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Biomedical subjects

M Horikawa

Publications and source records attributed to M Horikawa.

At least 91 records · Page 5Linked to original sources
PubMed1983

Synthesis of phosphono-pyrimidine and -purine ribonucleosides.

The reaction of the lithiated species of 2', 3', 5'-tri-O-protected uridines and 6-chloropurine ribonucleoside with diethyl chlorophosphate provided the corresponding diethyl phosphonate derivatives (III, IV and VIII). The Arbuzov-reaction of 2', 3', 5'-tri-O-protected 4-chloro-2(1H)-pyrimidinone ribonucleoside with triethyl phosphite afforded the diethyl phosphonate derivative (VI).

Chemical Phenomena↗
PubMed1980

Analyses of differential sensitivities of synchronized HeLa S3 cells to radiations and chemical carcinogens during the cell cycle. Par V. Radiation- and chemical carcinogen-induced mutagenesis.

8-Azaguanine(8AG)-resistant mutations induced by X-rays, ultraviolet radiation (UV) and a chemical carcinogen, 4-hydroxyaminoquinoline 1-oxide (4-HAQO) were examined during the cell cycle of synchronized HeLa S3 cells. Mutants induced by 400 R of X-rays occurred in a higher frequency in the X-ray-SENSITIVE Gl-S boundary phase than in the X-ray-resistant G1, S and early G2 phases. 8AG-resistant mutants induced by treatment with 10(-5) M 4-HAQO for 20 min appeared in a higher frequency in the early to middle S phases than in the other phases. In the case of UV, however, we found no significant difference in the induced mutation frequencies during the cell cycle, because the mutation frequencies induced by the UV doses (0-20 J/m2) used were too low for detection of the difference. These results suggest that there is a close correlation between the critical damage induced in DNA molecule(s) at the DNA-synthetic phase in the cell cycle and mutagenesis, because mitotic cells have a low mutability in spite of their high radio-sensitivity.

4-Hydroxyaminoquinoline-1-oxide↗
PubMed1980

The changes in pattern of myocardial shortening by reduction of regional coronary blood flow.

The relationship between the grade of a decrease in the regional coronary blood flow and the movement of ventricular myocardium of that region was investigated in open chest dog. Blood flow in left anterior descending artery (FLAD) was reduced by stepwise constriction of LAD with ligature. Ventricular segment length was measured in a circumferential plane on the endocardial surface by ultrasonic dimension system. For the elimination of the noise caused by ultrasonic dimension system, the synchronizer was inserted between sample clock of the dimension system and the trigger circuit of the electromagnetic flowmeter. A 20% reduction of FLAD affected the pattern of ischemic myocardial shortening very little. Discontinuance of shortening to the end of systole was occurred by a 20 to 60% reduction in FLAD. Early and/or late systolic bulging was induced by a 60% reduction of FLAD. Systolic bulging with early diastolic shortening was seen in the cases with a 60 to 80% reduction in FLAD. Frank systolic bulging which was always seen by complete occlusion of LAD was produced by a 60 to 90% reduction of FLAD in few cases.

Animals↗
PubMed1980

Coronary vascular reserve and regional myocardial contractile force with special reference to myocardial metabolism.

The relations among coronary vascular reserve, regional myocardial contractile force and myocardial metabolism were investigated in anesthetized dogs under open-chest condition. The reactive hyperemia response was examined during stepwise occlusion of circumflex artery. A change in percent repayment was used as an index of the coronary vascular reserve. Contractile force was measured with strain gauge arches sutured to ischemic and nonischemic areas of the left ventricle. The nonischemic muscle contractile force (NIMCF) increased or showed no significant change with the reduction of repayment by stepwise constriction of circumflex artery. The ischemic muscle contractile force (IMCF) began to decrease markedly following reduction of repayment below 50%. NIMCF was found to be slightly decreased by the severe reduction of coronary blood flow (CBF) in ischemic region. Thus there was a low (r = 0.39) correlation between NIMCF and CBF in ischemic region. However, the correlation between IMCF and CBF in ischemic region was relatively high (r = 0.68). The arterial and coronary sinus blood samples were obtained for the determination of oxygen content, lactate and potassium concentrations. In the range of constriction without reduction of CBF, IMCF decreased significantly following reduction of repayment below 50%, but O2, lactate and potassium extraction ratios were not significantly different. Application of further constriction revealed significant reductions of CBF, stroke volume, aortic pressure, IMCF and lactate extraction ratios, and it also revealed significant elevation of O2 extraction ratio. The above observation suggests that a reduction of coronary vascular reserve might affect regional contractile force without change in CBF, and reduction of CBF could decrease regional and global left ventricular performance with changes in myocardial metabolism.

Animals↗
PubMed1977

Analyses of differential sensitivities of synchronized HeLa S3 cells to radiations and chemical carcinogens during the cell cycle. Part IV. X-rays.

Radiation-induction and rejoining of single-strand breaks (SSBs) in the DNA of synchronized HeLa S3 cells were investigated by alkaline sucrose density gradients. We could not find any significant differences in the extent of SSBs induced in cellular DNA and in the extent of their rejoining throughout the cell cycle, including mitosis. The cyclic variation curve of the content of non-protein sylfhydryls (NPSH) during the cell cycle is similar to that of X-ray survivals except in mitosis, although there was no close correlation between the content of apparent total sulfhydryls (APSH) and X-ray survivals. Radiation-induced mutants resistant to 8-azaguanine (8AG) occurred in higher frequency in the radio-sensitive G1-S boundary phase than in the radio-resistant G1, S and early G2 phases. Further, the pre-irradiation treatment with 50 mM cysteamine prevented reproductive death and induction of 8AG-resistant mutants by X-rays throughout the cell cycle. These findings seem to indicate that there is a close correlation between the extent of lethal radiation damage to the cells and their mutability, and that sulfhydryls may play an important role as a factor governing cellular radio-sensitivity.

Azaguanine↗
PubMed1977

Repair of the sublethal and mutational damage induced by x-rays in Chinese hamster HAI cells in vitro.

The ability of Chinese hamster hai cells to repair damage related to cell death and mutational change induced by X-rays were examined by using a sensitive forward mutation system from prototrophic CH-hai Cl 23 cells to auxotrophs. The results obtained from the split dose experiments seem to suggest that Chinese hamster hai cells have the repair mechanisms for the sublethal and mutational damage induced by X-rays and that the repair mechanisms act in common for the repair of both cases of damage.

Cell Line↗
PubMed1977

Studies on the coronary circulation by a simulation method.

Some aspects of the control mechanism in the coronary circulation were investigated by using analog simulation. The simulation is designed to separate passive or mechanical factor from entire influence on the change in coronary flow consisting of passive and active factors, under different hemodynamic conditions. Simulated waveform was very similar to the blood flow pattern of the left circumflex artery actually obtained by an electromagnetic flowmeter. Pressure flow relationship was almost linear. Coronary flow increased with rise of aortic pressure, with the influence of active factors exceeding greatly that of the passive factors. When the heart rate was increased, the decrease in coronary flow due to the passive factors themselves was found. After the occlusion of the coronary artery the slight reactive hyperemia due to only passive factors was observed in the simulated flow.

Animals↗
PubMed1976

Comparison of clinical and laboratory findings of intrathoracic sarcoidosis between children and adults.

Children were different from adults in the following findings of intrathoracic sarcoidosis: All of the 69 pediatric patients studied had no complaints and were found by chest x-ray examinations, in contrast with 71% of the 62 adult patients studied. At the ages 10-14 yr there were far more boys than girls. In pediatric patients eye involvements were rare, blood eosinophilia was more frequent, biopsy of conjunctival follicles was more frequently positive, cold serum hemagglutinins were higher at first and decreased later, and the prognosis was far better than in adults.

Adolescent↗