Metabolic control of the circulation: implications for congestive heart failure

The role of metabolic processes in the control of the normal circulation will be discussed with particular emphasis on how metabolic events, particularly those that occur with the performance of exercise, result in production of vasoactive substances and sympathetic activation. Heart failure patients will have altered metabolism, particularly in skeletal muscle, that may result in a lesser degree of peripheral vasodilation and will also have an abnormal response to sympathetic stimuli, with less cardiac stimulation but preserved peripheral vasoconstriction. The consequences of these abnormalities on the hemodynamics and metabolic processes that occur with exercise in the heart failure patient will be discussed in detail. The effect of therapeutic interventions such as drug therapy and exercise training will be reviewed.

Effect of long-term enalapril therapy on neurohormones in patients with left ventricular dysfunction. SOLVD Investigators

The aim of this study was to compare the long-term effects of treatment with enalapril or placebo on plasma neurohormones in patients with left ventricular (LV) dysfunction. Elevated neurohormonal levels are associated with increased mortality in patients with congestive heart failure. Multiple studies have shown that angiotensin-converting enzyme inhibitors decrease mortality and morbidity in these patients. In Studies of Left Ventricular Dysfunction (SOLVD), enalapril significantly reduced mortality in patients with symptomatic LV dysfunction (treatment trial). In contrast, in patients with asymptomatic LV dysfunction (prevention trial), there was no significant reduction in mortality with enalapril therapy. The effect of enalapril was examined in 333 prevention trial and 129 treatment trial patients. Plasma norepinephrine (NE) and plasma renin activity were measured in these patients at baseline, and at 4 and 12 months of follow-up. In a subset of these patients, atrial natriuretic peptide (ANP) and arginine vasopressin were also measured. Analysis of covariance models were used to determine the effect of enalapril on each neurohormone. Participants in the treatment trial had significantly higher neurohormonal levels when compared with those in the prevention trial or normal control subjects. In the treatment trial, patients taking enalapril had a greater decrease in plasma NE levels than patients taking placebo (p < 0.08).(ABSTRACT TRUNCATED AT 250 WORDS)

Altered adenosine triphosphatase activities in pigs with naturally occurring hypertrophic cardiomyopathy

The purpose of this study was to determine whether myocardial adenosine triphosphatase (ATPase) activities were reduced in pigs with naturally occurring hypertrophic cardiomyopathy (HCM). The selection of hearts for the HCM and the normal control groups depended on histological examination. Specific ATPase activity and 5'-nucleotidase activity were measured in left ventricular myocardium obtained from HCM (n = 7) and normal control (n = 7) animals. The histological features of HCM included marked disorientation of muscle cells, thickening of the intramural coronary arterial wall with a narrowed lumen, endocardial fibrosis and myocardial fibrosis. The HCM group showed significant increases in both heart weight (32%) and heart weight to body weight ratio (46%). The total ATPase activity in crude homogenates from the HCM group was significantly decreased by 16%. Azide-sensitive ATPase (mitochondrial ATPase) activity, ouabain-sensitive ATPase (Na+, K+-ATPase) activity, basal Mg(2+)-ATPase activity and Ca(2+)-ATPase activity were all significantly decreased by 18%, 30%, 20% and 50%, respectively. In contrast, no significant decrease was found in the mean values for 5'-nucleotidase activity. These results suggest that myocardial ATPase activities are suppressed in pigs with naturally occurring HCM.

Neurohumoral variability in left ventricular dysfunction. SOLVD Investigators. Studies of Left Ventricular Dysfunction

The immediate and longer term variability of selected vasoactive- and volume-regulating neurohormones were measured in patients entering a substudy of the Studies of Left Ventricular Dysfunction--a randomized clinical trial in patients with left ventricular ejection fraction < or = 35%. The variability of these hormones has not been determined in a large cohort of patients. Immediate (short-term) variability was assessed by systematically comparing levels after 15 and 30 minutes of supine rest at the initial visit, and longer term variability was assessed by comparing 30-minute supine rest values at the initial visit with corresponding values taken at 30 minutes after 16 to 24 days of stable therapy. Initial values obtained at the first visit after 30-minute supine rest for all 209 patients were (mean +/- SEM) 512 +/- 21 pg/ml pg/ml for plasma norepinephrine, 1.9 +/- 0.2 ng/ml/hr for plasma renin activity, 3.0 +/- 0.1 pg/ml for plasma arginine vasopressin, and 129 +/- 5.3 pg/ml for plasma atrial natriuretic peptide. All variables were moderately increased relative to established normal values. There was a small but significant decrease from 15- to 30-minute supine posture in all neurohormones, except arginine vasopressin. In the presence of stable background therapy, no significant differences were found between measurements obtained after 30 minutes supine rest at the initial visit and 16 to 24 days later. Spearman correlation coefficients corresponding to immediate and longer term variability were high (range 0.55 to 0.79) (p < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Dobutamine effects on systole and diastole in rats with myocardial infarction

In this article, the authors attempt to determine the effect of catecholamine stimulation on the systolic and diastolic properties of the left ventricle (LV) in rats with chronic infarction. Male Sprague-Dawley rats underwent coronary artery ligation at 8-10 weeks of age. Baseline hemodynamics were measured 1-2 months after infarction. Dobutamine was administered in bolus injections of increasing concentrations, and peak hemodynamic response after each dose was recorded. Rats were divided into three groups: controls (n = 14), rats with infarct size less than 30% of LV (n = 13), and rats with infarct size at least 30% of LV (n = 9). Baseline hemodynamics were similar among the three groups. There was no significant difference in the maximal response of LV systolic pressure and heart rate between the three groups. Left ventricle +dP/dt increased with dobutamine in all three groups, but rats with infarct size of at least 30% had a significantly smaller increase above baseline as compared with control rats. In contrast, LV -dP/dt increased to a similar degree in all three experimental groups with dobutamine. Although hemodynamics can be affected by loading conditions in the intact animal, the magnitude of the change in +dP/dt with unaltered -dP/dt suggests that there is an impaired inotropic but not lusitropic response to catecholamine stimulation in rats with large chronic myocardial infarcts. The findings imply a differential effect of beta-agonist stimulation on systolic and diastolic properties of the heart.

Polymorphism of the gene encoding a human minimal potassium ion channel (minK)

A gene (minK) that encodes a minimal potassium channel has been cloned recently. We describe in this paper a human minK sequence which differs from the original sequence with a single A-->G at position 112. This resulted in a change from a Ser codon (AGT) to a Gly codon (GGT) and created a new MspAI restriction site. Of the 32 alleles from 16 subjects studied, 25 had this newly discovered sequence and 7 had the previously described sequence.

Reduced peak aerobic capacity in asymptomatic left ventricular systolic dysfunction. A substudy of the studies of left ventricular dysfunction (SOLVD). SOLVD Investigator. Studies of Left Ventricular Dysfunction

BACKGROUND

Peak oxygen consumption is reduced in patients with symptomatic congestive heart failure, but functional capacity of patients with asymptomatic left ventricular systolic dysfunction has not been assessed by measurement of peak oxygen consumption attained during graded exercise testing.

METHODS AND RESULTS

Peak oxygen consumption, that is, aerobic capacity (VO2, mL/kg per minute), was determined during graded treadmill exercise using the modified Naughton protocol in 40 patients with left ventricular systolic dysfunction (mean ejection fraction ranging from 14% to 35%; mean, 29%) who, while not receiving any cardiac medications, were totally asymptomatic, and in 41 age-matched normal subjects. Peak exercise duration and VO2 were significantly lower in patients with asymptomatic left ventricular systolic dysfunction than in normal subjects (948 +/- 273 versus 1239 +/- 372 seconds, P < .001, and 22.1 +/- 5.9 versus 29.8 +/- 7.7 mL/kg per minute, respectively, P < .001), while asymptomatic patients and normal subjects reached similar respiratory equivalents (1.14 +/- 0.11 versus 1.11 +/- 0.11 [NS]) and level of perceived exertion, using the modified Borg scale (7.4 +/- 2.6 versus 8.1 +/- 1.5 [NS]). Heart rate, systemic blood pressure, and oxygen pulse response to peak exercise were significantly lower in asymptomatic patients than in normal subjects.

CONCLUSIONS

Although patients with left ventricular systolic dysfunction can be totally asymptomatic in their daily activities, they have experienced a substantial reduction in peak aerobic capacity when compared with normal subjects of similar age.

National food contamination monitoring programmes-levels of mercury, lead and cadmium in Chinese foods

Six hundred and thirty-four food samples of six kinds were collected from Beijing, Shanghai, Jiangsu, Sichuan, Jilin and Guangdong areas, China and Hg, Pb, Cd contents were determined. The results showed that their levels in the Chinese foods were low; their levels in meat, egg, milk and fish were generally below the national hygienic standard. The average daily dietary intake of Hg, Pb, Cd were 7.25 micrograms, 103.77 micrograms and 30.72 micrograms respectively and they were all less than the ADI established by WHO.

Nitroprusside infusion improves arterial baroreflex control of heart rate in dogs with chronic congestive heart failure

To determine if nitroprusside improves arterial baroreflex responsiveness in chronic congestive heart failure (CHF), we administered nitroprusside to 11 conscious dogs with pacing-induced CHF. Baroreflex sensitivity was determined by plotting the R-R interval against systolic aortic pressure after a bolus injection of phenylephrine (PE). At baseline, dogs with CHF had higher heart rate (HR), increased left atrial blood pressure (BP), and reduced left ventricular (LV) dP/dt as compared with 10 sham-operated normal animals. Baroreflex sensitivity index was significantly lower in CHF dogs, (8.3 +/- 1.3 ms/mm Hg) than normal dogs (25.1 +/- 1.2 ms/mm Hg, p < 0.001). Intravenous (i.v.) administration of nitroprusside (1 microgram/kg/min) to CHF dogs decreased left atrial BP (23 +/- 1-17 +/- 1 mm Hg) and HR (131 +/- 4-115 +/- 4 beats/min), but had no significant effect on either cardiac output (CO) or systolic aortic BP. This resulted in a 58% increase in baroreflex sensitivity index to 13.1 +/- 1.3 ms/mm Hg (p < 0.001); and the change correlated significantly with magnitude of decrease in left atrial BP (r = 0.884, p < 0.001) but not with the increase in R-R interval (r = 0.390, p > 0.10). In contrast, administration of nitroprusside sufficient to decrease left atrial BP (9.0 +/- 1.4-6.4 +/- 1.2 mm Hg) did not alter baroreflex sensitivity (26.4 +/- 3.4-26.4 +/- 3.9 ms/mm Hg) in 5 normal dogs. The results suggest that nitroprusside infusion increases arterial baroreflex sensitivity only in dogs with CHF and that this effect is probably functionally linked to the reductions of cardiac filling pressure.

Contraction band necrosis: its modification by the free radical scavenger N-2-mercaptopropionyl glycine

Contraction band necrosis (CBN) may represent infarct extension from free radical generation during reperfusion. We sought to limit CBN with the free radical scavenger N-2-mercaptopropionyl glycine (MPG, 20 mg/kg). Sixteen chronically instrumented Beagles (8 control, and 8 MPG treated) underwent 90-min left anterior descending coronary artery (LAD) occlusion followed by 6-h reperfusion. Coronary blood flow (CBF) was measured by the radioactive microsphere technique. The dogs were killed, and the hearts were perfused with red and blue dyes to determine area at risk (AAR), stained with nitroblue tetrazolium for infarct localization, and sectioned for histologic analysis and BF measurements. In controls and MPG-treated animals, infarct/risk ratios were 40 +/- 5 and 38 +/- 6%, and epicardial collateral BFs were 0.21 +/- 0.037 and 0.15 +/- 0.034 ml/g/min, respectively (p = NS). Hemodynamic measurements did not differ between the two groups. However, CBN as a percentage of total infarct was reduced in controls (22 +/- 3%) as compared with MPG-treated animals (35 +/- 2%, p = 0.002). Thus, MPG altered the histologic composition of infarcts in this model, surprisingly increasing the amount of CBN without altering overall infarct size (IS). These results raise questions about the role of free radical scavengers in generation of CBN and suggest that a population of cells exists in which treatment with MPG may alter the mechanism of cell death.

Comparison of cardiovascular effects of mu- and delta-opioid receptor antagonists in dogs with congestive heart failure

We have shown previously that right heart failure (RHF) in dogs is associated with activated endogenous opiate systems, and that administration of the opioid receptor antagonist, naloxone, increases arterial pressure, cardiac contractile function and organ blood flows. To study whether the cardiovascular effects of naloxone are mediated via the mu- or delta-opioid receptors, we administered ICI-154,129, a delta-receptor antagonist, and naloxonazine, a mu-receptor antagonist, to 10 conscious dogs with RHF on 2 separate days. Like naloxone, ICI-154,129 increased mean aortic pressure, cardiac output, peak positive first derivative of left ventricular pressure, and blood flows to the myocardium, kidneys, splanchnic beds, and skeletal muscle. These changes were associated with increases in plasma epinephrine and norepinephrine. In contrast, naloxonazine had no effects on systemic hemodynamics, regional blood flow distribution, and plasma catecholamines in RHF. These findings suggest that the increased endogenous opioids during heart failure act on the delta-opioid receptors to decrease myocardial mechanical performance and alter regional blood flow distribution. Opioid receptor-blocking agents may exert beneficial cardiovascular effects in heart failure.

Beta-adrenoceptor downregulation in pacing-induced heart failure is associated with increased interstitial NE content

We used the rapid ventricular pacing model to examine myocardial norepinephrine (NE) uptake kinetics in congestive heart failure. Dogs subjected to pacing at 225 beats/min for 8 wk developed heart failure as evidenced by elevated left atrial pressure, depressed first derivative of left ventricular pressure with respect to time, and depressed cardiac output compared with dogs paced at 100 beats/min for 8 wk. Fast-paced dogs also exhibited an elevated plasma NE and reduced myocardial NE content. Myocardial NE uptake kinetics and interstitial NE concentration were measured in vivo using a triple-isotope intracoronary tracer technique. The rate constant of neuronal uptake of NE was significantly depressed in the fast-paced animals (0.224 +/- 0.027 vs. 0.725 +/- 0.097 s-1, P < 0.001), while the interstitial NE concentration was significantly increased in the heart (1.12 +/- 0.15 vs. 0.17 +/- 0.07 ng/ml, P < 0.001). Myocardial beta-adrenoceptor density was significantly reduced in the fast-paced animals (49 +/- 7 vs. 86 +/- 6 fmol/mg, P < 0.001), and there was a significant inverse correlation between beta-adrenoceptor density and interstitial NE concentration. Thus we conclude that excess myocardial interstitial NE content contributes to the abnormalities in the beta-adrenoceptor system.

Effects of metoprolol on left ventricular function in rats with myocardial infarction

To study the effect of beta-receptor-blocking agents in an animal model of left ventricular (LV) dysfunction, we measured LV performance in vivo and in vitro in 69 rats with or without metoprolol (M) treatment 3 wk after left coronary arterial ligation or sham operation. Rats were divided into six groups including control (C) and M noninfarct (C-N and M-N), C and M small infarct (C-S and M-S), and C and M large infarct (C-L and M-L). LV function was measured as slope of change in systolic vs. diastolic pressure (pressure-function curve) during pressor response after administration of a bolus of phenylephrine (5 micrograms/kg i.v.). Reduction of LV function was noted in C-L compared with C-N and C-S (slope of pressure-function curve 3.3 +/- 0.3 vs. 11.0 +/- 1.9 and 11.9 +/- 2.3, respectively) and in M-L compared with M-N and M-S rats (slope of 5.5 +/- 1.4 vs. 11.3 +/- 2.0 and 12.1 +/- 1.4, respectively). There was no significant difference between C and M rats, although there was a trend toward partial correction of the pressure-function curves in M-L compared with C-L rats. In muscle bath preparations the uninfarcted LV posterior papillary muscle from shams and rats with small infarcts showed a dose-related increase in peak rate of tension development with isoproterenol stimulation, but this response was lacking in both C-L and M-L. Tissue assays showed no change in beta-receptor number.(ABSTRACT TRUNCATED AT 250 WORDS)

Short-term effects of naloxone on hemodynamics and baroreflex function in conscious dogs with pacing-induced congestive heart failure

OBJECTIVES

The purpose of this study was to determine the effects of naloxone on systemic hemodynamics and reflex function in dogs with congestive heart failure induced by rapid pacing.

BACKGROUND

We have shown previously that naloxone, an opiate receptor antagonist, improves cardiac output, aortic blood pressure, systolic performance and the baroreflex function in conscious dogs with chronic right-sided congestive heart failure. However, whether endogenous opioids also play a role n mediating the reduction of myocardial and baroreflex function in animals with left heart failure remains controversial.

METHODS

We administered naloxone (1 mg/kg body weight) and normal saline solution to 15 dogs with pacing-induced congestive heart failure (225 beats/min for 8 weeks) and 11 control dogs. In addition to systemic hemodynamic measurements, the slope of pressure-area relation obtained from echocardiography with intravenous bolus injection of phenylephrine was taken as a load-independent index of myocardial contractility. Baroreflex function was estimated by the slope of the regression line relating systolic aortic pressure and RR interval.

RESULTS

Plasma beta-endorphin levels were elevated in dogs with congestive heart failure. Naloxone administration increased heart rate, mean aortic pressure, first derivative of left ventricular pressure, cardiac output and myocardial contractility in pacing-induced congestive heart failure. These changes correlated significantly with basal plasma beta-endorphin levels and were accompanied by increases in plasma beta-endorphin and catecholamines after naloxone administration. However, unlike the hemodynamic and cardiac effects of naloxone, baroreflex function did not change after naloxone in dogs with congestive heart failure.

CONCLUSIONS

The increase in basal plasma beta-endorphin suggests that the endogenous opiate system is activated in left-sided congestive heart failure. Because naloxone improves the systemic hemodynamics and myocardial contractile function under this condition, the endogenous opioids appear to play an important role in mediating the myocardial depression that occurs in heart failure. However, the endogenous opiate system has no apparent effect on the regulation of baroreflex control in heart failure induced by rapid pacing.

Comparison of nifedipine gastrointestinal therapeutic system and atenolol on antianginal efficacies and exercise hemodynamic responses in stable angina pectoris

A gastrointestinal therapeutic system (GITS) of nifedipine has been developed to provide a once-daily dosing, and predictable, relatively constant plasma concentrations. This study compared the antianginal efficacy of nifedipine GITS with a once-a-day beta-receptor blocker, atenolol. Seventeen patients with documented coronary artery disease and stable stress-induced angina pectoris were studied during a 2-week, single-blind, placebo baseline phase and a 12-week randomized, double-blind, active drug crossover efficacy phase, using the bicycle exercise test and ambulatory electrocardiographic recordings. Patients exercised significantly longer with nifedipine GITS (883 +/- 47 seconds) and atenolol (908 +/- 44 seconds) than with placebo (794 +/- 41 seconds). Nifedipine GITS reduced systolic blood pressure at all stages of exercise compared with placebo but, because heart rate tended to increase more during nifedipine therapy, there was no difference in rate-pressure products between the placebo and nifedipine GITS periods. In contrast, atenolol reduced heart rate, systolic blood pressure and rate-pressure product during exercise compared with placebo. Whereas left ventricular ejection fractions (by radionuclide angiocardiography) increased with exercise, the maximal increase was smaller with atenolol than with placebo and nifedipine. The net increase in left ventricular ejection fraction at the end of exercise was greater with nifedipine than with placebo or atenolol. Ambulatory electrocardiograms showed only a small number of ischemic events. Neither nifedipine GITS nor atenolol reduced the number of ischemic events or total duration of ST-segment deviations significantly. It is concluded that nifedipine GITS is as effective an antianginal agent as atenolol, but the hemodynamic effects of the 2 agents differ.(ABSTRACT TRUNCATED AT 250 WORDS)

Isoform-specific regulation of myocardial Na,K-ATPase alpha-subunit in congestive heart failure. Role of norepinephrine

BACKGROUND

Myocardial ouabain-binding sites and Na,K-ATPase activity are reduced in congestive heart failure (CHF), but the mechanisms by which CHF reduces the Na,K-ATPase remain unknown. We proposed to investigate whether the changes are accompanied by isoform-specific reductions of the Na,K-ATPase alpha-subunit proteins in CHF and whether similar changes could be produced by exogenous norepinephrine administration.

METHODS AND RESULTS

CHF was induced in dogs by rapid ventricular pacing at a rate of 225 beats per minute for 8 weeks (protocol 1). A second group of dogs were paced at 100 beats per minute and served as controls. In protocol 2, norepinephrine was infused in normal dogs using a subcutaneous osmotic minipump for 8 weeks. The control dogs received normal saline through the pump. Animals were studied after 8 weeks of pacing or norepinephrine infusion. After the baseline hemodynamics and interstitial norepinephrine concentration had been obtained, the hearts were removed for measuring [3H]ouabain-binding sites and Na,K-ATPase alpha-subunit proteins using isoform-specific monoclonal antibodies.

RESULTS

Myocardial [3H]ouabain-binding sites were reduced in dogs with CHF and chronic norepinephrine infusion. The Western blot analysis showed that adult canine hearts possess both alpha 1 and alpha 3 isoforms of the Na,K-ATPase alpha-subunit but not the alpha 2 isoform protein. CHF and NE infusion had no effect on the Na,K-ATPase alpha 1-subunit protein but did reduce the alpha 3 isoform protein significantly. In addition, there was a significant inverse correlation between the amount of myocardial alpha 3 isoform protein and interstitial norepinephrine content in the dogs. In contrast, the specific activity of the sarcolemmal marker 5'-nucleotidase did not differ among the groups of animals.

CONCLUSIONS

The reduction of myocardial Na,K-ATPase in CHF is limited to the alpha 3 isoform. Furthermore, because similar changes in myocardial ouabain-binding sites and Na,K-ATPase alpha 3 isoform were produced by chronic norepinephrine infusion, the decrease in the Na,K-ATPase in CHF is most likely mediated via excess sympathetic stimulation.

Reductions of myocardial Na-K-ATPase activity and ouabain binding sites in heart failure: prevention by nadolol

To study the changes in myocardial digitalis binding sites in heart failure, we measured myocardial ouabain binding sites, Na-K-adenosinetriphosphatase (ATPase) activity, and ventricular muscle mechanical responses to acetylstrophanthidin in dogs with right-heart failure (RHF) produced by tricuspid avulsion and pulmonary artery constriction. Sham-operated dogs were studied as the control. RHF produced a significant decrease in ouabain binding sites in the right and left ventricular myocardium, which was accompanied by a proportional decrease in Na-K-ATPase activity. However, RHF and sham-operated dogs did not differ in systemic hemodynamic or right ventricular trabeculate muscle isometric contractile responses to acetylstrophanthidin. To determine whether chronic beta-adrenergic stimulation contributed to the development of Na-K-ATPase downregulation, we administered nadolol (40 mg/day) to a separate group of dogs during an early stage of RHF development. Nadolol effectively prevented the reduction of myocardial ouabain binding sites that occurred in RHF. Thus we conclude that myocardial ouabain binding sites and Na-K-ATPase activity are reduced in dogs with experimental heart failure and that these changes probably occur as a result of the attendant heightened sympathetic activity.

Cardiac noradrenergic nerve terminal abnormalities in dogs with experimental congestive heart failure

BACKGROUND

We have shown previously that norepinephrine (NE) uptake activity is reduced in the failing right ventricle of animals with right heart failure (RHF) produced by tricuspid avulsion and progressive pulmonary constriction. However, it is unknown whether this defect in neuronal NE uptake is related to reduction of noradrenergic nerve terminals or whether these changes also occur in animals with left heart failure (LHF). It is also unknown whether increased NE release in heart failure contributes to the noradrenergic nerve abnormalities.

METHODS AND RESULTS

We measured myocardial NE content. NE uptake function, and noradrenergic nerve profiles in dogs with either RHF or LHF induced by rapid ventricular pacing. NE uptake activity was measured using [3H]NE, and noradrenergic nerve profiles were visualized by glyoxylic acid (SPG)-induced histofluorescence and tyrosine hydroxylase immunocytochemical staining. To study the effects of excess NE, we exposed normal dogs to 8 weeks of chronic NE infusion using subcutaneous osmotic minipumps. RHF and LHF animals exhibited reduced myocardial contractile function and congestive heart failure, as evidence by reduced cardiac output and elevated right atrial pressure. However, unlike that in LHF, left atrial pressure was not increased in RHF. The animals also showed an increase in plasma NE and a decrease in cardiac NE. In addition, SPG-induced histofluorescence correlated significantly with NE uptake activity (r = .712, P < .001) and tyrosine hydroxylase immunoreactive profiles (r = .569, P < .001) in the right ventricles of RHF dogs and in both ventricles of LHF dogs. The numbers of catecholaminergic profiles and tyrosine hydroxylase profiles significantly correlated with cardiac filling pressures. Chronic infusion of NE decreased heart rate in normal dogs but had no effect on either mean aortic pressure or left atrial pressure; like heart failure, it resulted in significant decreases in myocardial NE uptake activity and numbers of SPG-induced catecholaminergic histofluorescence and immunoreactive tyrosine hydroxylase profiles.

CONCLUSIONS

Myocardial NE uptake activity was reduced only in the failing ventricles with elevated filling pressure in RHF and LHF. These changes probably were caused by loss of noradrenergic nerve terminals in the failing ventricles, as evidenced by the reductions of catecholaminergic histofluorescence and tyrosine hydroxylase immunostained profiles. Furthermore, since similar reductions of myocardial NE uptake and noradrenergic nerve profiles could be produced by chronic NE infusion in normal dogs, elevated NE levels may play a role in the development of cardiac noradrenergic nerve abnormalities in congestive heart failure.

A fourth human MEF2 transcription factor, hMEF2D, is an early marker of the myogenic lineage

The transition from multipotent mesodermal precursor to committed myoblast and its differentiation into a mature myocyte involve molecular events that enable the cell to activate muscle-specific genes. Among the participants in this process is the myocyte-specific enhancer factor 2 (MEF2) family of tissue-restricted transcription factors. These factors, which share a highly conserved DNA-binding domain including a MADS box, are essential for the expression of multiple muscle genes with cognate target MEF2 sites in cis. We report here a new human MEF2 factor, hMEF2D, which is unique among the members of this family in that it is present not only in myotubes but also in undifferentiated myoblasts, even before the appearance of myogenin. hMEF2D comprises several alternatively spliced products of a single gene, one of which is the human homolog of the Xenopus SRF-related factor SL-1. Like its relatives, cloned hMEF2D is capable of activating transcription via sequence-specific binding to the MEF2 site, recapitulating endogenous tissue-specific MEF2 activity. Indeed, while MEF2D mRNAs are ubiquitous, the protein is highly restricted to those cell types that contain this activity, implicating posttranscriptional mechanisms in the regulation of MEF2D expression. Alternative splicing may be important in this process: two alternative MEF2D domains, at least one of which is specifically included during myogenic differentiation, also correlate precisely with endogenous MEF2 activity. These findings provide compelling evidence that MEF2D is an integral link in the regulatory network for muscle gene expression. Its presence in undifferentiated myoblasts further suggests that it may be a mediator of commitment in the myogenic lineage.

Clinical characteristics of patients in studies of left ventricular dysfunction (SOLVD)

The Studies of Left Ventricular Dysfunction (SOLVD) trials were designed to evaluate the effects of enalapril on long-term mortality in patients with severe left ventricular (LV) dysfunction. Patients with LV ejection fractions less than or equal to 0.35 and symptoms of congestive heart failure (CHF) were enrolled in the treatment trial, whereas those with no history of overt CHF and taking no treatment directed for LV dysfunction were enrolled in the prevention trial. The baseline clinical characteristics of SOLVD patients were compared to characterize differences between patients in these 2 separate but concurrent trials. From over 70,000 patients screened with LV dysfunction, 4,228 patients were enrolled in the prevention trial and 2,569 patients in the treatment trial. Ischemic heart disease was the primary cause of LV dysfunction in both prevention (83%) and treatment (71%) trial patients. Prior myocardial infarction was present in 80% of the prevention and 66% of the treatment trial patients (p less than 0.001). In the prevention trial, infarction was recent (less than or equal to 6 months) in 27% patients and remote (greater than 6 months) in 57% patients. Treatment trial patients had proportionately more women (20 vs 13%; p less than 0.001) and non-Caucasians (20 vs 14%; p less than 0.001), as well as the coexisting risk factors of hypertension (42 vs 37%; p less than 0.001) and diabetes (26 vs 15%; p less than 0.001) than did prevention trial patients. Clinical characteristics of patients in both trials were influenced by the gender and race of enrolled patients. Similarly, coronary artery bypass surgery was performed less often in women and non-Caucasians.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics of peak aerobic capacity in symptomatic and asymptomatic subjects with left ventricular dysfunction. The Studies of Left Ventricular Dysfunction (SOLVD) Investigators

Expired gas analysis was used to determine the aerobic exercise performance of subjects with depressed left ventricular (LV) systolic function and congestive heart failure (CHF). To determine whether subjects with no or minimal CHF have better aerobic exercise performance than do those with overt CHF, oxygen consumption (VO2) at anaerobic threshold (AT) and peak exercise was measured in 184 subjects with LV ejection fraction less than or equal to 0.35 who participated in the Studies of Left Ventricular Dysfunction. Subjects were divided into those with overt CHF needing treatment (treatment trial; n = 20) and those who had neither overt CHF nor treatment for CHF (prevention trial; n = 164). Treatment trial subjects had a lower LV ejection fraction (0.25 +/- 0.07) than did prevention trial ones (0.29 +/- 0.05; p = 0.001), but there were no differences in age, gender, body weight, resting heart rate and blood pressure. Treadmill exercise testing was performed after 2 to 3 weeks of placebo (no angiotensin-converting enzyme inhibitor) treatment. Treatment trial subjects exercised for a shorter time (493 +/- 160 seconds) and attained a lower peak VO2 (13 +/- 4 ml/kg/min) and VO2 at AT (11 +/- 4 ml/kg/min) than did prevention trial ones (842 +/- 277 seconds, and 20 +/- 6 and 16 +/- 5 ml/kg/min, respectively). Analysis of covariance showed that the differences in peak VO2 and VO2 at AT were statistically significant between the 2 trials after adjusting for age, gender, LV ejection fraction and New York Heart Association functional class.(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-adrenoceptor and adenylate cyclase function in the infarct model of rat heart failure

In order to determine the possible etiology for diminished inotropic responsiveness to catecholamines in the infarction model of chronic congestive heart failure in rats, we studied beta-adrenoceptor number and site-specific stimulated adenylate cyclase activity in noninfarcted left ventricular tissue of rats at 3 months after ligation of the left coronary artery. Rats were divided into sham, small infarct, and large infarct groups according to infarct size. The large infarct groups showed increased right ventricle to body weight ratio (0.93 +/- 0.07 mg/g for the large infarcts vs 0.52 +/- 0.02 and 0.54 +/- 0.02 mg/g for the shams and small infarcts, respectively). Beta-Adrenoceptor number among the groups was similar (shams, 27 +/- 1 fmol/mg; small infarcts, 26 +/- 1 fmol/mg; and large infarcts, 29 +/- 1 fmol/mg), as was Kd (20 +/- 1 pmol, 18 +/- 2 pmol, and 18 +/- 2 pmol, respectively). Site-specific stimulation of adenylate cyclase using isoproterenol, Gpp(NH)p, forskolin, and MnCl2 revealed no significant differences among the groups. We conclude that this system is not responsible for the altered inotropic responsiveness to catecholamines seen in this model.

Pregnancy enhances cardiotoxicity of cocaine: role of progesterone

Contraction dynamics of isolated papillary heart muscles from nonpregnant, pregnant, and progesterone-treated nonpregnant Long Evans rats were studied during exposure to cocaine. With increasing cocaine concentrations from 10(-16) to 10(-4) M, papillary muscles from nonpregnant rats demonstrated a biphasic pattern of positive, then negative, inotropy. Only negative inotropy with increasing cocaine concentrations was observed in papillary muscles from pregnant and progesterone-treated nonpregnant rats. Papillary muscles from pregnant and progesterone-treated nonpregnant rats became nonfunctional at cocaine concentrations 1-4 orders of magnitude lower than those for nonpregnant rats. These findings demonstrate that pregnancy and progesterone treatment alter cocaine effects upon cardiac papillary muscle function and response patterns and shift the cocaine dose-function curve to the left when compared to the nonpregnant group. We conclude that pregnancy increases the direct cardiotoxicity to cocaine, and progesterone may be responsible for this enhanced cocaine toxicity.

Effects of dichloroacetate on hemodynamic responses to dynamic exercise in dogs

To determine whether lactic acid production contributes significantly to the cardiac responses to muscular dynamic exercise, we administered intravenous sodium dichloroacetate (32 mumol.kg-1.min-1), a pyruvate dehydrogenase activator that facilitates lactate metabolism via the tricarboxylic cycle, in 12 dogs during two graded levels of treadmill exercise. Similar exercise was carried out in nine normal dogs receiving equimolar doses of NaCl. In the latter group, arterial lactate increased progressively from 0.80 +/- 0.11 (SE) mmol/l at rest to 2.13 +/- 0.28 mmol/l by the end of exercise. In contrast, arterial lactate did not change significantly (0.98 +/- 0.12 to 0.95 +/- 0.11 mmol/l) during exercise in dogs receiving dichloroacetate infusion. Dichloroacetate infusion also reduced the increases in plasma norepinephrine, heart rate, and left ventricular contractile indexes that occurred during exercise, suggesting that the sympathetic cardiac stimulation occurring during exercise may be related to the production of lactic acid. However, dichloroacetate affected neither the net increase in cardiac output nor the relationship between total body oxygen consumption and cardiac output that occurred during exercise. Thus we conclude that lactic acid production is not essential to the increase in cardiac output that occurs during mild-to-moderate exercise.

Both cell surface and internalized beta-adrenoceptors are reduced in the failing myocardium

To study myocardial beta-adrenoceptor internalization in heart failure, we measured beta-adrenoceptor density in the particulate, light vesicle and supernatant fractions of ventricular tissue of dogs with experimental right ventricular failure and sham-operated dogs. Tissue was fractionated by centrifugation, and beta-adrenoceptors were measured by [125I]iodocyanopindolol binding. Compared to sham-operated controls, beta-adrenoceptors were reduced in all fractions of right ventricular tissue from heart failure animals. Thus, the decreased surface (particulate fraction) receptors observed cannot be explained by internalization alone, and must be associated with altered receptor synthesis or degradation.