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Biomedical subjects

Y Doi

Publications and source records attributed to Y Doi.

At least 523 records · Page 29Linked to original sources
PubMed1981

[Cast fractures of dental Ni-Cr alloys (author's transl)].

Cast fractures of Ni-Cr alloys were investigated by means of scanning electron microscopy, energy dispersive X-ray spectrometry, electron-probe microanalysis, density measurements, setting and thermal expansion measurements and compressive tests. Three-Ni-Cr alloys for crowns and bridges were cast in spiral configurations by an argon-arc pressured type or an induction argon-pressured type-casting machine. The amount of cast fracture increase with an increase in cast temperature, but not with an increase of holding time at cast temperature. Ni-Cr alloys have more cast fractures in a phosphate-bonded investment than in a gypsum-bonded cristobalite investment. Fracture surfaces have an exposed dendrite structure, indicating the presence of cast porosity. The trigger of cast crack can be a cast porosity and the propagation of crack to fracture may be mainly due to the strength of investments.

Chromium Alloys↗
PubMed1980

Orientations of carbonate ions in human tooth enamel studied with use of the CO3-3 radical ions as probes.

With the use of CO3-3 radical ions as probes, it is concluded that the carbonate ions substitute in the apatite lattice of human tooth enamel in two different ways. Most of the carbonate ions in the apatite lattice are aligned with their symmetry axis parallel to the c axis, whereas the remaining carbonate ions are aligned with their symmetry axis perpendicular to the c axis.

Apatites↗
PubMed1979

Analysis of paramagnetic centers in X-ray-irradiated enamel, bone, and carbonate-containing hydroxyapatite by electron spin resonance spectroscopy.

Carbonate-containing hydroxyapatite, enamel, and bone were irradiated by an X-ray and investigated between 77 degrees and 350 degrees K by means of electron spin resonance (ESR) spectroscopy. The ESR spectrum of enamel irradiated at 77 degrees K in vacuum and observed at the same temperature was almost the same as that of the carbonate-containing hydroxyapatite. The temperature dependence of signal intensities confirms a spin-energy exchange between the mineral and organic constituents in bone, but in enamel no or very little spin-energy exchange between the mineral and organic constituents. Considerable similarity among the ESR spectra of enamel, bone, and carbonate-containing apatite was obtained after X-ray irradiation in air at 300 degrees K with both an X-band and a Q-band ESR spectrometer. The Q-band spectrum can be interpreted in terms of two paramagnetic species. One is identified as a CO3(3-) anion radical which has an axial symmetry with g factors of 2.0029 and 1.9972. The other species is found to be centered at g = 2.0019.

Animals↗
PubMed1979

Cardiac pumping ability in rats with experimental renal and genetic hypertension.

In two experimental models of established hypertension in the rat (two kidney, one clip renal and genetic hypertension), the maximum by which stroke volume and cardiac output could be increased during an acute preload stress was significantly reduced despite the concomitant development of left ventricular hypertrophy. Reversal of cardiac hypertrophy by prolonged treatment with methyldopa (range 3 to 6 weeks) during the established phase of spontaneous hypertension normalized arterial blood pressure and improved ventricular pumping ability. The improved performance was in part due to reduced impedance to ventricular ejection because it did not persist when peripheral resistance was increased by an acute administration of phenylephrine hydrochloride. Thus, hemodynamic as well as structural factors contribute to alterations in cardiac function during the chronic established phase of arterial hypertension.

Animals↗
PubMed1979

Purification of human plasma lecithin:cholesterol acyltransferase and its specificity towards the acyl acceptor.

A simple and convenient method for the purification of human plasma lecithin-cholesterol acyltransferase was developed. The method involves the adsorption of the enzyme from diluted human plasma on DEAE-Sephadex, treatment with 1-butanol in the presence of (NH4)2SO4, DEAE-Sephadex chromatography, treatment with dextran sulfate in the presence of Ca2+, and hydroxyapatite chromatography. The enzyme purified showed a single main band by polyacrylamide gel electrophoresis in the presence and absence of sodium dodecyl sulfate. In addition, the enzyme obtained was stable for more than four weeks, when it was kept at 4 degrees C under N2 in a buffer of low ionic strength. The purified enzyme was used to study its specificity toward the acyl acceptor. This specificity was found to be broad in that not only sterols but also long chain primary alcohols exhibited considerable acceptor activity. Furthermore, in agreement with our previous observations with crude enzyme (Piran, U. and Nishida, T. (1976) J. Biochem. (Tokyo) 80, 887-889), the purified enzyme was found to be capable of hydrolyzing the ester linkage at the carbon-2 position of phosphatidylcholine. The transesterification, as well as the hydrolytic reaction, required the presence of the cofactor polypeptide, apolipoprotein A-I.

Apolipoproteins↗
PubMed1979

Release of active and inactive renin by the human kidney.

1. Active and inactive renin were assayed in plasma of the renal veins and the inferior vena cava below the kidney in eight patients with hypertension and unilateral renal abnormalities, 20 min after the patients had resumed the upright position. 2. The concentration of active renin on the affected side was significantly higher than that on the non-affected side. The concentration of inactive renin on the affected side was significantly lower than that on the non-affected side and in the inferior vena cava. 3. These findings suggest either that the affected kidney mainly secretes active renin, which is then converted into inactive renin in the extrarenal circulation, or that the affected kidney activates inactive renin.

Enzyme Activation↗
PubMed1979

Dystrophic calcification in calcifying epithelial odontogenic tumor: an X-ray diffraction and electron spin resonance study.

X-ray diffraction and electron spin resonance (ESR) analyses were conducted on calcifying epithelial odontogenic tumor (CEOT) associated with abundant calcification in order to compare its mineral structure with that of surrounding cortical bone. The material under investigation was removed from the canine-premolar region of the left maxilla of a 39-year-old woman. The principal findings were that the mineral phase of CEOT consists of apatite crystals and that the crystallinity of the crystals is higher than that of bone apatite. ESR spectra of CEOT are similar to those of bone sample. Quantitative ESR analysis indicates that CEOT shows a higher crystallinity coefficient -- defined by Ostrowski et al. (1972, 1974) as the ratio of spin concentration to the ash content of the sample -- than bone. Based on the data, it can be concluded that the calcification in CEOT has a higher crystalline structure than the cortical bone.

Adult↗