Chronic adriamycin treatment impairs myocardial interstitial neuronal release of norepinephrine and epinephrine

Although chronic adriamycin (doxorubicin) treatment is known to induce cardiomyopathic heart failure with sympathetic neurohumoral activation in a dose-dependent manner, its effect on local neuronal catecholamine release at the cardiac sympathetic nerve terminals remains to be clearly determined. Using a cardiac microdialysis technique, we measured dialysate norepinephrine (NE) and epinephrine (Epi) concentrations as indices of myocardial interstitial NE and Epi levels. respectively, in rabbits with chronic adriamycin treatment (ADR) (4 mg/kg/week, 6 weeks, n = 8) and in control rabbits (CNT) (n = 6). Exocytotic release was evoked by the local administration of KCl (100 mM) through the dialysis probe. Basal levels of NE and Epi did not differ between the ADR and CNT groups (NE, 11.6 +/- 6.6 vs. 20.4 +/- 17.2 pg/ml; Epi, 4.0 +/- 0.1 vs. 4.6 +/- 1.7 pg/ml: mean +/- SD). The exocytotic release was suppressed in the ADR compared with the CNT group (NE, 191.4 +/- 144.7 vs. 760.5 +/- 337.8 pg/ml; p < 0.05: Epi, 4.2 +/- 0.4 vs. 20.8 +/- 9.9 pg/ml; p < 0.05). We conclude that chronic adriamycin treatment impairs the neuronal exocytotic release of catecholamine at the cardiac sympathetic nerve terminals.

Sympathetic stimulation produces a greater increase in both transmural and spatial dispersion of repolarization in LQT1 than LQT2 forms of congenital long QT syndrome

OBJECTIVES

The study compared the influence of sympathetic stimulation on transmural and spatial dispersion of repolarization between LQT1 and LQT2 forms of congenital long QT sYndrome (LQTS).

BACKGROUND

Cardiac events are more associated with sympathetic stimulation in LQT1 than in LQT2 or LQT3 syndrome. Experimental studies have suggested that the interval between Tpeak and Tend (Tp-e) in the electrocardiogram (ECG) reflects transmural dispersion of repolarization across the ventricular wall.

METHODS

We recorded 87-lead body-surface ECGs before and after epinephrine infusion (0.1 microg/kg/min) in 13 LQT1, 6 LQT2, and 7 control patients. The Q-Tend (QT-e), Q-Tpeak (QT-p), and Tp-e were measured automatically from 87-lead ECGs, corrected by Bazett's method (QTc-e, QTc-p, Tcp-e), and averaged among all 87-leads and among 24-leads, which reflect the potential from the left ventricular free wall. As an index of spatial dispersion of repolarization, the dispersion of QTc-e (QTc-eD) and QTc-p (QTc-pD) were obtained among 87-leads and among 24-leads, and were defined as the interval between the maximum and the minimum of the QTc-e and the QTc-p, respectively.

RESULTS

Epinephrine significantly increased the mean QTc-e but not the mean QTc-p, resulting in a significant increase in the mean Tcp-e in both LQT1 and LQT2, but not in control patients. The epinephrine-induced increases in the mean QTc-e and Tcp-e were larger in LQT1 than in LQT2, and were more pronounced when the averaged data were obtained from 24-leads than from 87-leads. Epinephrine increased the maximum QTc-e but not the minimum QTc-e, producing a significant increase in the QTc-eD in both LQT1 and LQT2 patients, but not in control patients. The increase in the QTc-eD was larger in LQT1 than in LQT2 patients.

CONCLUSIONS

Our data suggest that sympathetic stimulation produces a greater increase in both transmural and spatial dispersion of repolarization in LQT1 than in LQT2 syndrome, and this may explain why LQT1 patients are more sensitive to sympathetic stimulation.

Dialysate dihydroxyphenylglycol as a window for in situ axoplasmic norepinephrine disposition

To examine basal axoplasmic norepinephrine (NE) kinetics at the in situ cardiac sympathetic nerve ending, we applied a dialysis technique to the heart of anesthetized cats and performed the dialysate sampling with local administration of a pharmacological tool through a dialysis probe. The dialysis probe was implanted in the left ventricular wall, and dihydroxyphenylglycol (DHPG, an index of axoplasmic NE) levels were measured by liquid chromatogram-electrochemical detection. Control dialysate DHPG levels were 161+/-19 pg/ml. Pargyline (monoamine oxidase inhibitor, 1 mM) decreased the dialysate DHPG levels to 38+/-10 pg/ml. Further alpha-methyl-para-tyrosine, omega-conotoxin GVIA, desipramine (NE synthesis, release and uptake blockers) decreased the dialysate DHPG levels to 64+/-19, 106+/-15, 110+/-22 pg/ml, respectively. In contrast, reserpine (vesicle NE transport inhibitor, 10 microM) increased the dialysate DHPG levels to 690+/-42 pg/ml. Thus, NE synthesis, metabolism and recycling (release, uptake and vesicle transport) affected basal intraneuronal NE disposition at the nerve endings. Measurement of DHPG levels through a dialysis probe provides information about basal intraneuronal NE disposition at the cardiac sympathetic nerve endings. Yohimbine (alpha(2)-adrenoreceptor blocker, 10 microM) and U-521 (catechol-O-methyltransferase blocker, 100 microM) did not alter the dialysate DHPG levels. Furthermore, there were no significant differences in the reserpine induced DHPG increment between the presence and absence of desipramine (10 microM) or alpha-methyl-para-tyrosine (100 mg/kg i.p.). These results may be explained by the presence of two axoplasmic pools of NE, filled by NE taken up and synthesized, and by NE overflow from vesicle. The latter pool of NE may be closed to the monoamine oxidase system in the axoplasma.

Low compliance rather than high reflection of arterial system decreases stroke volume in arteriosclerosis: a simulation

Although various investigators have suggested that the left ventricles of aged subjects suffer from high-frequency reflection, arterial reflection is larger in the low-frequency range because of a larger impedance mismatch. It has not been quantified whether high-frequency reflection rather than low-frequency reflection has larger deleterious effects on stroke volume. We used a computer simulation method to evaluate how increases in high- and low-frequency arterial reflections associated with age-related arterial sclerosis affect left ventricular (LV) pump function. Low-frequency reflections derive principally from the total arterial compliance, and high-frequency reflections result from impedance fluctuations in the high-frequency range. We numerically coupled a time-varying elastance LV model with a variety of arterial impedances to quantitatively evaluate the effects of low- and high-frequency reflections on LV pump performance. When we simultaneously increased low- and high-frequency reflections to levels of sclerotic impedance (type A in Murgo et al., Circulation 62: 105-116, 1980), stroke volume decreased by 4.4%. Further increases of the reflections up to 8 times of the type A impedance lowered stroke volume by 15.9%. This trend was clearly seen with selective increases in low-frequency reflections (3.5 and 20.2% decrease in stroke volume, respectively), but not with those in high-frequency reflections (1.0% decrease and 0.9% increase in stroke volume, respectively). Thus we conclude that the detrimental effect of increases in arterial reflections associated with arterial sclerosis on stroke volume is mild and mainly attributable to decreased compliance rather than to increased high-frequency reflections.

Improved left ventricular contraction and energetics in a patient with Chagas' disease undergoing partial left ventriculectomy

A 43-year-old patient with heart failure, precluded from heart transplantation or dynamic cardiomyoplasty because of Chagas' disease cardiomyopathy, mitral regurgitation, and ventricular mural thrombi, underwent mitral valvuloplasty and partial left ventriculectomy (PLV) between the papillary muscles. Intraoperative pressure-volume relationship analyses suggested improvement in left ventricular contraction, energetics, isovolumic relaxation, and mitral valve competency. These improvements allowed prompt, short-term recovery despite unchanged myocardial pathology, which suggests that a surgical approach can alter anatomic-geometric factors and achieve clinical improvement in a dilated failing ventricle.

Vagosympathetic interactions in ischemia-induced myocardial norepinephrine and acetylcholine release

To elucidate the pathophysiological roles of vagosympathetic interactions in ischemia-induced myocardial norepinephrine (NE) and acetylcholine (ACh) release, we measured myocardial interstitial NE and ACh levels in response to a left anterior descending coronary occlusion in the following groups of anesthetized cats: intact autonomic innervation (INT, n = 7); vagotomy (VX, n = 6); local administration of atropine (Atro, n = 6); transection of the stellate ganglia (TSG, n = 5); local administration of phentolamine (Phen, n = 6); and combined vagotomy and transection of the stellate ganglia (VX+TSG, n = 5). The maximum NE release was enhanced in the VX group (141 +/- 30 nmol/l, means +/- SE, P < 0.05) compared with the INT group (61 +/- 12 nmol/l). Neither the Atro (50 +/- 24 nmol/l) nor VX+TSG groups (84 +/- 25 nmol/l) showed enhanced NE release. The maximum ACh release was unaltered in the TSG and Phen groups compared with the INT group (19 +/- 4, 18 +/- 4, and 13 +/- 3 nmol/l, respectively). These findings indicate that the cardiac vagal afferent but not efferent activity reduced the ischemia-induced myocardial NE release. In contrast, the cardiac sympathetic afferent and efferent activities played little role in the ischemia-induced myocardial ACh release.

Effects of partial left ventriculectomy on left ventricular pump function studied by theoretical analyses

Although partial left ventriculectomy (PLV) was devised to reduce myocardial wall stress in patients with severe heart failure, whether the operation acutely improves cardiac pump function has not been determined either clinically or experimentally. Because precise control of preload, afterload, and heart rate is virtually impossible in animal experiments as well as clinically before and after surgery, we took advantage of the theoretical analysis to study quantitatively the changes in pump function by PLV. We reconstructed the endsystolic and end-diastolic pressure-volume relationships based on two different geometric conditions (i.e., before and after volume reduction) but from the same myocardial stress-strain relationship. The effect of volume reduction surgery on left ventricular pump function depended on preoperative conditions. We found that the improvement in pump function was achieved only if elastance (Ees) was low and if the end-systolic strain-axis scaling parameter (k) value was low. The presence of hypertrophy amplified the improved function, but again with low Ees and low end-systolic k. We conclude that the favorable hemodynamics are expected only in limited cases during the acute phase. Candidates for favorable preoperative factors include low end-systolic Ees, an end-systolic pressure-volume relationship being less convexed toward the volume axis (low k), and large left ventricular mass.

Perioperative hemodynamics in patients undergoing partial left ventriculectomy

OBJECTIVES

Effects of partial left ventriculectomy (PLV) were studied by analyzing perioperative hemodynamics with measurements of left ventricular (LV) pressure-volume (PV) relationships and thermodilution catheter measurements in the pulmonary artery.

METHODS

Between July and October 1996, 43 consecutive patients underwent PLV with and without mitral valvuloplasty with a thermodilution catheter and PV loop analysis immediately before and after surgery. Patients were 52+/-13 years and 67+/-13 kg, with reduced functional capacity (New York Heart Association 3.3+/-0.3) due to cardiomyopathy (24), ischemic disease (13), valvular disease (3), and Chagas' disease (3).

RESULTS

PLV required cardiopulmonary bypass for 44+/-24 minutes, with the heart arrested in 10 patients for 26+/-22 minutes for coronary artery bypass grafting (8), aortic valve replacement (2), and autotransplantation (2). Two patients failed to come off bypass, six died in the hospital and 35 (35 [81.4%] of 43) were discharged. Changes in PV loops included decreased end-diastolic and end-systolic volume, resulting in no change in stroke volume. Pulmonary artery wedge pressure decreased despite elevated end-diastolic pressure. Ejection fraction, end-systolic elastance (E-max), afterload recruitable stroke work, and volume intercepts all improved and resulted in similar stroke work with less energy expenditure (less PV area), thus improving myocardial energetic efficiency.

CONCLUSION

Results suggest that PLV improves systolic function but decreases diastolic compliance, which results in reduced net ventricular function immediately after surgery. Thus, immediate hemodynamic improvements appeared to derive from reduced severity in mitral regurgitation and perioperative load manipulation. Improved myocardial energetics may ameliorate LV function and improve the course of underlying myocardial disease.

Effect of sodium channel blockers on ST segment, QRS duration, and corrected QT interval in patients with Brugada syndrome

INTRODUCTION

Brugada syndrome is characterized by an ST segment elevation in leads V1-V3 and a high incidence of ventricular fibrillation (VF). A mutation in a cardiac Na+ channel gene, SCN5A, has been linked to Brugada syndrome, and sodium channel blockers have been shown to be effective in unmasking the syndrome when concealed. The aim of this study was to examine the effects of Na+ channel blockers on ST segment elevation, QRS, corrected QT (QTc) interval, and ventricular arrhythmias in patients with Brugada syndrome.

METHODS AND RESULTS

We examined the effects of three different Na+ channel blockers (flecainide, disopyramide, and mexiletine) on the amplitude of the ST segment 20 msec after the end of QRS (ST20), QRS duration, QTc interval measured from 12-lead ECG, and ventricular arrhythmias in 12 Brugada and 10 control patients. Maximum ST20 observed in the V2 or V3 leads under baseline conditions was greater in the Brugada patients than in control patients, whereas QRS duration and maximum QTc interval were no different between the two groups. Flecainide and disopyramide, but not mexiletine, significantly increased maximum ST20 and QRS duration in both groups, although these effects were much more pronounced in the Brugada patients. The increases in ST20 and QRS duration with flecainide were significantly larger than those with disopyramide. An increase of 0.15 mV in ST20 with flecainide separated the two groups without overlap. Ventricular premature complexes developed only with flecainide in Brugada patients (3/12) displaying a marked ST elevation but not widening of QRS.

CONCLUSION

Our findings suggest that Na+ channel blockers amplify existing I(Na) and possibly other ion channel defects, with a potency inversely proportional to the rate of dissociation of the drug from the Na+ channel, thus causing a prominent elevation of the ST segment and, in some cases, prolongation of QRS duration in patients with Brugada syndrome.

Counteraction of aortic baroreflex to carotid sinus baroreflex in a neck suction model

Although neck suction has been widely used in the evaluation of carotid sinus baroreflex function in humans, counteraction of the aortic baroreflex tends to complicate any interpretation of observed arterial pressure (AP) response. To determine whether a simple linear model can account for the AP response during neck suction, we developed an animal model of the neck suction procedure in which changes in carotid distension pressure during neck suction were directly imposed on the isolated carotid sinus. In six anesthetized rabbits, a 50-mmHg pressure perturbation on the carotid sinus decreased AP by -27.4+/-4.8 mmHg when the aortic baroreflex was disabled. Enabling the aortic baroreflex significantly attenuated the AP response (-21.5+/-3.8 mmHg, P<0.01). The observed closed-loop gain during simulated neck suction was well predicted by the open-loop gains of the carotid sinus and aortic baroreflexes using the linear model (-0.43+/-0.13 predicted vs. -0.41 +/-0.10 measured). We conclude that the linear model can be used as the first approximation to interpret AP response during neck suction.

Single-beat estimation of end-systolic elastance using bilinearly approximated time-varying elastance curve

BACKGROUND

Although left ventricular end-systolic elastance (E(es)) has often been used as an index of contractility, technical difficulties in measuring volume and in changing loading conditions have made its clinical application somewhat limited. By approximating the time-varying elastance curve by 2 linear functions (isovolumic contraction phase and ejection phase) and estimating the slope ratio of these, we developed a method to estimate E(es) on a single-beat basis from pressure values, systolic time intervals, and stroke volume.

METHODS AND RESULTS

In 11 anesthetized dogs, we compared single-beat E(es) with that obtained with caval occlusion. Although the decrease (but not the increase) in contractility (5.3 to 11.4 mm Hg/mL) and the change in loading conditions (3.7 to 34.0 mm Hg/mL) over wide ranges significantly altered the slope ratio, the estimation of E(es) was reasonably accurate (y=0.97 x 0.46, r=0. 929, SEE=2.1 mm Hg/mL).

CONCLUSIONS

E(es) can be estimated on a single-beat basis from easily obtainable variables by approximating the time-varying elastance curve by a bilinear function.

Recovery time dispersion measured from 87-lead body surface potential mapping as a predictor of sustained ventricular tachycardia in patients with idiopathic dilated cardiomyopathy

INTRODUCTION

The clinical usefulness of QT dispersion in 12-lead ECG has been controversial in identifying subjects at risk for sustained ventricular tachycardia (VT) in patients with idiopathic dilated cardiomyopathy (DCM). We hypothesized that increasing the spatial resolution of the ECG improves the accuracy of risk stratification. The purpose of this study was to test the ability of recovery time dispersion measured from 87-lead body surface potential mapping (BSPM) to identify patients at risk for sustained VT in idiopathic DCM.

METHODS AND RESULTS

We obtained 87-lead BSPM and 12-lead ECG in 33 patients with idiopathic DCM (15 patients with a history of sustained VT [VT(+) group] and 18 patients without a history of sustained VT [VT(-) group]) and in 20 normal control subjects. We measured the corrected QT dispersion and corrected recovery time dispersion from 12-lead ECG (QTc-12 dispersion and RTc-12 dispersion, respectively) and 87-lead BSPM (QTc-87 dispersion and RTc-87 dispersion, respectively). Signal-averaged ECG also was recorded in 25 patients. Neither the QTc-12 nor QTc-87 dispersion discriminated between the VT(+) and VT(-) groups patients. The VT(+) group patients had a larger but insignificant RTc-12 dispersion than the VT(-) group patients. In contrast, the RTc-87 dispersion was significantly larger in the VT(+) group patients than in the VT(-) group patients (236 +/- 39 msec vs 184 +/- 28 msec, P < 0.001). Receiver operating curve analysis indicated that the RTc-87 dispersion was as good as late potentials in predicting susceptibility to sustained VT; its sensitivity, specificity, and negative predictive value were 73%, 76%, and 76%, respectively (cutoff value 200 msec). RTc-87 dispersion >200 msec combined with positive late potentials provide high sensitivity (92%) and high negative predictive value (88%) for sustained VT.

CONCLUSION

The RTc-87 dispersion is a useful tool to identify subjects at risk for sustained VT in patients with idiopathic DCM.

Closed-loop estimation of the open-loop carotid sinus baroreflex transfer function for the use of animal experiments in space

In order to develop effective counter measures to cardiovascular maladaptation associated with space flight, it is essential to know how dynamic characteristics of blood pressure regulation are altered in space. The open-loop transfer characteristics of the carotid sinus baroreflex can be divided into the neural arc and peripheral arc transfer functions (Ikeda et al. 1996). The neural arc transfer function represents the dynamic input-output characteristics from arterial pressure (AP) to efferent sympathetic nerve activity (SNA), while the peripheral arc transfer function represents those from SNA to AP. Although AP perturbation according to a white noise sequence can be used to estimate the transfer functions under baroreflex closed-loop conditions (Kwanda et al. 1997), arterial catheter implantation necessary to perturb AP limits the applicability of this method to freely moving animal experiments. To overcome this problem, we explored the closed-loop system identification method using electrical stimulation. We used aortic depressor nerve (ADN) stimulation and rapid pacing (RP) of the heart to perturb the arterial baroreflex system.

Single-beat estimation of ventricular end-systolic elastance-effective arterial elastance as an index of ventricular mechanoenergetic performance

BACKGROUND

The ratio of ventricular end-systolic elastance (Ees) to effective arterial elastance (Ea) is known to reflect not only ventricular mechanical performance but also energetic performance. Despite these useful features, technical difficulties associated with estimating Ees make the clinical application of Ees/Ea impractical. We developed a framework to estimate Ees/Ea without measuring ventricular volume or altering the loading condition.

METHODS

To achieve this goal, we approximated the ventricular time-varying elastance curve with two straight lines, one for the isovolumic phase and the other for the ejection phase, and characterized the curve with the slope ratio, k, of these two straight lines. Using the concept of the pressure-volume relationship, Ees/Ea is algebraically expressed as Ees/Ea = Pad/Pes (1 + k. ET/PEP) - 1, where Pes is end-systolic pressure, Pad is aortic diastolic pressure, ET is ejection time, and PEP is pre-ejection period. In 11 anesthetized dogs, we recorded arterial and ventricular pressures and ventricular volume and estimated Ees and Ea under various contractile states and loading conditions.

RESULTS

An empirical relation between k and Ees/Ea was found as k = 0.53 (Ees/Ea)0.51. Simultaneous solution of these two equations yielded Ees/Ea as a function of Pad/Pes and ET/PEP. The estimated Ees/Ea values correlated well with the measured Ees/Ea values ([Measured Ees/Ea] = 0.96 [Estimated Ees/Ea] + 0.098, r = 0.925, SEE = 0.051).

CONCLUSIONS

The proposed framework is capable of estimating Ees/Ea from ventricular and aortic pressure.

Closed-loop identification of carotid sinus baroreflex transfer characteristics using electrical stimulation

Although random aortic pressure (AOP) perturbation according to a binary white noise sequence enables us to estimate open-loop dynamic characteristics of the carotid sinus baroreflex under closed-loop conditions, the necessity of arterial catheter implantation limits the applicability of this method in freely moving animal experiments. Thus, we explored a closed-loop system identification method using electrical stimulation. In 6 anesthetized and vagotomized rabbits, we stimulated the aortic depressor nerve with a binary white noise sequence (0-10 Hz) under baroreflex closed-loop conditions while measuring cardiac sympathetic nerve activity (SNA) and AOP. We used a closed-loop identification method to estimate the peripheral arc transfer function from SNA to AOP. The peripheral arc transfer function approximated a second-order low-pass filter and its fitted parameters did not differ from those obtained by an open-loop identification method (dynamic gain: 1.16+/-0.32 vs. 1.02+/-0.11; natural frequency: 0.08+/-0.03 vs. 0.09+/-0.03 Hz; damping ratio: 1.53+/-0.15 vs. 1.57+/-0.21). In 6 different rabbits, we applied intermittent rapid pacing (396 beats/min) under baroreflex closed-loop conditions to estimate the neural arc transfer function from AOP to SNA. The neural arc transfer function approximated a first-order high-pass filter and its fitted parameters did not differ from those obtained by an open-loop identification method (dynamic gain: -1.15+/-0.45 vs. -1.06+/-0.05; corner frequency: 0.12+/-0.05 vs. 0.13+/-0.03 Hz). In conclusion, the closed-loop identification method using electrical stimulation is effective to estimate the neural and peripheral arc transfer functions.

Cyanide intoxication induced exocytotic epinephrine release in rabbit myocardium

Cyanide intoxication, which has been used as a model of energy depletion at cardiac sympathetic nerve terminals, causes non-exocytotic release of norepinephrine (NE). However, the effect of cyanide intoxication on cardiac epinephrine (Epi) release remains unknown. Using cardiac microdialysis in the rabbit, we measured dialysate Epi and NE concentrations as indices of myocardial interstitial Epi and NE levels, respectively. Local administration of sodium cyanide (30 mM) through the dialysis probe increased both Epi and NE levels (from 11.3+/-2.3 to 32.3+/-4.4 pg/ml and from 33.6+/-6.1 to 389.0+/-71.8 pg/ml, respectively, mean+/-S.E., P<0.01). Local desipramine (100 microM) administration suppressed the cyanide induced NE response without affecting the Epi response. In contrast, local omega-conotoxin GVIA (10 microM) administration partially suppressed the cyanide induced NE response and totally abolished the Epi response. In conclusion, cyanide intoxication causes N-type Ca(2+) channel dependent exocytotic Epi release as well as inducing N-type Ca(2+) channel independent non-exocytotic NE release.

Development of a servo-controller of heart rate using a cycle ergometer

In exercise training, precise control of exercise intensity would maximize the training efficacy while minimizing risks. To adjust work rate, heart rate (HR) has been used as a measure of exercise intensity. Thus, we developed a servo-controller of HR using a cycle ergometer. After estimating the transfer function from work rate to HR, we optimized feedback parameters for achieving a quick and stable HR response by means of a computer simulation. We then examined the performance of the servo-controller of HR in 55 healthy volunteers. We set the target HR at 60% and 75% of the age-predicted maximum HR. Times required for HR to reach 90% of the target HR were 136 +/- 33 and 137 +/-22s in the respective protocols. Standard deviations of the steady-state difference between the target and measured HRs were 2.5 +/- 0.6 and 3.8 +/- 1.1 beats/min. We conclude that the developed servo-controller makes it possible to precisely regulate HR and, thereby, exercise intensity.

Exercise-induced QRS prolongation in patients with mild coronary artery disease: computer analysis of the digitized multilead ECGs

Although exercise-induced QRS prolongation has been reported as a possible marker for inducible ischemia, subtleness of the prolongation makes it unidentifiable from standard, chart-recorded electrocardiograms (ECGs). To overcome such a limitation, we measured the QRS width using high-resolution ECGs and examined the diagnostic value of the exercise-induced QRS prolongation in patients before and after percutaneous transluminal coronary angioplasty (PTCA). In 16 patients with single- (n = 12) or double-vessel disease (n = 4), treadmill exercise ECG tests were performed before and after PTCA, while continuously recording 8-lead ECGs at 500 Hz. The onset of the QRS complexes was defined by the earliest deflection, and the end was defined as the latest deflection among 8 leads with the use of algebraic sum of the absolute voltage and their time derivatives (dV/dt) from all 8 leads. We compared QRS complexes before and 1 minute after exercise. Before PTCA, exercise prolonged the QRS width in all but 3 patients (unchanged in 2, decreased in 1) (84 +/- 7 to 87 +/- 8 ms, P < .005). After PTCA, it decreased in 4, was unchanged in 5, and increased in 7 (83 +/- 7 to 83 +/- 6 ms, not significant). PTCA shortened postexercise QRS width in all but 3 (unchanged in 2, increased in 1: 83 +/- 6 to 87 +/- 8 ms, P < .001). High-resolution ECGs enabled us to measure subtle QRS prolongation induced by mild ischemia. Because the QRS prolongation and ST-segment changes would reflect different aspects of myocardial ischemia, incorporating this measure into ST segment criteria might significantly improve the diagnostic accuracy for coronary artery disease.

The inhibitory effect of hormones associated with stress on Na appetite of sheep

Stress is a large stimulus of Na appetite in rabbits, rats, and mice. This study investigated the influence of some peptides implicated in stress, i.e., adrenocorticotropin (ACTH), corticotropin-releasing factor (CRF), and the recently discovered member of the CRF family, urocortin, on the ingestive behavior of sheep. Intracerebroventricular infusion of these peptides over 4 days decreased the need-free Na intake of Na-repleted sheep. Intracerebroventricular infusion of urocortin, however, did not alter Na intake of Na-depleted sheep. Systemic infusion of ACTH increased, whereas systemic infusion of either urocortin or CRF decreased, Na intake of Na-repleted sheep. The increase in Na intake caused by the peripheral infusion of ACTH was blocked by concurrent i.v. infusion of urocortin, substantiating the inhibitory role of this peptide on Na appetite. Central administration of all peptides and i.v. administration of urocortin or urocortin and ACTH combined decreased food intake. Water intake was not directly influenced by the peptides. Rather, decreased water intake, when observed, was secondary to decreased food intake, as determined by pair-feeding experiments. Whereas systemic infusion of ACTH mimics the increase in Na intake observed in several different stressful situations, CRF and urocortin actually inhibit Na intake, indicating a direct central action overriding any effect of these peptides on ACTH release. Indeed, the inhibition of Na intake by urocortin occurred despite its stimulation of ACTH release and the subsequent increase in peripheral level of cortisol. Thus it would appear that hormones associated with stress have both excitatory and inhibitory influences on Na intake. Presumably, other physiological processes entrained by stress also will be important in determining the quantitative outcome on Na appetite.

Differential acetylcholine release mechanisms in the ischemic and non-ischemic myocardium

To understand better the pathophysiological roles of the vagal efferent system in ischemic heart diseases, we examined endogenous acetylcholine (ACh) release in the myocardium in vivo. Acute myocardial ischemia was induced in anesthetized cats by a 60-min occlusion of the left anterior descending coronary artery (LAD). We implanted dialysis probes in the left ventricular free wall and measured the dialysate ACh concentration using liquid chromatography. In the ischemic region, the ACh level increased from 0.68+/-0.12 to 12.3+/-3.3 n M (mean+/-S.E., P<0.01) by LAD occlusion. Bilateral vagotomy did not inhibit ischemia-induced ACh release (20.3+/-6.4 n M). In vagotomized animals, inhibition of the N-type Ca(2+)channel by intravenous administration of omega-conotoxin GVIA (10microg/kg) also failed to suppress ACh release (15.9+/-2.0 n M). However, the inhibition of intracellular Ca(2+)mobilization by local administration of 3,4,5-trimethoxybenzoic acid 8-(dietyl amino)-octyl ester (1 m M) suppressed ACh release (4.4+/-0.8 n M, P<0.05 compared with no pharmacological intervention). In the non-ischemic region, the ACh level increased from 1.9+/-0.4 to 6. 0+/-1.0 n M (P<0.05) by LAD occlusion, which was completely abolished by vagotomy. We concluded that ACh release in the ischemic region was mainly attributed to a local release mechanism, whereas that in the non-ischemic region depended on the presence of intact vagal activity. The local release mechanism would depend on intracellular Ca(2+)mobilization but not on N-type Ca(2+)channel opening.

A novel servo-control system that imposes desired aortic input impedance on in situ rat heart

To clarify the pathophysiological role of dynamic arterial properties in cardiovascular diseases, we attempted to develop a new control system that imposes desired aortic impedance on in situ rat left ventricle. In 38 anesthetized open-chest rats, ascending aortic pressure and flow waveforms were continuously sampled (1,000 Hz). Desired flow waveforms were calculated from measured aortic pressure waveforms and target impedance. To minimize the difference between measured and desired aortic flow waveforms, the computer generated commands to the servo-pump, connected to a side branch of the aorta. By iterating the process, we could successfully control aortic impedance in such a way as to manipulate compliance and characteristic impedance between 60 and 160% of their respective native values. The error between desired and measured aortic flow waveforms was 70 +/- 34 microl/s (root mean square; 4.4 +/- 1.4% of peak flow), indicating reasonable accuracy in controlling aortic impedance. This system enables us to examine the importance of dynamic arterial properties independently of other hemodynamic and neurohumoral factors in physiological and clinical settings.

Increased brain angiotensin receptor in rats with chronic high-output heart failure

BACKGROUND

The renin-angiotensin system (RAS) plays a key role in the pathophysiology of chronic heart failure (CHF). In rats, we reported that CHF enhances dipsogenic responses to centrally administered angiotensin I, and central inhibition of the angiotensin-converting enzyme (ACE) prevents cardiac hypertrophy in CHF. This suggests that the brain RAS is activated in CHF. To clarify the mechanism of the central RAS activation in CHF, we examined brain ACE and the angiotensin receptor (AT) among rats with CHF.

METHODS AND RESULTS

We created high-output heart failure in 22 male Sprague-Dawley rats by aortocaval shunt. Four weeks after surgery, we examined ACE mRNA by reverse transcriptase polymerase chain reaction (RT-PCR) and AT by binding autoradiography. ACE mRNA levels were not significantly increased in the subfornical organ (SFO), the hypothalamus, or in the lower brainstem of CHF rats (n = 5) compared with sham-operated rats (SHM) (n = 6). Binding densities for type 1 AT (AT1) in the SFO (P < .05), paraventricular hypothalamic nuclei (P < .05), and solitary tract nuclei (P < .05) were higher in rats with CHF (n = 5) than in SHM rats (n = 6). Thus, in rats with CHF, AT1 expression is increased in brain regions that are closely related to water intake, vasopressin release, and hemodynamic regulation.

CONCLUSIONS

The fact that AT1 expression was upregulated in important brain regions related to body fluid control in CHF rats indicates that the brain is a major site of RAS action in CHF rats and, therefore, a possible target site of ACE-inhibitors in the treatment of CHF.