vessels from subcutaneous gluteal biopsy specimens after treatment with ACE inhibitors and the persistence of improved vascular compliance after withdrawal of therapy indicate that these agents may produce long-term vascular remodeling. Although few studies have been done, angiotensin II receptor antagonists improve vascular compliance, possibly by blocking angiotensin II-mediated cell proliferation and increasing apoptosis via unopposed AT1 receptor stimulation. In contrast, calcium antagonists and beta-blockers have variable effects on vascular compliance, although beta-blockers with intrinsic sympathomimetic activity improve vascular compliance. Diuretics have little effect on vascular compliance beyond their blood pressure-lowering actions, except for spironolactone, which by improving vascular compliance may have contributed to the reduction in heart failure mortality seen in the Randomized Aldactone Evaluation Study.

Increased generation of superoxide by angiotensin II in smooth muscle cells from resistance arteries of hypertensive patients: role of phospholipase D-dependent NAD(P)H oxidase-sensitive pathways

OBJECTIVE

We tested the hypothesis that increased responsiveness of phospholipase D (PLD) to angiotensin II (Ang II) is associated with increased oxidative stress and exaggerated growth responses in vascular smooth muscle cells (VSMC) from untreated essential hypertensive patients.

DESIGN

VSMCs from peripheral resistance arteries of normotensive and hypertensive subjects were studied. Production of reactive oxygen species (ROS) was measured with the fluoroprobe 5-(and 6)-chloromethyl-2',7'-dichlorodihydrofluorescein diacetate (CM-H2DCFDA). PLD and reduced nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) oxidase were assessed with the inhibitors, dihydro-D-erythro-sphingosine (sphinganine) and diphenylene iodinium (DPI), respectively, and protein kinase C (PKC) effects were determined using chelerythrine chloride and calphostin C. PLD activity was measured by the transphosphatidylation assay.

RESULTS

Ang II increased the CM-H2DCFDA fluorescence signal, derived predominantly from H2O2. Ang II-induced generation of DPI-inhibitable ROS was significantly enhanced in cells from hypertensives compared with normotensives (Emax = 72 +/- 2 versus 56.9 +/- 1.8 fluorescence units, P< 0.01). PLD inhibition attenuated Ang II-induced ROS generation, with greater effects in the hypertensive group than the normotensive group (delta = 42 +/- 3.3 versus 21 +/- 2 units). PKC inhibition partially decreased Ang II-elicited signals. Ang II-stimulated PLD activity and DNA and protein synthesis were significantly greater in cells from hypertensives than normotensives. These effects were normalized by DPI and sphinganine.

CONCLUSIONS

Our results suggest that in essential hypertension enhanced oxidative stress and augmented growth-promoting actions of Ang II are associated with increased activation of PLD-dependent pathways. These processes may contribute to vascular remodeling in hypertension.

Peripheral vascular disease and hypertension: a forgotten association?

Peripheral vascular disease (PVD) is associated with a high cardiovascular morbidity and mortality. Intermittent claudication is the most common symptomatic manifestation of PVD, but is also an important predictor of cardiovascular death, increasing it by three-fold, and increasing all-cause mortality by two to five-fold. Hypertension is a common and important risk factor for vascular disorders, including PVD. Of hypertensives at presentation, about 2-5% have intermittent claudication, with this prevalence increasing with age. Similarly, 35-55% of patients with PVD at presentation also have hypertension. Patients who suffer from hypertension with PVD have a greatly increased risk of myocardial infarction and stroke. Apart from the epidemiological associations, hypertension contributes to the pathogenesis of atherosclerosis, the basic underlying pathological process underlying PVD. Hypertension, in common with PVD, is associated with abnormalities of haemostasis and lipids, leading to an increased atherothrombotic state. Nevertheless, none of the large antihypertensive treatment trials have adequately addressed whether a reduction in blood pressure causes a decrease in PVD incidence. There is therefore an obvious need for such outcome studies, especially since the two conditions are commonly encountered together.

Small artery remodeling in hypertension: can it be corrected?

Vascular structure, function, and mechanics are altered in hypertension, which contributes to an important degree to complications of elevated blood pressure. Vascular hypertrophy with collagen deposition and increased stiffness is found in large arteries, whereas in small arteries, smooth muscle cells are restructured around a smaller lumen, and there is no net growth of the vascular wall, particularly in milder forms of hypertension. Hypertrophic remodeling and increased small artery stiffness may be found in more severe hypertension. Endothelial dysfunction occurs in large or smaller vessels in a variable percentage of patients, particularly in presence of other risk factors such as diabetes, smoking, dyslipidemia, and advanced atherosclerosis. In clinical trials, 1-year treatment with angiotensin-converting enzyme inhibitors, angiotensin AT1 receptor antagonists, and long-acting calcium channel blockers corrected small artery structure and endothelial dysfunction in hypertensive patients, whereas beta-adrenergic receptor blockers did not. Improved outcomes in hypertensive patients demonstrated in recent trials with some but not others of these agents could be a consequence, at least in part, of vascular protection offered by some antihypertensive agents.

The beta blockers: are they as protective in hypertension as in other cardiovascular conditions?

Beta blockers are frequently used to treat hypertension because of their well established safety and efficacy. Large clinical trials yield a 12%--20% decline in cardiovascular end points in hypertensive patients treated with beta blockers. However, beta blockers account for only 11% of antihypertensive prescriptions, and their use appears to be declining as newer agents with fewer side effects become available. The metabolic side effects of beta blockers have recently been examined. While they may raise triglycerides, lower high-density lipoprotein cholesterol, induce glucose intolerance, and possibly unmask diabetes, these effects have not been shown to impact their clinical effectiveness. For hypertension, beta blockers are still recommended as first-line therapy in many patients, particularly those at high risk for cardiovascular disease. They are also indicated for other cardiovascular disorders, such as congestive heart failure and postmyocardial infarction, in which mortality reductions exceed that seen with hypertension treatment in patients without cardiovascular complications. (c)2001 Le Jacq Communications, Inc.

Dose-dependent blockade of the angiotensin II type 1 receptor with losartan in normal volunteers

Losartan, an angiotensin II type 1 receptor (AT1) antagonist, was developed as a more specific alternative to angiotensin-converting enzyme (ACE) inhibitors. At a daily dose of 50 mg, losartan is currently evaluated in large outcome trials involving patients with hypertension and postmyocardial infarction. The current study evaluated the level and duration of blockade of a pressor response to angiotensin II by 50 and 150 mg of losartan, compared with 32 mg of candesartan. Eight normotensive volunteers were randomly assigned to a single dose of losartan 50 or 150 mg, candesartan 32 mg, or placebo. Subjects were re-randomized after a 2-week washout period to complete all four study arms. Radial artery systolic pressure response to exogenous angiotensin II was measured at 2, 6, 12, and 24 h after administration of drug. Losartan 50 mg reduced the pressure response to exogenous angiotensin II significantly only at 6 h. In contrast, candesartan and losartan 150 mg produced a greater reduction in the pressure response to angiotensin II throughout the 24-h period. This suppression was not paralleled by a reduction in resting systemic arterial pressure. Higher doses than 50 mg of losartan might be evaluated to elicit optimal clinical effects.

Vasodilatation, not hypotension, improves resistance vessel design during treatment of essential hypertension: a literature survey

Correction of structural abnormalities in resistance arteries of patients with essential hypertension is a potential treatment goal, in addition to blood pressure reduction. However, available evidence from human as well as from animal studies indicates that antihypertensive therapy is not always accompanied by normalization of resistance vessel structure, despite normalization of blood pressure. Thus, blood pressure is not the only factor determining resistance vessel structure, and experimental studies show that several factors could play a role, including shear stress and hormonal stimulation. To date, there has been no systematic review of the many published papers which have studied the structural effects of antihypertensive therapy, and it is not known which conditions are best able to normalize resistance vessel structure. We have therefore made a survey of the available literature. The survey shows that change in blood pressure in indeed a poor indicator of change in resistance vessel structure. However, it is a remarkably consistent finding that normalization of resistance vessel structure is obtained with therapeutic regimens which reduce blood pressure by vasodilation rather than by lowering cardiac output Thus, to the extent that normalization of resistance vessel structure is deemed a goal of antihypertensive treatment, the survey points towards the importance of considering not only the treatment effect on blood pressure, but also the haemodynamic effects within patients with essential hypertension.

Add-on angiotensin receptor blockade with maximized ACE inhibition

BACKGROUND

Prolonged angiotensin-converting enzyme (ACE) inhibitor therapy leads to angiotensin I (Ang I) accumulation, which may "escape" ACE inhibition, generate Ang II, stimulate the Ang II subtype 1 (AT1) receptor, and exert deleterious renal effects in patients with chronic renal diseases. We tested the hypothesis that losartan therapy added to a background of chronic (>3 months) maximal ACE inhibitor therapy (lisinopril 40 mg q.d.) will result in additional Ang II antagonism in patients with proteinuric chronic renal failure with hypertension.

METHODS

Sixteen patients with proteinuric moderately advanced chronic renal failure completed a two-period, crossover, randomized controlled trial. Each period was one month with a two-week washout between periods. In one period, patients received lisinopril 40 mg q.d. along with other antihypertensive therapy, and in the other, losartan 50 mg q.d. was added to the previously mentioned regimen. Hemodynamic measurements included ambulatory blood pressure monitoring (ABP; Spacelabs 90207), glomerular filtration rate (GFR) with iothalamate clearances and cardiac outputs by acetylene helium rebreathing technique. Supine plasma renin activity and plasma aldosterone and 24-hour urine protein were measured in all patients.

RESULTS

Twelve patients had diabetic nephropathy, and four had chronic glomerulonephritis. The mean age (+/- SD) was 53 +/- 9 years. The body mass index was 38 +/- 5.7 kg/m(2), and all except two patients were males. Seated cuff blood pressure was 156 +/- 18/88 +/- 12 mm Hg. The pulse rate was 77 +/- 11 per min, and the cardiac index was 2.9 +/- 0.5 L/min/m(2). Mean log 24-hour protein excretion/g creatinine or overall ABPs did not change. Mean placebo subtracted, losartan-attributable change in protein excretion was +1% (95% CI, -20% to 28%, P = 0.89). Similarly, the change in systolic ambulatory blood pressure (ABP) was 4.6 mm Hg (-5.7 to 14.9, P = 0.95), and diastolic ABP was 1.5 mm Hg (-4.5 to 7.6, P = 0.59). No change was seen in cardiac output. However, there was a mean 14% increase (95% CI, 3 to 26%, P = 0.017) in GFR attributable to losartan therapy. A concomitant fall in plasma renin activity by 32% was seen (95% CI, -15%, - 45%, P = 0.002). No hyperkalemia, hypotension, or acute renal failure occurred in the trial. These results were not attributable to sequence or carryover effects.

CONCLUSIONS

Add-on losartan therapy did not improve proteinuria or ABP over one month of add on therapy. Improvement of GFR and fall in plasma renin activity suggest that renal hemodynamic and endocrine changes are more sensitive measures of AT1 receptor blockade. Whether add-on AT1 receptor blockade causes antiproteinuric effects or long-term renal protection requires larger and longer prospective, randomized controlled trials.

[New pharmacological agents in heart failure]

Heart failure is a common and growing public health problem, with increasing incidence and prevalence over the last 2 decades. Despite improvements in its current management, heart failure is still associated with significant morbidity and mortality. This has motivated the search for newer therapeutic modalities, which are based on a better understanding on the pathophysiologic events that lead to heart failure. This review summarizes the potential role of new pharmacological agents in the treatment of heart failure. These potential new agents can be classified according to their role in the modulation of the main pathophysiologic abnormalities that characterized heart failure, that include: cellular-extracellular abnormalities, endothelial dysfunction, neurohormonal and immunologic activation.

Small artery remodeling is the most prevalent (earliest?) form of target organ damage in mild essential hypertension

BACKGROUND

The heart and blood vessels are exposed to elevated blood pressure (BP) in hypertensive patients, but their changes in response to BP or non-hemodynamic stimuli may be different, and occur with different time-courses. To evaluate this, we studied the prevalence of structural and functional alterations of resistance arteries and cardiac hypertrophy in patients with mild essential hypertension.

METHODS

Resistance arteries were dissected from gluteal subcutaneous tissue from 38 hypertensive patients (47 +/- 1 years; 71% male; BP 148 +/- 2/99 +/- mmHg), studied on a pressurized myograph, and compared to those from 10 normotensives (44 +/- 3 years; 40% male; BP 113 +/- 4/76 +/- 2 mmHg).

RESULTS

The prevalence of abnormal structure (media-to-lumen ratio, M/L) and impaired endothelial function (maximal acetylcholine response) was 97 and 58% (abnormal was defined as greater than mean + 1 SD of normotensives), or 63 and 34% (abnormal defined as greater than mean +/- 2SD). Thirty four percent of hypertensive patients exhibited left ventricular hypertrophy by echocardiography. When grouped into tertiles according to increasing ambulatory systolic BP (SBP), the highest BP tertile showed increased M/L (P< 0.01) and left ventricular mass index (LVMI, P < 0.05) and marginally decreased endothelial function (P= 0.07). LVMI was greatest in the tertile of patients with highest M/L (P< 0.05). Endothelial function was decreased in the tertile with greatest vascular stiffness (P< 0.01). By multivariate analysis, M/L correlated with ambulatory SBP (beta = 0.40, P= 0.02), and LVMI correlated with ambulatory SBP (beta = 0.41, P = 0.001) and body mass index (beta = 0.30, P< 0.05). Female sex influenced endothelial function negatively (beta = -0.63, P< 0.01).

CONCLUSION

Structural alterations of resistance arteries were demonstrated in most hypertensive patients, followed by endothelial dysfunction and cardiac hypertrophy in a smaller number of hypertensives. Small artery structural remodeling may precede most clinically relevant manifestations of target organ damage in mild essential hypertension.

Angiotensin II and the pathophysiology of cardiovascular remodeling

Hypertension is associated with a number of adverse morphologic and functional changes in the cardiovascular system. These include remodeling of the left ventricle, alterations in the morphology and mechanical properties of the vasculature, and the development of endothelial dysfunction. Recent studies have shown that angiotensin II is capable of mediating these changes via its interaction with the angiotensin II type 1 receptor. These nonhemodynamic effects of angiotensin II are independent of its effect on blood pressure. Thus, elevated levels of angiotensin II may lead directly to many hypertension-associated pathologies. Recent evidence that mechanical strain, oxidized low-density lipoprotein cholesterol, and aldosterone can cause upregulation of angiotensin II type 1 receptors indicates that activation of the renin-angiotensin system is not necessary for the actions of angiotensin II to be amplified. Because the strain on the vessel wall may be increased under conditions of hypertension, increased arterial pressure may amplify the actions of angiotensin II without a discernible increase in plasma angiotensin II levels. In both the myocardium and the peripheral vasculature, fibrosis is a major component of the remodeling that occurs in hypertension. There is substantial evidence that transforming growth factor beta-1 (TGF-beta(1)) mediates angiotensin-II-induced fibrosis in patients with hypertension and in those with a variety of nephropathies. Mechanical strain also induces fibrosis in a mechanism mediated by TGF-beta(1). This cytokine thus represents a common pathway by which angiotensin II and increased arterial pressure may induce cardiovascular fibrosis.

Formulating clinical strategies for angiotensin antagonism: a review of preclinical and clinical studies

Extensive animal studies and a growing number of human clinical trials have now definitively demonstrated the central role of the renin-angiotensin-aldosterone system in the expression and modulation of cardiovascular disease. In contrast to the original hypothesis, the benefits of angiotensin antagonism do not emanate from the antihypertensive effect alone. Subsequent extensive investigations of angiotensin blockade suggest that the benefits of this approach may also result from the pharmacologic alteration of endothelial cell function and the ensuing changes in the biology of the vasculature. The more recent availability of direct antagonists of the AT(1) angiotensin receptor has introduced an element of doubt into this realm of clinical decision making. The receptor antagonists and the more widely studied converting-enzyme inhibitors share many endpoint attributes. Nevertheless, the partially overlapping mechanisms of action for the two classes of angiotensin antagonists confer distinct pharmacologic properties, including side effect profiles, mechanisms of action, and theoretic salutary effects upon the expression of cardiovascular disease. The current review will attempt to contrast the biology of angiotensin converting-enzyme inhibition with angiotensin II receptor antagonism. A discussion of the differential effects of these drug classes on endothelial cell function and on the modulation of vascular disease will be utilized to provide a theoretic framework for clinical decision making and therapeutics.

Correlation of endothelial function in large and small arteries in human essential hypertension

OBJECTIVES

The structure and function of blood vessels varies along the vascular tree, and alterations found in hypertension are also different. The aim of this study was to determine whether non-invasive measurement of endothelial function in conduit arteries reflects that of subcutaneous resistance arteries measured in vitro.

METHODS AND RESULTS

Sixteen essential hypertensive patients (aged 50 +/- 2 years) were studied. Flow-mediated dilation (FMD) during reactive hyperemia (endothelium-dependent) and sublingual nitroglycerin (NTG)-induced dilatation (endothelium-independent) were assessed in brachial arteries by ultrasound. Structure, and acetylcholine (10(-9) to 10(-4) mol/l) and sodium nitroprusside (SNP, 10(-8) to 10(-3) mol/l)-induced vasorelaxation of resistance arteries dissected from gluteal subcutaneous biopsies were measured in vitro using a pressurized myograph. Brachial artery FMD and NTG-induced dilatation were 8.4 +/- 1.0 and 18.1 +/- 1.4%, respectively. Resistance arteries of hypertensive patients showed greater media:lumen ratio (8.6 +/- 0.4 versus 5.9 +/- 0.3% in normotensive subjects, P< 0.01), and maximal acetylcholine responses was diminished to 75 +/- 6% compared to normotensive subjects (97 +/- 2%, P< 0.01). FMD correlated with maximal acetylcholine responses (r2 = 0.57, P< 0.001). FMD did not correlate significantly with the media: lumen ratio of resistance arteries (r2 = -0.22, P= 0.07). By multivariate analysis, FMD predicted resistance artery endothelial function independently of age, sex, body mass index, blood lipid status and lumen diameter of brachial artery (beta = 0.81, P< 0.001).

CONCLUSIONS

Endothelial dilatory responses are similar in large and small arteries in hypertensive patients. Abnormal FMD in the brachial artery predicts the presence of endothelial dysfunction in human resistance arteries, suggesting that impairment of endothelial function is a generalized alteration in hypertension. Ultrasound measurement of endothelial dysfunction in the brachial artery appears to be less sensitive than in-vitro measurement in resistance arteries.

Effects of omapatrilat on systemic arterial function in patients with chronic heart failure

The mechanisms of action of omapatrilat, an agent that inhibits both neutral endopeptidase 24.11 and angiotensin-converting enzyme, on arterial function in patients with heart failure have not been previously reported. Forty-eight patients in New York Heart Association functional class II to III, left ventricular ejection fraction < or = 40%, and in sinus rhythm were randomized to a dose-ranging (2.5, 5, 10, 20, or 40 mg) study of omapatrilat for 12 weeks. Measurements were obtained at baseline and 12 weeks. Decreases in systolic (25.0 +/- 4.5 vs 2.8 +/- 5.0 mm Hg, p < 0.05) and mean arterial (13.9 +/- 3.0 vs 0.3 +/- 3.3 mm Hg, p < 0.05) pressure were seen after 12 weeks of therapy with higher doses. Ventricular-arterial coupling was improved with a dose-related decrease in augmentation index (-13.8 +/- 1.7% vs +6.1 +/- 2.1%, p < 0.01). There was no change in resting forearm blood flow between groups; however, maximum forearm vasodilator response during reactive hyperemia increased in the high-dose groups compared with the control group (+266 +/- 43% vs - 14 +/- 92%, p < 0.05). Omapatrilat induced an increase in postdose plasma atrial natriuretic peptide levels (30 +/- 11 vs -2 +/- 7 pmol/L, p < 0.01) in high-dose groups consistent with endopeptidase 24.11 inhibition. Omapatrilat shows beneficial changes in ventricular-vascular coupling and arterial function in heart failure.

Differential activation of extracellular signal-regulated protein kinase 1/2 and p38 mitogen activated-protein kinase by AT1 receptors in vascular smooth muscle cells from Wistar-Kyoto rats and spontaneously hypertensive rats

OBJECTIVES

The present study investigates effects of angiotensin II on activation of extracellular signal-regulated protein kinase (ERK) 1/2, p38 mitogen activated-protein kinase (p38MAPK) and c-Jun amino terminal kinase (JNK) in vascular smooth muscle cells from spontaneously hypertensive rats (SHR).

METHODS

Vascular smooth muscle cells (VSMC) from mesenteric arteries of Wistar-Kyoto (WKY) rats and SHR were studied. Angiotensin II-induced phosphorylation of ERK1/2, JNK and p38MAPK were assessed by Western blot analysis. c-fos mRNA expression by angiotensin II was determined by reverse transcriptase-polymerase chain reaction in the absence and presence of PD98059, selective inhibitor of ERK1/2-dependent pathways and SB202190, selective p38MAPK inhibitor.

RESULTS

Angiotensin II increased phosphorylation of ERK1/2 and p38MAPK, but not JNK. Responses were significantly increased in SHR compared with WKY. Irbesartan, AT1 receptor antagonist, but not PD123319, AT2 receptor blocker, abolished angiotensin II-induced effects. PP2, selective Src inhibitor, decreased angiotensin II-mediated activation of MAP kinases. Angiotensin II increased c-fos mRNA expression in SHR and had a small stimulatory effect in WKY. These actions were inhibited by PD98059, whereas SB202190 had no effect.

CONCLUSIONS

Angiotensin II-induced activation of vascular ERK1/2 and p38MAPK is increased in SHR. These effects are mediated via AT1 receptors, which activate Src-dependent pathways. Overexpression of c-fos mRNA in SHR is due to ERK1/2-dependent, p38MAPK-independent pathways. Our results suggest that angiotensin II activates numerous MAP kinases in VSMCs and that differential activation of these kinases may be important in altered growth signaling in VSMCs from SHR.

The renin angiotensin system as a risk factor for coronary artery disease

The renin angiotensin system was demonstrated to play a significant role in the genesis of hypertension and regulation of vascular tone over 100 years ago. The early investigations were subsequently expanded to implicate the renin angiotensin system in a variety of physiologic processes that may play a significant role in the initiation and progression of atherosclerosis. The renin angiotensin system modulates vascular structure and left ventricular hypertrophy via a number of trophic effects. Elevated levels of angiotensin II are associated with the generation of oxidative stress, and may thus play a significant role in the earliest phases of atherosclerosis. The role inflammation plays in atherosclerosis is amplified by the renin angiotensin system via the effects on adhesion molecules, growth factors, and chemoattractant molecules, which modulate the migration of inflammatory cells into the subendothelial space. The effects of angiotensin II, which may be at least partially genetically mediated, have been implicated in epidemiologic and clinical studies as a risk factor for the development of atherosclerosis. This review centers on the potential role that the renin angiotensin system plays as a risk factor for the development of atherosclerosis, and the role of converting enzyme inhibition or angiotensin receptor blockade as a mechanism to decrease the initiation, progression, and clinical consequences of the atherosclerotic process.

Expression and function of angiotensin converting enzyme, chymase, and angiotensin II in the human radial artery and internal thoracic artery

BACKGROUND

The potential role of the local renin-angiotensin system to differentially affect radial artery and internal thoracic artery graft performance has not been examined.

METHODS

Contractile responses to angiotensin I and II in the radial artery and the internal thoracic artery were examined in vitro. The expression function, and localization of angiotensin receptors, angiotensin converting enzyme, and chymase were studied in radial artery and internal thoracic artery segments.

RESULTS

Angiotensin I and II contractions were significantly greater (p < 0.05) in the radial artery compared to the internal thoracic artery. In both arteries, angiotensin II responses were mediated via the AT1 receptor. Messenger RNA transcripts for angiotensin-converting enzyme and chymase were detected in both arteries. Angiotensin-converting enzyme was localized to luminal and vaso vasorum endothelial cells and smooth muscle cells in both vessels, while chymase was colocalized with mast cells in adventitial and medial layers. An angiotensin converting enzyme or a chymase inhibitor singularly had no effect on angiotensin I contractions, however, when combined, a marked inhibition of the angiotensin I response was observed in both vessels.

CONCLUSIONS

Our results illustrate the complexities which exist within the local renin angiotensin system and suggest that clinical trials which may modulate the system are warranted.

Effects of antihypertensive therapy on hypertensive vascular disease

Hypertension is associated with alterations in the structure, function, and mechanical properties of large and small arteries. Changes in the endothelium, smooth muscle cell, extracellular matrix, and possibly the adventitia, contribute to complications of hypertension. In large arteries, vascular hypertrophy is found, often with increased stiffness of media components. In small arteries, particularly in mild hypertension, rearrangement of smooth muscle cells around a smaller lumen without changes in media volume (eutrophic remodeling) occurs; in more severe hypertension, hypertrophic remodeling with increased vascular stiffness can be found. Vascular remodeling is accompanied by an increase in the extracellular matrix, particularly collagen deposition. Recent studies have demonstrated that vascular remodeling and endothelial dysfunction of small and large vessels may be normalized by treatment with some antihypertensive agents (angiotensin converting enzyme inhibitors, angiotensin AT(1) receptor antagonists, and long-acting calcium channel blockers). Angiotensin converting enzyme inhibitors have now been shown to improve outcomes in hypertensive patients, an effect that may in part be related to the vascular protective effects reviewed here.

Reduction of resistance artery stiffness by treatment with the AT(1)-receptor antagonist losartan in essential hypertension

In spontaneously hypertensive rats resistance artery structure, endothelial dysfunction and geometry-independent wall stiffness were reduced by an angiotensin AT(1)-receptor antagonist. In previous studies of human hypertension, interruption of the renin-angiotensin system corrected small artery structure and endothelial dysfunction, whereas the beta-blocker atenolol did not. We hypothesized that the AT(1)R antagonist losartan, but not the beta-blocker atenolol, would reduce stiffness of gluteal subcutaneous small arteries in essential hypertensive patients. Seventeen untreated mild essential hypertensive patients (47+/-2 years; 75% male) were randomly assigned in double-blind fashion to losartan or atenolol treatment for one year. Small, resistance size arteries were studied on pressurized myographs. Blood pressure (mmHg) was reduced (p<0.01) from 145 +/- 4/101 +/- 2 and 147 +/- 6/98 +/- 2 to 128 +/- 4/86 +/- 2 and 131 +/- 3/84 +/- 1 by losartan and atenolol, respectively. The media/lumen ratio of small arteries was unaffected by atenolol (8.3+/-0.3% before and 8.8+/-0.5% after treatment). In contrast, losartan reduced media/lumen ratio from 8.4+/-0.4% to 6.7+/-0.3% (p<0.01). Whereas isobaric elastic modulus was unaffected by either treatment, geometry-independent stiffness (slope of elastic modulus vs. stress) was reduced from 9.7+/-1.2 to 6.1+/-0.9 (P<0.05) under losartan treatment, but was unchanged by atenolol (8.2+/-1.3 to 7.8+/-0.6). In conclusion, treatment with losartan reduced stiffness and structural alterations of subcutaneous resistance arteries of previously untreated essential hypertensive patients, whereas atenolol failed to do so.