Influence of nifedipine on ventricular function and myocardial hypertrophy in spontaneously hypertensive rats

Positive inotropic effect of exogenous and endogenous NO in hypertrophic rat hearts

1. Recent evidence suggests that nitric oxide (NO) modulates the contractile force of isolated cardiomyocytes in a biphasic manner. We sought to examine whether myocardial hypertrophy induced by long-term hypertension changes the effects of NO on myocardial contractility. 2. We used constant flow perfused non-paced Langendorff preparations of hearts of 3 months old Wistar rats (WIS, n = 23) and of stroke-prone spontaneously hypertensive rats (SHR) at the age of 10 months (SHR10, n = 16) and 15 months (SHR15, n = 8). Changes of left ventricular peak pressure (LVP), +dP/dt(max), -dP/dt(max), coronary perfusion pressure (CPP) and heart rate (HR) were recorded after infusion of noradrenaline (NA, 0.1 micromol l(-1)), glyceryl trinitrate (GTN, 1-100 micromol l(-1)), S-nitroso-N-acetyl-D,L-penicillamine (SNAP, 1-10 micromol l(-1)) and N(omega)-nitro-L-arginine (L-NOARG, 0.1-1 mmol l(-1)). 3. Long-term hypertension induced myocardial hypertrophy and an abnormal response to NA. The relative heart weight (in mg kg(-1)) increased from 2.95 +/- 0.04 (WIS) to 6.67 +/- 0.34 (SHR15), while the increase in +dP/dt(max) induced by NA was absent in SHR15. Hearts of SHR10 showed an intermediate response. 4. Both SNAP and GTN significantly increased LVP, +dP/dt(max) and -dP/dt(max) in hearts of WIS and of SHR. In WIS but not in SHR10, SNAP also increased HR. In SHR10 the lowest concentration of SNAP (1 micromol l(-1)) showed no effect on contractility but a significantly diminished reduction of CPP suggesting inactivation of extracellularly released NO in the coronary circulation of SHR. 5. L-NOARG significantly reduced contractility in hearts of WIS and of SHR to a similar extent. At a concentration of 1 mmol l(-1) L-NOARG also reduced HR. 6. These results suggests that positive inotropic effects of exogenous and endogenous NO are not changed in hypertension induced myocardial hypertrophy.

Comparative effects of type 1 angiotensin II-receptor blockade with angiotensin-converting-enzyme inhibitor on left ventricular distensibility and collagen metabolism in spontaneously hypertensive rats

We compared the cardiac effects of the selective angiotensin II type 1 (AT1)-receptor blockade, FK-739, with an angiotensin-converting-enzyme (ACE) inhibitor, enalapril, on left ventricular (LV) distensibility and collagen metabolism in spontaneously hypertensive rats (SHRs). We treated 14-week-old SHRs with FK-739 (30 mg/kg/day) or enalapril (10 mg/kg/day) for 6 weeks. Both FK-739 and enalapril induced a significant decrease in blood pressure (p < 0.001) and regression of LV hypertrophy (p < 0.001) compared with vehicle, with no differences between the treated groups. Furthermore, FK-739 caused a greater decrease in LV collagen content than did enalapril (FK-739-treated group, 3.06 +/- 0.11 mg/g; enalapril-treated group, 3.47 +/- 0.05 mg/g; p = 0.015) with no change in collagen phenotypes. Hearts taken from rats treated with FK-739 also showed greater LV distensibility than those taken from enalapril-treated rats (FK-739-treated group vs. enalapril-treated group at > or = 15 mm Hg, p < 0.001). These results suggest that, compared with ACE inhibition, AT1-receptor blockade may have additional effects on LV distensibility and collagen metabolism in the regression of LV hypertrophy induced by pressure overload.

Effects of tetrandrine on left ventricle hypertrophy in deoxycorticosterone acetate-salt hypertensive rats

The effect of regression of left ventricular hypertrophy was studied in deoxycorticosterone-acetate-salt hypertensive rats (DOCA-salt hypertensive rats) treated with tetrandrine. Treatment with tetrandrine (by gastric intubation, 50 mg/kg per day for 9 weeks) lowered systolic blood pressure, left ventricular weight, Ca2+ of mitochondria, and markedly decreased the density (Bmax) and total number of dihydropyridine binding sites in hypertrophic left ventricle (P < 0.001). There was no difference between groups in dissociation constant (Kd) values of dihydropyridine binding sites. These facts indicate that tetrandrine decreased cardiac mass in DOCA-salt hypertensive rats through mechanisms that may be associated with the density and the total number of dihydropyridine binding sites, Ca2+ and blood pressure control.

Hypertension and left ventricular hypertrophy: is drug therapy beneficial?

Left ventricular hypertrophy (LVH) is a consequence of long-standing hypertension and is considered to be an independent risk factor for cardiovascular morbidity and mortality. Several antihypertensive agents are capable of inducing regression of LVH, but it is not known which class of drugs is most effective. The impact of drug-induced reversal of hypertrophy on ventricular function remains a controversial issue. Furthermore, the long-term clinical benefits of LVH regression have yet to be documented. Controversies also exist regarding the clinical outcomes associated with drug-induced LVH regression.

Effects of sustained-release isradipine on left ventricular anatomy and function in systemic hypertension

With use of digitized M-mode echocardiograms and 24-hour noninvasive ambulatory blood pressure (BP) monitoring, the effects of chronic treatment with sustained-release isradipine on left ventricular (LV) morphology and function in hypertensive patients were evaluated. We selected 12 patients with LV hypertrophy and normal LV diastolic diameter. Echocardiograms and 24-hour BP monitoring were performed after 2 weeks of placebo and after 6 months of oral treatment with sustained-release isradipine (5 mg once daily). Therapy significantly reduced BP without changes in heart rate. LV mass decreased in all patients and peak lengthening rate of LV diameter, index of diastolic function, increased in all, with normalization in 7 of the 9 with basal diastolic impairment. Peak shortening rate of LV diameter, index of systolic function, was normal in all patients at basal evaluation and did not change after therapy. Reduction in LV mass significantly (p < 0.05) correlated with the decrease in average 24-hour and daytime systolic and diastolic BP. Sustained-release isradipine administered once daily is an effective antihypertensive agent; the drug also induces regression of LV hypertrophy, with significant improvement in LV diastolic function and no deterioration in systolic function.

Salt and water retention and calcium blockade in uremia

Blood pressure, echocardiography, and aortic and peripheral arterial pulse-wave velocity were studied in 40 hypertensive patients on long-term hemodialysis during a 24-week administration of nitrendipine (1,4-dihydro-2,6-dimethyl-4-[m-nitrophenyl]-3,5-pyridine-dicarboxylic acid ethyl methylester) monotherapy. In a double-blind placebo-randomized study, nitredipine effectively lowered the blood pressure (p less than 0.001) before hemodialysis without causing postdialysis hypotension. The antihypertensive effect of nitrendipine was greater in patients with significant salt and water retention, as indicated by interdialytic body weight gain (delta BW), that is, a significant correlation was observed between delta BW and the decrease in blood pressure (r = 0.72; p less than 0.001). The antihypertensive effect was not related to age, pretreatment plasma renin activity, or serum-ionized calcium concentration. After nitrendipine, a time-related decrease in aortic (p less than 0.005) and femoral (p less than 0.05) pulse-wave velocity was observed with a significant time-treatment interaction (p less than 0.01). Nitrendipine treatment did not influence left ventricular mass (which was positively correlated with delta BW; p less than 0.01) but was associated with an increase in the left ventricular ejection fraction. The increase in ejection fraction was correlated with changes in aortic pulse-wave velocity (r = 0.548; p less than 0.02) but not with changes in blood pressure (r = 0.352; p = 0.19) or delta BW.(ABSTRACT TRUNCATED AT 250 WORDS)

Significance of coronary circulation in hypertensive heart disease for development and prevention of heart failure

Coronary hemodynamics (coronary blood flow, coronary reserve, myocardial oxygen consumption) were analyzed in both experimental and clinical essential hypertension. Significant reduced coronary reserve was found in hypertensive patients with left ventricular hypertrophy. Extracoronary reasons for these phenomena were ruled out. Considerable thickening of the coronary resistance vessels (medial hypertrophy) in hypertensive hypertrophy associated with a marked increase in the wall thickness/radius ratio was considered sufficient to explain the impairment of coronary flow. After long-term pharmacotherapy there was normalization of both medial hypertrophy and coronary reserve. This small-vessel abnormality correlates well with clinical findings in hypertensive heart disease (angina and electrocardiographic changes despite normal coronary arteriogram). Moreover, this structural adaptation of the small vessels may carry the inherent risk of an impaired oxygen supply to the hypertrophied myocardium. Thus, late cardiac failure of the hypertrophied heart in hypertension may be attributed, in part, to this microcirculation disorder. Conversely, reversal of left ventricular hypertrophy and of hypertrophy of vascular smooth muscle by specific pharmacotherapy can be considered a possible approach to the rational prevention of cardiac failure in hypertensive patients. For future investigations, controlled clinical trials are needed to confirm these findings with regard to prevention of heart failure, and pharmacotherapeutic studies are necessary to define the optimal drug regimen for reversal of vascular smooth muscle hypertrophy.

Effect of diltiazem on left ventricular mass and diastolic filling in mild to moderate hypertension

It is still uncertain whether antihypertensive therapy with calcium antagonists in general, and diltiazem in particular, can reduce left ventricular (LV) mass index and improve LV diastolic filling in hypertension. Therefore, 24 patients with mild to moderate hypertension (diastolic blood pressure 95 to 114 mm Hg before therapy) were randomly assigned to receive either a sustained-release preparation of diltiazem (n = 13) or placebo (n = 11) for 16 weeks in a double-blind, parallel-group protocol. M-mode and pulsed Doppler echocardiograms were performed at baseline and at the end of monotherapy. Echocardiograms were read blindly by 2 independent observers. The patients who received placebo exhibited no change in blood pressure, cardiac dimensions or LV function. Diltiazem significantly reduced both systolic pressure (151 +/- 14 to 139 +/- 12 mm Hg) and diastolic pressure (101 +/- 4 to 90 +/- 7 mm Hg, both p less than 0.05). Posterior wall and septal wall thicknesses decreased, but the changes were not statistically significant. End-diastolic dimension was reduced by diltiazem from 53 +/- 5 to 51 +/- 5 mm (p less than 0.05). LV mass index decreased significantly with diltiazem by 10%, from 125 +/- 21 to 113 +/- 23 g/m2 (p less than 0.05). The LV wall thickness to radius ratio remained unchanged during both diltiazem and placebo treatments. Changes in LV mass index and blood pressure did not correlate, suggesting that this response is influenced by factors other than pressure reduction alone.(ABSTRACT TRUNCATED AT 250 WORDS)

High-energy phosphates, myocardial contractile function and material properties after short periods of oxygen deficiency

To investigate myocardial performance and diastolic properties after repeated periods of oxygen deficiency auxotonic and isovolumic measurements were performed after three periods (4 min) of asphyxia in Wistar rats (n = 19). Additionally, the response of the peak isovolumic left ventricular pressure to postextrasystolic potentiation was measured. The hemodynamic results were compared to the levels of high-energy phosphates. Already after 15 min of recovery from asphyxia auxotonic measures of systolic function were completely normal compared to the control group (n = 19). Isovolumic measurements after 20 min of postasphyctic recovery, however, demonstrated a considerable reduction of the peak left ventricular pressure (226.5 +/- 7.5 mm Hg vs. 262.6 +/- 3.4 mm Hg in controls, mean +/- SEM (p less than 0.01) indicating persistence of decreased postischemic contractile performance. The relative effect of postextrasystolic potentiation was similar in both groups, but could not compensate for the reduced performance of the postasphyctic hearts: the absolute postextrasystolic peak isovolumic pressure of the postasphyctic hearts was lower than the value of the regular isovolumic peak pressure in the controls. Diastolic properties (pressure/volume and stress/strain relationships) of the postasphyctic myocardium remained unchanged. The total sum of the adenine-nucleotides decreased from 7.2 +/- 0.2 to 5.6 +/- 0.3 mumol/gww (p less than 0.01). ATP was reduced from 4.8 +/- 0.2 to 3.9 +/- 0.3 mumol/gww (p less than 0.01). Phosphocreatine was elevated to 7.0 +/- 0.6 mumol/gww, x +/- SEM (p less than 0.01). Our results demonstrated normal postasphyctic basal hemodynamics and material properties. Thus, the energy supply was sufficient to maintain steady state conditions - in spite of decreased overall adenine-nucleotide levels. Isovolumic measurements and postextrasystolic potentation tests, however, indicated that the contractile performance of the postischemic myocardium was still reduced. This functional limitation cannot be explained by altered material properties and is probably not causally related to the decreased overall ATP content.

Propranolol and thyroxine-induced hypertrophic rabbit hearts: effect on heart size and regional O2 supply/consumption variables

The purpose of this study was to determine the effect of acute and chronic propranolol on heart size and regional O2 supply/consumption variables in thyroxine (T4)-treated rabbit hearts. New Zealand white rabbits were given 0.5 mg/kg T4 for 3 or 16 days with and without concomitant 2 mg/kg propranolol. Another group was given 16 days of propranolol alone and another 3-day T4 group was given 2 mg/kg propranolol 1 h before the experiment began. Another group served as control. Myocardial blood flows were determined using radioactive microspheres and small arteriolar and venous O2 saturations were determined using microspectrophotometry. Treatment with T4 for 3 or 16 days increased the heart weight/body weight ratio, myocardial blood flow, and regional O2 consumption. 16-day T4 treatment resulted in myocardial flow 195% and O2 consumption 300% above control group values. When propranolol was given chronically along with T4, heart weight/body weight ratios did not increase to the degree seen with 3 or 16 days of T4, alone. Propranolol given acutely in 3-day T4-treated animals, resulted in a reduced O2 consumption and O2 extraction, though not to the extent seen with chronic propranolol treatment of T4-treated animals. Acute propranolol treatment slightly reduced myocardial blood flow in 3-day T4-treated animals, while chronic treatment significantly reduced it. Chronic propranolol treatment in 16-day T4-treated animals resulted in a significant reduction in flow and O2 consumption. Thus, T4 treatment increased O2 consumption, flow, and heart size and these effects could be attenuated using acute and chronic propranolol.

The total vascular burden, peripheral and coronary: vasodilator effects of nifedipine

While the total ischemic burden on the left ventricle represents the combined effects of both symptomatic and asymptomatic myocardial ischemia, the total vascular burden has many components including an increased systemic peripheral vascular resistance, an increased pulmonary vascular resistance, and an increased coronary vascular resistance. These factors may all influence ventricular function. Hypertension contributes significantly to the vascular burden, especially when combined with left ventricular hypertrophy, which predisposes to ischemia by multiple mechanisms. In patients with hypertension and cardiomegaly, sublingual nifedipine has been shown to increase left ventricular (LV) ejection fraction and the average diastolic filling rate. In the presence of acute myocardial infarction, nifedipine moves the LV function curve onto a better Frank-Starling relationship as pulmonary wedge pressure falls or stays the same and cardiac output rises. However, because of the delicate balance between myocardial perfusion and the benefits of afterload reduction, including improved remodelling, nifedipine should be given only to selected patients. In congestive heart failure, low-dose nifedipine reduces the afterload and has been shown to have beneficial effects in the majority of patients. Two specific adverse outcomes in only two patients have been reported, one with initial hypotension and one given high-dose nifedipine. Combination nifedipine-beta blocker therapy has been shown to be favorable in the treatment of all varieties of angina, hypertension, and hypertrophic cardiomyopathy. Therefore, when administered appropriately, nifedipine reduces the total vascular burden on the heart in a variety of cardiovascular diseases, with consequent improvement in LV function and a diminished threat of potential myocardial ischemia.

Role of nisoldipine on blood pressure, cardiac hypertrophy, and atrial natriuretic peptides in spontaneously hypertensive rats

The effect of long-term treatment with the calcium antagonist nisoldipine on development of hypertension, cardiac hypertrophy, and plasma levels of atrial natriuretic peptides (ANP) was determined in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) of the same age. Measurement of immunoreactive ANP in plasma provided a sensitive marker for the severity of hypertension and the associated cardiac overload. Long-term treatment with nisoldipine prevented the development of hypertension, the associated heart failure, and the increase of plasma levels of ANP in SHR but had no effect on systolic blood pressure, heart weight, and plasma levels of ANP in WKY. In addition, nisoldipine had a therapeutic effect in old SHR with manifest cardiac failure in end-stage hypertension, as evidenced not only by the reduction of blood pressure but also by the reduction of cardiac hypertrophy, of elevated immunoreactive ANP in plasma, and of increased plasma renin activity.

Calcium channel blockers and treatment of hypertension

Over the past years, research efforts have been focused on the pathophysiologic role of calcium ions, and the implication for the potential role of calcium channel blockers in the management of essential hypertension. Numerous studies have shown that nifedipine and verapamil are effective antihypertensive agents, initial experience with diltiazem is also encouraging. The magnitude of blood pressure reduction with these drugs is related to the pre-treatment blood pressure. In refractory hypertension, combination with other antihypertensive agents provide additive effect. In the elderly population and in patients with ischemic heart disease, supraventricular arrhythmia, bronchospastic disease, peripheral vascular disease or diabetes mellitus, the calcium channel blockers offer potential advantages over other antihypertensive agents. Experimental studies also suggest that these drugs may reverse ventricular hypertrophy. When long-term safety with these drugs is documented from well-controlled clinical trials, the calcium channel blockers may be our first line of therapy for the management of hypertension.

Calcium-channel blockers for combined angina pectoris and systemic hypertension

Calcium-channel blockers have been successfully used in the treatment of angina of effort and systemic hypertension. Many patients present with concomitant angina pectoris and hypertension. Controlled clinical trials demonstrate that the calcium-channel blockers are safe and effective as monotherapy in the treatment of these patients, and that their use compares favorably with that of propranolol. The effectiveness of these agents in hypertension appears to be primarily due to their ability to induce systemic vasodilation. Calcium-channel blockers have several therapeutic effects in angina pectoris. Beneficial actions on the major determinants of oxygen consumption, i.e. heart rate, blood pressure and contractility, are generally seen. The potent coronary vasodilating actions of these agents allow for increased coronary blood flow. Improvements in ventricular compliance, regression of left ventricular hypertrophy and cardioprotection appear to be additional effects of the calcium-channel blockers; their contribution to the drugs' overall therapeutic efficacy is presently being evaluated. Calcium-channel blockers are a welcome addition to drug regimens available for the management of patients with coexisting angina pectoris and hypertension.

Prevention of hypertensive hypertrophy by medical therapy: effects on systolic wall stress and systolic function

Left ventricular (LV) hypertrophy and LV systolic pumping function of spontaneously hypertensive rats (SHR) treated for 40 weeks with hydralazine (n = 8), metoprolol (n = 8) and both metoprolol and hydralazine (n = 9) were compared with those of 25 age-matched untreated SHR. LV pressure (PLV), peak systolic wall stress (SWS), cardiac index (CI), LV ejection fraction (EF), LV muscle mass to body weight ratio (LV/BW) and the mass volume ratio (M/V) were determined. In the rats treated with hydralazine and metoprolol and hydralazine combined PLV was 28.7% (129 +/- 19 mm Hg) and 31.5% (124 +/- 17 mm Hg) lower compared to the untreated control group (181 +/- 18 mm Hg). In spite of the same amount of blood pressure reduction, LV hypertrophy was less expressed after treatment with metoprolol and hydralazine than after hydralazine only (LV/BW: 2.48 +/- 0.17 versus 2.67 +/- 0.24 mg/g, p less than 0.01; M/V: 2.43 +/- 0.59 versus 3.09 +/- 0.47 mg/microliter, p less than 0.05 respectively). In the group treated with metoprolol and hydralazine LV systolic ejection function parameters (CI, EF) did not differ from those untreated due to an unchanged LV afterload as demonstrated by identical systolic wall stress values (169 +/- 43.4 X 10(3) versus 171 +/- 26.0 X 10(3) dyn/cm2, ns). The identical systolic wall stress values indicate that cardiac hypertrophy had regressed in proportion to the reduced LV peak systolic pressure. Following hydralazine therapy systolic wall stress was even lower (140 +/- 26.5 X 10(3) dyn/cm2) in comparison to the untreated group (171 +/- 26.0 X 10(3) dyn/cm3, p less than 0.05). This reflects an inappropriate low muscle mass reduction in relation to blood pressure reduction. In conclusion (I) antihypertensive therapy with an arteriolar vasodilator in combination with a beta-receptor blocker is more effective in preventing cardiac hypertrophy than therapy with a vasodilator only. (II) Myocardial working capacity remained unaltered after prevention of cardiac hypertrophy as well as LV pumping function.

Renal and cardiovascular effects of acute and chronic administration of felodipine to SHR

Renal function and salt and water turnover were studied in SHR during acute and chronic administration of felodipine, which is an efficient antihypertensive vasodilating Ca2+ antagonist. In conscious SHR acute administration of felodipine in hypotensive doses increased renal sympathetic nerve activity but caused renal vasodilation, increases in GFR and a 2-3 fold increase in urinary flow rate and sodium excretion. The fraction of filtered sodium excreted (FENa) was approximately doubled. The diuretic and natriuretic effects of felodipine are therefore suggested to be due to a direct inhibitory action on the renal tubular cells, resulting in reduced sodium reabsorption. Nifedipine also induced diuresis and natriuresis in this system, while minoxidil reduced water and sodium excretion. Throughout 6 months of felodipine treatment, the mean arterial pressure (MAP), remained 25-20 per cent reduced. Felodipine in combination with metoprolol reduced MAP 25-30 per cent and also caused regression of left ventricular hypertrophy, while felodipine alone prevented its further progression. Also during chronic administration, felodipine induced diuresis but had no effect on plasma volume and on sodium or potassium excretion in SHR. It is concluded that in SHR felodipine induces diuresis; on acute treatment this is secondary to reduced tubular sodium reabsorption, although during chronic treatment the sodium loss is compensated for while the diuresis remains. Thus, the cardiovascular and renal effects of Ca2+ antagonists like felodipine differ substantially from those of other potent antihypertensive vasodilators e.g. minoxidil.

Calcium channel blockers as antihypertensive agents

Because of their unique action on the cardiovascular system, the calcium channel blockers have generated a great deal of excitement among pharmacologists, physiologists, and clinicians. One obvious potential application for these drugs is in antihypertensive therapy and, although experience with these agents for this indication is limited in the United States, it is considerable in Europe and Japan. These agents' ultimate role in antihypertensive therapy, however, has not been established. Since the available calcium channel blockers are structurally diverse, it is uncertain whether they will have comparable effects in hypertension. The rationale for the use of calcium channel blockers in treating hypertension and the relevant pharmacologic actions of these agents is discussed, along with a summary of some of the clinical trials, observations from our own experience with these drugs, and speculation about their future role in antihypertensive therapy.