Cardiac sympathetic nerves as the final common pathway in the induction of adaptive cardiac hypertrophy

Influence of chronic captopril therapy on the mechanical performance of the infarcted rat heart

The influence of angiotensin converting enzyme inhibition of hemodynamic changes, development of postinfarction myocardial hypertrophy and left ventricular performance was studied in rats. Infarction was produced under ether anaesthesia by ligature of the descending anterior branches of the left coronary artery. Control rats were submitted to a sham surgery. Groups of infarcted (Inf) and sham-operated control (SO) animals were daily treated with intraperitoneal injections of captopril (Cap, 30 mg kg-1) or saline (Sal) for 4-5 weeks. This Cap dose produced a similar decrease in arterial blood pressure in Inf and SO animals. The intraventricular pressures measured in anaesthetized rats showed a marked elevation in the right ventricular systolic (38 +/- 4 mmHg) and end diastolic (4 +/- 1 mmHg) pressures in the Inf group compared with the SO group (24 +/- 1 mmHg and 1 +/- 0.4 mmHg, respectively). Cap did not change the pressure overload in the right ventricle. In the left ventricle, however, the end diastolic pressure of the Inf group under Cap was significantly reduced in relation to Sal (12 +/- 3 mmHg and 19 +/- 2 mmHg, respectively, P < 0.05). The post infarction myocardial hypertrophy was depressed by Cap only in the right heart chambers. Thus the right ventricular weight to body weight ratio (mg/g) increased from 0.56 +/- 0.03 in the SO-Sal group to 0.96 +/- 0.07 (P < 0.05) in the Inf-Sal group and decreased to 0.73 +/- 0.04 (P < 0.05) in the Inf group under Cap. The infarction-induced hypertrophy of the left heart chambers was unaffected by Cap. Left ventricular function was assessed in the hearts perfused in vitro according to the Langendorff technique. The peak isovolumic systolic pressure (ISP) developed at different diastolic pressures (0-30 mmHg) and Ca2+ concentrations (0.62 and 1.25 mM) was measured. The ISP and the positive inotropic response to Ca2+ was similarly depressed in both groups of infarcted hearts. Thus the chronic administration of Cap to Inf rats reduces the left ventricular filling pressure but does not reduce the postinfarction pulmonary hypertension. Despite this latter finding, Cap therapy was able to significantly reduce the post-infarction hypertrophy in both right heart chambers. Cap therapy did not change significantly left ventricular systolic function and Ca2+ responsiveness of the myocardium surviving to infarction.

Left ventricular mass and cardiovascular reactivity in young men

The relation between left ventricular wall thickness and mass, arterial plasma catecholamines, and blood pressure at rest and during a mental arithmetic challenge and a cold pressor test was examined in 69 healthy men 19 years of age. The subjects were recruited from the 1st (n = 21), 50th (n = 26), and 99th (n = 22) percentiles in mean blood pressure. All underwent echocardiography to determine mean wall thickness and left ventricular mass. Continuous intra-arterial blood pressure, electrocardiogram, and arterial sampling of plasma catecholamines were performed after 30 minutes of supine rest, during a 5-minute mental arithmetic challenge, and during a 1-minute cold pressor test. Stepwise multiple-regression analyses considering mean wall thickness and left ventricular mass as the dependent variables were applied. Intra-arterial systolic blood pressure (r = .54, P < .0001) and arterial plasma epinephrine (r = .31, P = .009) after 30 minutes of supine rest were the only independent explanatory variables of mean wall thickness (multiple R2 = .33, P < .0001). Blood pressure at screening and during mental stress and cold pressor tests were not independent explanatory variables. The present study suggests that resting arterial blood pressure and plasma epinephrine may be of importance for development of left ventricular hypertrophy.

Role of preclinical cardiovascular disease in the evolution from risk factor exposure to development of morbid events

Conventional risk factors (especially high arterial pressure, elevated cholesterol and glucose levels, and cigarette smoking) are useful predictors of morbid atherosclerotic and hypertensive events, and their control variably reduces the incidence of events. However, both the ability to predict risk and the ability to reduce it by modification of established risk factors are limited. These limitations occur in part because the progression from risk factor exposure to morbid events depends on the variable likelihood that individuals exposed to the same risk factors will progress through two stages: the development of asymptomatic or "preclinical" anatomic and functional cardiovascular disease in response to standard risk factors and other variables, and the precipitation of morbid events by progression of preclinical disease or by the action of additional "triggering" mechanisms in the presence of preclinical disease. Advances in diagnostic methodology now make possible accurate noninvasive detection in many asymptomatic individuals of preclinical disease such as left ventricular hypertrophy, carotid atherosclerosis, and renal dysfunction. Progress in elucidating stimuli to left ventricular hypertrophy and systemic atherosclerosis suggests that focusing research separately on these two stages of disease evolution is a fruitful strategy. The closer relation of measures of preclinical disease than risk factors with the subsequent risk of complications indicates that their detection improves clinical risk stratification. However, critical testing of whether clinical outcome is improved or treatment cost is lowered by basing antihypertensive or antihyperlipidemic treatment decisions in part on the presence of preclinical cardiovascular disease is needed before this strategy is adopted on a widespread scale.

Plasma growth factor activity and cardiac wall thickness

OBJECTIVES

The aim of this study was to investigate the growth factor activity in plasma (GFAP) in hypertension, and the correlation of GFAP to blood pressure levels, cardiac structural changes and platelet activation at rest and during exercise.

SUBJECTS

Fifteen untreated hypertensive subjects and 15 normotensive controls were recruited from a blood pressure screening programme.

INTERVENTIONS

GFAP before and after 30 min of strenuous exercise was analysed as the ability of patient or control plasma to stimulate incorporation of 3H-thymidine in cultured human smooth muscle cells. M-mode echocardiography was performed and platelet activity was measured by the excretion of the urinary metabolite of thromboxane A2.

RESULTS

There were no significant differences in GFAP or platelet activation at rest or after exercise between the groups. The fractions of labelled cells were 52.6% vs. 56.6% (HT vs. NT) at rest. Septum and posterior wall end-diastolic thicknesses (PWT[D]) were significantly increased in the HT group (10.4 +/- 0.3 vs. 9.2 +/- 0.3 mm and 11.4 +/- 0.5 vs. 10.0 +/- 0.4 mm, respectively, P < 0.05). PWT(D) was significantly correlated to GFAP (r = 0.40, P = 0.04) and to blood pressure (r = 0.53, P < 0.005) but there was no correlation between blood pressure and GFAP.

CONCLUSION

The data suggest that GFAP could play a role in the early development of cardiac hypertrophy in hypertension, but that this effect does not seem to be directly linked to blood pressure levels alone.

Repeated normoxic hyperbaric exposures induce haemodynamic and myocardial changes in rats

The effect of repeated exposure to ambient pressures of 5 bar (500 kPa), in atmospheres comprising normal partial pressures of oxygen [0.2 bar (20 kPa)] and nitrogen [0.8 bar (80 kPa)] and 4 bar (400 kPa) helium, on cardiac function and morphology was assessed in conscious rats. Ten test rats underwent chamber dives daily for 40 consecutive days, and ten control rats were exposed in the same chamber for an equal period of time, but in air at 1 bar (100 kPa). Cardiac output (Qc) and myocardial blood flow (Qmyocardial) were determined by the microsphere method. After 40 days, the body mass was 7% greater in the control than in the test rats (P < 0.05), although they were given exactly the same amount of standard food. The test rats had a significantly higher (7% absolute, 12% ventricular mass to body mass, P < 0.05) heart mass (left ventricular myocardium, including the ventricular septum) than the control rats. The percentage tissue dry mass of the right and left ventricles was equal in the two groups. Microscopic examination revealed a number of small focal necroses in the left ventricle of the test rats but none in the control rats. The left ventricular pressure (LVP) and the maximum velocity of LVP increase (contractility) and decrease were significantly increased (25%-96%, P < 0.001) in the pre-exposed compared to the control rats at 1 bar (100 kPa). The systolic arterial pressure, heart rate and respiratory frequency were similar in the two groups at 1 bar (100 kPa).(ABSTRACT TRUNCATED AT 250 WORDS)

ACE-inhibitors and coronary microcirculation

Arterial hypertension is the most frequent cause of a disturbance of coronary microcirculation. Inspite of having normal epicardial coronary arteries, patients with arterial hypertension often have symptoms of angina pectoris and a positive exercise tolerance test. The angina pectoris-symptoms in patients with arterial hypertension are due to functional and structural alterations of the coronary microcirculation. Consequently, an antihypertensive therapy should not only aim at lowering blood pressure and reversing myocardial hypertrophy, but also improve coronary microcirculation in order to avoid the consequences of chronic ischemia on the myocardium. Until now, only experimental studies have indicated that antihypertensive therapy can improve coronary flow reserve. To determine to what extent under clinical conditions coronary flow reserve can be improved, in hypertensive patients maximal coronary blood flow, minimal coronary resistance, and coronary reserve (Dipyridamol) were studied before and after a long-term antihypertensive treatment (9-12 months) with the ACE-inhibitor enalapril (10-20 mg/d). To assess the chronic effects rather than the acute effects of the antihypertensive pharmacon, the coronary microcirculation was studied after intermission of medical therapy for a period of 1 week. Along with a decrease in LV muscle mass by about 8%, coronary reserve was improved after enalapril by 48%. It is likely that the observed increase in coronary reserve is related to the reversal of structural vascular abnormalities at the level of the coronary microcirculation. Consequently, it seems that reparation of hypertensive remodeling of the coronary microcirculation can be induced by ACE-inhibitor therapy.

Relationship between cyclic-AMP content, regional myocardial function and O2 consumption in experimental left ventricular hypertrophy: effect of negative inotropes

The aim of this study was to examine the hypothesis that negative inotropic agents that lower myocyte cyclic-AMP by different means would have similar effects on local myocardial segment work and O2 consumption in control hearts, but that this response would differ in left ventricular hypertrophy (LVH) induced by aortic valve stenosis. Open chest anesthesized LVH and control dogs were studied before and during esmolol (100 micrograms/kg/min) and acetylcholine (100 micrograms/kg/min) infusion. Regional work was calculated as the integrated product of instantaneous force (miniature transducer) and shortening (sonomicrometry) per min. Regional O2 consumption was calculated from blood flow (radioactive microspheres) and O2 saturation of small frozen vessels (microspectrophotometry). Cyclic-AMP level was determined with a competitive binding assay using 3H-cyclic-AMP and was found to be 731 +/- 90 (mean +/- S.D.) pmol/g in control and 711 +/- 163 in LVH. There were similar decreases in cyclic-AMP levels in control hearts with acetylcholine (365 +/- 135) and the beta adrenergic blocker (430 +/- 95). In LVH, esmolol lowered cyclic-AMP (383 +/- 39), but acetylcholine did not (689 +/- 105). In control animals, regional O2 consumption (7.7 +/- 0.6, 5.6 +/- 0.4 and 5.6 +/- 0.5 ml O2/min/100 g, control, acetylcholine, esmolol, respectively) and segment work (878 +/- 82, 546 +/- 80, 627 +/- 66 g*mm/min) fell to similar levels with these agents. Similar decreases were found in LVH with esmolol for O2 consumption (7.1 +/- 1.2, 5.1 +/- 1.0, baseline, esmolol) and segment work (895 +/- 140, 427 +/- 65). Acetylcholine had no significant effect on segment work (800 +/- 201), but did lower regional O2 consumption (4.0 +/- 0.7) in LVH dogs. It is concluded that there is a strong relationship between the level of cyclic-AMP and myocardial function and O2 consumption in control hearts. The action of acetylcholine is altered in LVH leading to an uncoupling between regional cyclic-AMP, function and metabolism.

Increased heart rate prevents the isomyosin shift after cardiac transplantation in the rat

The heterotopically transplanted rat heart undergoes significant atrophy and a shift from V1 to V3 isomyosin. The purpose of this study was to pace the cardiac isograft and determine whether an increase in heart rate would attenuate the changes in cardiac mass and isoenzyme distribution. Nonpaced transplanted hearts were compared with hearts in which pacing was initiated at 7 Hz, 24 hours after transplantation, and continued for 7 days. There was a 29% decrease in myosin ATPase activity and a 22% decrease in alpha-myosin in the nonpaced isograft; both decreases were completely prevented by pacing. The decrease in cardiac mass was also significantly attenuated. Pacing did not alter intrinsic heart rate, systolic pressure, dP/dt, or norepinephrine concentration in the isograft. These results suggest that the adaptation in both cardiac mass and isoenzymes may be related to the rate or the rate-pressure product in the transplanted paced heart independent of left ventricular pressure, tissue catecholamines, or neural activity.

Sympathetic modulation of the cardiac myocyte phenotype: studies with a cell-culture model of myocardial hypertrophy

Myocardial hypertrophy is the common endpoint of many cardiovascular stimuli such as hypertension, myocardial infarction, valvular disease, and congestive failure. Catecholamines have long been implicated in the pathogenesis of myocardial hypertrophy, however, it is very difficult to sort out catecholamine mechanisms in vivo. We have developed a cell-culture model which excludes hemodynamic effects and allows the assignment of receptor specificity to catecholamine effects. Utilizing this system, we have shown that stimulation of the alpha 1 adrenergic receptor leads to the development of myocardial hypertrophy and results in the selective up-regulation of the fetal/neonatal mRNAs encoding skeletal alpha-actin and beta-MHC, a pattern similar to that seen with hypertrophy in-vivo. Utilizing a co-transfection assay, we have also obtained data that suggest that the beta-PKC isozyme is in a pathway regulating transcription of the beta-MHC isogene. Beta adrenergic stimulation of the cultured cardiac myocytes also results in a modest degree of hypertrophy, however, this effect may be dependent upon myocyte contractile activity and may involve, at least in part, the non-muscle cells present in the culture system.

Effects of long-term treatment with prazosin on left ventricular diastolic function in mild to moderate hypertension

It is not well established if blood pressure control is associated with an improvement in diastolic function, whose impairment represents an early marker of cardiac involvement in systemic hypertension. The purpose of this study was to evaluate whether a prolonged treatment with an alpha 1-blocking agent can lead to a reversal of the abnormalities of left ventricular filling. Eleven never-treated patients with mild to moderate essential hypertension were examined before and after at least six months of treatment with prazosin. Cardiac function and left ventricular mass were measured by means of radionuclide ventriculography and echocardiography. Average blood pressure values significantly decreased during the treatment period: from 163.54 +/- 17.80 mm Hg to 146.81 +/- 13.14 mm Hg for systolic blood pressure and from 106.09 +/- 6.96 mm Hg to 92.90 +/- 8.93 mm Hg for diastolic blood pressure. All the indices of left ventricular mass showed a trend toward reduction, but the differences with respect to the baseline values did not reach statistical significance. Average value of ejection fraction was normal before treatment and did not change significantly after treatment. All indices of diastolic function were significantly lower than normal controls' values at the beginning of the study and tended to worsen at the end of the study. Our findings suggest that diastolic function is not consistently affected by the therapy with alpha 1-adrenoreceptor antagonists despite good blood pressure control.

Modulation of sympathetic activity by brain neuropeptide Y in cardiac hypertrophy

Several observations now support the view that the sympathetic system actively participates in the development of cardiac hypertrophy. Since norepinephrine (NE)-containing neurons involved in cardiovascular regulation in the brain are known to coexist with neuropeptide Y (NPY), it is possible that a functional interaction between NPY and NE exists centrally. In an effort to clarify whether or not central catecholamine systems are modulated by NPY soon after imposing an increased pressure overload on the heart, male Sprague-Dawley rats underwent aortic constriction and were examined 14 days later. Rats were anesthetized and subjected to microdialysis sampling by stereotaxically implanting a probe into the caudal ventrolateral medulla (A1). Perfusate was collected after a 1-hour stabilization period, purified, and analyzed for interstitial concentrations of NE and other catecholamines using high-performance liquid chromatography with an electrochemical detector. Extracellular NE concentrations in the A1 area were found to be decreased. These results were associated with increased rate of change in the specific activity of NE (NE turnover) in heart, indicating increased sympathetic activity and an increased left ventricular weight. Also, infusion of NPY (10(-9) mol/L) by microdialysis in the A1 area resulted in the reduction of NE concentration; epinephrine and dopamine levels were also decreased. In contrast, methionine-enkephalin, another neuropeptide, had no effect on the extracellular catecholamine concentrations in the A1 area. Since neurons of the A1 group project almost exclusively to forebrain structures inhibiting sympathetic activity, it is concluded that decreases of NE and other catecholamines in afferent pathways regulating the caudal ventrolateral medulla may lead to an enhanced sympathetic activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood pressure and left ventricular anatomy and function after heart transplantation

To determine whether hypertension occurring after heart transplant causes the development of cardiac hypertrophy, changes in pressure load (N = 13) and left ventricular anatomy (N = 11) were evaluated up to 1 year after heart transplant in a prospective longitudinal study. Pressure load was evaluated by 24-hour ambulatory blood pressure monitoring, and left ventricular anatomy and function were assessed by M-mode echocardiography under two-dimensional guidance. Body weight increased by 11 to 12 kg. Blood pressure showed a gradual increase during the first few months after transplant: diastolic pressure by 15 to 18 mm Hg and systolic pressure by 12 to 15 mm Hg, with hypertension persisting during the night. Nearly all patients required treatment with one or two antihypertensive drugs. The increase in blood pressure was related to increased total peripheral resistance with minor decreases in cardiac output. Both septal and posterior wall thickness and left ventricular mass (by 25 to 30 gm/m2) decreased during the initial months after transplant and subsequently remained at "normal" levels (100 gm/m2). The persistence of normal left ventricular mass may indicate either that the increases in daily pressure load and body weight were not sufficient to induce myocardial growth or that the latter was prevented by, for example, absence of cardiac sympathetic nerve activity.

Selective alpha 1-adrenoreceptor blockers in the treatment of hypertension: should we be using them more?

It has become apparent in recent years that in the treatment of essential hypertension, reduction of blood pressure alone is not sufficient to reduce significantly the morbidity and mortality from ischaemic heart disease. Since the emergence of a multifactorial approach to the prevention of cardiovascular disease, the potential interaction between antihypertensive therapy and metabolic factors, such as control of blood glucose and lipid levels, has become an important consideration. Abnormal function of the sympathetic nervous system may contribute to both the initiation, or maintenance, of hypertension and the associated metabolic disturbances. The new generation of selective alpha 1-adrenoreceptor blockers, besides lowering blood pressure, appear to have favourable effects on lipid and glucose metabolism. The use of these drugs and their place in the treatment of hypertension are discussed.

Relationship between adenylate cyclase activity and regional myocardial energetics in experimental left ventricular hypertrophy

The aim of this study was to examine the responsiveness of the hypertrophied left ventricle to beta-adrenergic stimulation in a pressure overload model produced by valvular aortic stenosis and characterized by reduced beta-adrenoceptor number. The study was designed to correlate changes in global and regional cardiac work and energetics in response to isoproterenol with adenylate cyclase activity. Eleven anesthetized dogs with left ventricular hypertrophy and 11 controls were studied at rest and during 0.5 and 1.0 micrograms/kg/min isoproterenol infusion. We measured regional work from segment length and force changes with ultrasonic dimension crystals and miniature force gauges in addition to arterial and left ventricular blood pressure and cardiac output. Regional myocardial oxygen consumption was calculated from O2 extraction using microspectrophotometry and blood flow using radioactively labeled microspheres. Adenylate cyclase activity was assayed at baseline and after stimulation with forskolin. Isoproterenol significantly increased heart rate, dP/dtmax, cardiac output, and external work to similar levels in control and hypertrophied animals. Similarly, regional work increased from 463 +/- 115 to 995 +/- 584 g x mm/min for controls and from 392 +/- 156 to 1175 +/- 577 for hypertrophied dogs with high dose isoproterenol. Regional O2 consumption also increased to similar levels (20.3 +/- 14.7 vs 16.2 +/- 6.3 ml O2/min/100 g) in both groups. Adenylate cyclase activity was lower in hypertrophy at baseline (23.9 +/- 7.3 vs 62.9 +/- 14.2 pM/min/mg protein for controls), but was the same as for controls with forskolin stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention of cold-induced increase in blood pressure of rats by captopril

To assess the possibility that the renin-angiotensin system may play a role in the development of cold-induced hypertension, three groups of rats were used. Two groups were exposed to cold (5 +/- 2 degrees C) while the remaining group was kept at 26 +/- 2 degrees C. One group of cold-treated rats received food into which captopril (0.06% by weight) had been thoroughly mixed. The remaining two groups received the same food but without captopril. Systolic blood pressure of the untreated, cold-exposed group increased significantly above that of the warm-adapted, control group within 4 weeks of exposure to cold. In contrast, chronic treatment with captopril prevented the elevation of blood pressure. Rats were killed after 4 months of exposure to cold. At death, the heart, kidneys, adrenal glands, and interscapular brown fat pad were removed and weighed. Although captopril prevented the elevation of blood pressure in cold-treated rats, it did not prevent hypertrophy of the kidneys, heart, and interstitial brown adipose tissue that characteristically accompanies exposure to cold. Thus, chronic treatment with captopril prevented the elevation of blood pressure when administered at the time exposure to cold was initiated. It also reduced the elevated blood pressure of cold-treated rats when administered after blood pressure became elevated. This suggests that the renin-angiotensin system may play a role in the elevation of blood pressure during exposure to cold.

Cardiac hypertrophy due to pressure and volume overload: distinctly different biological phenomena?

Myocardial hypertrophy is a morphological adaptive response to chronic work overload imposed on the heart. It has been categorized into two distinct basic types: concentric hypertrophy, occurring in response to a sustained pressure overload in which wall thickness increases without chamber enlargement, and eccentric hypertrophy, in response to a chronic volume overload in which chamber volume enlarges without a relative increase in its wall thickness. It should be emphasized, in this context, that these adjectives are somewhat confusing, since the hypertrophy observed is not eccentric in the fashion often seen in the left ventricle of patients with hypertrophic cardiomyopathy. In fact, the hypertrophy is concentric in both instances, but is associated with an increase in chamber volume when described as eccentric, yet occurring with a maintained volume when said to be concentric. In rats made anemic by iron deficiency, the volume overloaded heart achieves an adaptive increase in mass characterized as hypertrophy occurring in the setting of dilated ventricle. This so-called eccentric hypertrophy depends on catecholamines as possible signals for myocardial growth, and progresses with preserved ultrastructure and contractile performance of the cardiac muscle. A gradually imposed volume overload results in a harmonious growth of the heart (it retains a relative normal shape, becoming a magnified normal heart), probably mediated by release of catecholamines into the myocardium. This process resembles the normal cardiac growth in response to the obligatory volume load imposed by an increasing cardiac output (greater metabolic demands) and blood volume.(ABSTRACT TRUNCATED AT 250 WORDS)

Norepinephrine-induced cardiac hypertrophy of the cat heart

Norepinephrine administration causes progressive hypertrophy of the mammalian heart as measured by myocardial mass. The purpose of this study was to determine the growth response of the myocardial tissue components as well as the myocardial cell itself to norepinephrine. Young, adult cats were given low doses of norepinephrine in dextrose or dextrose alone twice daily for 15 days. On day 16, there were no changes in the animals body weight, right ventricular systolic pressure, right ventricular end-diastolic pressure, heart rate, cardiac index, or blood pressure. However, the right ventricle/body weight, the left ventricle/body weight and the total heart weight/body weight were increased significantly in the norepinephrine treated animals. The increase was on the order of 40%. The cardiac muscle cell was also significantly increased in size and both the right and left ventricular cardiac muscle cells exhibited a dramatic increase in size as measured by cross sectional area. Upon stereological examination it was found that the amount of hypertrophy as seen in the cardiac muscle cells was paralleled by the hypertrophy seen in the other tissue components of the myocardium. The volume density of the muscle cells, the interstitial components, as well as the blood vessel compartment were identical in the control and in the norepinephrine-treated groups. In conclusion, this study demonstrates that the response of the myocardium to norepinephrine is similar to that seen in response to a volume overload rather than that seen in response to pressure overload.

Adrenergic regulation of the skeletal alpha-actin gene promoter during myocardial cell hypertrophy

The skeletal alpha-actin gene is expressed in fetal rat heart and is induced during norepinephrine (NE)-stimulated hypertrophy in cultures of neonatal rat cardiac myocytes. Here we report that NE positively regulates the human skeletal alpha-actin gene promoter in transiently transfected neonatal rat cardiac myocytes. NE increased expression from the full-length promoter by 2.4-fold. A DNA region required for NE responsiveness but not for tissue-specific expression was located between base pair -2000 and base pair -1300. Distinct regions required for cardiac myocyte expression were located between -1300 to -710 and -153 to -87. None of these elements separately conferred tissue specificity or adrenergic responsiveness on a heterologous promoter, although the intact promoter from -2000 to -36 conferred both when cloned in its correct position and orientation. Additional elements in the basal promoter (-87 to +187) were required for maximal NE responsiveness. The NE induction was mediated by the beta-adrenergic receptor in high-density cultures (3-4 x 10(6) cells per 60-mm dish), as was induction of hypertrophy, contractility, and endogenous skeletal alpha-actin gene expression. The beta-adrenergic agonist isoproterenol was as potent as NE in inducing expression. Furthermore, beta-adrenergic antagonists inhibited the effects on skeletal alpha-actin gene expression but alpha 1-adrenergic antagonists did not. The alpha 1-adrenergic system was intact in these high-density cultures, since the effects of NE on the expression of another contractile protein gene, alpha-myosin heavy chain, were blocked by alpha 1- but not by beta-adrenergic antagonists. In these high-density cultures, cell contact and intermyocardiocyte bridging were prevalent. When cardiac myocytes were plated at a low density, minimizing cell contact, NE induction of skeletal alpha-actin gene expression and hypertrophy was mediated by the alpha 1-adrenoceptor. Factors related to cell communication may influence the pathways mediating NE-regulated gene transcription during cardiac myocyte hypertrophy.

Sodium-induced cardiac hypertrophy. Cardiac sympathetic activity versus volume load

To investigate the possible contributions of cardiac volume overload and cardiac sympathetic hyperactivity in the effects of sodium on cardiac mass, we evaluated the effects of treatment with saline (1%) and deoxycorticosterone acetate + saline (DOCA/saline) for 10 days and 3 and 6 weeks on ventricular anatomy and intracardiac pressures. Sympathetic activity in the heart and other tissues was assessed at 10 days and 3 weeks by catecholamine turnover rates and tyrosine hydroxylase activity. Both saline and DOCA/saline produced concentric left ventricular (LV) hypertrophy. Right ventricular weight showed only small increases. Saline treatment did not affect LV end-systolic pressure, whereas DOCA/saline caused a moderate increase (to 159 mm Hg). Right atrial pressure was not affected by either treatment, whereas LV end-diastolic pressure increased but only after the development of LV hypertrophy. Both saline and DOCA/saline decreased LV norepinephrine concentration; only DOCA/saline decreased norepinephrine content per LV. However, neither treatment altered the norepinephrine turnover rate constant, the absolute turnover rate, or the tyrosine hydroxylase activity. The results demonstrate that increased saline intake or DOCA/saline produces concentric LV hypertrophy without any increase in blood pressure in the case of saline and with increases in LV filling pressure following rather than preceding the appearance of LV hypertrophy. The lack of an increase in LV norepinephrine turnover and tyrosine hydroxylase activity suggests that the hypertrophy is not mediated through increased cardiac neuronal sympathetic activity.

Pathogenesis of hypertrophic cardiomyopathy: another viewpoint

A genetically determined error in the handling of catecholamines by the developing heart has been speculated to cause hypertrophic cardiomyopathy. A critical appraisal of the published literature reveals that there is little actual experimental or clinical evidence favouring the role of catecholamines in the pathogenesis of hypertrophic cardiomyopathy. Other factors seem to be more important. An abnormality of myocardial growth, either induced by excessive growth promoting substance, or a genetically determined abnormality in myocardial responses to normal growth factors during life (but not in the fetal handling of catecholamines) is likely to be responsible for hypertrophic cardiomyopathy.

Early regression of left ventricular diastolic abnormalities in hypertensive patients treated with nifedipine

The effects of nifedipine on blood pressure (BP), left ventricular hypertrophy, and diastolic function were evaluated in 14 patients with essential hypertension (EH). All males with a mean age of 44 +/- 6 years (range 35-58 years), and in ten normotensive subjects (control group) aged 32-42 years (mean age 36 +/- 4). A complete echocardiogram (ECHO) was performed in basal conditions after 1 and 6 months of therapy with nifedipine (20-40 mg/day). Left ventricular echocardiograms (LV ECHO, M-mode, two-dimensional guided) were plotted with a simultaneous ECG tracing by means of a computerized system that allows evaluation of the following parameters: LV end-diastolic and systolic diameters (EDD, ESD); variations in LV diameter and volume during the entire cardiac cycle, and the velocities of such variations; end-diastolic thicknesses of the interventricular septum and posterior wall (ST, PWT); LV mass, mass/volume (M/V) index, end-diastolic diameter/thickness (D/Th) index, and LV ejection fraction (EF). Left ventricular volume curves were obtained and the contributions of rapid filling (RF) and atrial systole (AS) to EDV were evaluated. Filling velocities during RF (vRF) and AS (vAS) were estimated, as well as the isovolumic relaxation period (IR). No significant changes were observed in the heart rate. After 1 month of therapy, systolic and diastolic BP were significantly decreased (p less than 0.05). ST and PWT were reduced, with a simultaneous increase in EDD and EDV (p less than 0.01). LV mass was slightly reduced, as was the M/V index. The D/Th index was increased (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Differential therapy of hypertensive heart disease

Hypertensive damage to the target organ "heart" comprises the sum and interactions of the cardiac organ manifestations of arterial hypertension such as myocardial hypertrophy and disease of large and small coronary arteries. Because the prognosis of arterial hypertension is determined to a considerable extent by these cardiac complications, the aim of treatment of hypertensive heart disease is reversal of the myocardial hypertrophy in order to prevent later progression to hypertensive heart failure. A further goal of therapy is reversal of the hypertensive small coronary disease in order to improve the coronary reserve. Once the stage of hypertensive heart failure is reached, the principles of medical management of heart failure with digitalis, diuretics and angiotensin-converting enzyme inhibitors apply. Whereas the evidence that regression of hypertrophy can be induced by suitable antihypertensive drugs (calcium channel blockers of the dihydropyridine type, angiotensin-converting enzyme inhibitors and sympathicolytic substances) is practically conclusive, clinical evidence of reversal of the hypertensive disease of small coronary arteries has yet to be provided. Moreover, to what extent the prognosis of hypertensive heart disease can be improved by reversal of hypertrophy is still unknown.

Intraventricular septal hypertrophy in type 1 diabetic patients with microalbuminuria or early proteinuria

To investigate whether the slightly increased blood pressure that occurs in early diabetic renal disease is associated with hypertensive left ventricular hypertrophy, M-mode echocardiograms were recorded in 11 non-diabetic control subjects and four groups of Type 1 diabetic patients. These were 15 patients without microvascular complications, 10 with microalbuminuria, 12 with early persistent proteinuria, and 8 with established renal impairment. Mean blood pressure was 133/80 mmHg (uncomplicated patients), 143/85 mmHg (microalbuminuria), 147/92 mmHg (early proteinuria) and 158/85 mmHg (renal impairment). Mean intraventricular septal width in the uncomplicated diabetic patients was 9.8 (SE 1.2) mm which did not differ from non-diabetic control subjects. Mean septal width was significantly greater in the other groups (microalbuminuria, 12.7 (1.1) mm, p less than 0.02; proteinuria, 12.0 (0.7) mm, p less than 0.05; renal impairment, 15.5 (1.8) mm, p less than 0.001). Left ventricular mass increased progressively between groups and was significantly increased in those with renal impairment (140 (21) vs 103 (5) g m-2 in uncomplicated patients, p less than 0.05). Septal width in the diabetic population not receiving antihypertensives (n = 37) was significantly correlated with systolic blood pressure (r = 0.45, p less than 0.005) which was the only variable independently related to septal width and ventricular mass. It appears that the slight increase in blood pressure that occurs in microalbuminuria and early proteinuria is frequently associated with hypertensive left ventricular hypertrophy.

Relation of left ventricular hemodynamic load and contractile performance to left ventricular mass in hypertension

The weak relation of systolic blood pressure to left ventricular mass in hypertensive patients is often interpreted as evidence of nonhemodynamic stimuli to muscle growth. To test the hypothesis that left ventricular chamber size, reflecting hemodynamic volume load and myocardial contractility, influences the development of left ventricular hypertrophy in hypertension, we studied actual and theoretic relations of left ventricular mass to left ventricular diastolic chamber volume, pressure and volume load, and an index of contractility. Data were obtained from independently measured M-mode and two-dimensional echocardiograms in 50 normal subjects and 50 untreated patients with essential hypertension. Two indices of overall left ventricular load were assessed: total load (systolic blood pressure x left ventricular endocardial surface area) and peak meridional force (systolic blood pressure x left ventricular cross sectional area). A theoretically optimal left ventricular mass, allowing each subject to achieve mean normal peak stress, was calculated as a function of systolic blood pressure and M-mode left ventricular end-diastolic diameter. Left ventricular mass measured by M-mode echo correlated better with two-dimensional echocardiogram derived left ventricular end-diastolic volume (r = 0.56, p less than 0.001) than with systolic blood pressure (r = 0.45, p less than 0.001) and best with total load or peak meridional force (r = 0.68 and 0.70, p less than 0.001). In multivariate analysis both end-diastolic volume and blood pressure were independent predictors of systolic mass (p less than 0.001) and explained most of its variability (R = 0.75, p less than 0.001). Theoretically optimal left ventricular mass was more closely related to end-diastolic volume (r = 0.72, p less than 0.001) than to systolic blood pressure (r = 0.46, p less than 0.001); thus, the relatively weak correlation between blood pressure and optimal mass reflected the influence of left ventricular cavity size, rather than a lack of proportionality between load and hypertrophy. Actual and theoretically optimal left ventricular mass were closely related (r = 0.76, p less than 0.001), indicating that left ventricular hypertrophy in most cases paralleled hemodynamic load. Left ventricular mass was positively related to stroke index and inversely to contractility (as estimated by the end-systolic stress/volume index ratio), the main determinants of left ventricular chamber volume. In multivariate analysis, systolic blood pressure, stroke index, and the end-systolic stress/volume index ratio were each independently related to left ventricular mass index (all p less than 0.001, multiple R = 0.81) and accounted for 66% of its overall variability.(ABSTRACT TRUNCATED AT 400 WORDS)

Significance of myocardial alpha- and beta-adrenoceptors in catecholamine-induced cardiac hypertrophy

The role of alpha- and beta-adrenoceptors in the development of catecholamine-induced cardiac hypertrophy in vivo was investigated. Rats received a constant intravenous infusion of norepinephrine or sodium chloride (control) for 3 days. The norepinephrine infusion was combined with the alpha-blocker prazosin, the beta-blocker metoprolol, or both blockers. For modulation of the work load of the heart, the calcium channel blocker verapamil was added to the norepinephrine infusion. A further group of animals was treated with the alpha-adrenergic stimulator norfenephrine, which also was combined with prazosin or verapamil. Norepinephrine induced significant increases in mean aortic pressure, left ventricular dP/dtmax, heart rate, and total peripheral resistance. The left ventricular weight/body weight ratio was significantly elevated and was accompanied by an increase in the RNA concentration and the RNA/DNA ratio. Prazosin as well as metoprolol partially antagonized the increase in left ventricular weight and RNA concentration, whereas simultaneous prazosin and metoprolol treatment prevented the norepinephrine-induced alterations. Although combination of norepinephrine with verapamil resulted in considerable reduction of all functional parameters, the development of cardiac hypertrophy and the elevated RNA/DNA ratio were not significantly influenced. Stimulation of alpha-receptors with norfenephrine elicited an increase in total peripheral resistance and in left ventricular weight, which was abolished by prazosin. Verapamil did not affect the norfenephrine-induced cardiac hypertrophy, although it normalized essentially all functional parameters. Thus, the rapid development of cardiac hypertrophy in the norepinephrine model seems to be directly mediated by stimulation of myocardial alpha- and beta-adrenoceptors rather than by hemodynamic changes.

Altered sympathetic system and adrenoceptors during the development of cardiac hypertrophy

Increasing experimental evidence suggests that the development of cardiac hypertrophy may involve the sympathetic system and associated receptor mechanisms. However, very little work has been done so far to understand changes in the sympathetic system and cardiac adrenoceptors soon after an increased work load is imposed on the heart. Accordingly rat hearts subjected to aortic banding-induced pressure overload were assessed 3, 7, and 14 days postoperatively. Sham-operated rats without aortic banding were used as a control group. Rats with aortic constriction had increases in heart rate, left ventricular systolic pressure, and total mechanical energy during the entire study period. The cardiac RNA level was increased without a significant increase in left ventricular mass on days 3 and 7 in aortic-banded animals; these results were associated with a decrease in the cardiac norepinephrine (NE) store and an increase in the plasma level of NE and dopamine beta-hydroxylase (DBH) activity. By day 14 a significant increase in left ventricular mass and the NE store were found; both plasma NE and DBH remained elevated. Catecholamines in other tissues such as the spleen and kidney were depleted in the banded group, whereas the dopamine level, particularly in the brain, was significantly higher during the entire study. Furthermore, the density of alpha-adrenoceptors was higher on day 3 of aortic banding, and a reciprocal correlation was evident between cardiac alpha- and beta-adrenoceptors on day 14; the density of beta-adrenoceptors was increased, whereas that of alpha-adrenoceptors was decreased in the banded group.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac norepinephrine kinetics in hypertrophic cardiomyopathy

We examined the uptake and release of norepinephrine in the cardiac circulation and other regional vascular beds in 11 patients with hypertrophic cardiomyopathy (HCM) and in 10 control subjects during simultaneous infusion of tracer-labeled norepinephrine and isoproterenol. Cardiac neuronal uptake of norepinephrine was assessed by comparing regional removal of tracer-labeled norepinephrine with that of tracer-labeled isoproterenol (which is not a substrate for neuronal uptake) and by the relation between production of dihydroxyphenylglycol (DHPG), an exclusively intraneuronal metabolite of norepinephrine, and regional spillover of norepinephrine. Cardiac extraction of norepinephrine averaged 59 +/- 17% in the patients with HCM, significantly less than in the control subjects (79 +/- 13%, p less than 0.05), whereas cardiac extraction of isoproterenol was similar in the two groups (13 +/- 23% versus 13 +/- 14%), indicating that neuronal uptake of norepinephrine was decreased in the patients with HCM. The cardiac arteriovenous difference in norepinephrine was significantly larger in the patients with HCM than in the control subjects (73 +/- 77 versus 13 +/- 50 pg/ml, p less than 0.05), as was the product of the arteriovenous difference in norepinephrine and coronary blood flow (7.3 +/- 7.3 versus 0.8 +/- 3.0 ng/min, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of chronic antihypertensive therapy on the index of left ventricular mass in patients with essential hypertension

M-mode echocardiography was used in 80 patients with essential hypertension to study changes in the index of left ventricular mass during treatment over 3 years with reserpine, prazosin, indapamide and atenolol, separately or in combination. Forty patients completed a follow-up period of 36 months, while 5 patients died during this period. In all 5 groups, the index of left ventricular mass decreased significantly from the baseline after 1 and 3 years of treatment, except in those patients receiving prazosin in which there was no significant difference in the index of left ventricular mass between 1 and 3 years of treatment. Our results confirm that effective treatment of blood pressure results in a significant reduction in the index of left ventricular mass. Furthermore, this reduction was seen with all modes of treatment and suggests that it was reduction of blood pressure rather than any specific pharmacological property of the drugs that was of major importance.

Left ventricular structural characteristics in unilateral renovascular hypertension and primary aldosteronism

To assess the importance of the renin-angiotensin system and plasma volume as determinants of hypertensive left ventricular hypertrophy and its anatomy, patients with unilateral renovascular hypertension and primary aldosteronism were studied by echocardiography. Blood pressure, age and sex were matched as closely as possible. The 19 patients with unilateral renovascular hypertension and the 19 patients with primary aldosteronism were similar in age, sex and blood pressure (168 +/- 19/97 +/- 11 and 163 +/- 17/99 +/- 10 mm Hg, respectively), but plasma volume was increased in the patients with primary aldosteronism. Interventricular septal thickness, left ventricular posterior wall thickness, left ventricular mass index and relative wall thickness did not differ between the 2 groups of patients. There was a significant correlation between the level of systolic blood pressure and either left ventricular mass index (r = 0.34, p less than 0.05) or relative wall thickness (r = 0.58, p less than 0.001) in both groups of patients. Left ventricular end-diastolic dimension index was increased in the patients with primary aldosteronism compared with those with unilateral renovascular hypertension (3.2 +/- 0.4 vs 2.9 +/- 0.3 cm/m2, p less than 0.02). When confined to the patients with systolic pressure greater than or equal to 150 mm Hg, relative wall thickness was significantly increased in the patients with unilateral renovascular hypertension. Patients with primary aldosteronism and unilateral renovascular hypertension of similar blood pressure levels, age and sex have almost identical degrees of left ventricular hypertrophy and anatomy. In contrast, the patients with primary oldosteronism had increased left ventricular dimension index.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemodynamic, humoral and volume findings in systemic hypertension with isolated ventricular septal hypertrophy

To analyze the hemodynamic, endocrine and volume characteristics of isolated septal hypertrophy (ISH) in established systemic hypertension, 22 patients with ISH were compared to 23 patients with symmetric hypertrophy and to 28 without left ventricular (LV) hypertrophy. Mean arterial pressure and 24-hour ambulatory pressure readings did not differ between the 2 groups. At the same level of arterial pressure, patients with ISH had a high cardiac index (p less than 0.02) and a faster heart rate (p less than 0.05); consequently, total peripheral resistance was decreased (p less than 0.05). Although there was no change in intravascular volume, central blood volume was expanded (p less than 0.02), and the ratio of central to peripheral blood volume was increased (p less than 0.02), thereby indicating peripheral venoconstriction. Patients with isolated ISH had greater responses of diastolic pressure and heart rate (p less than 0.05) to isometric stress than the other 2 groups. A hyperdynamic circulatory state is a hemodynamic hallmark of ISH in early essential hypertension that might be produced by increased sympathetic activity.

Beta-adrenoceptor and adenylate cyclase regulation in cardiac myocyte growth

We studied the effect of growth on beta-adrenergic receptor properties of neonatal rat heart myocytes cultured in serum-free medium with transferrin and insulin. Growth was induced by addition of 1 microM (-)-norepinephrine for two days, 200 nM of the tumor-promoting phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) for two days, or 30 nM T3 for six days. The Kd values for beta-receptor binding (125I-ICYP) were unaffected by growth. The maximum number of beta-receptor binding sites calculated as sites/cell was increased 1.47-fold by T3 (p less than .005), but was decreased to 54% of control values by (-)-norepinephrine (p less than .005): TPA had no effect on either Kd or Bmax values. (-)-Isoproterenol-stimulated adenylate cyclase activity was augmented only in membranes from T3-treated cells and was reduced by 69% in membranes from (-)-norepinephrine treated cells. TPA had no effect on (-)-isoproterenol-stimulated adenylate cyclase activity. We conclude that the mechanisms controlling beta-adrenergic receptor number may be distinct from those controlling growth, since receptor number does not correlate with cell enlargement. Furthermore, in (-)-norepinephrine-stimulated growth, which we have shown previously is an alpha 1-adrenoceptor mediated response, beta-adrenergic signal transduction is modulated in a directionally opposite fashion.

Relationship between ambulatory and exercise blood pressure and cardiac structure

Recent research using automated ambulatory blood pressure recorders and echocardiography has revealed a closer relationship between LV structure and blood pressure during usual activity than with physician measurements of blood pressure. Because increased LV mass is a strong predictor of an adverse prognosis, this suggests that ambulatory blood pressure may also be more predictive of prognosis than casual readings, a view supported by preliminary evidence. Ambulatory blood pressure monitoring has already proved useful to identify patients with "white coat" hypertension or "office" hypertension, whose hearts appear normal by echocardiography. Further research is needed to determine the relative predictive value and comparative cost-effectiveness of ambulatory blood pressure monitoring and echocardiography for identification of patients in whom hypertension does or does not constitute a cardiovascular disease that requires antihypertensive therapy.

Dietary salt intake. A determinant of cardiac involvement in essential hypertension

Because a given increase in afterload does not consistently produce the same degree of left ventricular hypertrophy, we evaluated several clinical, hemodynamic, and endocrine factors that are prone to modify the adaptation of left ventricular structure in patients with mild essential hypertension (World Health Organization stages I or II). Dietary salt intake assessed by sodium excretion over 24 hours was a powerful determinant of posterior wall thickness (r = 0.64, p less than 0.001), relative wall thickness (r = 0.67, p less than 0.001), and left ventricular mass (r = 0.37, p less than 0.05). In contrast, diastolic pressure, body mass index, hematocrit, and epinephrine were found to be weaker determinants of left ventricular structure (r = 0.31-0.40, p less than 0.05). A stepwise multiple regression analysis revealed that sodium excretion was the strongest predictor for posterior wall thickness (p less than 0.02) and relative wall thickness (p less than 0.05) independent of the other examined variables. These results identify dietary salt intake as a strong determinant of cardiac structural adaptation to a persistent increase in arterial pressure. Consequently, a high salt intake might aggravate and, conversely, dietary salt restriction might prevent (or at least mitigate) the development of left ventricular hypertrophy in patients with essential hypertension.

Reversible induction of right ventricular atriopeptin synthesis in hypertrophy due to hypoxia

Right ventricular hypertrophy produced in rats exposed to 10% oxygen for 3 weeks resulted in a ninefold increase in atriopeptin immunoreactivity (APir) and a 160-fold increase in atriopeptin messenger RNA (AP mRNA) in the right ventricular myocardium. A small but significant increase in left ventricular APir and AP mRNA was also present, probably representing the interventricular septum. Right atrial APir was decreased by 50%, but left atrial APir was not different from normoxic controls. Purification of ventricular tissue extracts by high-performance liquid chromatography revealed primarily the high molecular weight prohormone. The development of right ventricular hypertrophy and right ventricular APir content followed a similar time course, each evident at 7 days of hypoxia and reaching a plateau at 14 days. Hypoxia followed by normoxia caused right ventricular APir to fall to control levels within 3 days, despite persistent right ventricular hypertrophy. This data demonstrates that hypoxia can reversibly induce extra-atrial expression of atriopeptin synthesis in the cardiac ventricle.

Effects of chronic dobutamine administration on hearts of normal and hypertensive rats

We have previously shown that physical conditioning in the rat improves cardiac mechanics and biochemistry and normalizes the cardiac contractile protein abnormalities associated with renovascular hypertension. Since chronic adrenergic stimulation with dobutamine simulates some aspects of physical conditioning, this study was undertaken to investigate the effects of chronic dobutamine administration on normal and hypertensive rat hearts. Four groups of female animals were studied: controls, dobutamine-treated (2 mg/kg twice daily), renovascular hypertensives, and dobutamine-treated hypertensives. Animals were killed after 8-10 weeks and cardiac histology, myosin biochemistry, and mechanics in an isolated heart perfusion apparatus were studied. Dobutamine, unlike hypertension, was not associated with histological evidence of myocardial damage but did increase cardiac mass by 10% and calcium-activated myosin ATPase activity by 13%. Hypertension was associated with a 24% increase in mass, a 24% decrease in ATPase activity, and a shift in the myosin isoenzyme pattern from V1 to V3. The combined stimuli caused additive hypertrophy (44%) and normalized myosin biochemistry and isomyosin distribution. Dobutamine treatment was not associated with significant improvements in pump or muscle function in control or hypertensive hearts. Thus chronic dobutamine treatment, like physical conditioning, induces a physiological cardiac hypertrophy in rats that is associated with improved myosin enzymology and normalization of the contractile protein abnormalities associated with hypertension. Unlike physical conditioning, however, these biochemical alterations do not result in improved contractile function as measured in an isolated buffer-perfused heart apparatus.

Cardiac involvement in hypertension

Despite improved patient detection and pharmacologic therapy, the effect of treatment of hypertension on mortality from coronary artery-related events remains unresolved. Left ventricular (LV) hypertrophy, a known consequence of hypertension, is associated with an excess mortality independent of other known cardiovascular risk factors. Recently, LV hypertrophy accompanying hypertension has been associated with ominous ventricular arrhythmias. However, it does not necessarily follow that regression of LV hypertrophy will reduce this increased mortality. Diastolic dysfunction, manifested by reduced ventricular distensibility of the hypertrophying left ventricle, appears to be an early characteristic of the hypertensive heart since echocardiographic techniques have demonstrated diastolic filling abnormalities in untreated essential hypertensives even before significant LV hypertrophy appears. Not all antihypertensive agents diminish LV mass and improve diastolic dysfunction. Certain sympatholytic agents, calcium antagonists, beta-adrenergic blockers, and the angiotensin-converting enzyme inhibitors appear to diminish LV hypertrophy. However, future studies are needed to determine if these agents that appear to reverse findings of LV hypertrophy and improve diastolic dysfunction will also reduce risk of coronary artery disease and related events.

Effects of arterial vasodilators on cardiac hypertrophy and sympathetic activity in rats

In spontaneously hypertensive rats (SHR), the progression (or absence of regression) of cardiac hypertrophy despite adequate blood pressure (BP) control by arterial vasodilators has been attributed to increased cardiac sympathetic activity. We evaluated changes in indices of general and cardiac sympathetic tone in relation to changes in cardiac anatomy during treatment of normotensive rats and SHR with hydralazine, 120 mg/L, or minoxidil, 120 mg/L of drinking water. In SHR, both vasodilators reduced BP rapidly and consistently. Significant increases in heart rate and plasma norepinephrine were observed only in the initial 2 days of arterial vasodilator treatment. After 5 weeks of treatment, marked increases in left and right ventricular sympathetic activity (as assessed by norepinephrine turnover rates) were present, but no increase was seen in heart rate and plasma norepinephrine. Intravascular volume expansion was observed on Day 14 of minoxidil and Day 35 of hydralazine treatment. Prolonged treatment with minoxidil induced significant increases in left ventricular internal diameter, as well as in left and right ventricular weights, but not in the wall thickness of the left ventricle. Treatment with hydralazine did not affect left ventricular weight and caused a small increase in the weight of the right ventricle. In normotensive rats, both vasodilators initially decreased BP, but tolerance developed within 1 to 2 weeks of treatment. Plasma norepinephrine and heart rate showed increases only at Day 1 of either treatment, whereas cardiac sympathetic hyperactivity persisted at 2 and 5 weeks of treatment. Changes in cardiac anatomy were qualitatively similar to those observed in SHR. We conclude that, during treatment of normotensive rats and SHR with arterial vasodilators, cardiac sympathetic hyperactivity persists and may be involved in the cardiac effects of arterial vasodilators. However, other mechanisms, such as chronic cardiac volume overload, may also play an important role, particularly with minoxidil.

Does the renin-angiotensin-aldosterone system modify cardiac structure and function in essential hypertension?

To determine the impact of the renin-angiotensin-aldosterone system on left ventricular function and structure, 36 untreated patients with essential hypertension (WHO class I and II) were examined. Posterior wall thickness, relative wall thickness, and left ventricular mass were determined by M-mode echocardiography. Plasma renin activity, aldosterone, angiotensin I, and angiotensin II levels were measured by radioimmunoassay. Plasma renin activity was related to 24-hour urinary sodium excretion. Of all the endocrine parameters, only the angiotensin II level correlated with posterior wall thickness (r = 0.50, p less than 0.05) and relative wall thickness (r = 0.46, p less than 0.05). This relationship was confirmed by stepwise multiple regression analysis taking arterial pressure, obesity, and sodium excretion into account (p less than 0.05). Plasma renin activity but not the angiotensin II level correlated positively with the ejection fraction (r = 0.42, p less than 0.05) and velocity of circumferential fiber shortening (r = 0.57, p less than 0.01). Thus, angiotensin II emerged as a determinant of left ventricular structural adaptation in essential hypertension.

Induction of the skeletal alpha-actin gene in alpha 1-adrenoceptor-mediated hypertrophy of rat cardiac myocytes

Myocardial hypertrophy in vivo is associated with reexpression of contractile protein isogenes characteristic of fetal and neonatal development. The molecular signals for hypertrophy and isogene switching are unknown. We studied alpha (sarcomeric)-actin messenger RNA (mRNA) expression in cultured cardiac myocytes from the neonatal rat. In the cultured cells, as in the adult heart in vivo, expression of cardiac alpha-actin (cACT) predominated over that of skeletal alpha-actin (sACT) mRNA, the fetal/neonatal isoform. alpha 1-Adrenergic receptor stimulation induced hypertrophy of these cells, increasing total RNA and cytoskeletal actin mRNA by 1.8-fold over control, and total alpha-actin mRNA by 4.3 fold. This disproportionate increase in total alpha-actin mRNA was produced by a preferential induction of sACT mRNA, which increased by 10.6-fold over control versus only 2.6-fold for cACT mRNA. The alpha 1-adrenoceptor is the first identified molecular mediator of early developmental isogene reexpression in cardiac myocyte hypertrophy.

Cardiac involvement in essential hypertension. Prevalence, pathophysiology, and prognostic implications

The understanding of the complex involvement of the heart in human hypertension has been substantially advanced by the development of methods that detect left ventricular hypertrophy. This article reviews the literature regarding cardiac involvement in systemic hypertension, blood pressure relations to cardiac hypertrophy or clinical prognosis, relation between cardiac structure and cardiac performance in hypertensive patients, and finally, neurohormonal influence on the activity of the heart.

Effects of chronic progressive myocardial hypertrophy on indexes of cardiac autonomic innervation

The development of cardiac hypertrophy is associated with marked changes in cardiac autonomic innervation. Significant and sustained reductions of myocardial catecholamine stores and activities of tyrosine hydroxylase and dopamine beta-hydroxylase have been reported in models of acutely induced ventricular hypertrophy. Conversely, activity of choline acetyltransferase, a marker of parasympathetic nervous function, shows transient increases during the development of acute right ventricular hypertrophy. The potential physiological importance of these changes prompted us to examine a clinically more relevant model of slowly progressive ventricular hypertrophy. Application of a loose band around the pulmonary artery of weanling guinea pigs resulted in a growth-related progressive right ventricular pressure overload. Right ventricular weight-to-body-weight ratio was increased significantly and progressively at 9 and 18 weeks in banded animals (0.92 +/- 0.05 and 1.31 +/- 0.11 mg/g, respectively, p less than 0.01) compared with sham-operated controls (0.55 +/- 0.02 and 0.59 +/- 0.01 mg/g, respectively) but showed no further gain at 27 weeks (1.41 +/- 0.10 mg/g). Activities of tyrosine hydroxylase and dopamine beta-hydroxylase remained unchanged in all experiment groups, while right ventricular contents of norepinephrine in banded animals at 18 and 27 weeks exhibited sustained and progressive increases (2.45 +/- 0.11 and 3.40 +/- 0.19 micrograms/right ventricle, respectively) over controls (1.80 +/- 0.13 and 2.40 +/- 0.22 micrograms/right ventricle, respectively, p less than 0.01). The activity of choline acetyltransferase was markedly elevated in banded animals at 18 weeks (32.6 +/- 2.7 nmol/hr/right ventricle) but returned to baseline by 27 weeks (22.8 +/- 1.4 nmol/hr/right ventricle).(ABSTRACT TRUNCATED AT 250 WORDS)

Preserved cardiac beta-adrenergic sensitivity in early renovascular hypertension

To determine the mechanism of blunted sympathetic reflex responses in early renovascular hypertension, we measured inotropic and chronotropic responses of the heart to beta-adrenergic stimulation in vivo and myocardial beta-adrenergic receptor number and adenylate cyclase activity in 10 dogs during an early stage of one-kidney renal hypertension. Mean aortic pressure was higher in the hypertensive dogs (152 +/- 4 mm Hg) than in eight sham-operated dogs (122 +/- 1 mm Hg; p less than 0.001), but heart rate, cardiac output, and left atrial pressure did not differ between the two groups. Blood pressure reduction with a direct-acting vasodilator, pinacidil, resulted in marked increases in heart rate (+97 +/- 12 beats/min) and rate of change of left ventricular pressure (dP/dt; +1447 +/- 367 mm Hg/sec) in normotensive dogs but only blunted heart rate (+54 +/- 12 beats/min) and minimal left ventricular dP/dt (+376 +/- 264 mm Hg/sec) responses in hypertensive dogs. In contrast, intravenously administered isoproterenol produced similar increases in heart rate and left ventricular dP/dt in the two groups. These two groups also did not differ in either left ventricular beta-adrenergic receptor number and affinity or basal, isoproterenol-stimulated, and fluoride-stimulated adenylate cyclase activity. Thus, despite blunted reflex responses to blood pressure reduction, hypertensive dogs showed neither reduction in chronotropic and inotropic responses to direct beta-adrenergic stimulation nor beta-adrenergic desensitization of the myocardium, as assessed by beta-adrenergic receptor number and adenylate cyclase activity. Blunted reflex responses in this model of early hypertension must be due to factors operating at some locus other than the beta-adrenergic receptor-adenylate cyclase complex.

Left ventricular hypertrophy in hypertension. Prevalence and relationship to pathophysiologic variables

In less than a decade since development of echocardiographic measurement of left ventricular muscle mass, studies using this technique have provided considerable information about the prevalence and pathophysiology of left ventricular hypertrophy in human hypertension. Increased left ventricular mass has been found in a significant minority of patients with systemic hypertension, with the exact prevalence dependent both on how a population is selected and on the sex, race, and possibly age composition of its members. All published studies have reported that left ventricular hypertrophy is more closely related to blood pressure recorded in the patient's natural setting during normal activity or exercise-whether measured by portable recorder or home manometer-than to blood pressure measured by the physician. In addition, studies indicate that the classic hypertensive abnormalities of concentric left ventricular hypertrophy and increased peripheral resistance are interrelated, while left ventricular hypertrophy is absent in a subgroup of patients with mild essential hypertension who exhibit high cardiac output and evidence of supernormal myocardial contractility. Conversely, the left ventricular functional response to exercise is inversely related to the degree of hypertrophy. High levels of blood viscosity, which would tend to blunt the reduction in peripheral resistance expected during sleep or exercise, have also been associated with left ventricular hypertrophy in patients with essential hypertension. Echocardiographic studies have provided evidence both for and against the hypothesis that activity of the sympathetic or reninangiotensin systems plays a direct role in causing hypertensive cardiac hypertrophy. These findings demonstrate the useful role that echocardiographic assessment of left ventricular structure and function may play in hypertension research.

Chronic cardiac reactions. III. Factors involved in the development of structural dilatation

The significance of various factors for the development of structural dilatation in the chronically pressure-loaded and failing heart were evaluated. The investigations were performed on male rats with renal (Goldblatt II) and spontaneous (Aoki-Okamoto) hypertension at different stages of haemodynamic overload. Two groups of SHR were submitted to intermittent feeding (SHR IF); one group received additionally the beta-blocking agent atenolol (50 mg/kg b.w.; SHR IF + beta Bl.). Haemodynamic measurements were carried out under open chest conditions. Myosin isoenzyme pattern, hydroxyproline concentration and circulating blood volume were determined. Transformation to slower myocardium per se, induced by IF, did not lead to significant change in ventricular configuration. After additional blockade of beta-adrenergic receptors there were indications of unfavourable development of left ventricular configuration. Inhibition of hypertrophic mass increase due to curtailed adrenergic stimulation could be an influential factor in the development of dilatation. Further investigations, however, are required to establish the relationship between the adrenergic system, on the one hand, and degree of hypertrophy as well as structural dilatation of the ventricle, on the other hand. The established marked increase in hydroxyproline concentration of the dilated ventricle of SHR in congestive failure is consistent with the assumption of a causal link between the degree of fibrosis and structural dilatation. Observations on rats with aorto-caval shunt and Goldblatt II rats with eccentric hypertrophy and corresponding increase in filling potential or circulating blood volume indicate a correlation between the latter and ventricular size. Thus, we assume that curtailed protein synthesis, fibrosis and regulatory processes related to water and electrolyte balance, but not myocardial transformation per se, play a role in the development of structural dilatation. The relative contribution of each factor, however, may depend on the experimental model that is used.