Myocardial hypertrophy, angiotensin, and ACE inhibitors

A comparison between imidapril and ramipril on attenuation of ventricular remodeling after myocardial infarction

BACKGROUND

Angiotensin converting enzyme inhibitors have been used clinically to prevent myocardial infarction (MI). The angiotensin converting enzyme inhibitors attenuated ventricular remodeling and improved cardiac function by inhibition of matrix metalloproteinases after MI. Although the effect is thought to be a class effect, there are significant differences among the drugs. The aim of this study was to compare the effects of imidapril and ramipril on ventricular remodeling after MI.

METHODS

The middle portion of left anterior descending artery was ligated to induce a moderate size MI in rats (moderate MI group). The proximal portion of the artery was ligated to induce a large size MI (large MI group). The animals were assigned to subgroups in moderate MI group and large MI group: (1) nontreated group, (2) ramipril group (1 mg/kg daily), and (3) imidapril group (1 mg/kg daily). All rats were killed on day 28 after the MI operation.

RESULTS

Although the nontreated MI group showed impaired ventricular contraction and severe fibrosis, imidapril significantly negated ischemia-induced changes. Imidapril had a superior effect for preventing ventricular remodeling characterized by fibrosis and collagen accumulation in left ventricle compared with ramipril in the moderate and large MI groups, even though the dosage used in this study was too small to reduce systemic blood pressure.

CONCLUSIONS

Imidapril can be used as a substitute for ramipril to prevent ventricular remodeling after MI.

Hypertension and the heart

Sustained increase in arterial pressure causes left ventricular hypertrophy and adversely affects all myocardial compartments: myocytes, interstitium, and coronary vasculature. Ventricular hypertrophy significantly increases the risk for cardiovascular morbidity and mortality in hypertensive disease. Impairments in coronary circulation and ventricular fibrosis, which are an essential part of hypertensive disease, contribute to that increased risk. This report discusses the mechanisms of hypertension-induced myocardial collagen accumulation and impairments in coronary hemodynamics. Particular attention is given to the interaction of hypertension and aging because aging aggravates hypertensive changes and the incidence of hypertension increases with aging. The effect of therapy on hypertension-induced ventricular fibrosis and impairment in coronary hemodynamics and the risk associated with these changes are also discussed.

Complementation of reduced survival, hypotension, and renal abnormalities in angiotensinogen-deficient mice by the human renin and human angiotensinogen genes

The aim of this study was to determine whether elements of the human renin-angiotensin system (RAS) could functionally replace elements of the mouse RAS by complementing the reduced survival and renal abnormalities observed in mice carrying a gene-targeted deletion of the mouse angiotensinogen gene (mAgt). Double transgenic mice containing the human renin (HREN) and human angiotensinogen (HAGT) genes were bred to mice heterozygous for the mAgt deletion and the compound heterozygotes were identified and intercrossed. The resulting progeny (n = 139) were genotyped at each locus and the population was stratified into two groups: the first containing both human transgenes (RA+) and the second containing zero or one, but not both human transgenes (RA-). Despite appropriate Mendelian ratios of RA- mice that were wildtype (+/+), heterozygous (+/-), and homozygous (-/-) for the deletion of mAgt at birth, there was reduced survival of RA- mAgt-/- mice to adulthood (P < 0.001 by chi2). In contrast, we observed appropriate Mendelian ratios of RA+ mAgt+/+, RA+ mAgt+/-, and RA+ mAgt-/- mice at birth and in adults (P > 0.05 by chi2). These results demonstrate that the presence of both human transgenes rescues the postnatal lethality in mAgt-/- mice. The renal histopathology exhibited by RA- mAgt-/- mice, including thickened arterial walls, severe fibrosis, lymphocytic infiltration, and atrophied parenchyma, was also rescued in the RA+ mAgt-/- mice. Direct arterial blood pressure recordings in conscious freely moving mice revealed that BP (in mmHg) varied proportionally to mAgt gene copy number in RA+ mice (approximately 20 mmHg per mAgt gene copy, P < 0.001). BP in RA+ mAgt-/- mice (132+/-3, n = 14) was intermediate between wild-type (RA- mAgt+/+, 105+/-2, n = 9) and RA+ mAgt+/+ (174+/-3, n = 10) mice. These studies establish that the human renin and angiotensinogen genes can functionally replace the mouse angiotensinogen gene, and provides proof in principle that we can examine the regulation of elements of the human RAS and test the significance of human RAS gene variants by a combined transgenic and gene targeting approach.

The natural history of left ventricular wall thickening in hypertrophic cardiomyopathy

BACKGROUND

Hypertrophic cardiomyopathy (HCM) is associated with mutations of genes coding for major sarcomeric proteins, but the mechanism of hypertrophy is unknown. As hypertrophy may not develop until adolescence, an altered response to physiological growth stimuli may regulate the hypertrophy process.

AIMS

This study examined the relationship between age and changes in left ventricular (LV) wall thickness in patients with HCM.

METHODS

Forty-three patients who had definite electrocardiographic and echocardiographic evidence of HCM were studied with serial 2D and M-mode echocardiograms at least two years apart (mean interval 5.5 +/- 3.0 years). LV cavity dimensions, septal and posterior wall thicknesses, and LV mass indices were compared with data from an age- and gender-matched control group.

RESULTS

In patients with HCM aged ten to 20 years (n = 9), there was an increase in septal wall thickness during the study period from 15.9 +/- 6.2 mm to 19.3 +/- 2.1 mm (p < 0.01). This increase (3.4 +/- 2.5 mm) greatly exceeded the change in septal thickness observed in the control group between the ages of ten and 20 years (0.8 +/- 0.3 mm, p < 0.01). There was a lesser increase in posterior wall thickness from 9.8 +/- 2.1 mm to 11.5 +/- 3.5 mm (p = 0.07). In patients with HCM aged 21-40 years (n = 11), there was also an increase in septal wall thickness during the study period from 16.0 +/- 2.2 mm to 17.8 +/- 3.0 mm (p < 0.05), but no change in septal thickness in the control group. In contrast, the patients aged > 40 years (n = 23) showed no significant change in either septal or posterior wall thickness during the study period. LV mass index increased in the ten to 20 years age group from 128 +/- 24 g/m2 to 164 +/- 20 g/m2 (p = 0.01), but this increase was not observed in the older age groups.

CONCLUSIONS

LV hypertrophy is progressive, particularly in the septum, during adolescence and early adult life in patients with HCM. As progressive hypertrophy may continue after somatic growth has ceased, an abnormal myocardial response to physiological growth regulators is less likely to be the principal stimulus to hypertrophy. Gene-gene interactions, changes in haemodynamic load or environmental factors may modulate the development of hypertrophy. Serial measurements of ventricular wall thickness in the first two decades of life, and probably until the fourth decade of life are advisable in patients suspected of having HCM.

Fish oil and other nutritional adjuvants for treatment of congestive heart failure

Published clinical research, as well as various theoretical considerations, suggest that supplemental intakes of the 'metavitamins' taurine, coenzyme Q10, and L-carnitine, as well as of the minerals magnesium, potassium, and chromium, may be of therapeutic benefit in congestive heart failure. High intakes of fish oil may likewise be beneficial in this syndrome. Fish oil may decrease cardiac afterload by an antivasopressor action and by reducing blood viscosity, may reduce arrhythmic risk despite supporting the heart's beta-adrenergic responsiveness, may decrease fibrotic cardiac remodeling by impeding the action of angiotensin II and, in patients with coronary disease, may reduce the risk of atherothrombotic ischemic complications. Since the measures recommended here are nutritional and carry little if any toxic risk, there is no reason why their joint application should not be studied as a comprehensive nutritional therapy for congestive heart failure.