Protective Effects of an Angiotensin II Receptor Blocker and a Long-Acting Calcium Channel Blocker against Cardiovascular Organ Injuries in Hypertensive Patients

Myocardial Interstitial Fibrosis in Hypertensive Heart Disease: From Mechanisms to Clinical Management

Hypertensive heart disease (HHD) can no longer be considered as the beneficial adaptive result of the hypertrophy of cardiomyocytes in response to pressure overload leading to the development of left ventricular hypertrophy. The current evidence indicates that in patients with HHD, pathological lesions in the myocardium lead to maladaptive structural remodeling and subsequent alterations in cardiac function, electrical activity, and perfusion, all contributing to poor outcomes. Diffuse myocardial interstitial fibrosis is probably the most critically involved lesion in these disorders. Therefore, in this review, we will focus on the histological characteristics, the mechanisms, and the clinical consequences of myocardial interstitial fibrosis in patients with HHD. In addition, we will consider the most useful tools for the noninvasive diagnosis of myocardial interstitial fibrosis in patients with HHD, as well as the most effective available therapeutic strategies to prevent its development or facilitate its regression in this patient population. Finally, we will issue a call to action for the need for more fundamental and clinical research on myocardial interstitial fibrosis in HHD.

Angiotensin-converting enzyme inhibitors increase anti-fibrotic biomarkers in African Americans with left ventricular hypertrophy

Angiotensin‐converting enzyme inhibitors (ACEi) are part of the indicated treatment in hypertensive African Americans. ACEi have blood pressure‐independent effects that may make them preferred for certain patients. We aimed to evaluate the impact of ACEi on anti‐fibrotic biomarkers in African American hypertensive patients with left ventricular hypertrophy (LVH). We conducted a post hoc analysis of a randomized controlled trial in which hypertensive African American patients with LVH and vitamin D deficiency were randomized to receive intensive antihypertensive therapy plus vitamin D supplementation or placebo. We selected patients who had detectable lisinopril (lisinopril group) in plasma using liquid‐chromatography/mass spectrometry analysis and compared them to subjects who did not (comparison group) at the one‐year follow‐up. The pro‐fibrotic marker type 1 procollagen C‐terminal propeptide (PICP) and the anti‐fibrotic markers matrix metalloproteinase‐1 (MMP‐1), tissue inhibitor of metalloproteinases 1 (TIMP‐1), telopeptide of collagen type I (CITP), and N‐acetyl‐seryl‐aspartyl‐lysyl‐proline (Ac‐SDKP) peptide were measured. Sixty‐six patients were included, and the mean age was 46.2 ± 8 years. No difference was observed in the number and intensity of antihypertensive medications prescribed in each group. Patients with detectable lisinopril had lower blood pressure than those in the comparison group. The anti‐fibrotic markers Ac‐SDKP, MMP‐1, and MMP‐1/TIMP‐1 ratio were higher in patients with detectable ACEi (all p < .05). In a model adjusted for systolic blood pressure, MMP‐1/TIMP‐1 (p = .02) and Ac‐SDKP (p < .001) levels were associated with lisinopril. We conclude that ACEi increase anti‐fibrotic biomarkers in hypertensive African Americans with LVH, suggesting that they may offer added benefit over other agents in such patients.

Persistent phenotypic shift in cardiac fibroblasts: impact of transient renin angiotensin system inhibition

Fibrotic cardiac remodeling ultimately leads to heart failure - a debilitating and costly condition. Select antihypertensive agents have been effective in reducing or slowing the development of cardiac fibrosis. Moreover, some experimental studies have shown that the reduction in fibrosis induced by these agents persists long after stopping treatment. What has not been as well investigated is whether this transient treatment results in a protection against future fibrotic cardiac remodeling. In the present review, previously published studies are re-examined to assess whether the relative percent increase in collagen deposition over an off-treatment period is attenuated, relative to control, following transient antihypertensive treatment in young or adult rats. Present findings suggest that transient inhibition of the renin angiotensin system (RAS) not only produces a sustained reduction in cardiac fibrosis, but also results in a degree of protection against future collagen deposition. In addition, prior transient RAS inhibition appears to alter the cardiac fibroblast phenotype such that these cells show a muted response to myocardial injury - namely reduced proliferation, chemokine release, and collagen deposition. This review puts forth several potential mechanisms underlying this long-term cardiac protection that is afforded by transient RAS inhibition. Specifically, fibroblast phenotypic change, cardiac fibroblast apoptosis, sustained suppression of the RAS, persistent reduction in left ventricular hypertrophy, and persistent reduction in arterial pressure are each discussed. Identifying the mechanisms ultimately responsible for this change in cardiac fibroblast response to injury, hypertension, and aging may reveal novel targets for therapy.

The effect of amlodipine besylate, losartan potassium, olmesartan medoxomil, and other antihypertensives on central aortic blood pressure and biomarkers of vascular function

Biomarkers are being increasingly used in the study of cardiovascular disease because they provide readily quantifiable surrogate endpoints and allow accurate assessment of the effects of therapy on particular pathological processes. However, in order to be useful, biomarkers must be relevant, predictable, accurate, and reproducible. There is compelling evidence from large-scale clinical trials that inhibitors of the renin-angiotensin system [angiotensin-converting enzyme inhibitors and angiotensin type II receptor blockers (ARBs)] and calcium channel blockers (CCBs) may have beneficial effects beyond blood pressure control in the treatment of hypertension. Biomarkers are expected to provide further insight into these beneficial effects and allow for quantitative assessment. This review summarizes the published clinical evidence on the effects of various antihypertensive drugs, particularly ARBs (e.g. losartan and olmesartan medoxomil) and CCBs (e.g. amlodipine), alone and in combination with other agents (e.g. hydrochlorothiazide), on central aortic pressure and the biomarkers high-sensitivity C-reactive protein (hsCRP), adiponectin, cystatin C, homeostasis model assessment of insulin resistance (HOMA-IR), procollagen, tumor necrosis factor-α, and interleukin-6. Of these biomarkers, the benefits of antihypertensive therapy on hsCRP, adiponectin, and HOMA-IR reflect a potential for quantifiable long-term vascular benefits.

Use of dihydropyridine calcium channel blockers in the management of hypertension in Eastern Asians: a scientific statement from the Asian Pacific Heart Association

Dihydropyridine calcium channel blockers (CCBs) are widely prescribed for the management of hypertension in Eastern Asians. In this study, the Asian Pacific Heart Association's Writing Committee reviewed randomized controlled trials that were conducted in the Eastern Asian region and compared a CCB with an antihypertensive drug of another class. These trials studied ambulatory blood pressure, measures of target organ damage and cardiovascular events as outcomes. Eleven trials studied ambulatory blood pressure in hypertensive patients and demonstrated that the 24-h blood pressure reduction with CCBs was greater than with other classes of antihypertensive drugs, with a weighted mean difference of 5 mm Hg systolic and 3 mm Hg diastolic. Twelve trials that studied various measurements of target organ damage in hypertensive patients produced inconsistent results when comparing CCBs and other classes of antihypertensive drugs. Four trials that studied the hard outcomes had limited power, but confirmed the findings of previous placebo-controlled trials in the region and actively controlled trials in Europe and North America; they suggested that CCBs provided superior protection against stroke and that some agents, such as amlodipine, also provided similar protection against myocardial infarction. In conclusion, CCBs should be recommended as a preferred drug for the management of hypertension in the Eastern Asian region to improve blood pressure control and to confront the aggravating epidemic of stroke and coronary heart disease.

Effects of telmisartan on insulin resistance in Japanese type 2 diabetic patients

OBJECTIVE

PPARgamma agonists are widely used in type 2 diabetic patients to reduce insulin resistance. Recently, telmisartan, an AT1 receptor antagonist, was reported to function as a partial agonist of PPARgamma based on in vitro experiments. The aim of the present study was to investigate whether the PPARgamma enhancing activity of telmisartan is exerted clinically in diabetic patients.

METHODS

We compared the effects of telmisartan with those of candesartan, on insulin sensitivity, the serum levels of various adipocytokines and oxidative stress.

PATIENTS

In total, 85 Japanese type 2 diabetic patients with hypertension, maintained on 8 mg per day of candesartan, were randomly assigned to the TM group (candesartan switched to 40 mg of telmisartan, n=38) or the CD group (no treatment change, n=47).

RESULTS

After 3 months, oxidized lipids were significantly decreased only in the TM group. Although the homeostasis assessment model of insulin resistance (HOMA-R) tended to be improved and serum concentrations of HDL-cholesterol and HMW adiponectin tended to be increased only in the TM group, these alterations were too small to be significant by unpaired t-test. Interestingly, in subgroup analysis, the alterations of HOMA-R, serum concentrations of oxidized lipids, and HMW adiponectin were more apparent in obese TM group subjects and the changes reached statistical significance.

CONCLUSION

Switching from candesartan to telmisartan in obese subjects increases serum adiponectin and improves both insulin resistance and oxidative stress, while these effects were not statistically apparent in the total patient population. These results support the idea that telmisartan exerts its PPARgamma enhancing activity clinically in obese type 2 diabetic patients.

Pioglitazone, a thiazolidinedione derivative, attenuates left ventricular hypertrophy and fibrosis in salt-sensitive hypertension

Thiazolidinediones, which stimulate peroxisome proliferator-activated receptor gamma, have been shown to prevent cardiovascular injury. However, little is known about their effects on salt-sensitive hypertension. We thus investigated whether or not pioglitazone affects left ventricular (LV) hypertrophy in Dahl salt-sensitive rats, then compared its effects to those of an angiotensin II receptor blocker, candesartan. Rats were used at 16 weeks of age after they had been fed either a low-salt (0.3%; DSL) or high-salt (8%; DSH) diet for 10 weeks; some of the DSH rats were treated with pioglitazone (10 mg/kg/day) or candesartan (4 mg/kg/day). Both drugs decreased the elevated blood pressure in DSH rats, although it was still higher than in DSL rats. Both drugs decreased plasma insulin levels, but neither affected plasma glucose levels. The thiobarbituric acid reactive substance level in the LV was decreased by both drugs. LV hypertrophy evaluated by echocardiography in DSH rats was nearly normalized by both drugs, whereas only candesartan decreased LV diameter. In histological analysis, both drugs ameliorated LV fibrosis and myocardial cell hypertrophy. Both drugs decreased elevated gene expression levels of transforming growth factor-beta1 and collagen type I, although the pioglitazone action was slightly modest. The metalloproteinase activity was increased in DSH rats, but both drugs decreased this level. Taken together, these findings indicate that pioglitazone reduced LV hypertrophy and fibrosis in salt-sensitive hypertension. Improvement in blood pressure, insulin level, and oxidative stress may be associated with this beneficial action of pioglitazone.

Control of left ventricular mass by moxonidine involves reduced DNA synthesis and enhanced DNA fragmentation

BACKGROUND AND PURPOSE

Left ventricular hypertrophy (LVH) is a maladaptive process associated with increased cardiovascular risk. Regression of LVH is associated with reduced complications of hypertension. Moxonidine is an antihypertensive imidazoline compound that reduces blood pressure primarily by central inhibition of sympathetic outflow and by direct actions on the heart to release atrial natriuretic peptide, a vasodilator and an antihypertrophic cardiac hormone. This study investigated the effect of moxonidine on LVH and the mechanisms involved in this effect.

EXPERIMENTAL APPROACH

Spontaneously hypertensive rats were treated with several doses of moxonidine (s.c.) over 4 weeks. Blood pressure and heart rate were continuously monitored by telemetry. Body weight and water and food intake were measured weekly. Measurements also included left ventricular mass, DNA content, synthesis, fragmentation, and apoptotic/anti-apoptotic pathway proteins.

KEY RESULTS

The decrease in mean arterial pressure stabilized at approximately -10 mm Hg after 1 week of treatment and thereafter. Compared to vehicle-treated rats (100%), left ventricular mass was dose- and time-dependently reduced by treatment. This reduction remained significantly lower after normalizing to body weight. Moxonidine reduced left ventricular DNA content and inhibited DNA synthesis. DNA fragmentation transiently, but significantly increased at 1 week of moxonidine treatment and was paralleled by elevated active caspase-3 protein. The highest dose significantly decreased the apoptotic protein Bax and all doses stimulated anti-apoptotic Bcl-2 after 4 weeks of treatment.

CONCLUSIONS AND IMPLICATIONS

These studies implicate the modulation of cardiac DNA dynamics in the control of left ventricular mass by moxonidine in a rat model of hypertension.

Myocardial fibrosis and diastolic dysfunction in patients with hypertension: results from the Swedish Irbesartan Left Ventricular Hypertrophy Investigation versus Atenolol (SILVHIA)

OBJECTIVES

Hypertensive left ventricular hypertrophy (LVH) is associated with cardiomyocyte hypertrophy and an excess in myocardial collagen. Myocardial fibrosis may cause diastolic dysfunction and heart failure. Circulating levels of the carboxy-terminal propeptide of procollagen type I (PICP), an index of collagen type I synthesis, correlate with the extent of myocardial fibrosis. This study examines myocardial fibrosis in relation to blood pressure, left ventricular mass (LVM), and diastolic function.

METHODS

We examined PICP levels in 115 patients with hypertensive LVH, 38 with hypertension but no hypertrophy, and 38 normotensive subjects. Patients with LVH were subsequently randomly assigned to the angiotensin II type 1 receptor blocker irbesartan or the beta1 receptor blocker atenolol for 48 weeks. Diastolic function was evaluated by tissue velocity echocardiography (n=134). We measured basal septal wall velocities of early (Em) and late (Am) diastolic myocardial wall motion, Em velocity deceleration time (E-decm), and isovolumic relaxation time (IVRTm).

RESULTS

Compared with the normotensive group, PICP was elevated and left ventricular diastolic function was impaired in the hypertensive groups, with little difference between patients with and without LVH. PICP related to blood pressure, IVRTm, Em, and E/Em, but not to LVM. Irbesartan and atenolol reduced PICP similarly. Only in the irbesartan group did changes in PICP relate to changes in IVRTm, and LVM.

CONCLUSION

Myocardial fibrosis and diastolic dysfunction are present in hypertension before LVH develops. The findings with irbesartan suggest a role for angiotensin II in the control of myocardial fibrosis and diastolic function in patients with hypertension with LVH.

Efficacy of azelnidipine on home blood pressure and pulse rate in patients with essential hypertension: comparison with amlodipine

Recently it has been recognized that not only blood pressure (BP) but also pulse rate (PR) assessed in the setting of the patient's home by a home BP monitoring device has higher predictive power for cardiovascular events than similar measurements made in the office setting. In this study, we compared the efficacy of azelnidipine to that of amlodipine in lowering morning BP and reducing PR in outpatients with essential hypertension. Patients were assigned to receive once daily administration of azelnidipine 8-16 mg/day (n = 54) or amlodipine 2.5-5 mg/day (n = 54) for 8 weeks. Morning BP and PR were evaluated by assessing patients' self-monitored BP and PR in the home environment. The mean reductions of morning systolic/diastolic BP (SBP/DBP) in the azelnidipine and amlodipine groups were similar (-24.1 +/- 11.8/-14.1 +/- 10.7 vs. -20.4 +/- 11.7/-12.2 +/- 7.7 mmHg). However, whereas azelnidipine decreased mean PR by -6.4 +/- 8.3 beats/min (p < 0.05 vs. baseline), amlodipine did not cause significant reduction of this parameter (-2.1 +/- 8.2 beats/min). Although neither drug changed PR in patients in whom baseline PR was < 70 beats/min, azelnidipine significantly lowered PR in patients whose baseline PR was > 70 beats/min. These results suggest that oral azelnidipine administration may be an effective therapy in the setting of chronic morning hypertension as well as for home PR control.

Urinary albumin excretion and the renin-angiotensin system in cardiovascular risk management

Microalbuminuria has been shown to be a strong predictor of cardiovascular morbidity and mortality in diabetic and hypertensive patients, but also in the general population. Moreover, several reports suggest that reduction of urinary albumin excretion (UAE) is associated with improvement of cardiovascular prognosis. Reduction of UAE can be achieved by lowering arterial blood pressure, but blockers of the renin-angiotensin system (RAS) with their specific renal actions have demonstrated to be able to reduce UAE more than might be expected from reduction of blood pressure alone. Consequently, angiotensin-converting enzyme inhibitors and angiotensin receptor blockers may also provide superior cardiovascular protection, especially in subjects with higher levels of albuminuria, but evidence is still scarce. The ability of both angiotensin-converting enzyme inhibitors and angiotensin receptor blockers to reduce UAE and provide cardiovascular protection suggests that the RAS may play a central role. New developments in this area include the use of aldosterone antagonists in albuminuric/proteinuric subjects, and the development of oral renin inhibitors. Combinations of the aforementioned drugs may have the ability to fully block the RAS, potentially avoiding all detrimental effects of this hormonal cascade. However, combination therapy is expected to also increase the incidence of side effects, such as hyperkalaemia and acute renal insufficiency. The current knowledge of microalbuminuria represents the proverbial tip of the iceberg, and future studies should focus on the underlying pathophysiological mechanism of urinary albumin excretion in relation to cardiovascular protection. Only then can a better understanding of the problem be achieved and the optimal pharmacological approach be ascertained.

Regression of atherosclerosis by amlodipine via anti-inflammatory and anti-oxidative stress actions

We examined whether amlodipine, an L-type calcium channel blocker (CCB), has an inhibitory effect on oxidative stress and inflammatory response, and thereby atherosclerosis, in apolipoprotein E-deficient (ApoEKO) mice. Adult male ApoEKO mice (6 weeks of age) were fed a high-cholesterol diet (HCD) for 8 or 10 weeks with or without oral administration of amlodipine (3 mg/kg/day) for 10 weeks or for only the last 2 weeks of the HCD. After HCD feeding, atherosclerotic lesion formation, in situ superoxide production and nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase activity were evaluated in the proximal aorta. The expressions of NADPH oxidase subunits (p47(phox) and rac-1), monocyte chemoattractant protein-1 (MCP-1), intercellular adhesion molecule-1 (ICAM-1), and vascular cell adhesion molecule-1 (VCAM-1) were determined with immunohistochemistry and quantitative real-time reverse-transcription polymerase chain reaction. After 8 to 10 weeks of HCD administration to ApoEKO mice, marked atherosclerotic lesion formation was observed in the proximal aorta. In the atherosclerotic lesion, superoxide production, the expression of NADPH oxidase subunits, and NADPH oxidase activity were enhanced, and the expressions of MCP-1, ICAM-1, and VCAM-1 were increased. These changes were suppressed in mice that were treated with amlodipine for 10 weeks concomitant with HCD administration, with no significant change in blood pressure and plasma cholesterol level. We also observed that treatment with amlodipine for only the last 2 weeks regressed the atherosclerotic lesions with a decrease in oxidative stress and vascular inflammation. Inhibition of the atherosclerotic lesion area and lipid area in the proximal aorta by amlodipine was correlated with its inhibitory actions on oxidative stress, inflammation and the production of adhesive molecules. These results suggest that amlodipine not only inhibits atherosclerotic lesion formation, but also regresses atherosclerosis, and that these effects are at least partly due to inhibition of oxidative stress and inflammatory response.

Amlodipine-induced reduction of oxidative stress in the brain is associated with sympatho-inhibitory effects in stroke-prone spontaneously hypertensive rats

Amlodipine is a dihydropyridine calcium channel blocker that is widely used for the treatment of hypertensive patients and has an antioxidant effect on vessels in vitro. The aim of the present study was to examine whether treatment with amlodipine reduced oxidative stress in the brains of stroke-prone spontaneously hypertensive rats (SHRSP). The animals received amlodipine, nicardipine or hydralazine for 30 days in their drinking water. Levels of thiobarbituric acid-reactive substances (TBARS) in the brain (cortex, cerebellum, hypothalamus, and brainstem) were measured before and after each treatment. Systolic blood pressure decreased to similar levels in the amlodipine-, nicardipine-, and hydralazine-treated groups. Urinary norepinephrine excretion was significantly reduced in SHRSP after treatment with amlodipine, but not with nicardipine or hydralazine. Levels of TBARS in the cortex, cerebellum, hypothalamus, and brainstem were significantly higher in SHRSP than in Wistar-Kyoto rats (WKY), and were reduced in amlodipine-treated, but not in nicardipine- or hydralazine-treated, SHRSP. Electron spin resonance spectroscopy revealed increased levels of reactive oxygen species in the brains of SHRSP, which were reduced by treatment with amlodipine. Intracisternal infusion of amlodipine also reduced systolic blood pressure, urinary norepinephrine excretion, and the levels of TBARS in the brain. These results suggested that oxidative stress in the brain was enhanced in SHRSP compared with WKY rats. In addition, antihypertensive treatment with amlodipine reduced oxidative stress in all areas of the brain examined and decreased blood pressure without a reflex increase in sympathetic nerve activity in SHRSP.

Elevation of serum soluble E- and P-selectin in patients with hypertension is reversed by benidipine, a long-acting calcium channel blocker

Hypertension is a major risk factor for atherosclerotic cardiovascular disease. Selectins, cell-surface adhesion molecules involved in leukocyte rolling and attachment to the vascular endothelium, play a role in the initiation of atherosclerosis. We investigated whether or not serum levels of soluble adhesion molecules are elevated in patients with essential hypertension (EH) and examined whether antihypertensive therapy lowers such levels. Twenty-one patients who had untreated mild to moderate EH without diabetes mellitus, hyperlipidemia, or obesity were recruited at a clinic for hypertensive patients. Blood pressure was measured, and the serum levels of soluble E-selectin, P-selectin, L-selectin, intercellular adhesion molecule 1 (ICAM-1), and vascular-cell adhesion molecule 1 (VCAM-1) were determined by enzyme-linked immunosorbent assays before and after 12, 24, and 53 weeks of antihypertensive treatment with benidipine, a long-acting calcium channel blocker, given at a dose of 6 mg/day for 53 weeks. As a control, 21 age- and sex-matched patients without hypertension were studied. Serum E- and P-selectin levels were significantly higher in the subjects with EH than in the controls (p < 0.01). There were no differences in serum levels of soluble L-selectin, VCAM-1, or ICAM-1 levels between the patients with EH and the controls. Treatment with benidipine decreased the elevated blood pressure over a 53-week study period (mean blood pressure: 119.8 +/- 6.5 mmHg at baseline, 101.0 +/- 5.9 mmHg at 12 weeks, 98.6 +/- 7.3 mmHg at 24 weeks, and 93.9 +/- 5.5 mmHg at 53 weeks). Serum levels of soluble E- and P-selectin decreased after the initiation of benidipine treatment and correlated with diastolic blood pressure. Serum levels of soluble L-selectin, VCAM-1, and ICAM-1 did not change significantly during the period of benidipine treatment. Benidipine treatment reduced the content of P-selectin in the platelets from patients with EH, as determined by Western blot analysis. In conclusion, decreased blood pressure may reduce the rate of progression of atherosclerosis by affecting the expression of E- and P-selectin in the endothelium, the platelets, or both. Benidipine may be protective against vascular damage in people with hypertension, not only by lowering blood pressure, but also by inhibiting the expression of selectins.

Tissue Inhibitor of Metalloproteinase-3 Plays Important Roles in the Kidney Following Unilateral Ureteral Obstruction

Tissue inhibitor of metalloproteinase-3 (Timp-3), an inhibitor of matrix-degrading enzymes, is an important molecule for maintenance of the extracellular matrix. In this study, we generated Timp-3-deficient mice and used them to examine the effect of Timp-3-deficiency on blood pressure and to investigate the role of Timp-3 in the kidney following unilateral ureteral obstruction. The blood pressure and heart rate of Timp-3-deficient mice were not significantly different from those of wild-type mice. On the other hand, the obstructed kidneys of Timp-3-deficient mice developed more severe hydronephrosis than those of wild-type animals. Matrix metalloproteinase activities assessed by in situ zymography and transforming growth factor-beta expression were elevated in Timp-3-deficient mice. The renal tissues were thinner and the ratio of renal medulla to cortex was significantly lower in the obstructed Timp-3-deficient kidneys. These findings indicate that Timp-3-deficiency does not substantially affect the blood pressure in mice, and that Timp-3 plays an important role in the maintenance of renal macrostructure after unilateral ureteral obstruction.

Different Effects of Amlodipine and Enalapril on the Mitogen-Activated Protein Kinase/Extracellular Signal-Regulated Kinase Kinase-Extracellular Signal-Regulated Kinase Pathway for Induction of Vascular Smooth Muscle Cell Differentiation In Vivo

Although recent clinical trials have shown that amlodipine exerts antiatherogenic effects, the mechanism of these effects remains unknown. This study was designed to examine which signal transduction pathway might be important for the antiatherogenic property of amlodipine, as assessed by aortic smooth muscle cell (SMC) phenotypes in hypertension in vivo. Stroke-prone spontaneously hypertensive rats (SHRSP) were randomly treated with a vehicle, amlodipine, or enalapril while Wistar-Kyoto rats (WKY) used as controls were treated with only the vehicle. Both drugs were equally effective at reducing systolic blood pressure, and inhibiting the progression of aortic remodeling and fibrosis in comparison to those of vehicle-treated SHRSP. In the aortas of vehicle-treated SHRSP, the level of contractile-type smooth muscle (SM) myosin heavy chain (MHC) SM2 was significantly lower, whereas the level of synthetic-type MHC NMHC-B/SMemb was significantly higher compared with those in the WKY aortas. Compared to the vehicle-treated SHRSP group, both drugs significantly and equally shifted the aortic SMC phenotype in SHRSP toward the differentiated state by reducing NMHC-B/SMemb and increasing SM2. The levels of MKK6, p38 MAPK, MEK1 and p-42/44 ERK were significantly higher in the vehicle-treated SHRSP than in the WKY. Both drugs significantly reduced these values in the SHRSP aorta. Furthermore, the levels of MEK1 and p-42/44 ERK were significantly lower in the amlodipine- than in the enalapril-treated SHRSP group, whereas enalapril was more effective than amlodipine at increasing p-Akt and endothelial NO synthase in SHRSP aortas, which were significantly lower in the vehicle SHRSP group than in the WKY group. Thus, the MEK-ERK pathway might be one of the crucial determinants of the aortic SMC phenotype activated by amlodipine treatment of hypertension in vivo.