Detection and quantification of protein residues in food grade amino acids and nucleic acids using a dot-blot fluorescent staining method

Food allergies represent an important health problem in industrialized countries, such that detection and quantitative analysis of the protein considered to be the main allergen is crucial. A dot-blot fluorescent staining method for the detection and quantitative analysis of protein residues in food grade amino acids and nucleic acids is presented. This method combines fluorescence staining with dot-blotting onto PVDF membrane. Several standard proteins, such as bovine serum albumin (66 kDa), lysozyme (14 kDa), ubiquitin (8.6 kDa), bovine insulin (5.7 kDa), and oxidized insulin B chain (3.5 kDa), were detectable at 0.1 ppm using SYPRO Ruby blot stain. Twenty-five different amino acids and two different nucleic acids of food grade were analyzed using this method combined with an internal standard addition method using BSA as an internal standard. All amino acids and nucleic acids were dissolved in 3.6% aqueous HCl and dot-blotted onto PVDF membrane before a large amount of amino acids and nucleic acid were removed. Protein residues and the internal standard protein immobilized on the membrane were stained using SYPRO ruby blot stain. The internal standard in all samples was detectable at 0.1 ppm. Samples were dissolved at 120 or 70 mg/mL, according to their solubility under acidic conditions. The detection limit of protein residues per weight was 0.8-1.4 ppm in amino acids and nucleic acids; residual protein was not detected in any sample.

[Stenting in obstruction of superior vena cava; clinical experience with the self-expanding endovascular prosthesis]

From August 1997 to December 2002, 14 consecutive patients with superior vena cava syndrome with the self-expanding endovascular prosthesis. Diagnoses were adenocarcinoma in 6, small cell carcinoma in 4, squamous cell carcinoma in 1, metastatic lung cancer in 2, and invasive thymoma in 1. Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) were measured on their admission and perioperative period. Expecting only 1 patient complete symptomatically relieved within 3 days of stent implantation. Superior vena cava pressure or radial pressure of the stent was sufficient to relieve obstruction. Preoperative ANP level were normal, BNP level were increased. Postoperatively both ANP level and BNP level were slightly increased under intravenous dopamine hydrochloride. Implantation of the self-expanding stent endovascular prosthesis for superior vena cava syndrome provides rapid symptomatic relief and improves the patient's quality of life.

Integration of On-Line Protein Digestion, Peptide Separation, and Protein Identification Using Pepsin-Coated Photopolymerized Sol−Gel Columns and Capillary Electrophoresis/Mass Spectrometry

A miniaturized pepsin reactor was prepared inside a fused-silica capillary (i.d. 75 microm) by coating a pepsin-containing gel on a photopolymerized porous silica monolith. The pepsin-encapsulated film was prepared by a sol-gel method. The sol-gel reaction was optimized so that the sol solution containing pepsin forms a thin film on the photopolymerized sol-gel (PSG) monolith that was initially fabricated at the inlet of the capillary. Pepsin was encapsulated into the gel matrix without losing its activity. The large surface area of the PSG monolith enabled the immobilized pepsin to achieve a high catalytic turnover rate, and the porous nature of the PSG promotes penetration of large molecular proteins into the column. The immobilized pepsin-digested peptides and proteins, and the resulting mixture of peptide fragments, could be directly separated in the portion of the capillary where no PSG monolith exists. The durability and repeatability of the fabricated pepsin-coated column was tested and found to be satisfactory. An acidic solution consisting of 0.5 M formic acid was used as the running buffer, because it suppresses the adsorption of proteins or peptides on the inner surface of the capillary as well as enables direct connection of the output of the capillary electrophoresis column to a mass spectrometer. The on-line digestion of insulin chain beta and lysozyme provides identification of the proteolytic peptides. Recovery was achieved for 100% of the insulin chain beta amino acid sequence and 73% of the lysozyme amino acid sequence.

Noninvasive cardiac output measurement using partial carbon dioxide rebreathing is less accurate at settings of reduced minute ventilation and when spontaneous breathing is present

BACKGROUND

Although evaluation of cardiac output by the partial carbon dioxide rebreathing technique is as accurate as thermodilution techniques under controlled mechanical ventilation, it is less accurate at low tidal volume. It is not clear whether reduced accuracy is due to low tidal volume or low minute ventilation. The effect of spontaneous breathing on the accuracy of partial carbon dioxide rebreathing measurement has not been fully investigated. The objectives of the current study were to investigate whether tidal volume or minute ventilation is the dominant factor for the accuracy, and the accuracy of the technique when spontaneous breathing effort is present.

METHODS

The authors enrolled 25 post-cardiac surgery patients in two serial protocols. First, the authors applied three settings of controlled mechanical ventilation in random order: large tidal volume (12 ml/kg), the same minute ventilation with a small tidal volume (6 ml/kg), and 50% decreased minute ventilation with a small tidal volume (6 ml/kg). Second, when the patient recovered spontaneous breathing, the authors applied three conditions of partial ventilatory support in random order: synchronized intermittent mandatory ventilation-pressure support ventilation, pressure support ventilation with an appropriately adjusted rebreathing loop, and pressure support ventilation with the shortest available loop. After establishing steady state conditions, the authors measured cardiac output using both partial carbon dioxide rebreathing and thermodilution methods. The correlation between the data yielded by the two methods was determined by Bland-Altman analysis and linear regression.

RESULTS

Cardiac output with the carbon dioxide rebreathing technique correlated moderately with that measured by thermodilution when minute ventilation was set to maintain normocapnia, regardless of tidal volumes. However, when minute ventilation was set low, the carbon dioxide rebreathing technique underreported cardiac output (y = 0.70x; correlation coefficient, 0.34; bias, -1.73 l/min; precision, 1.27 l/min; limits of agreement, -4.27 to +0.81 l/min). When there was spontaneous breathing, the correlation between the two cardiac output measurements became worse. Carbon dioxide rebreathing increased spontaneous tidal volume and respiratory rate (20% and 30%, respectively, during pressure support ventilation) when the rebreathing loop was adjusted for large tidal volume.

CONCLUSIONS

During controlled mechanical ventilation, minute ventilation rather than tidal volume affected the accuracy of cardiac output measurement using the partial carbon dioxide rebreathing technique. When spontaneous breathing is present, the carbon dioxide rebreathing technique is less accurate and increases spontaneous tidal volume and respiratory rate.

[Recruitment maneuver and high PEEP in a patient with severe reperfusion pulmonary edema after pulmonary thromboendarterectomy]

Recently open lung approach such as recruitment maneuver and high PEEP has been applied in patients with acute respiratory distress syndrome. We report here a 29-year-old man with chronic pulmonary thromboembolism (CPTE). In this case, recruitment maneuver and high PEEP relieved postoperative respiratory failure. The major complications after pulmonary thromboendarterectomy (PTE) for CPTE are: reperfusion pulmonary edema (RPE), pulmonary hypertension (PH), hypoxia and bronchial bleeding, all of which the patient has demonstrated. Preoperative examination showed high pulmonary artery pressure (85/41, mean 50 mmHg), and high pulmonary vascular resistance predicted poor postoperative course. After PTE, he developed severe RPE, PH, hypoxia and bronchial bleeding, resulting in failed weaning from cardiopulmonary bypass. Therefore he required mechanical support of percutaneous cardiopulmonary support (PCPS). In ICU we repeated recruitment maneuver (PEEP: 30 cmH2O, peak inspiratory pressure: 42 cmH2O, respiratory rate; 15 breaths.min-1, for 1 min) and kept high PEEP (15 cmH2O). After initiating this ventilatory strategy, RPE was gradually relieved, followed by improvement of oxygenation and PH. We successfully weaned him from PCPS 38 hr after surgery and he was discharged alive on the 90 post-operative day. We conclude that recruitment maneuver and high PEEP may be useful for RPE developed after PTE.

[Venoarterial bypass in children with congenital heart disease--a retrospective study]

To investigate prognostic factors for patients supported by venoarterial (VA) bypass, we analyzed retrospectively 31 patients with congenital heart diseases supported by VA bypass between 1997 and 2000. Median age was 3.6 months and median body weight was 4.0 kg. Causes of VA bypass were difficult weaning from cardiopulmonary bypass in 8 patients, postoperative cardiac dysfunction in 5 and cardiopulmonary resuscitation in 18. Six (19.4%) of 31 patients were weaned successfully from VA bypass, and 2 (6.5%) survived to hospital discharge. In patients who were weaned from VA bypass successfully, VA bypass was instituted more quickly (41.6 +/- 5.0 vs 62.5 +/- 35.9 min), and good tissue perfusion was established in association with lower lactate levels at 12 hr (7.0 +/- 5.9 vs. 16.4 +/- 15.4 mmol.l-1) and larger urine output during first 24 h (81 +/- 68 vs. 22 +/- 43 ml.kg-1.day-1), compared to those who failed to be weaned. Major complications were intracranial hemorrhage in the newborn (50%), and hypoxic brain damage in patients with palliative operation (35%). It is necessary to establish guidelines of entry, weaning, and withholding of this support.

Effect of ventilatory settings on accuracy of cardiac output measurement using partial CO(2) rebreathing

BACKGROUND

Recently, a new device has been developed to measure cardiac output noninvasively using partial carbon dioxide (CO(2)) rebreathing. Because this technique uses CO(2) rebreathing, the authors suspected that ventilatory settings, such as tidal volume and ventilatory mode, would affect its accuracy: they conducted this study to investigate which parameters affect the accuracy of the measurement.

METHODS

The authors enrolled 25 pharmacologically paralyzed adult post-cardiac surgery patients. They applied six ventilatory settings in random order: (1) volume-controlled ventilation with inspired tidal volume (V(T)) of 12 ml/kg; (2) volume-controlled ventilation with V(T) of 6 ml/kg; (3) pressure-controlled ventilation with V(T) of 12 ml/kg; (4) pressure-controlled ventilation with V(T) of 6 ml/kg; (5) inspired oxygen fraction of 1.0; and (6) high positive end-expiratory pressure. Then, they changed the maximum or minimum length of rebreathing loop with V(T) set at 12 ml/kg. After establishing steady-state conditions (15 min), they measured cardiac output using CO(2) rebreathing and thermodilution via a pulmonary artery catheter. Finally, they repeated the measurements during pressure support ventilation, when the patients had restored spontaneous breathing. The correlation between two methods was evaluated with linear regression and Bland-Altman analysis.

RESULTS

When VT was set at 12 ml/kg, cardiac output with the CO(2) rebreathing technique correlated moderately with that measured by thermodilution (y = 1.02x, R = 0.63; bias, 0.28 l/min; limits of agreement, -1.78 to +2.34 l/min), regardless of ventilatory mode, oxygen concentration, or positive end-expiratory pressure. However, at a lower VT of 6 ml/kg, the CO(2) rebreathing technique underestimated cardiac out-put compared with thermodilution (y = 0.70x; R = 0.70; bias, -1.66 l/min; limits of agreement, -3.90 to +0.58 l/min). When the loop was fully retracted, the CO(2) rebreathing technique overestimated cardiac output.

CONCLUSIONS

Although cardiac output was underreported at small VT values, cardiac output measured by the CO(2) rebreathing technique correlates fairly with that measured by the thermodilution method.

Heart rate-independent vagal effect on end-systolic elastance of the canine left ventricle under various levels of sympathetic tone

BACKGROUND

Although we have shown that in rabbits the direct (heart rate [HR]-independent) vagal effect on left ventricular end-systolic elastance (E(es)) was negligible under minimal sympathetic tone, how underlying sympathetic tone modulates the inotropic response to vagal stimulation remains unknown.

METHODS AND RESULTS

We used an isolated canine heart preparation with functioning autonomic nerves. We examined the direct vagal inotropic effect by measuring E(es) under fixed-rate atrial pacing with or without concomitant sympathetic nerve stimulation. Right and left vagal stimulation at 20 Hz decreased HR by 27+/-3% and 14+/-2%, respectively, and decreased E(es) by 11+/-2% and 6+/-2%, respectively. When we fixed HR by atrial pacing, right and left vagal stimulation at 20 Hz did not decrease E(es) (0.01+/-0.3% and 0.3+/-0.4%; NS). Concomitant left sympathetic nerve stimulation at 4 Hz enhanced direct vagal negative inotropism to -19+/-3% and -34+/-5% for 20-Hz right and left vagal stimulation (interaction, P<0.01).

CONCLUSIONS

Direct vagal negative inotropism was unobservable with minimal sympathetic tone in dogs but was enhanced with concomitant sympathetic stimulation.

Effect of synchronized intermittent mandatory ventilation on respiratory workload in infants after cardiac surgery

BACKGROUND

Synchronized intermittent mandatory ventilation (SIMV) is commonly used in infants and adults. However, few investigations have examined how SIMV reduces respiratory workload in infants. The authors evaluated how infants' changing respiratory patterns when reducing SIMV rate increased respiratory load. The authors also investigated whether SIMV reduces infant respiratory workload in proportion to the rate of mandatory breaths and which rate of SIMV provides respiratory workloads similar to those after tracheal extubation.

METHODS

When 11 post-cardiac surgery infants aged 2-11 months were to be weaned with SIMV, the authors randomly applied five levels of mandatory breathing: 0, 5, 10, 15, and 20 breaths/min. All patients underwent ventilation with SIMV mode: pressure control ventilation, 16 cm H2O; inspiratory time, 0.8 s; triggering sensitivity, 0.6 l/min; and positive endexpiratory pressure, 3 cm H2O. After establishing steady-state conditions at each SIMV rate, arterial blood gases were analyzed, and esophageal pressure, airway pressure, and airflow were measured. Inspiratory work of breathing, pressure-time products, and the negative deflection of esophageal pressure were calculated separately for assisted breaths, for spontaneous breaths, and for total breaths per minute. Measurements were repeated after extubation.

RESULTS

As the SIMV rate decreased, although minute ventilation and arterial carbon dioxide tension were maintained at constant values, spontaneous breathing rate and tidal volume increased. Work of breathing, pressure-time products, and negative deflection of esophageal pressure increased as the SIMV rate decreased. Work of breathing and pressure-time products after extubation were intermediate between those at a SIMV rate of 5 breaths/min and those at 0 breaths/min.

CONCLUSION

When the load to breathing was increased progressively by decreasing the SIMV rate in post-cardiac surgery infants, tidal volume and spontaneous respiratory rate both increased. In addition, work of breathing and pressure-time products were increased depending on the SIMV rate.

Laterality in direct and indirect inotropic effects of sympathetic stimulation in isolated canine heart

Although sympathetic nerve stimulation is known to increase ventricular contractility, concomitant increases in heart rate (HR) make it difficult to separate its direct inotropic effect from indirect inotropic effect through a force-frequency mechanism. We stimulated the stellate ganglia in 8 isolated canine hearts with functional sympathetic nerves. Right sympathetic stimulation at 10 Hz increased ventricular end-systolic elastance (E(es)) by 95.7 +/- 7.5% (p < 0.001) and HR by 32.5 +/- 4.2% (p < 0.05). In contrast, left sympathetic stimulation at 10 Hz increased E(es) by 70.7 +/- 6.5% (p < 0.001) without significant changes in HR. Preventing the chronotropic response by fixed-rate pacing attenuated the E(es) response to right sympathetic stimulation at 5 Hz (52.0 +/- 5.1 vs. 22.8 +/- 2.8%, p < 0.001), but not to left sympathetic stimulation at 5 Hz (54.5 +/- 3.4 vs. 53.3 +/- 2.2%, NS). In the isolated canine heart, the right sympathetic nerve affected E(es) by both the direct inotropic effect and the indirect HR-dependent inotropic effect. In contrast, the left sympathetic nerve regulated E(es) primarily by its direct inotropic effect.

Psychological, autonomic and neuroendocrine responses to acute stressors in the combined dexamethasone/CRH test: a study in healthy subjects

The combined dexamethasone/CRH test (DEX/CRH test) is reported to produce augmented ACTH and cortisol responses in various psychiatric disorders as well as in some non-psychiatric conditions. To examine whether stress affects the outcome of DEX/CRH test, two stress groups in a repeated measures design were compared to an age-matched control group with regard to the psychological, autonomic and neuroendocrine responses after the combined dexamethasone and CRH challenge. Cold pressor (4 degrees C, total 10 min) produced stronger subjective distress than mental arithmetic (15 min). Cold exposure, but not the mental test, elevated systolic and diastolic blood pressure, whereas the mental test increased pulse rate and skin conductance level more markedly than cold exposure. Neither stressor produced a significantly enhanced response of ACTH and cortisol in DEX/CRH test, and there was no correlation between psychological and neuroendocrine responses. These findings suggest that different stressors induce different patterns of sympathetic activation and that acute stress is unlikely to affect the results of DEX/CRH test.

Effect of patient-triggered ventilation on respiratory workload in infants after cardiac surgery

BACKGROUND

Patient-triggered ventilation (PTV) is commonly used in adults to avoid dyssynchrony between patient and ventilator. However, few investigations have examined the effects of PTV in infants. Our objective was to determine if pressure-control PTV reduces infants' respiratory workloads in proportion to the level of pressure control. We also explored which level of pressure control provided respiratory workloads similar to those after the extubation of the trachea.

METHODS

When seven post-cardiac surgery infants, aged 1 to 11 months, were to be weaned with the pressure-control PTV, we randomly applied five levels of pressure control: 0, 4, 8, 12, and 16 cm H2O. All patients were ventilated with assist-control mode, triggering sensitivity of 1 l/min, and positive end-expiratory pressure of 3 cm H2O. After establishing steady state conditions at each level of pressure control, arterial blood gases were analyzed and esophageal pressure (Pes), airway pressure, and airflow were measured. Inspiratory work of breathing (WOB) was calculated using a Campbell diagram. A modified pressure-time product (PTPmod) and the negative deflection of Pes were calculated from the Pes tracing below the baseline. The measurement was repeated after extubation.

RESULTS

Pressure-control PTV supported every spontaneous breath. By decreasing the level of pressure control, respiratory rate increased, tidal volume decreased, and as a result, minute ventilation and arterial carbon dioxide partial pressure were maintained stable. The WOB, PTPmod, and negative deflection of Pes increased as pressure control level was decreased. The WOB and PTPmod at 4 cm H2O pressure control and 0 cm H2O pressure control and after extubation were significantly greater than those at the pressure control of 16, 12, and 8 cm H2O (P < 0.05). The WOB and PTPmod were almost equivalent after extubation and at 4 cm H2O pressure control.

CONCLUSIONS

Work of breathing and PTPmod were changed according to the pressure control level in post-cardiac surgery infants. PTV may be feasible in infants as well as in adults.

Effects of nitric oxide inhalation after pulmonary thromboendarterectomy for chronic pulmonary thromboembolism

STUDY OBJECTIVES

To examine the hypothesis that nitric oxide (NO) inhalation improves hemodynamics and gas exchange in patients with chronic pulmonary thromboembolism after pulmonary thromboendarterectomy.

DESIGN

Prospective crossover clinical study.

SETTING

: Surgical ICU in a national education and research hospital.

PATIENTS

: Seven patients (mean age +/- SD, 54 +/- 11 years) who underwent elective pulmonary thromboendarterectomy for chronic pulmonary thromboembolism.

INTERVENTIONS

Patients breathed 20 parts per million of NO gas for 30 min at 12-h intervals until extubation of the trachea.

MEASUREMENTS AND RESULTS

Hemodynamics and arterial blood gas levels were analyzed before, during, and after NO inhalation. Waveform of pulmonary artery pressure (PAP) was evaluated using fractional pulse pressure (PPf): (systolic PAP - diastolic PAP)/mean PAP. After surgery, pulmonary vascular resistance decreased, PPf decreased, and cardiac index increased significantly. At the first trial, NO inhalation resulted in a slight improvement in arterial oxygen tension (from 173 +/- 33 to 196 +/- 44 mm Hg; p < 0.05), while hemodynamics did not change significantly. Twelve hours later, NO inhalation decreased pulmonary vascular resistance index (from 312 +/- 98 to 277 +/- 93 dyne.s. cm(-5)/m(2); p < 0.01), while the change in oxygenation was not significant.

CONCLUSIONS

Immediately after pulmonary thromboendarterectomy for chronic pulmonary thromboembolism, NO inhalation improved oxygenation; at 12 h after surgery, NO inhalation resulted in decreased pulmonary vascular resistance, although both changes were small.

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.

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.

Development of a servo-controller of heart rate using a treadmill

Although treadmill exercise involves a more familiar range of motions and is thus more physiological in terms of daily activity than cycle ergometer exercise, difficulties in controlling the exercise intensity have limited its utility. As heart rate (HR) has been used as a measure of exercise intensity, controlling HR should allow for the proper control of exercise intensity during treadmill exercise. Thus, a servo-controller framework was applied to regulate HR during treadmill exercise. After estimating an averaged transfer function from speed command to HR, feedback parameters were optimized via a computer simulation in order to achieve a quick and stable HR response. The performance of the servo-controller of HR was then examined in 10 healthy subjects. Standard deviations of the steady-state difference between the target and measured HRs were 2.7+/-0.9 and 5.0+/-1.4 beats/min in the stepwise and ramp target HR protocols, respectively. The rise time to reach 90% of the target HR was 93+/-20 s in the stepwise protocol. It was concluded that a treadmill implemented with a negative feedback mechanism made it possible to precisely regulate HR and thus exercise intensity.

Dynamic counterbalance between direct and indirect vagal controls of atrioventricular conduction in cats

The vagal system regulates the atrioventricular conduction time (TAV) via two opposing mechanisms: a direct effect on the atrioventricular node and an indirect effect through changes in heart period (TAA). To evaluate how dynamic vagal activation affects TAV, we stimulated the vagal nerve with frequency-modulated Gaussian white noise and estimated the transfer function from vagal stimulation to the TAV response under conditions of no pacing and constant pacing in anesthetized cats. The effect of changes in TAA on TAV was estimated by a random-pacing protocol. The transfer function from vagal stimulation to TAV has low-pass filter characteristics. Constant pacing increased the maximum step response in TAV (2.4 +/- 1.2 vs. 6.3 +/- 2.2 ms/Hz, P < 0.01). The time constant did not differ between the vagal effect on TAV and that on TAA (2.9 +/- 1.2 vs. 2.3 +/- 0.5 s). Because changes in TAA reciprocally affected TAV without significant delay, the direct and indirect effects were dynamically counterbalanced and exerted stable TAV transient response during vagal stimulation under normal sinus rhythm.

Novel method to estimate ventricular contractility using intraventricular pulse wave velocity

We developed a novel technique for estimating ventricular contractility using intraventricular pulse wave velocity (PWV). In eight isolated, cross-circulated canine hearts, we used a fast servo pump to inject a volume pulse into the base of the left ventricular chamber at late diastole and at late systole. We measured the transit time of the volume pulse wave as it traversed the distance from base to apex and calculated the intraventricular PWV. The intraventricular PWV increased from diastole (2.3 +/- 0.4 m/s) to systole (11.7 +/- 2.4 m/s, P < 0.0001 vs. diastole). The square of the intraventricular PWV at late systole correlated linearly with the left ventricular end-systolic elastance (r = 0.939, P < 0.0001) and with the end-systolic Young's modulus (r = 0.901, P < 0.0001). Moreover, the intraventricular PWV was insensitive to preload. We conclude that the intraventricular PWV at late systole reflects left ventricular end-systolic elastance reasonably well. The fact that estimation of PWV does not require volume measurement or load manipulation makes this technique an attractive means of assessing ventricular contractility.

Neuronal uptake affects dynamic characteristics of heart rate response to sympathetic stimulation

Recently, studies in our laboratory involving the use of a Gaussian white noise technique demonstrated that the transfer function from sympathetic stimulation frequency to heart rate (HR) response showed dynamic characteristics of a second-order low-pass filter. However, determinants for the characteristics remain to be established. We examined the effect of an increase in mean sympathetic stimulation frequency and that of a blockade of the neuronal uptake mechanism on the transfer function in anesthetized rabbits. We found that increasing mean sympathetic stimulation frequency from 1 to 4 Hz significantly (P < 0.01) decreased the dynamic gain of the transfer function without affecting other parameters, such as the natural frequency, lag time, or damping coefficient. In contrast, the administration of desipramine (0.3 mg/kg iv), a neuronal uptake blocking agent, significantly (P < 0.01) decreased both the dynamic gain and the natural frequency and prolonged the lag time. These results suggest that the removal rate of norepinephrine at the neuroeffector junction, rather than the amount of available norepinephrine, plays an important role in determining the low-pass filter characteristics of the HR response to sympathetic stimulation.

Simultaneous identification of static and dynamic vagosympathetic interactions in regulating heart rate

We earlier reported that stimulation of either one of the sympathetic and vagal nerves augments the dynamic heart rate (HR) response to concurrent stimulation of its counterpart. We explained this phenomenon by assuming a sigmoidal static relationship between nerve activity and HR. To confirm this assumption, we stimulated the sympathetic and/or vagal nerve in anesthetized rabbits using large-amplitude Gaussian white noise and determined the static and dynamic characteristics of HR regulation by a neural network analysis. The static characteristics approximated a sigmoidal relationship between the linearly predicted and the measured HRs (response range: 212.4 +/- 46.3 beats/min, minimum HR: 96.0 +/- 28.4 beats/min, midpoint of operation: 196.7 +/- 31.3 beats/min, maximum slope: 1.65 +/- 0.51). The maximum step responses determined from the dynamic characteristics were 7.9 +/- 2.9 and -14.0 +/- 4.9 beats. min-1. Hz-1 for the sympathetic and the vagal system, respectively. Because of these characteristics, changes in sympathetic or vagal tone alone can alter the dynamic HR response to stimulation of the other nerve.

Nitric oxide inhalation as a chemical assist for circulation in patients after cardiovascular surgery

The objective of this study was to investigate whether nitric oxide (NO) inhalation might be an alternative strategy as a chemical assist for the circulation in patients showing a deterioration in oxygen delivery. Twelve adult patients whose oxygen delivery indices (DO2I) were less than 400 ml/min/m2 after cardiovascular surgery were included in this study. NO was administered via a premixing system or a side stream system at doses between 1 and 10 (5.1+/-2.4) ppm. Data obtained before and during a 120 min NO inhalation were compared using the paired Student's t-test. The increase in PaO2/FiO2 resulting from NO inhalation was significant (from 162 to 251 mm Hg). DO2I increased significantly from 326 to 417 ml/min/m2 concomitantly with significant increases in both arterial oxygen content (CaO2) and cardiac index (CI) (from 14.1 to 15.4 vol% and from 2.31 to 2.71 L/min/m2 , respectively). The increase in SvO2 during NO inhalation was significant (from 55.2 to 62.6%). Among the other hemodynamic parameters, both total pulmonary resistance and systolic pulmonary arterial pressure (SPAP) showed significant decreases during NO inhalation, but right atrial pressure did not change significantly. There was a close relationship between the baseline SPAP level (bSPAP) and the decrease in SPAP during NO inhalation (dSPAP) (r = -0.88). However, negative correlations were observed between bSPAP and percentage increase in CI (%CI) (r = -0.61) and between bSPAP and percentage increase in DO2I (%DO2I) (r = -0.48). Moreover, positive relationships were observed between dSPAP and %CI (r = 0.62) and between dSPAP and %DO2I (r = 0.45). Hemoglobin (Hb) increased significantly from 11.0 to 11.4 g/dl. There were no significant changes in Fio2, pH, PacO2, or base excess (BE) during NO inhalation. The level of methemoglobin measured during the study period remained within the normal range (0.86+/-0.23%). In conclusion, NO inhalation could be an efficient and alternative assist for the circulation in patients whose oxygen delivery deteriorates after cardiovascular surgery.

New simple methods for isolating baroreceptor regions of carotid sinus and aortic depressor nerves in rats

We developed new methods for isolating in situ baroreceptor regions of carotid sinus and aortic depressor nerves in halothane-anesthetized rats. After ligation of the root of the external carotid artery, the internal carotid and pterygopalatine arteries were embolized with two ball bearings of 0.8 mm in diameter. Bilateral carotid sinus pressures were changed between 60 and 180 mmHg in 20-mmHg steps lasting 1 min each. The sigmoidal steady-state relationship between aortic and carotid sinus pressures in 11 rats indicated the maximum gain of the carotid sinus baroreflex to be -2. 99 +/- 0.75 at 120 +/- 5 mmHg. An in situ isolation of the baroreceptor area of the right aortic depressor nerve could be made by ligation of the innominate, common carotid, and subclavian arteries in 9 rats. Pressure imposed on the subclavian baroreceptor was altered between 40 and 180 mmHg in 20-mmHg steps lasting 1 min each. The sigmoidal steady-state relationship between the aortic depressor nerve activity and imposed pressure showed that the baroreceptor gain peaked at 118 +/- 4 mmHg. We established an easy approach to the rat baroreflex and baroreceptor research.

Acute effect of tumor necrosis factor-alpha is minimal on mechanics but significant on energetics in blood-perfused canine left ventricles

OBJECTIVES

We hypothesized that tumor necrosis factor-alpha (TNF-alpha) acutely alters left ventricular mechanoenergetics in blood-perfused hearts. To test this hypothesis, we examined the relation between left ventricular mechanics and energetics, both before and after infusion of TNF-alpha.

DESIGN

Prospective, experimental study.

SETTING

Research laboratory.

SUBJECTS

Nine isolated, blood-perfused canine hearts.

INTERVENTIONS

Recombinant human TNF-alpha (90 microg/min) was infused into the coronary circulation of the isolated hearts for 20 mins.

MEASUREMENTS AND MAIN RESULTS

In the isolated, cross-circulated, blood-perfused canine left ventricles, left ventricular contractility was assessed through measurement of end-systolic elastance (Ees). Energetics were examined in terms of the end-systolic pressure-volume area-myocardial oxygen consumption (MVo2) relation. TNF-alpha concentration in coronary venous blood was >1000 ng/mL throughout the experiments. Nevertheless, infusion of TNF-alpha barely affected contractility acutely, i.e., there was a minimal decrease during the infusion (8.1+/-2.8% at 10 mins, p < .01) and a minimal increase after the infusion (11.2+/-2.5% at 10 mins, p< .01). Neither did the TNF-alpha infusion affect the slope of the end-systolic pressure-volume area-MVo2 relation. This finding indicated that the chemomechanical conversion efficiency remained unchanged. However, TNF-alpha infusion significantly increased the oxygen cost of contractility by 40% (1.25+/-0.13 vs. 1.75+/-0.24 mL oxygen.mL/mm Hg/beat, p< .05), indicating that MVo2 for the excitation-contraction coupling increased.

CONCLUSIONS

TNF-alpha minimally alters left ventricular mechanics, but significantly changes energetics. The latter effect may result from changes in intracellular calcium handling.

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.

Dynamic sympathetic regulation of left ventricular contractility studied in the isolated canine heart

We investigated the dynamic sympathetic regulation of left ventricular end-systolic elastance (Ees) using an isolated canine ventricular preparation with functioning sympathetic nerves intact. We estimated the transfer function from both stellate ganglion stimulation to Ees and ganglion stimulation to heart rate (HR) for both left and right ganglia by means of the white noise approach and transformed those transfer functions into corresponding step responses. The HR response was much larger with right sympathetic stimulation than with left sympathetic stimulation (4.3 +/- 1.4 vs. 0.7 +/- 0.6 beats . min-1 . Hz-1, P < 0.01). In contrast, the Ees responses without pacing were not significantly different between left and right sympathetic stimulation (0.72 +/- 0.34 vs. 0.76 +/- 0. 42 mmHg . ml-1 . Hz-1). Fixed-rate pacing significantly decreased the Ees response to right sympathetic stimulation (0.53 +/- 0.43 mmHg . ml-1 . Hz-1, P < 0.01), but not to left sympathetic stimulation (0.67 +/- 0.32 mmHg . ml-1 . Hz-1, not significant). Although the mechanism by which the sympathetic nervous system regulates cardiac contractility is different depending on whether the left or right sympathetic nerves are activated, this difference does not affect the apparent response of Ees to dynamic sympathetic stimulation.

Accumulation of cAMP augments dynamic vagal control of heart rate

Recent investigations in our laboratory using a Gaussian white noise perturbation technique have shown that simultaneous sympathetic stimulation augmented the gain of the transfer function from vagal stimulation frequency to heart rate response. However, the mechanism of that augmentation remains to be elucidated. In this study, we examined in anesthetized rabbits how three pharmacological interventions known to cause intracellular accumulation of cAMP affected the transfer function. Isoproterenol (0.3 microg . kg-1 . min-1 iv) increased the dynamic gain of transfer function from 7.12 +/- 0.67 to 12.4 +/- 1.21 beats . min-1 . Hz-1 (P < 0.05) without changing the corner frequency or the lag time. Similar augmentations were observed when forskolin (5 microg . kg-1 . min-1 iv) or theophylline (20 mg/kg iv) was administered under conditions of beta-adrenergic blockade. These results suggest that the accumulation of cAMP at postjunctional effector sites contributes, at least in part, to the sympathetic augmentation of the dynamic vagal control of heart rate.

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.

The brain is a possible target for an angiotensin-converting enzyme inhibitor in the treatment of chronic heart failure

BACKGROUND

Although many lines of evidence have shown beneficial effects of angiotensin-converting enzyme (ACE) inhibitors on patients with chronic heart failure (CHF) after myocardial infarction (MI), the target of ACE inhibitors still remains unclear. The objectives of the present study were to evaluate the dipsogenic response to centrally administered angiotensin and to examine the effect of central administration of an ACE inhibitor on cardiac remodeling in rats with CHF after large MI.

METHODS AND RESULTS

The drinking responses to intracerebroventricular (i.c.v.) injections of saline and angiotensin I (100 ng) were measured in 22 male Sprague-Dawley rats with or without CHF at 2-5 weeks after the ligation of the left coronary artery. The dipsogenic responses to i.c.v. angiotensin I were significantly larger in rats with CHF and large MI (infarct size > 30%) than in sham-operated rats. Pretreatment with losartan abolished the significant difference between the two groups. Left ventricular (LV) weights of 32 surviving rats with CHF were measured after the 3-week subcutaneous infusions of vehicle (s.c.-VEH) and captopril (1 mg x kg(-1) x h(-1), s.c.-CAP) or the 3-week i.c.v. infusions of vehicle (i.c.v.-VEH) and captopril (50 microg x kg(-1) x h(-1), i.c.v.-CAP). The LV weights normalized by body weights of s.c.-CAP rats were significantly smaller than those of s.c.-VEH rats (1.73 +/- 0.04 vs 2.08 +/- 0.09 g x kg(-1); P < .01); those of i.c.v.-CAP rats were also significantly smaller than those of i.c.v.-VEH rats (1.84 +/- 0.08 vs 2.1 +/- 0.10 g x kg(-1); P < .05).

CONCLUSIONS

These results suggest that the brain is a possible target for ACE inhibitors in the treatment of CHF after MI.

ESPVR of in situ rat left ventricle shows contractility-dependent curvilinearity

We developed a miniaturized conductance catheter for in situ rat left ventricular (LV) volumetry. After the validation study of the conductance volumetry in 11 rats, we characterized the end-systolic pressure-volume relationship (ESPVR) in 24 sinoaortic-denervated, vagotomized and urethan-anesthetized rats. Stroke volume (SV) measured with the conductance catheter correlated closely with that measured by electromagnetic flowmetry (r > 0.95). No significant difference was found between the in situ LV end-diastolic volumes measured by conductance volumetry and postmortem morphometry; a linear regression analysis indicated that the correlation coefficient was 0.934, that the slope was not significantly different from 1, and that the intercept was not significantly different from 0. During cardiac sympathotonic conditions, the ESPVR was curvilinear. The estimated slope of ESPVR (end-systolic elastance, Ees) by quadratic curve fitting at end-systolic pressure of 100 mmHg was 2,647 +/- 846 mmHg/ml. Bilateral cervical and stellate ganglionectomy depressed contractility and made the ESPVR linear; a quadratic equation did not improve the fit. Ees was 946 +/- 55 mmHg/ml with the volume-axis (V0) intercept of 0.076 +/- 0.007 ml. Administration of propranolol (1 mg/kg) further reduced Ees (573 +/- 61 mmHg/ml, P < 0.001) and increased V0 slightly (0.091 +/- 0.011 ml). We conclude that the conductance catheter method is useful for the assessment of the ESPVR of the in situ rat left ventricle and that the ESPVR displays contractility-dependent curvilinearity.

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.

Dynamic transduction properties of in situ baroreceptors of rabbit aortic depressor nerve

We developed a new method for isolating in situ baroreceptor regions of the rabbit aortic depressor nerve (ADN) and estimated the transfer function from pressure to afferent nerve activity in the frequency range of 0.01-5 Hz by a white noise technique. Complete isolation of the baroreceptor area of the right ADN was made in situ by ligation of the innominate artery and the right subclavian and common carotid arteries. We altered the pressure in the isolated baroreceptor area according to a binary quasi-white noise between 80 and 100 mmHg in 12 urethan-anesthetized rabbits. The gain increased two to three times as the frequency of pressure perturbation increased from 0.01 to 2 Hz and then decreased at higher frequencies. The phase slightly led below 0.2 Hz. The squared coherence value was > 0.8 in the frequency range of 0.01-4 Hz. The step responses estimated from the transfer function were indistinguishable from those actually observed. We conclude that the baroreceptor transduction of the ADN is governed by linear dynamics under the physiological operating pressure range.

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.

Closed-loop identification of carotid sinus baroreflex open-loop transfer characteristics in rabbits

In the circulatory system, a change in blood pressure operates through the baroreflex to alter sympathetic efferent nerve activity, which in turn affects blood pressure. Existence of this closed feedback loop makes it difficult to identify the baroreflex open-loop transfer characteristics by means of conventional frequency domain approaches. Although several investigators have demonstrated the advantages of the time domain approach using parametric models such as the autoregressive moving average model, specification of the model structure critically affects their results. Thus we investigated the applicability of a nonparametric closed-loop identification technique to the carotid sinus baroreflex system by using an exogenous perturbation according to a binary white-noise sequence. To validate the identification method, we compared the transfer functions estimated by the closed-loop identification with those estimated by open-loop identification. The transfer functions determined by the two identification methods did not differ statistically in their fitted parameters. We conclude that exogenous perturbation to the baroreflex system enables us to estimate the open-loop baroreflex transfer characteristics under closed-loop conditions.

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.

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.

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.

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.

Lack of increased coronary atherosclerotic risk due to elevated lipoprotein(a) in women > or = 55 years of age

BACKGROUND

Numerous studies have indicated that there is an association between lipoprotein(a) [Lp(a)] and coronary artery disease (CAD) in middle-aged men; however, few studies have addressed this issue in women or the elderly.

METHODS AND RESULTS

Serum Lp(a) concentrations were determined in 354 women and 706 men with or without angiographically defined CAD (one or more coronary arteries with narrowing of > or = 75%). The age-specific impact of elevated Lp(a) (> or = 30 mg/dL) on CAD was examined in each sex. In the younger age group (< 55 years old), elevated Lp(a) was independently associated with CAD in both sexes (adjusted odds ratio [OR]: women, 6.90, P < .01; men, 2.63, P < .05). The age-specific ORs declined with age, and elevated Lp(a) no longer conferred an increased CAD risk in either elderly men or women > or = 65 years old. In the age group of 55 to 64 years, elevated Lp(a) was positively associated with CAD for men (adjusted OR: 2.45, P < .05) but not for women (adjusted OR: 0.56, P = NS).

CONCLUSIONS

For both sexes, elevated Lp(a) appears to be an independent risk factor for premature CAD and the importance of Lp(a) appears to decrease with age. However, for women, the risk estimate of Lp(a) began to decline at an age approximately 10 years younger than for men. These data suggest that not only age- but also sex-specific factors such as menstrual status may interact with the association between Lp(a) and CAD.

Neural arc of baroreflex optimizes dynamic pressure regulation in achieving both stability and quickness

The baroreflex loop consists of a fast neural arc and a slow mechanical arc. We hypothesized that the neural baroreflex arc compensates the slow mechanical response and thus improves the quality of blood pressure regulation. We estimated the open-loop transfer characteristics of the neural baroreflex arc (HP), i.e., from carotid sinus pressure to sympathetic nerve activity (SNA), and that of the effective peripheral baroreflex arc (Hp), i.e., from SNA to arterial pressure, in anesthetized rabbits. The gain of Hn was constant below 0.12 +/- 0.057 Hz and increased with a slope of 6.1 +/- 0.06 dB/octave above its frequency up to 1 Hz. In contrast, the gain of Hp was constant below 0.071 +/- 0.03 Hz and decreased with a slope of -11.0 +/- 1.48 dB/octave above the frequency. These data indicate that Hn accelerates slow peripheral responses in the frequency range of 0.1-1 Hz. Although too much acceleration in the high-frequency range could result in instability of the system, numerical analysis of the closed-loop baroreflex response indicated that the neural arc optimized arterial pressure regulation in achieving both stability and quickness.

Effectiveness of probucol in preventing restenosis after percutaneous transluminal coronary angioplasty

Lipid lowering therapies were employed to prevent restenosis following elective percutaneous transluminal coronary angioplasty (PTCA). The effect of probucol was compared to that of Pravastatin in 141 coronary atherosclerosis patients. Probucol (750 mg/day) was administered for at least 30 days prior to PTCA (34 patients, group P-1) or less than 14 days prior to PTCA (27 patients, group P-2). Pravastatin (10 mg/day) was administered for at least 30 days prior to PTCA (38 patients, group V-1) or less than 14 days prior to PTCA (42 patients, group V-2). In group P-1, the patient restenosis rate was 17.6% and lesion restenosis rate was 14%. These rates were significantly lower than those of group V-1, which were 44.7% and 40.4% respectively (p < 0.05). The respective values were 48.1% and 51.8% in group P-2 (p < 0.05, vs group P-1) and 35.7% and 34% (p < 0.05, vs group P-1) in group V-2. Probucol seems to work, not only by lowering cholesterol but also by its antioxidative properties when administered for a sufficient period prior to PTCA.

Effects of replacement of Lys25 with Gln on the conformation of ribonuclease T1: sequence-specific 1H NMR resonance assignments of Gln25 ribonuclease T1 by two-dimensional NMR spectroscopy

Two isozymes of ribonuclease (RNase) T1 exist in nature, i.e. Gln25 RNase T1 and Lys25 RNase T1. Gln25 RNase T1 is less stable than Lys25 RNase T1, although the enzymatic activity is not distinguishable between these two isozymes. To elucidate the effects of the replacement of Lys25 with Gln on the conformation and microenvironments of RNase T1 in detail, two-dimensional NMR spectra were measured, sequence-specific 1H NMR resonance assignments of Gln25 RNase T1 were performed, and then the determined parameters and microenvironments of Gln25 RNase T1 were compared with those of Lys25 isozyme [Hoffmann, E. and Rüterjans, H. (1988) Eur. J. Biochem. 177, 539-560]. The main chain protons were assigned for 101 out of the total of 104 amino acid residues. Secondary structure elements were identified from analysis of characteristic NOE patterns, interstrand NOE connectivities, and hydrogen-deuterium exchange rates of main chain amide protons. The results indicated that Gln25 RNase T1 contains a single alpha-helix and seven beta-strands. The secondary structure of Gln25 RNase T1 is, thus, essentially the same as that of Lys25 RNase T1. On the other hand, comparison of the conformation-dependent shifts of Gln25 RNase T1 with these of Lys25 RNase T1 showed that the replacement of Lys25 with Gln has significant effects on the C-terminal part of the alpha-helix region and the base-binding site. These results may indicate that the base-binding site is relatively flexible in the RNase T1 molecule. Among the residues of the C-terminal part of the alpha-helix region, the protons of Asp29 were most affected in terms of their chemical shifts, which may indicate that the side chain carboxylate anion of Asp29 is the counterpart of the electrostatic interaction of Lys25 in Lys25 RNase T1. The Gln25 of Gln25 RNase T1 may have little or no interaction with Asp29, and this may be the reason why Gln25 RNase T1 is less stable than the Lys25 isozyme.

Relation of saphenous vein graft obstruction to serum cholesterol levels

OBJECTIVES

To determine the potential of lipid-lowering therapy to reduce saphenous vein graft obstruction, we retrospectively studied the association between graft obstruction and serum cholesterol levels.

BACKGROUND

Atherosclerosis is the major cause of vein graft obstruction. Approximately 50% of grafts are occluded by 10 years after operation. It remains to be established whether lipid control affects long-term graft survival.

METHODS

We carried out a retrospective review of all 284 patients who had undergone coronary artery bypass graft surgery at Juntendo University Hospital between 1976 and 1991 and met the following additional criteria: at least one saphenous vein graft, repeat coronary arteriography at some point after coronary artery bypass graft surgery and a serum cholesterol level > or = 200 mg/dl before operation. Saphenous vein graft obstruction rates were compared among three groups classified by serum cholesterol levels at follow-up arteriography: group I < 200 mg/dl; group II 200 to 239 mg/dl; group III > or = 240 mg/dl. A vein graft was considered obstructed if it was narrowed by > or = 70%.

RESULTS

In group I, 88% of grafts were not obstructed 7 years after operation. The respective rates were 61% in group II and 57% in group III (p < 0.005). This relation was true for vein grafts to the left anterior descending and other coronary arteries.

CONCLUSIONS

Lower serum cholesterol levels are associated with lower rates of vein graft obstruction for up to 7 years. This suggests that cholesterol-lowering therapy may improve long-term saphenous vein graft survival after coronary artery bypass surgery.

Thermal stabilization of ribonuclease T1 by carboxymethylation at Glu-58 as revealed by 1H nuclear magnetic resonance spectroscopy

Ribonuclease T1 (RNase T1) carboxymethylated at the gamma-carboxyl group of Glu-58 with iodoacetic acid is known to be completely inactive while it retains an almost full substrate-binding ability. In order to further clarify the effects of the carboxymethylation, the thermal stabilities of intact and Glu-58-carboxymethylated (CM-) RNase T1 were compared by measuring 1H NMR spectra at various temperatures. The transition curves of unfolding were obtained by plotting, as a function of temperature, the peak areas for the alpha and delta protons of Asn-81 and Ile-90, respectively, which are well apart from each other in the three-dimensional structure of the enzyme. For each of intact and CM-RNase T1, the transition curve of the Asn-81 alpha proton was identical with that of the Ile-90 delta methyl protons, suggesting that the thermal unfolding occurred simultaneously in every part of the molecule of CM-RNase T1 as well as of intact RNase T1. The midpoint of unfolding was 52 degrees C for intact RNase T1, and was increased by 9 degrees C upon carboxymethylation at Glu-58. This marked stabilization by carboxymethylation is thought to be due to formation of a salt bridge between the introduced carboxymethyl group and the neighboring guanidium group of Arg-77.