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.

Cholinesterase affects dynamic transduction properties from vagal stimulation to heart rate

Recent investigations in our laboratory using a Gaussian white noise technique showed that the transfer function representing the dynamic properties of transduction from vagus nerve activity to heart rate had characteristics of a first-order low-pass filter. However, the physiological determinants of those characteristics remain to be elucidated. In this study, we stimulated the vagus nerve according to a Gaussian white noise pattern to estimate the transfer function from vagal stimulation to the heart rate response in anesthetized rabbits and examined how changes in acetylcholine kinetics affected the transfer function. We found that although increases in the mean frequency of vagal stimulation from 5 to 10 Hz did not change the characteristics of the transfer function, administration of neostigmine (30 microg . kg-1 . h-1 iv), a cholinesterase inhibitor, increased the dynamic gain from 8.19 +/- 3.66 to 11.7 +/- 4.88 beats . min-1 . Hz-1 (P < 0.05), decreased the corner frequency from 0.12 +/- 0.05 to 0.04 +/- 0.01 Hz (P < 0.01), and increased the lag time from 0.17 +/- 0.12 to 0.27 +/- 0.08 s (P < 0.05). These results suggest that the rate of acetylcholine degradation at the neuroeffector junction, rather than the amount of available acetylcholine, plays a key role in determining the dynamic properties of transduction from vagus nerve activity to heart rate.

A new method to measure regional myocardial time-varying elastance using minute vibration

We developed a new technique to evaluate regional myocardial elastance using minute vibration. In 13 isolated cross-circulated canine hearts, we applied small sinusoidal vibrations of displacement to the left ventricular surface at various frequencies (50-100 Hz). Using the measured displacement and force between the vibrator head and myocardium, we derived myocardial elastance on the basis of the equation of motion for a given moment of the cardiac cycle. Simultaneous solution of the equations of motion at different frequencies yielded a unique value of elastance. Time-varying myocardial elastance increased from diastole (0.028 +/- 0.211 x 10(6) dyn/cm) to systole (0.833 +/- 0.391 x 10(6) dyn/cm). The end-systolic elastance (ees) linearly correlated with end-systolic left ventricular elastance (r = 0.717, P < 0.001) and also with the end-systolic Young's modulus (r = 0.874, P < 0.0001). We also measured ees at both ischemic and nonischemic regions during coronary occlusion. Young's modulus, estimated by normalizing ees by the wall thickness and by the estimated mass, did not change significantly at the nonischemic regions, whereas it decreased significantly from 2.303 +/- 0.556 to 1.173 +/- 0.370 x 10(6) dyn/cm2 at the ischemic region after coronary occlusion (P < 0.005). We conclude that this technique is useful for the quantitative assessment of regional myocardial elastance.

Summation of dynamic transfer characteristics of left and right carotid sinus baroreflexes in rabbits

Although interactions among parallel negative-feedback baroreflex systems have been extensively investigated with respect to their steady-state responses, the dynamic interactions remain unknown. In anesthetized, vagotomized, and aortic-denervated rabbits, we perturbed isolated intracarotid sinus pressure (CSP) unilaterally or bilaterally around the physiological operating pressure according to binary white noise. The neural arc transfer function from CSP to cardiac sympathetic nerve activity (SNA) and the peripheral arc transfer function from SNA to aortic pressure were estimated. The gain values of the neural arc at 0.01 Hz estimated by the left (L) and right (R) CSP perturbations were 0.94 +/- 0.31 and 0.96 +/- 0.25, respectively. The gain value increased to 2.17 +/- 0.97 during the bilateral identical CSP perturbation and was not significantly different from L + R. The phase values of the neural arc did not differ among protocols. No significant differences were observed in the peripheral arc transfer functions among protocols. We conclude that summation of the dynamic transfer characteristics of the bilateral carotid sinus baroreflexes around the physiological operating pressure approximates simple addition.

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.

Supplemental utility of nested PCR for the pathological diagnosis of disseminated trichosporonosis

Disseminated trichosporonosis is known to be a severe opportunistic mycosis and has a high mortality rate. In autopsy cases, it is often difficult to diagnose as trichosporonosis because the causative Trichosporon species are pathologically similar to other fungi, especially the Candida species. Immunohistochemical analysis is essential for the differential diagnosis, but an antibody to Trichosporon is not available commercially. In the present study, we investigated the supplemental utility of nested polymerase chain reaction (PCR) for the pathological diagnosis of trichosporonosis from formalin-fixed and paraffin-embedded tissues. Total DNA was purified from 30 major organs in three autopsy cases, and Trichosporon DNA was specifically amplified by nested PCR using three sets of primers. Of 22 organs in which Grocott's stain was positive for fungal infection, 170- and 259-bp PCR products were detected in 20 (91%) and 12 (55%) organs, respectively. In short-term fixation (about 1 day), these bands were highly detected in ten (100%) and nine (90%) organs, whereas the detection efficiency tended to decrease after long-term fixation and decalcification. No PCR product of 412 bp was detected in any organs. These findings suggest that nested PCR from short-term-fixed tissues is useful for supportive pathological diagnosis of disseminated trichosporonosis.

Vagal stimulation decreases left ventricular contractility mainly through negative chronotropic effect

Although an increase in vagal tone is known to slow heart rate (HR), whether it also depresses left ventricular contractility through mechanisms independent of the bradycardic effect remains unknown. The chief aim of this investigation, therefore, was the separation of the observed vagally mediated depression of ventricular contractility into direct and indirect vagal effects, the latter resulting via negative chronotropism. In 12 anesthetized, sympathectomized open-chest rabbits, we measured left ventricular contractility through determination of the end-systolic elastance (Ees). We found that tonic vagal stimulation administered at 0, 5, and 10 Hz decreased both HR (226.9 +/- 39.7, 201.9 +/- 25.7, and 171.3 +/- 18.5 beats/min, respectively; P = 0.0003) and Ees (109.5 +/- 25.7, 85.1 +/- 34.1, and 71.9 +/- 33.1 mmHg/ml, respectively; P = 5 x 10(-6)) in a frequency-dependent fashion. However, we observed that as long as HR was kept constant through fixed-rate atrial pacing, vagal stimulation resulted in little or no change in Ees. Thus we conclude that the negative inotropic effect of vagal stimulation is attributable primarily to its negative chronotropic effect when sympathetic tone is minimal.

Interstitial norepinephrine level by cardiac microdialysis correlates with ventricular contractility

Although a cardiac microdialysis technique has made it possible to estimate myocardial interstitial norepinephrine (NE) levels, whether such levels reflect the local NE concentration that would regulate ventricular contractility remains unknown. If such levels indicate locally regulating NE concentration, then ventricular contractility should be a unique function of the interstitial NE level regardless of how the latter is altered. To examine this hypothesis, we altered the interstitial NE level endogenously by stimulating the cardiac sympathetic nerves at 1 and 2 Hz while monitoring ventricular contractility. We also altered the interstitial NE level exogenously by means of intravenous NE infusions at 10 and 40 micrograms.kg-1.h-1. The basal NE levels did not differ between the stimulation and the infusion experiments (42.9 +/- 11.2 vs. 40.1 +/- 6.2 pg/ml, means +/- SE). The slopes of regression lines relating ventricular contractility and interstitial NE level were also not different between the two experiments [1.13 +/- 0.20 vs. 1.17 +/- 0.20%/(pg/ml), means +/- SE]. We conclude that the interstitial NE level estimated by cardiac microdialysis reflects the local NE concentration regulating ventricular contractility.

Integrative sympathetic baroreflex regulation of arterial pressure

The baroreflex system is the most important negative feedback control system functioning physiologically to attenuate the effects of rapid perturbation in arterial pressure. However, the complexity of the system resulting from the closed-feedback loop, nonlinearity, and system memory makes detailed quantitative characterization of the baroreflex system difficult. To overcome such limitations, we proposed a framework to decompose the baroreflex loop into two major arcs, that is, the mechanoneural arc and neuromechanical arc. Steady state analysis indicated that such decomposition allowed us to analytically determine the operating point by equilibrating two respective function curves. Dynamic analysis suggested that the mechanoneural arc accelerated the slow mechanical response of the neuromechanical arc. The acceleration mechanism in the mechanoneural are optimized arterial pressure regulation in achieving both stability and quickness. Establishment of such an integrative framework allowed the development of an artificial feedback control system able to regulate sympathetic vasomotor tone.

Dynamic vagosympathetic interaction augments heart rate response irrespective of stimulation patterns

We previously demonstrated that tonic stimulation of either the sympathetic or the vagal nervous system augmented the dynamic heart rate response to the other of the two systems. We characterized the phenomenon as bidirectional augmentation of heart rate regulation. The question remained unanswered, however, as to whether such augmentation could occur under simultaneous dynamic stimulation of the two systems. The transfer characteristics from nerve stimulation to heart rate were well described by linear systems analysis, although no attention was paid to the aphasic nature of the stimuli in relation to each R-R interval. When we stimulated the two nerves with statistically independent Gaussian white noises, gain of the transfer function increased by 63.2 +/- 47.4% relative to individual stimulation (P < 0.05). When we stimulated the two nerves with mutually reciprocal Gaussian white noises, gain of the transfer function increased by 54.9 +/- 49.1% (P < 0.05). Thus simultaneous dynamic stimulation of the sympathetic and vagal systems bidirectionally augmented heart rate regulation irrespective of the pattern of the stimulation signals.

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.

A new method to identify dynamic transduction properties of aortic baroreceptors

We identified, in 17 alpha-chloralose-anesthetized rabbits, the dynamic transduction characteristics of the aortic arch baroreceptors using a "white-noise technique." We recorded aortic pressure and aortic depressor nerve activity while perturbing pressure by rapid, intermittent ventricular pacing (400 beats/min). Dividing the cross-power spectrum between nerve activity and pressure by the power spectrum of pressure yielded the transfer function. The gain of the transfer function increased threefold as the frequency increased from 0.005 to 5 Hz, suggesting that the baroreceptors responded primarily to dynamic rather than to static changes in pressure. To quantify the nonlinear properties of baroreceptor transduction, we compared measured instantaneous nerve activity with that linearly predicted. We demonstrated that the major nonlinearity was attributable to "threshold". The overall baroreceptor transduction properties could be represented by a cascade connection of a linear subsystem followed by a nonlinear subsystem with threshold. The white-noise technique made it possible to identify the unbiased linear properties in a nonlinear system, and thus was very useful in identifying complex biological systems.

Regional cerebral blood flow during rewarming of cardiopulmonary bypass correlates with posthypothermic regional glucose use

BACKGROUND AND OBJECTIVES

Although global measurements of cerebral blood flow and metabolism during and after profoundly hypothermic cardiopulmonary bypass have been performed both in experimental animals and in human beings, little is known about their regional changes. The purpose of this study was to investigate the changes in regional cerebral blood flow during profoundly hypothermic cardiopulmonary bypass and regional cerebral glucose use after cardiopulmonary bypass.

METHODS

We measured regional cerebral blood flow with positron emission tomography during both the cooling (n=5) and rewarming (n=5) of hypothermic cardiopulmonary bypass in anesthetized dogs by continuously infusing 15O-labeled water. We altered the core temperature between 20 degrees and 37 degrees C. To assess the integrity of brain metabolism, we measured the regional cerebral glucose use by bolus injections of 18F-labeled 2-fluoro-2-deoxy-D-glucose.

RESULTS

Regional cerebral blood flow decreased homogeneously during cooling. The regional cerebral blood flow at 20 degrees C was about one fourth of that at 37 degrees C. In contrast, at 24 degrees, 28 degrees , and 32 degrees C during rewarming, there were significant interregional differences in the regional cerebral blood flow for given temperatures (p=0.0075, 0.034, and 0.048, respectively). These interregional differences disappeared after rewarming. Although the regional cerebral blood flow significantly correlated with the regional cerebral glucose use in the control condition at 37 degrees C without cardiopulmonary bypass (r=0.75; p=0.00012), this correlation disappeared after profoundly hypothermic cardiopulmonary bypass (r=0.204; p=0.388). Regional cerebral blood flow at 32 degrees C during rewarming positively correlated with the regional cerebral glucose use after cardiopulmonary bypass (r=0.655; p=0.0017).

CONCLUSION

The altered regional cerebral blood flow during rewarming of profoundly hypothermic cardiopulmonary bypass might affect regional brain metabolism.

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.

Inhibition of NO synthesis minimally affects the dynamic baroreflex regulation of sympathetic nerve activity

The purpose of this investigation was to examine the role of nitric oxide (NO) in the dynamic baroreflex regulation of cardiac sympathetic nerve activity. In anesthetized rabbits, we imposed random pressure perturbations on the isolated carotid sinuses before and after the intravenous administration of NG-monomethyl-L-arginine. We characterized the dynamic properties relating carotid sinus pressure input to sympathetic nerve activity by means of a transfer function analysis. NG-monomethyl-L-arginine decreased the corner frequency of the transfer function (0.100 +/- 0.054 vs. 0.074 +/- 0.035 Hz; P < 0.05), whereas other parameters such as the steady-state gain and transmission lag time remained unchanged. Although cursory examination of these findings would suggest a possible contribution of NO in the dynamic baroreflex regulation of sympathetic nerve activity, quantitative assessment of the transfer function reveals only a minimal effect on the baroreflex regulation of arterial pressure, particularly under closed-loop conditions. We conclude that NO noticeably affects the dynamic baroreflex regulation of sympathetic nerve activity. However, it may not significantly affect arterial pressure regulation through central modulation of the carotid sinus baroreflex.

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.

Conserved sequences of BART and BHRF regions encoding viral microRNAs in Epstein-Barr virus-associated lymphoma

Objective

Epstein-Barr virus (EBV) encodes at least 25 pri-microRNAs (miRNAs) in two regions of its DNA genome, BART and BHRF. B95-8, an EBV reference strain, has a deletion in the BART region. However, no information is available on the deletions or mutations in the BART and BHRF regions in clinical samples of EBV-associated lymphoma.

Results

Nine DNA fragments encoding miR-BARTs and two coding miR-BHRF1s were amplified by PCR from DNA samples extracted from 16 cases of EBV-associated lymphoma. All the PCR products were sequenced directly. DNA fragments encoding miR-BARTs and miR-BHRF1-1 were successfully amplified from all samples. An adenine-to-guanine mutation in the DNA fragment encoding miR-BART2-3p was detected in four of the 16 cases, and a cytosine-to-thymidine mutation in the DNA fragment encoding miR-BART11-3p was detected in one of the 16 samples. These mutations were not associated with any histological categories of lymphoma. In conclusion, mutations were rarely observed in the DNA encoding viral miRNAs in cases of lymphoma. This suggests that the DNA sequences of EBV-encoded miR-BARTs and miR-BHRF1-1 are conserved in EBV-associated lymphoma.

omega-Conotoxin GVIA and desipramine insensitive norepinephrine efflux from cardiac sympathetic nerve terminal

Using dialysis technique, prominent accumulation of norepinephrine (NE) in the myocardial interstitial space was observed under local administration of a monoamine oxidase inhibitor (pargyline, 10 mM), and a vesicle uptake inhibitor (reserpine, 10 microM). Accumulation of NE in the myocardial interstitial space was associated with a reduction of dihydroxyphenylglycol levels. Pretreatment with omega-conotoxin GVIA (10 microM) or desipramine (10 microM) did not suppress this response. A brisk increase in dialysate NE levels might occur as a consequence of exocytotic or neurotransporter insensitive efflux of NE.

Inhibition of NO synthesis does not potentiate dynamic cardiovascular response to sympathetic nerve activity

We examined whether the inhibition of nitric oxide (NO) synthesis potentiates the dynamic sympathetic regulation of the cardiovascular system through the baroreflex. In anesthetized rabbits, we imposed random pressure perturbations on the isolated carotid sinuses to evoke random changes in sympathetic nerve activity (SNA). We estimated the transfer functions from SNA to both aortic pressure (AoP) and heart rate (HR). The inhibition of NO synthesis by NG-monomethyl-L-arginine (L-NMMA, 40 mg/ kg) altered neither the transfer function from SNA to AoP nor that from SNA to HR. In contrast, sodium nitroprusside (3-6 micrograms.kg-1.min-1) significantly decreased the steady-state gain (40.3 +/- 11.7% of the control, P < 0.05) of the transfer function from SNA to AoP without affecting the HR responses. We conclude that the basal release of NO may have a role in the tonic blood pressure regulation, whereas it may not be involved in the dynamic sympathetic regulation of AoP or HR through the baroreflex.

Local epinephrine release in the rabbit myocardial interstitium in vivo

Although several investigations have suggested cardiac epinephrine (Epi) release, local Epi release in the myocardial interstitium in vivo has not been measured. Using cardiac microdialysis in the rabbit, we measured dialysate Epi and norepinephrine (NE) concentrations as indices of myocardial interstitial Epi and NE levels, respectively. Exocytotic release induced by local administration of KCl (100 mM) through the dialysis probe increased Epi to 24.2 +/- 13.2 pg/ml from a control value of 3.2 +/- 3.6 pg/ml (P < 0.01, n = 6). Non-exocytotic release induced by the local administration of tyramine (10 microg/ml) also increased Epi to 34.6 +/- 15.3 pg/ml (p < 0.05 from control, n = 6). We conclude that Epi can be released via both exocytotic and non-exocytotic release mechanisms from the heart.

Characterization of ouabain-induced noradrenaline and acetylcholine release from in situ cardiac autonomic nerve endings

AIM

Although ouabain modulates autonomic nerve ending function, it is uncertain whether ouabain-induced releasing mechanism differs between in vivo sympathetic and parasympathetic nerve endings. Using cardiac dialysis, we examined how ouabain induces neurotransmitter release from autonomic nerve ending.

METHODS

Dialysis probe was implanted in left ventricle, and dialysate noradrenaline (NA) or acetylcholine (ACh) levels in the anaesthetized cats were measured as indices of neurotransmitter release from post-ganglionic autonomic nerve endings.

RESULTS

Locally applied ouabain (100 microm) increased in dialysate NA or ACh levels. The ouabain-induced increases in NA levels remained unaffected by cardiac sympathetic denervation and tetrodotoxin (Na+ channel blocker, TTX), but the ouabain-induced increases in ACh levels were attenuated by TTX. The ouabain-induced increases in NA levels were suppressed by pretreatment with desipramine (NA transport blocker) and augmented by reserpine (vesicle NA transport blocker). In contrast, the ouabain-induced increases in ACh levels remained unaffected by pretreatment with hemicholinium-3 (choline transport blocker) but suppressed by vesamicol (vesicle ACh transport blocker). The ouabain-induced increases in NA levels were suppressed by pretreatment with omega-conotoxin GVIA (N-type Ca2+ channel blocker), verapamil (L-type Ca2+ channel blocker) and TMB-8 (intracellular Ca2+ antagonist). The ouabain-induced increases in ACh levels were suppressed by pretreatment with omega-conotoxin MVIIC (P/Q-type Ca2+ channel blocker), and TMB-8.

CONCLUSIONS

Ouabain-induced NA release is attributable to the mechanisms of regional exocytosis and/or carrier-mediated outward transport of NA, from stored NA vesicle and/or axoplasma, respectively, while the ouabain-induced ACh release is attributable to the mechanism of exocytosis, which is triggered by regional depolarization. At both sympathetic and parasympathetic nerve endings, the regional exocytosis is because of opening of calcium channels and intracellular calcium mobilization.

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.

How to encode arterial pressure into carotid sinus nerve to invoke natural baroreflex

The purpose of this study was to develop an artificial baroreceptor that was capable of invoking the "natural" baroreflex by electrically stimulating the afferent nerve. In six anesthetized, vagotomized dogs, we first identified, using the white-noise method, the transfer function from carotid sinus pressure to aortic pressure (HCSP.AoP) and that from the electrical carotid sinus nerve stimulation to aortic pressure (HCSN.AoP). We then backcalculated the transfer function required for the artificial baroreceptor (HCSP.CSN) as the ratio of HCSP.AoP to HCSN.AoP. To activate the artificial baroreceptor, we electrically stimulated the carotid sinus nerve with the frequency-modulated pulse train obtained in real time by convolving the impulse response of HCSP.CSN with instantaneous aortic pressure. We tested performance of the artificial baroreceptor by imposing random changes in blood volume. The pressure-stabilizing effects of the artificial baroreceptor were indistinguishable from those of the native one. We conclude that the artificial baroreceptor can invoke the natural baroreflex. The proposed framework generally would be applicable to interface artificial devices with the central nervous system.