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Biomedical subjects

C Nakamura

Publications and source records attributed to C Nakamura.

At least 163 records · Page 9Linked to original sources
PubMed1980

Simultaneous measurements of shifts of the center of gravity caused by ventilation and cardiac motions towards three body axes.

A method is described for the simultaneous measurements of three dimensional shifts of the gravitational center of the body caused by ventilatory and cardiac motions. The measuring system consists fundamentally of three load cells which support an aluminum die-casting platform. Measurement of the shift towards the X axis (front-to-back) was achieved by double integration of the outputs of load cells in order to convert acceleration into a shift of gravity. The records of a volunteer subjects measured with ECG and ventilatory flow showed two cardinal oscillations; one coinciding with the heat rate and the other with the ventilatory frequency. This became clear when recorded through either a low-pass or high-pass filter. Animal who breathed a SF6-O2 mixture into one side of the lungs or those with partial occlusion of a bronchus showed distinct changes in the pattern of the Y axis (right-to-left). These preliminary experiments convinced us that the system can serve as a non-invasive monitoring system of cardiopulmonary functions.

Animals↗
PubMed1980

Diffusion, convection and their coupling as gas transport mechanisms in the lungs: a model experiment.

The roles of diffusion and convection in gas transport were studied by means of a lung model with a hollow bronchial cast of a dog. He, Ar and SF6 were chosen as indicators with different diffusivities. Axial dispersion of a heavier gas was much better, but the concentration gradient in a static gas phase was greater for a heavier gas, i.e., there was a larger stratified inhomogeneity for a less diffusible gas. Crossings of He and SF6 concentration curves were observed between diffusion distances of 6 and 8 cm, which could be assumed to be a critical point of conversion where either convective mixing or diffusion favored gas transport. The results observed also suggested that the effective diffusion coefficient and speed of respiration affected the efficiency of gas transport.

Animals↗
PubMed1979

Thiourea and cyanamide as inhibitors of thyroid peroxidase: the role of iodide.

Thiourea, methylmercaptoimidazole, propylthiouracil, and thiouracil are all potent inhibitors of thyroid peroxidase (TPO)-catalyzed iodination. Unlike the cyclic thioureylenes, thiourea at 5 mM has no effect on guaiacol oxidation. If iodide is added to guaiacol assays containing thiourea, enzyme activity is lost. The latter observation may be explained as follows. In the presence of iodide, the iodinating species [TPO.Ioxid], oxidizes thiourea to formamidine disulfide. This product decomposes to cyanamide at neutral pH. We have shown cyanamide to be an inhibitor of the peroxidative and iodinating functions of TPO. Studies in rats demonstrate that doses of thiourea which completely inhibit in vivo protein-bound iodine formation have no irreversible effect on TPO, as measured by guaiacol peroxidation after removal of the thyroids. The major in vivo action of cyanamide is similar to that of thiourea. The data suggest that the primary in vivo and in vitro mode of action of thiourea is the reversible Ioxid-trapping mechanism. The anomalous inhibition of guaiacol peroxidation seen in the presence of thiourea plus iodide derives from the formation of formamide disulfide, followed by its nonenzymic decomposition to cyanamide.

Animals↗
PubMed1978

Serum thyrotropin releasing hormone (TRH)-degrading activity: a sensitive and rapid radiochemical assay procedure.

A rapid and sensitive method has been developed to assay thyrotropin releasing hormone (TRH)-degrading activity in serum. In this assay, the formation of proline, a major serum degradation product of TRH (pGlu-His-Pro-NH2), is measured. The procedure is based on the finding that proline can be readily separated from TRH with Dowex 50 by a batchwise procedure in a test tube.

Animals↗
PubMed1978

Lower levels of thyrotropin-releasing hormone-degrading activity in human cord and in maternal sera than in the serum of euthyroid, nonpregnant adults.

Thyrotropin-releasing hormone (TRH)-degrading activity was investigated in human cord, maternal, and euthyroid adult sera by measuring (a) the rate of disappearance of TRH and (b) the rate of formation of degradation products. The rate of TRH degradation in cord and maternal sera was 25-33% of that in euthyroid adult serum. Concomitantly, in cord and maternal sera, the rate of formation of proline, a major TRH degradation product in serum, was one-quarter to one-third that in euthyroid adult sera. The differences were highly significant (P less than 0.001). The decreased levels of TRH-degrading activity in cord and maternal sera cannot be explained by (a) the presence of a dialyzable inhibitor, (b) the absence of an activator of TRH degradation, or (c) a reversal of the degradation process. There was no difference in the types of radioactive degradation products formed by cord, maternal, and euthyroid adult sera. The low level of TRH-degrading activity and its possible relationship to high thyrotropin-stimulating hormone levels in cord serum suggest that TRH-degrading activity may be a factor to consider in investigations of the perinatal pituitary-thyroid axis, but further studies are needed to determine the role of serum degradation of TRH in regulating physiological levels of TRH.

Adult↗