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M Okada

Publications and source records attributed to M Okada.

At least 1,549 records · Page 86Linked to original sources
PubMed1984

[Quantitative correlation between thallium-201 myocardial emission computed tomography and left ventriculography in old myocardial infarction].

We evaluated a clinical usefulness of quantitative analysis of myocardial emission computed tomographic (ECT) images in 28 patients with old myocardial infarction and 10 healthy volunteers. Circumferential profile analysis was performed in five or six short-axial images of the left ventricle reconstructed from ECT. Mean regional anterior, inferoposterior, lateral and septal percent thallium uptakes were calculated from three short-axial (basal, central and apical) images. The percent infarct size was evaluated as a percentage of the thallium perfusion defect volume to the total left ventricular myocardial volume. Left ventricular hemiaxis shortening was calculated at three ventricular levels corresponding to the three short-axial ECT images. Mean value of all hemiaxis shortening in RAO and LAO projections (total hemiaxis shortening) and left ventricular ejection fraction (EF) were obtained. There was a significant correlation between mean percent thallium uptake and percent hemiaxis shortening in the left ventricular anterior and inferoposterior segments. On the contrary, no statistically significant correlation was shown between these two parameters in the left ventricular lateral and septal segments. Percent infarct size obtained with ECT significantly correlated with total hemiaxis shortening and EF (r = -0.63 and -0.60, respectively). It was concluded that there is a close relationship between the size of infarcted myocardium evaluated by ECT and either of the regional or global left ventricular dysfunction assessed by LVG.

Adult↗
PubMed1984

[Quantitative analysis of exercise 201Tl myocardial emission CT in patients with coronary artery disease].

The clinical usefulness of quantitative analysis of exercise thallium-201 myocardial emission computed tomography (ECT) was evaluated in coronary artery disease (CAD). The subjects consisted of 20 CAD patients and five normal controls. All CAD patients underwent coronary angiography. Tomographic thallium-201 myocardial imaging was performed with a rotating gamma camera, and long-axial and short-axial myocardial images of the left ventricle were reconstructed. The tomographic images were interpreted quantitatively using circumferential profile analysis. Based on features of regional myocardial thallium-201 kinetics, two types of abnormalities were studied: diminished initial distribution (stress defect) and slow washout of thallium-201, as evidenced by patients' initial thallium-201 uptake and 3-hour washout rate profiles which fell below the normal limits, respectively. Two diagnostic criteria including the stress defect and a combination of the stress defect and slow washout were used to detect coronary artery lesions of significance (greater than or equal to 75% luminal narrowing). The ischemic volumes were also evaluated by quantitative analysis using thallium-201 ECT. The diagnostic accuracy of the stress defect criterion was 95% for left anterior descending, 90% for right, and 70% for left circumflex coronary artery lesions. The combined criteria of the stress defect and slow washout increased detection sensitivity with a moderate loss of specificity for identifying individual coronary artery lesion. A relatively high diagnostic accuracy was obtained using the stress defect criterion for multiple vessel disease (75%). Ischemic myocardial volume was significantly larger in triple vessel than in single vessel disease (p less than 0.05) using the combined criteria.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1984

Metabolism of N-nitrodialkylamines.

The in-vitro and in-vivo metabolism of N-nitramines was investigated to compare it with that of N-nitrosamines. N-Nitrodibutylamine and N-nitrodiethylamine were incubated with rat liver microsomes and hepatocytes, and the products were analysed by high-performance liquid chromatography and gas-liquid chromatography. The in-vitro metabolic pattern of these N-nitramines was similar to that of the corresponding N-nitrosamines, except that N-nitromonoalkylamines (produced by alpha-hydroxylation) were isolated and identified after incubation of N-nitrodialkylamines. Seven N-nitramines, including glucuronides, were isolated and identified from urine of rats given N-nitrodibutylamine, produced by omega, omega-1, and alpha oxidations of the N-nitramine. The in-vivo metabolic pattern of N-nitrodibutylamine was also similar to that of N-nitrosodi-n-butylamine except that N-nitromonobutylamine (a product of alpha-hydroxylation) was isolated and identified. N-Nitramines were mutagenic to Escherichia coli WP2 hcr-, but not to Salmonella typhimurium TA 1535. N-Nitrodibutylamine and N-nitrodiethylamine were mutagenic only in the presence of hepatic microsomes, while N-nitromonobutylamine and N-nitromonoethylamine were direct mutagens. Thus, the N-nitrodialkylamine is also metabolically activated to a mutagen through an alpha-hydroxylation.

Animals↗
PubMed1984

Mutagenicity of alpha-hydroxy N-nitrosamines in V79 Chinese hamster cells.

N-Nitrosodialkylamines are activated metabolically by alpha-hydroxylation. Chemical properties and bacterial mutagenicity of alpha-hydroxy N-nitrosamines have been reported previously. This paper describes potent and direct mutagenicity of four N-nitroso-N-(hydroxymethyl)alkylamines in V79 Chinese hamster cells, using ouabain resistance as an indicator. The mutagenic potency depended on the alkyl group, decreasing in the following order: methyl greater than ethyl greater than propyl, butyl. A similar order was observed for cytotoxicity. Mutagenic and cytotoxic potencies of these alpha-hydroxy N-nitrosamines in V79 cells were well correlated not only with those of model compounds (alpha-acetoxy and alpha-hydroperoxy N-nitrosamines), but also with their alkylating ability, measured by alkylation of thiophenol. The mutagenic activity of the alpha-hydroxy N-nitrosamines in V79 cells was shown to be parallel to that in Salmonella typhimurium TA1535 and to that of N-nitrosodialkylamines in V79 cells, after metabolic activation by rat hepatocytes. The results obtained here further support the conclusion that the alpha-hydroxy N-nitrosamine is the active species in the metabolic activation of carcinogenic and mutagenic N-nitrosodialkylamines.

Animals↗
PubMed1984

Arrest of intravitelline mitoses in Drosophila embryos by u.v. irradiation of the egg surface.

The intravitelline mitosis in Drosophila was arrested at the anaphase within the span of a single cell cycle after irradiation with 300 nm u.v. Embryos at and before the 8-nucleus stage were influenced by the u.v. only when irradiated anteriorly, while at and after the 16-nucleus stage, embryos are sensitive to either anterior or posterior irradiation. In embryos anteriorly irradiated at or before the 8-nucleus stage all nuclei in the embryo were prevented from performing mitosis. When irradiated at or after the 16-nucleus stage, inhibition of the intravitelline mitosis is limited to the nuclei in approximately anterior-half region of embryos in anterior irradiation, and to those in approximately posterior-half region in posterior irradiation, resulting in incomplete blastoderm formation. Sites sensitive to 300 nm u.v. are postulated to be present in the peripheral cytoplasmic region of the embryo and not in the nucleus, because the half-attenuation thickness of 300 nm u.v. light for the Drosophila egg cytoplasm is 3 microns and nuclei are at least 50 microns away from the periphery at the stage of irradiation. In addition lateral irradiation of a portion of an egg where there is no nucleus underneath was also effective in arresting division of nuclei in the same egg. It is suggested that the effects of 300 nm u.v. may not be conveyed to the nuclei from the periphery by simple diffusion of a substance, and a hypothesis is proposed for the involvement of cytoskeletal elements associated with the u.v. sensitive sites on the surface to the control mechanism of the intravitelline mitosis of the Drosophila embryo.

Animals↗
PubMed1984

[Variations in spinal cord blood flow in stepwise spinal cord impaction injury].

Referring to the experimental study on acute spinal cord injury, it is known that gray matter falls into an ischemia after injury, but opinions have not been unanimous whether or not the white matter falls into ischemia or hyperemia. The blood flow through the white matter varies according to the severity of the injury and degree of resultant paraplegia. Using rabbits, the authors carried out a series of experimental acute spinal cord impaction injury giving impactions at different strength stepwise, i.e., 400, 300, 200 and 100 gcf (g X cm X force) respectively at the 9th thoracic level of the spinal cord. Thus, upon observation of the paralysed levels and measurement of variable spinal cord blood flows according to the hydrogen clearance method, it was concluded as follows: In the 400 and 300 gcf impaction groups a complete paraplegia was observed with a decrease of spinal cord blood flow both in the gray and white matters. In the 200 gcf group mainly incomplete paraplegia was occurred, and while gray matter showed ischemia, white matter showed indefinite response consisting of both ischemia and hyperemia. In the 100 gcf impaction group the gray matter fell into ischemia, but white matter showed a biphasic increase of blood flow. From the above results it was noted that upon impaction causing complete paraplegia spinal white matter shows ischemia and upon impaction giving transient paraplegia blood flow increases. Ischemia thus does not appear to be a common behavior of spinal cord blood flow spinal cord injury.

Animals↗