Haruka Okino

Nitric Oxide Reversibly Suppresses Xanthine Oxidase Activity

The effects of nitric oxide (NO) on xanthine oxidase (XOD) activity and the site(s) of the redox center(s) affected were investigated. XOD activity was determined by superoxide (O2-) generation and uric acid formation. NO reversibly and dose-dependently suppressed XOD activity in both determination methods. The suppression interval also disclosed a dose-dependent prolongation. The suppression occurred irrespective of the presence or absence of xanthine; indicating that the reaction product of NO and O2-, peroxynitrite, is not responsible for the suppression. Application of synthesized peroxynitrite did not affect XOD activity up to 2 microM. Methylene blue, which is an electron acceptor from Fe/S center, prevented the NO-induced inactivation. The results indicate that NO suppresses XOD activity through reversible alteration of the flavin prosthetic site.

Three-dimensional analysis of left ventricular ejection using computational fluid dynamics

We present in this study a method for constructing computational fluid mechanical models in order to study the effects of time-varying left ventricular ejection. A spherical left ventricular model was implemented in which three dimensional flow fields were obtained. The time course of the ventricular wall changes were assumed to have a trigonometrically varying nature. The wall grid was reformed 25 times during the calculation since the left ventricular wall motion was assumed to follow the blood flow, and the ventricle wall radius was reduced by 60 percent in 0.25 seconds. Centerline and cross-sectional velocity vectors greatly increased in magnitude at the aortic outlet, and pressure dropped from 1.17 x 10(4) dynes/cm2 (8.8 mmHg) to zero in the top 10 percent of the heart. The modeling framework will be used with left ventricular cast data coordinates in future studies. There is presently a lack of three-dimensional data based on a realistic model, and the computational method should make it possible to compare simulation results with important measurement techniques such as echocardiography and magnetic resonance imaging.

The Effects of Cardiac Infarction on Realistic Three-Dimensional Left Ventricular Blood Ejection

The effect of cardiac infarction on the flow patterns in cardiac left ventricular ejection was studied using a realistic model which was made from the profile of the left ventricle of a dog heart in diastole. A coordinate measuring machine was used to measure the left ventricular coordinates, and these were input into a three-dimensional flow simulation package. The left ventricular wall motion was described by having the walls moved towards the center of the aortic outlet, and in the case of infarcted tissue, the ventricular wall movement was diminished to simulate infarction flow behavior. The final ventricular volume varied from 25 percent to 54.1 percent of the initial volume in cases without and with infarction, respectively. The maximum blood ejection velocities and ventricular pressure decreased significantly in the presence of infarction. Infarcted areas showed complex blood flow vortex formation not present in the healthy ventricles. The computational technique presented here predicts infarction flow effects which could be observed with measurement techniques such as ultrasound and magnetic resonance imaging, allowing a finer detail of understanding than using either simulation or experimental measurements alone.

The effects of supravalvular aortic stenosis on realistic three-dimensional left ventricular blood ejection.

The effect of supravalvular aortic stenosis on cardiac left ventricular ejection was determined from a realistic left ventricle (LV) model built from the profile of a diastolic dog LV. The ejection fraction was considered to be 75% of the diastolic volume. The maximum blood ejection velocities and ventricular pressure occurred at the start of the diastolic flow since the ventricular walls moved the fastest at this point. Going from a healthy non-stenotic LV to one with 64% stenosis increased the maximum ejection velocity from 117 cm/sec to 269 cm/sec, and the maximum relative pressure increased from 10,420 dynes/cm2 to 33,550 dynes/cm2 (7.82 to 25.16 mm Hg). The supravalvular stenotic aorta showed major flow disturbances as the degree of stenosis increased. The computational technique using a realistic model gives predictions in general agreement with observed experimental results, and allows a complex determination of the three-dimensional flow patterns.

The detection of technical failures in perfused heart with ischemia and reperfusion by epicardial NADH fluorescence

SummaryThis study documents the value of continuous observation of nicotinamide adenine dinucleotide (NADH) fluorescence (NADH-F). NADH-F monitoring is used to identify ischemic regions for the recognition of minor technical failures associated with ischemia and reperfusion experiments in the isolated perfused heart system. The visualization of NADH-F is possible by simply irradiating the heart with ultraviolet light. Rat hearts, in the working-heart mode, were subjected to occlusion/reperfusion of the left coronary artery, and analyzed. The perfusate was filtered through a 5 µm pore membrane. Out of 281 hearts which were judged to be free of technical failures by conventional physiological indices (heart rate >200/min, cardiac output >34 ml/min, and coronary flow 9–14 ml/min), 43 (15%) disclosed an abnormal NADH-F area prior to the coronary intervention. During coronary intervention, 29 technical failures were detected as indicated by sparse NADH-F distribution with occlusion, delayed disappearance of NADH-F upon reperfusion, or the exhibition of an abnormal NADH-F region unassociated with the coronary artery supply area. These technical failures are not detectable without the use of NADH-F, although the actual number of failures detected may depend on the skill of the operator. We recommend NADH-F monitoring for any preparations which do not contain hemoglobin, since NADH-F is an intrinsic probe for ischemia and is easily applicable to a variety of experiments.

Cardiac Output and Regional Blood Flow Measurement with Nonradioactive Microspheres by X-Ray Fluorescence Spectrometry in Rats

Since its introduction (Rudolph and Heymann, 1967) a number of studies have employed the radioactive microsphere method to evaluate changes in cardiac output, regional blood flow, and distribution of pulmonary blood flow under various experimental conditions. Unfortunately, the storage, handling, processing and disposing of radioactive materials requires many precautions and restrictions. Recently, an X-ray fluorescence system and the technique of labeling microspheres with stable heavy elements were developed and used to assess the coronary, hepatic and renal blood flow of large animals (Morita et al., 1990; Mori et al., 1992; Sakamoto et al., 1992). However, this method has not been applied to the measurement of blood flow in small animals such as rats. Rats are one of the most commonly used experimental animals, since entire organs can be easily analyzed because of their relatively small size.

Electrical analogy of diastolic pressure difference between left atrium and ventricle

We proposed a mathematical model to describe the early filling process of the left ventricle and applied the model toin vivo experiments. The solution of a second-order differential equation indicated that the pressure difference between the left atrium and ventricle during ventricular filling (PD) could be explained by a transient response, i.e. decremental oscillation, in an LCR circuit. Thereafter, we analysed the sequence of PD during vagal stimulation with two catheter-tip manometers in 12 anaesthetised dogs and evaluated changes in the parameters of the system under various haemodynamic conditions. The values of ωn and ξ were quite stable among beats within an episode of vagal stimulation, between episodes and even among dogs, despite the changes in haemodynamic variables. Pericardiotomy and partial discommunication of the mitral valve with the left ventricular free wall by cutting the mitral chordal tendons decreased ωn and increased ζ, mainly because of the increase in CLV. Occlusion of the coronary vascular beds with large numbers of microspheres increased ωn and decreased ζ, mainly because of the decrease in CLV. Mitral obstruction with an inflated balloon (increase in R) abolished the oscillatory changes and produced and exponential decay sequence of PD. In conclusion, both the logical and experimental approaches indicated that the sequence of PD could be considered as decremental oscillation in the LCR circuit and the parameters ωn and ξ could be good indices of the diastolic property of the left ventricle

The failure of radical scavengers to attenuate the incidence of reperfusion arrhythmias despite improvement of cardiac function

SummaryWe studied the concomitant effects of scavengers of reactive oxygen species (ROS) on both cardiac function and the incidence of arrhythmias. Isolated rat heart was perfused with a working mode paced at 300 beats/min. The left coronary artery was occluded for 5, 7, 15, or 60 min and reperfused thereafter for 30 min. Superoxide dismutase and catalase were infused from 5 min prior to reperfusion to the end of reperfusion in the scavenger treatment group. In the 60-min ischemia group with scavenger treatment, the cardiac output was significantly higher than that in the untreated group at both 10 and 30 min of reperfusion (P < 0.01). In the 15-min ischemia group with scavenger treatment, the cardiac output showed a tendency toward a higher value than that in the untreated group. The incidence of reperfusion arrhythmias occurring after a short ischemic time (5, 7, or 15 min) were similar in the scavenger treated and untreated groups; but, with a preceding ischemia of 60 min, the incidence of ventricular tachycardia was higher in the scavenger treated group than in the untreated group (P < 0.02). In conclusion, scavengers improved contractile dysfunction but did not attenuate the incidence of arrhythmias.

Identification of Free Radical Species in the Myocardium

With the increasing interest in the role of oxygen-derived free radical generation in various diseases, several attempts to directly evaluate free radicals in tissue have been performed using EPR.1–8 However, none of the previous studies has fully determined the species of the radicals and none has deliberated on the possible existence of artifactual radicals which are likely to be generated during sample handling. The purposes of this study were 1) to establish an artifact-free sampling method for the quantification of freeze-trapped free radicals in myocardium by EPR, 2) to identify artifact radicals and the radicals native to the myocardium and 3) to demonstrate the relationship of these radicals to reperfusion injury.