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Biomedical subjects

N Horiuchi

Publications and source records attributed to N Horiuchi.

At least 109 records · Page 6Linked to original sources
PubMed1983

Graded nephron mass reduction and renal synthesis of 1,25-dihydroxyvitamin D3 in the rat.

The effect of graded nephron mass reduction by partial nephrectomy and the influence of parathyroid hormone and dietary phosphorus (P) on the production of 1,25-dihydroxy-vitamin D [1,25(OH)2D] were studied in vitamin D deficient rats. At 48 hours (acute experiments) or 2 weeks (chronic experiment) after partial nephrectomy, the rates of [3H]1,25(OH)2D production from [3H]25 hydroxyvitamin D (25-OHD) were measured in vivo. The production of 1,25(OH)2D decreased in proportion to the remaining nephron mass, and it was not greater in chronic experiments than in acute experiments at any level of nephron mass reduction. By contrast, plasma creatinine was elevated in 5 of 6 nephrectomized rats in acute, but not in chronic, experiments, suggesting the compensatory mechanism for renal excretory function but not for 1,25(OH)2D production. Further, at any level of nephron mass reduction, the production of this active metabolite was not greater in rats fed low P diet than those fed normal or high P diets. Thyroparathyroidectomy at 12 hours prior to a dose of [3H]-25)OHD suppressed 1,25(OH)2D production at any level of nephron mass reduction in rats fed normal or high P diet. These data suggest that in both experimental acute and chronic renal failure 1,25(OH)2D production is proportional to residual nephron mass and that parathyroid hormone may enhance the metabolism of 25OHD in renal failure and also may be critical for 1,25(OH)2D in normal or high P diet.

Animals↗
PubMed1982

Development of diabetes in Japanese subjects with impaired glucose tolerance: a seven year follow-up study.

Five hundred and seven subjects with postprandial glycosuria underwent a 50g oral glucose tolerance test in an epidemiological survey of diabetes mellitus carried out in 1964-1965 in the town of Osaka, Japan. The oral glucose tolerance test was repeated 7 years late in 207 (40.8%) of the subjects. The results of the initial and the follow-up test were classified into three categories according to the new WHO criteria: normal, impaired glucose tolerance and diabetes. Most of the diabetic subjects (84.8%) remained unchanged between the initial and follow-up test. Of the subjects with impaired glucose tolerance at the time of the initial test, 38.5% showed diabetes in the follow-up test, while another 38.5% returned to normal. On the other hand, 13.5% of the normal subjects in the initial test developed impaired glucose tolerance or diabetes in the follow-up test. The rate of worsening to diabetes was related closely to the 2-h blood glucose value at the initial test. In addition, the rate of worsening was higher in males and obese subjects than in females and non-obese subjects. A multiple logistic analysis indicated that the fasting and 2-h glucose values were significantly predictive of worsening to diabetes.

Adolescent↗
PubMed1982

Serum levels of acetate and TCA cycle intermediates during hemodialysis in relation to symptoms.

In order to study the metabolism of acetate transferred from dialysate, the plasma concentrations of organic acids including the tricarboxylic acid cycle (TCA cycle) intermediates were measured during hemodialysis in a comparative study between acetate dialysate and bicarbonate dialysate in 17 patients on maintenance hemodialysis treatment. Continuous measurements of serum concentrations of these organic acids during hemodialysis were performed using the filtrate obtained through an ultrafiltrate sampling device. The organic acids were measured by isotachophoresis. Serum acetate, malate and citrate concentration increased with time in acetate dialysis compared with bicarbonate dialysis. Correlations were found between these organic acids. Isocitrate became detectable when the serum acetate concentration was over 7 mmol/l which was correlated to the acetate concentration, and was accompanied by the development of symptoms. The above results suggest that an acetate overload on the patients during acetate dialysis affects acetate metabolism through the TCA cycle resulting in an accumulation of organic acids in the serum and the development of symptoms.

Acetates↗
PubMed1982

[A new correction method for radionuclide formation in neutron activation analysis using a reactor power meter coupled with a microcomputer].

Neutron flux and irradiation time should be accurately known in neutron activation analysis using very short lived nuclides in which conventional monitoring methods i.e., a comparator method, flux monitor method and so on cannot be used satisfactorily. Especially, fluctuation of neutron flux has not been corrected. We noted a change of reactor power at a pneumatic operation, and found out a new correction method for its correction in activation analysis. In our small nuclear reactor, TRIGA-II, the reactor power increased rapidly a few % when a pneumatic-operated capsule arrived at a core of the reactor, and decreased when the capsule left from the core. If the duration between these two changes of the reactor power is equal to the irradiation time, and that the reactor power is proportional to the neutron flux, we can regard an activity formation as a time integration of the reactor power. Then, the correction system was made of a reactor power meter, a V-F converter (voltage to frequency converter), a clock time, a counter, a microcomputer, electric circuits and so on. The signal of the reactor power during the irradiation was counted through the V-F converter, and was accumulated in a memory of the microcomputer. The neutron fluence was calculated in this microcomputer. This method was examined by means of activation of copper and selenium standard samples by 9-11 sec irradiations. The observed activity involved +/- 10% error. However, the error in the corrected activity was decreased to a few % using this correction method. As a result, we found that this method can be used to obtain accurate value for radionuclide formation.

Activation Analysis↗
PubMed1981

Regulation and its refractoriness of 25-hydroxyvitamin D3 metabolism in vitamin D deficiency.

The time course of change in plasma calcium levels and renal metabolism of 25-hydroxyvitamin D3 [25(OH)D3] was investigated in chicks maintained on a vitamin D-deficient diet for 4 weeks. Plasma calcium concentrations dropped sharply between the 7th and 14th day of the feeding period. Renal 25(OH)D3-1 alpha-hydroxylase activity was reciprocally enhanced concurrently with the decrease in plasma calcium levels. The elevated activity of 1 alpha-hydroxylase had declined significantly by the 21st and 28th days in spite of the more severe hypocalcemia. When graded amounts of vitamin D3 were administered to the chicks maintained on this diet for 14 or 28 days, there were considerable differences in the change of plasma calcium levels and 25(OH)D3 metabolism induced by vitamin D3 administration between the 14-day and 28-day birds. The minimal dose levels of vitamin D3 to completely suppress renal 1 alpha-hydroxylase activity were 25 micrograms in the 14-day, and 2.5 mg in the 28-day birds. These differences were not observed between the 14-day and 28-day birds when 1 alpha-hydroxyvitamin D3 [1 alpha(OH)D3] was administered. Renal adenylate cyclase activity induced by parathyroid hormone (PTH) was much lower in the 28-day chicks than that in 1-day-old and the 14-day birds. These results are explained by the hypersecretion of PTH and the subsequent refractoriness of the target organs in severe vitamin D deficiency. Plasma calcium levels per se did not appear to be a major factor in the regulation of 25(OH)D3 metabolism.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed1980

Metabolites of 24,25-dihydroxyvitamin D3 made in the kidney of chicks supplemented with vitamin D3.

Metabolism of 25-hydroxyvitamin D3 (25-OH-D3) was examined in chicks supplemented with vitamin D3. Kidney homogenates metabolized in vitro [3H]-25-OH-D3 to 3 new metabolites (peaks A, C and E) by way of 24,25-dihydroxyvitamin D3. The enzymes responsible for the synthesis of these metabolites appeared to be induced by 1 alpha,25-dihydroxyvitamin D3. Production of these metabolites was increased in parallel with the increase of the supplemented levels of vitamin D3, while recovery of the radioactivity in the chloroform phase was sharply decreased. The production of peak C was considered to be closely related to the transfer of the radioactive metabolites to the water-soluble phase. These results may indicate that 24-hydroxylation is a degradation step in the 25-OH-D3 metabolism.

24,25-Dihydroxyvitamin D 3↗