Quinapril, an angiotensin converting enzyme inhibitor, prevents cardiac hypertrophy during episodic hypertension

Evidence for a role of an intracardiac renin-angiotensin system in normal and failing hearts

Although substantial evidence of a cardiac RAS has been obtained in the past decade, a number of important questions remain unanswered. These include identification and localization of the cell types responsible for production of the system's components as well as the regulation of synthesis, storage, and secretion pathways for each component. Future studies, which will utilize tools of molecular biology that have become recently available (for example, transgenic animal models), renin inhibitors, angiotensin receptor antagonists, and bradykinin antagonists, will help to elucidate specific roles of the cardiac RAS in normal and failing hearts.

Myocardial remodeling in low-renin hypertension: molecular pathways to cellular injury in relative aldosteronism

The pathologic hypertrophy of hypertensive heart disease is related to the quality, not the quantity, of myocardium; the presence of fibrosis is inevitably linked to structural and functional insufficiencies with increased cardiovascular risk. Elevations in plasma aldosterone that are inappropriate relative to dietary sodium, or relative aldosteronism, are accompanied by suppressed plasma renin activity, elevation in arterial pressure, and dyshomeostasis of divalent cations. The accompanying hypocalcemia, hypomagnesemia, and hypozincemia of aldosteronism contribute to the appearance of secondary hyperparathyroidism. Parathyroid hormone-mediated intracellular calcium overloading of cardiac myocytes and mitochondria leads to the induction of oxidative stress and molecular pathways associated with cardiomyocyte necrosis and scarring of myocardium, whereas the dyshomeostasis of zinc compromises antioxidant defenses. This dys-homeostasis of calcium and zinc, intrinsically coupling prooxidant calcium and antioxidant zinc, raises the prospect for therapeutic strategies designed to mitigate intracellular calcium overloading while enhancing zinc-mediated antioxidant defenses, thus preventing adverse myocardial remodeling with fibrosis, associated diastolic dysfunction, and cardiac arrhythmias.

What is the white-coat effect and how should it be measured?

The white coat effect is conceived as a measure of the blood pressure response to a clinic visit, but there is no agreement as to exactly how it should be defined. The most widely used definition is the difference between the average clinic and daytime ambulatory blood pressures, but other methods that have been used include the difference between clinic and home pressures, measurements using ambulatory blood pressures only, clinic measurements only, and laboratory (reactivity) testing. Few studies have compared the different methods, but the reactivity method has reported bigger changes of blood pressure and heart rate than the others. The effect tends to be greater in older than younger patients, in women than in men, but is present to a greater or lesser degree in almost all hypertensive patients. It is diminished but not obliterated by drug treatment. It is not closely related to overall blood pressure variability, and does not predict cardiovascular risk. The white coat effect appears to be idiosyncratic to the clinic setting.

Segregation analysis of cardiovascular reactivity to laboratory stressors

To better understand the contribution of major gene influences to individual differences in cardiovascular reactivity, we performed a segregation analysis on blood pressure responses to two laboratory tasks, mental arithmetic and bicycle exercise. The study population consisted of 1,451 adults (age > or = 18 years) who were members of 81 Utah pedigrees. Only 864 members performed the bicycle task because persons age 60 years or older or with heart disease were excluded. Blood pressure reactivity to mental arithmetic was defined as change from resting values, and reactivity to the bicycle task was defined as the difference between maximum blood pressure during exercise and resting values adjusted for the individual's workload. Complex segregation analysis and likelihood procedures were used to test for a major gene effect controlling blood pressure reactivity to each task. Two modifiers of the penetrance, age and sex, were considered parameters in these models. We found that diastolic blood pressure (DBP) but not systolic blood pressure reactivities to the mental arithmetic and bicycle exercise tasks were controlled by major gene effects. The best-fitting model, however, differed for the two tasks. For DBP reactivity to mental arithmetic, a major codominant model with gene frequency 0.10 was the best-fitting model; for the bicycle task, the best-fitting model was a mixed recessive model with gene frequency 0.21. Sex differences in DBP reactivity were significant in both tasks: the effect of age was significant only for the mental arithmetic task. These results suggest a significant genetic component for DBP reactivity to laboratory stressors.

Anxiety and cardiovascular reactivity in the Tecumseh population

OBJECTIVE

Increased cardiovascular reactivity has been proposed to be a critical mediator in the development of hypertension and cardiovascular disease. The personality factors associated with cardiovascular reactivity are still subject to debate. The studies reported here were undertaken to examine the relationship between trait anxiety and cardiovascular stress reactivity in a community-based sample (Tecumseh).

DESIGN AND METHODS

All studies were carried out in an outpatient setting. Cardiovascular reactivity to isometric handgrip and mental arithmetic was assessed and recorded by automatic blood pressure monitoring in 832 subjects aged 19-41 years. Spielberger trait and state anxiety measures were collected immediately before the stressors were applied.

RESULTS

No differences in baseline heart rate, systolic or diastolic blood pressure were observed across anxiety categories. There was a clear negative correlation between trait anxiety and cardiovascular reactivity to mental arithmetic. The pattern was less clear in response to isometric handgrip.

CONCLUSIONS

These results suggest that individuals with high trait anxiety demonstrate reduced cardiovascular reactivity while those with low trait anxiety demonstrate increased reactivity, whereas the opposite might have been expected.

Intra-arterial blood pressure during exercise and left ventricular indices in normotension and borderline and mild hypertension

Our objective was to study the usefulness of BP responses to exercise compared to postural BP values for prediction of left ventricular (LV) indices in 28 normotensive (NT), 14 borderline hypertensive (BHT), and 24 mildly hypertensive (HT) men (aged 35-45 years) using intra-arterial BP, the "gold standard" measurement during a series of postures (10 min supine, 10 min sitting, 9 min standing), and exercise (isometric; hand grip, and dynamic; cycle ergometer). LV indices were studied by echocardiography. The highest postural BP correlation was obtained between LV mass index (LVMI) and standing systolic BP (SBP, r = .39, p < .01). Achieved exercise BP did not improve the result compared to standing BP (isometric SBP r = .41, p < .01, dynamic SBP r = .39, p < .01). When exercise responses were expressed as BP change (exercise BP-supine BP) they showed lower correlations with LVMI than achieved exercise BP readings. Using linear multiple regression including all the BP variables, the achieved SBP with isometric exercise explained 17% of LVMI variance (F = 12.9, p = .0006) without any additive value of other variable. In a forced linear regression using BP with various postures as the first variable, the achieved BP with dynamic exercise did not add to the explanation of LVMI variance. However the SBP during isometric exercise added 6% (F = 4.9, p < .05) for the explanation of LVMI variance with sitting SBP as baseline, and also 7% (F = 5.0, p < .05) with supine SBP and diastolic BP as baselines, but no additive value was seen with standing BP. We conclude, that BP levels during various postures were well related to LVMI. Achieved BP or BP change with dynamic exercise did not improve the prediction of the LVMI, and even the best single predictor, BP with isometric exercise, added only little to the power of prediction obtainable from postural values. With mild elevation of BP the clinical utility of dynamic exercise in evaluation of left ventricle is questionable whereas the utility of isometric exercise is marginal. Relatively low correlation values in this study suggest that BP is only one of many factors affecting the cardiac anatomy in the early phases of hypertension.

The evidence for a pathophysiologic significance of the sympathetic overactivity in hypertension

Interest for the role of the sympathetics in the genesis of hypertension has come full circle from early enthusiasm, through a period of neglect, to present understanding that strong evidence cannot be ignored. Sympathetic overactivity starts in childhood and is easily evident in 30% of patients with incipient hypertension. Later, in advanced hypertension, altered cardiovascular responsiveness obscures the obvious signs of sympathetic overactivity but the brain maintains its decisive pathophysiologic role. The early onset, the bimodal distribution of the neurogenic "hyperkinetic" pattern and familial aggregation suggest a genetic component in sympathetic overactivity. Patients with hypertension are at high risk for coronary disease and some of that risk is not directly related to blood pressure elevation. High sympathetic tone explains the pathophysiology of "pressure-independent" risk for premature coronary atherosclerosis in hypertension and for excess mortality/morbidity in patients who had already developed coronary heart disease.

Therapeutic, but not low-dose, angiotensin-converting enzyme inhibition causes regression of cardiovascular changes in spontaneously hypertensive rats

Therapy with angiotensin II-converting enzyme (ACE) inhibitors has been suggested to prevent cardiovascular hypertrophy in hypertension even in doses that are subantihypertensive. We investigated the effects of two different ACE inhibitors on blood pressure and cardiovascular changes during as well as after discontinuation of treatment in spontaneously hypertensive rats (SHR). SHR were treated with either enalapril (ENA) or ramipril (RAM) from age 12 to age 20 weeks. Each drug was given in either an antihypertensive (ENA 15 mg center dot kg-1, RAM 3 mg center dot kg-1) or a subantihypertensive (ENA 50 mu g center dot kg-1, RAM 10 mu g center dot kg-1) dose. Mean arterial pressure (MAP) was reduced with antihypertensive doses of ENA (26%) as well as RAM (21%). Regression of cardiovascular changes occurred as reduction in left ventricular (LV) weight/body weight ratio (25 and 21% for ENA and RAM, respectively), reduction in perfusion pressure at maximal vasodilation of the perfused hindquarter (PPdil, 17 and 17%), and reduction in maximal developed pressure (PPmax, 13 and 17%). These effects partly persisted 10 weeks after treatment was discontinued. However, treatment with subantihypertensive doses of ENA and RAM had no effect on MAP, LV/body weight ratio, PPdil, or PPmax. Overall, regression of cardiovascular parameters correlated closely to the decrease in MAP. Similarly, no changes in MAP, LV weight/body weight ratio, PPdil, or PPmax were noted when young SHR were treated with subantihypertensive doses of RAM from age 6 to age 12 weeks, during which time hypertension becomes established. At doses having equal effects on blood pressure, plasma concentrations of RAM were considerably lower than those of ENA. Skeletal muscle concentrations were very low or undetectable in comparison to plasma concentrations for both drugs. Therefore, both RAM and ENA caused regression of cardiovascular changes that could be explained by a concomitant reduction in blood pressure. This regression persisted for a considerable time after discontinuation of treatment. On the other hand, no specific antitrophic effects in the absence of blood pressure reduction was evident with either drug. Furthermore, despite substantial differences in plasma concentrations, RAM, and ENA administered chronically appeared to affect cardiovascular parameters equally in the adult SHR.

Angiotensin II receptor antagonism: losartan - sites and mechanisms of action

This review surveys the basic pharmacology of angiotensin II receptors and their antagonism; reviews the existing clinical experience with losartan, the first approved nonpeptide angiotensin II antagonist; suggests other possible clinical areas for angiotensin II receptor antagonism; and compares angiotensin-converting enzyme inhibition with angiotensin receptor antagonism.

Gender differences in patterns of dynamic cardiovascular regulation

The purpose of this research was to examine the role of gender in hemodynamic response patterns to stress. Sixty-four male and 55 female young adults were administered a protocol of rest, mental arithmetic, video game, and anger recall interview while blood pressure, heart rate, and cardiac impedance measures were obtained. Men had higher levels of systolic blood pressure and cardiac output and greater reactivity to tasks, indexed by increases in cardiac output and diastolic blood pressure. Extreme groups of myocardial and vascular reactors were formed from cardiac output and total peripheral resistance change scores during mental arithmetic. The myocardial reactors exhibited greater sensitivity to task demands, whereas vascular reactors exhibited comparable total peripheral resistance increases to all tasks. Vascular reactors exhibited greater diastolic blood pressure reactivity than myocardial reactors. Future studies should address the predictive validity of these reactor patterns for the subsequent development of coronary heart disease.

The defense reaction: a common denominator of coronary risk and blood pressure in neurogenic hypertension?

In addition to high blood pressure, patients with hypertension often have insulin resistance, dyslipidemia and increased sympathetic tone. An increased sympathetic tone can negatively affect glucose utilization through three distinct mechanisms; a direct beta-adrenoreceptor-mediated insulin resistance, through conversion to more insulin resistant fast twitch fibers and through alpha-adrenergic vasoconstriction which may decrease the delivery of insulin and glucose to the skeletal muscle cells. The insulin resistance in turn may be responsible for the observed dyslipidemia in hypertension. The sympathetic overactivity in hypertension reflects a chronic activation of defense/vigilance reaction. The increase of cardiac output, blood pressure and insulin resistance in the course of the defense reaction are viewed as an appropriate preparatory response to facilitate muscular exercise (through higher cardiac output and increased pressure) and preserve (through insulin resistance) the optimal supply of glucose to the brain. The defense reaction may have been useful in evolution and may have offered survival advantage. In modern times with prolonged life expectancy the previously useful response (in evolutionary terms) contributes to a faster and deleterious wear and tear of the cardiovascular system.

Angiotensin II induces fibronectin expression associated with cardiac fibrosis in the rat

Fibronectin expression was studied in the heart of rats given a continuous infusion of angiotensin II (Ang II). Northern blot analysis showed that left ventricular fibronectin steady-state mRNA increased fivefold to eightfold in response to pressor doses of Ang II after 24 hours. Accumulation of immunodetectable fibronectin in the ventricles occurred after the mRNA levels increased. The changes in fibronectin expression were reversible when Ang II treatment was withdrawn. The Ang II-induced increase in fibronectin mRNA accompanied similar increases for collagen type I, collagen type IV, and atrial natriuretic factor steady-state mRNA. Interstitial and perivascular fibrosis was identified in both ventricles of angiotensin-treated rats within 3 days. In situ hybridization identified cells associated with areas of fibrosis as the principal site of fibronectin mRNA accumulation in treated animals. By comparison, normal hearts showed fibronectin expression primarily within ventricular vascular tissue and the atrial endocardium. A dose-dependent reduction of fibronectin expression followed treatment with losartan, indicating an Ang II type 1 receptor-mediated effect. Normalization of blood pressure during Ang II infusion by either hydralazine or prazosin had different effects on the level of fibronectin steady-state mRNA, indicating that blood pressure elevation was not the principal factor responsible for fibronectin induction. Concurrent administration of angiotensin-converting enzyme inhibitors with Ang II attenuated the increased fibronectin expression. Our data indicate that Ang II induces an acute fibrotic response within the heart and suggests that Ang II stimulates fibronectin expression within nonmyocytic cardiac cells by a direct action.

Angiotensin converting enzyme binding sites in human heart and lung: comparison with rat tissues

1. Angiotensin converting enzyme (ACE), a dipeptidyl carboxypeptidase which catalyzes the final activation step in the formation of angiotensin II, was identified by radioligand studies in rat heart and lung. In this work we identified ACE binding sites in human left ventricle and lung by radioligand binding using the ACE inhibitor [3H]-ramiprilat in all tissues tested was saturable, temperature and zinc-dependent, and inhibited by EDTA. In human left ventricle homogenate we found a density of binding sites of 121 +/- 15 fmol mg-1 protein (n = 4) with an affinity (Kd) of 850 +/- 55 pM, whereas in rat left ventricle the same values were 23 +/- 4 fmol mg-1 protein and 315 +/- 30 pM, (n = 4), respectively. 3. [3H]-ramiprilat binding to rat (n = 4) and human lung (n = 4) showed a binding site density of 2132 +/- 155 and 1085 +/- 51 fmol mg-1 protein respectively with an affinity of 639 +/- 54 and 325 +/- 22 pM. The lung:heart ratio of ACE binding site density was about 9:1 in man and 100:1 in rat. 4. The binding affinities of 13 ACE inhibitors were evaluated on human heart and lung: the drugs tested showed a wide range of affinities for the ACE binding sites in both tissues, and the affinity for lung was significantly greater than for heart for most of the drugs. 5. The greater potency of some ACE inhibitors in displacing [3H]-ramiprilat in human lung compared with the heart indicates differences between ACE binding sites in these tissues and suggests the possibility of a selective organ-targeted therapeutic approach.