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Biomedical subjects

Y Masuda

Publications and source records attributed to Y Masuda.

At least 829 records · Page 46Linked to original sources
PubMed1983

Effects of digoxin on the control of heart rate and atrioventricular conduction in the dog.

The effects of digoxin on the chronotropic and dromotropic responses of the heart to autonomic neural stimulation were determined in anaesthetised, open chest dogs. Digoxin did not alter the negative chronotropic response of the heart to vagal stimulation. In contrast, digoxin reduced the positive chronotropic response to sympathetic stimulation by 40%. There was a pronounced vagal-sympathetic interaction such that the positive chronotropic response to strong sympathetic stimulation was attenuated by 72% when a near maximal vagal stimulation was delivered concurrently. However, digoxin did not alter this autonomic interaction. In addition, digoxin did not alter the positive dromotropic response evoked by the sympathetic stimulation. In contrast, digoxin potentiated the increase in A-V conduction time evoked by vagal stimulation (10 Hz) by 147%. No significant vagal-sympathetic interaction in the autonomic control of the dromotropic response was observed; ie, the responses of A-V conduction to combined sympathetic and vagal stimulation were essentially the algebraic sum of the responses to the individual stimulations. This lack of autonomic interaction in modulating A-V conduction time was not altered by digoxin, despite its potentiation of the dromotropic response to vagal stimulation.

Animals↗
PubMed1983

Retarded mesangial transport and its pathomorphologic sequelae in human and experimental renal diseases.

Human renal biopsy specimens (472 cases) from varied kidney diseases, especially minimal glomerular change group and other idiopathic glomerular diseases having nephrotic manifestation of mainly juvenile individuals, showed morphologic evidence of paraarterial deposits of afferent arterioles at the glomerular entrances in more than 50% of examined cases. Because these deposits were often accompanied with concomitant mesangial, intraarterial and subendothelial deposits of afferent arterioles, it was felt that retarded mesangial transport which is ordinarily associated with certain glomerular diseases might be an important factor to produce these particular paraarterial deposits. The referred deposits of minimal glomerular change group cases were thought to predispose the occurrence of focal sclerotic capillary lesions at the vascular poles of glomeruli. The experimental chronic nephrotic rats produced by daily administration of aminonucleoside of puromycin revealed mesangial dysfunction with increased uptake and retarded disposal of secondarily overloaded aggregated human gamma globulin at mesangial areas in glomeruli. Besides, the increased deposits of autologous serum proteins in mesangial areas and arteriolar walls were common findings in those rats, and these deposits were observed to be always preceded to the occurrence of segmental sclerotic changes of glomeruli, which were often associated in the later stage of this experiment.

Adolescent↗
PubMed1983

Heart rate as a determinant of the decay rate of the cardiac inotropic response to sympathetic nervous activity.

The cardiac responses to sympathetic nerve stimulation were measured in a series of open-chest, anesthetized dogs. In half the animals, the hearts were in a sinus rhythm; in the remaining animals, the hearts were in an atrioventricular (AV) junctional rhythm. Cocaine markedly prolonged the decay times of the chronotropic responses after cessation of sympathetic stimulation, regardless of the type of rhythm. The decay times of the inotropic responses were only slightly prolonged by cocaine in animals with a sinus rhythm, but the prolongations were pronounced in animals with an AV junctional rhythm. The lower basal heart rate appeared to be more responsible for the greater decay times of the inotropic responses in the animals with an AV junctional rhythm than in those with a sinus rhythm. In a second series of dogs, complete heart block was produced, cocaine was given, AND the hearts were paced at four different frequencies. The mean decay time of the inotropic response to sympathetic stimulation varied inversely AND substantially with the pacing frequency. The change in contraction frequency probably affects the rate of neurotransmitter dissipation from the ventricular myocardium, by altering either the coronary blood flow or the massaging action of the cardiac contractions.

Animals↗
PubMed1983

Studies on the hypotensive effects of platelet activating factor (PAF, 1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine) in rats, guinea pigs, rabbits, and dogs.

Platelet activating factor (PAF) showed profound and long-lasting hypotensive effects in normotensive and spontaneously hypertensive rats, guinea pigs, rabbits and dogs. Sensitivity to PAF was different among the animal species. The magnitude and duration of the hypotensive effect was dose-dependent. Pharmacological studies suggested that the hypotensive action was unlikely to be caused by the actions on the central or autonomic nervous systems but seemed to be mainly due to some direct action(s) on the peripheral blood vessels.

Animals↗
PubMed1983

Carbon tetrachloride-induced hepatotoxicity in rats: evidence for different susceptibilities of rat liver lobes.

The hepatotoxic effect of carbon tetrachloride (CCl4), reflected by augmented blood aspartate aminotransferase and alanine aminotransferase activities and the extent of histological liver damage, was observed following oral administration of CCl4 to rats. A marked increase of blood transaminase activities and severe degeneration of hepatocytes in the centrilobular region were detected 1-2 days after the administration, while the cytochrome P-450 content and the drug metabolizing activity in livers were depressed immediately after the administration. Based on these results, the effect of CCl4 on hepatic cytochrome P-450 and the histological pattern of liver cells was observed using tissue samples obtained from various liver lobes of rats given CCl4 24 hr previously. Dose-dependent inactivation of cytochrome P-450 by the administration of CCl4 was observed throughout the liver, with the most extensive decrease in the cytochrome content in the median lobe. The extent of liver damage (hydropic swelling degeneration and central necrosis in lobule) was also greater in the median and right liver lobes than in the left lobe. When a small amount of CCl4 was administered, degeneration of liver cells was detected only in the median and right lobes with only slight degeneration in the left lobe. These results indicate different susceptibilities of rat liver lobes to CCl4.

Alanine Transaminase↗
PubMed1983

[Positron computed tomography for the assessment of myocardial infarction].

Positron computed tomography (PCT) was performed on 2 normal subjects and 3 patients with myocardial infarction. The PCT device "Positologica-II" developed at the National Institute of Radiological Science Japan was used in this study (Fig. 1). This is a whole body positron CT consisting of 3 detector rings that provide 5 sliced images simultaneously. The radiopharmaceutical 13N-ammonia (13NH3) synthesized by the cyclotron at the institute was used as an indicator of myocardial blood flow. Immediately after the intravenous administration of 13NH3, five serial 1-min PCT scans were performed with 3 additional scans that provided 15 static images spaced 6 mm apart. Cardiac blood pool images were obtained from the first scan. A patient with extensive anterior myocardial infarction revealed an outward bulging of the blood pool compatible with aneurysmal formation (Fig. 2). Three additional late scans provided high quality cross-sectional images of the distribution of 13N in the left ventricular myocardium. Although 13N distribution in myocardium was uniform in normal subjects (Figs. 3 & 4), the patients with myocardial infarction revealed defects in the accumulation of 13N at the sites corresponding to the infarction (Figs. 5, 6, 7 & 8). The conclusions are as follows: (1) serial PCT scans with 13NH3 provide cardiac blood pool images, and (2) myocardial 13N tissue concentration seems to reflect myocardial blood flow.

Adult↗
PubMed1983

[Diagnostic value of CT in congenital disorders of the great vessels].

Computed tomographic (CT) studies of the cardiovascular system were performed on 850 cases at our institute during the last five years. The aorta was clearly demonstrated by CT from the aortic root to the bifurcation of the iliac artery, and in most cases the main aortic branches including the coronary, brachiocephalic, common carotid, subclavian, celiac, superior mesenteric, renal and iliac arteries were satisfactorily evaluated (Fig. 1-3). Therefore CT renders us encouraging to detect the abnormality of these arteries. This paper described the CT findings of congenital anomalies of the great vessels in 14 patients with 16 anomalies including two cases of l-corrected transposition of the great vessels, two of double aortic arch, one of aneurysm of the sinus of Valsalva, six of patent ductus arteriosus (PDA) and five of right-sided descending aorta, two of which had double aortic arch aforementioned and the remaining three had dextrocardia. The diagnosis of these abnormalities except for PDA were made only by CT. For instance, l-corrected transposition of the great vessels was diagnosed easily by observing the side-to-side relationship of the great vessels, the aorta is situated to the left and anterior to the pulmonary artery. In the case of double aortic arch, not only the left and right aortic arch, but also the degree of narrowing as well as compression of the trachea and esophagus were well evaluated. The diagnosis of aneurysm of the sinus of Valsalva was made by the characteristically marked dilatation of the aorta at the level of sinus of Valsalva on CT. Only in one case of PDA, the ductus connecting the descending aorta to the left pulmonary artery was demonstrated by CT. Plain CT was well tolerable, but enhanced CT was much more informative to detect cardiovascular abnormalities, and moreover, dynamic CT was rewarding in the detailed evaluation of blood flow in the cardiovascular system.

Adult↗
PubMed1983

[Diagnosis of myocardial infarction by CT: the study of an initial filling defect and late enhancement of the infarcted myocardium after injection of contrast material].

Several animal experimental studies have shown that the enhanced CT gives the direct evidence of acute myocardial infarction characterized by an initial filling defect and late enhancement in the site of the damaged myocardium. Therefore, we studied experimentally and clinically the diagnostic value of these CT findings in detecting and quantitating recent and remote myocardial infarctions. Sixteen mongrel dogs with anterior myocardial infarction were subjected to the present study. The cardiac infarction within one month after coronary arterial ligation was visualized as a filling defect by early CT scan after intravenous injection of contrast material. The delayed scan after the injection showed late enhancement of the infarcted area in both acute and chronic phases. Post mortem histologic studies confirmed that the area of filling defect coincided with the necrotic myocardium and late enhancement coincided with the totally infarcted myocardium including healed scar. The total infarct size measured from CT images was closely correlated with histo-pathological infarct volume (r = 0.96). In the clinical study, the enhanced CT was performed on 112 patients with myocardial infarction and 12 patients with angina pectoris. The filling defect and late enhancement of the infarcted myocardium in the antero-septal or apical wall were detected as clearly as in the animal experiment; the former was found in 85% of the patients with recent infarction, and the latter was detected in about a half of the patients with both recent and remote infarctions. However, these CT findings were not clearly recognized in the patients with infero-posterior infarction, subendocardial infarction or angina pectoris. These results indicate the usefulness of CT in the noninvasive diagnosis and a follow-up study of myocardial infarction.

Animals↗
PubMed1983

[Evaluation of constrictive pericarditis by computed tomography].

Since extensive studies of constrictive pericarditis by CT have not been reported, we performed a plain and contrast enhanced CT on 4 patients of constrictive pericarditis diagnosed by cardiac catheterization or echocardiography and confirmed at the time of surgical operation. The CT findings were as follows: The normal pericardium was smooth, could be visualized in the right and anterior regions of the heart, and was approximately or less 2 mm in thickness. On the other hand, the pericardium in constrictive pericarditis was irregularly thickened, was visualized even in the left and posterior regions of the heart, and was more than 2 mm in thickness. The mean CT value of the pericardium in constrictive pericarditis was significantly increased as compared with that of the normal pericardium. The contrast enhanced CT image revealed a marked dilatation of superior and inferior caval veins (SVC and IVC) even in the cases with normal size of each cardiac chamber. The ECG gated CT performed on one case demonstrated the impaired ventricular expansion. After pericardiectomy, the ventricular chambers showed a tendency to dilate, and the dimension of the SVC and IVC were reduced. Thus, CT is thought to be a useful noninvasive technique in evaluating the thickness of the pericardium, its pathology and the degree of dilatation in each cardiac chamber or the vena cavae.

Adult↗