Biomedical subjects

Yoji Suzuki

Publications and source records attributed to Yoji Suzuki.

10 recordsLinked to original sources

PubMed2006

Triglyceride in plasma: prospective effects on microcirculatory functions.

The effect of triglyceride in plasma on RBC aggregation was examined, and the prospective influence on the flow of RBCs in microcirculation and the O2 release was discussed. To minimize the individual differences, blood samples were collected from one subject 2 hrs after high-fat and low fat meals. Triglyceride content in plasma was measured by an enzymatic method, and the rate of rouleaux formation was measured with a low shear rheoscope. The rate of rouleaux formation was increased with the increase of triglyceride concentration. Our previous findings suggested some functional impairment in microcirculation. (1) The enhanced RBC aggregation tends to reduce flow resistance in arterioles, but results in inhomogeneous flow of RBCs in capillaries. (2) The sclerotic change of microvessels alters flow behavior of RBCs, and thereby flow resistance is increased. (3) The enhanced RBC aggregation reduces O2 release from RBCs flowing in microvessels. In conclusion, high triglyceride level in plasma not only changes flow behavior of RBCs in microcirculation and thus increases flow resistance, but also prevents homogeneous tissue oxygenation.

Blood Viscosity↗

PubMed2006

Connective tissue growth factor is released from platelets under high shear stress and is differentially expressed in endothelium along atherosclerotic plaques.

Connective tissue growth factor (CTGF) is overexpressed in atherosclerotic blood vessels. To further investigate the role of CTGF in atherosclerosis, we examined whether CTGF is released from platelets by high shear stress, and whether the expression of CTGF along the atherosclerotic lesions depends on local hemodynamic conditions. Human platelets were subjected to 10 dyn/cm2 or 120 dyn/cm2 and analysed by Western blotting. Furthermore, longitudinal sections of 25 carotid plaques were immunohistochemically analysed for the endothelial expression of CTGF. A very low CTGF amount was secreted from platelets at low shear stress (11.4 +/- 3.9% of total CTGF in platelets). On the contrary, high shear stress caused a markedly increased CTGF release from platelets (29 +/- 13.8%, p = 0.07 vs low shear stress, n = 4). Immunohistochemical analyses showed that the mean numbers of CTGF-positive endothelial cells were significantly higher up-stream as compared with down-stream regions of the luminal surface of atherosclerotic vessels (21.3 +/- 3.6 vs 13.9 +/- 2.8 down-stream, p < 0.001). Moreover, in plaques undergoing intimal neovascularization, newly formed vessels accumulated particularly in up-stream parts of the lesions. In conclusion, this study demonstrated that CTGF is released from platelets by high shear stress. Furthermore, disturbed flow along atherosclerotic vessels may induce endothelial CTGF expression and contribute to the progress of atherosclerotic lesions.

Atherosclerosis↗

PubMed2005

Energy expenditure in males with mental retardation.

Previously, we reported that males with mental retardation (MR) (MR group) expended more energy than males without MR (control group) at a given work load. The precise physiological mechanisms for this difference remain unclear. Using the same set of subjects (23 age-, height-, and weight-matched male pairs, mean age: 36.3 y), we examined possible causes for the observed metabolic difference by monitoring physical movements and evaluating the metabolic capability of the skeletal muscles. In the supine position when no body movements were detected for any subjects, oxygen consumption (VO2) and heart rate (HR) were not markedly different between the MR and the control groups. By contrast, in the sitting and standing positions and during walking at 30 and 50 m/min, when significantly larger body movements were monitored in the MR group, VO2 and HR were significantly higher in this group than in the control group. Linear regression analyses, performed separately in the MR and control groups, revealed that the slope of the regression line of HR on relative exercise intensity (%VO2max) during walking, that of VO2 on walking speeds, and that of VO2 on the number of steps in the MR group were almost identical with those in the control group. These results suggest that the capability of skeletal muscles was not so different between the two groups. Thus, the high energy expenditure in the MR group was suggested to be a result of excessive body movements rather than an intrinsic incapability of skeletal muscles.

Adult↗

PubMed2003

O2 release from Hb vesicles evaluated using an artificial, narrow O2-permeable tube: comparison with RBCs and acellular Hbs.

A phospholipid vesicle that encapsulates a concentrated hemoglobin (Hb) solution and pyridoxal 5'-phosphate as an allosteric effector [Hb vesicle (HbV) diameter, 250 nm] has been developed to provide an O2 carrying ability to plasma expanders. The O2 release from flowing HbVs was examined using an O2-permeable, fluorinated ethylenepropylene copolymer tube (inner diameter, 28 microm) exposed to a deoxygenated environment. Measurement of O2 release was performed using an apparatus that consisted of an inverted microscope and a scanning-grating spectrophotometer with a photon-count detector, and the rate of O2 release was determined based on the visible absorption spectrum in the Q band of Hb. HbVs and fresh human red blood cells (RBCs) were mixed in various volume ratios at a Hb concentration of 10 g/dl in isotonic saline that contained 5 g/dl albumin, and the suspension was perfused at the centerline flow velocity of 1 mm/s through the narrow tube. The mixtures of acellular Hb solution and RBCs were also tested. Because HbVs were homogeneously dispersed in the albumin solution, increasing the volume of the HbV suspension resulted in a thicker marginal RBC-free layer. Irrespective of the mixing ratio, the rate of O2 release from the HbV/RBC mixtures was similar to that of RBCs alone. On the other hand, the addition of 50 vol% of acellular Hb solution to RBCs significantly enhanced the rate of deoxygenation. This outstanding difference in the rate of O2 release between the HbV suspension and the acellular Hb solution should mainly be due to the difference in the particle size (250 vs. 7 nm) that affects their diffusion for the facilitated O2 transport.

Allosteric Regulation↗

PubMed2003

Changes of RBC aggregation in oxygenation-deoxygenation: pH dependency and cell morphology.

The effects of the oxygenation-deoxygenation process on red blood cell (RBC) aggregation were examined in relation to morphological changes in RBCs and the contribution of CO(2). A low-shear rheoscope was used to measure the rate of rouleaux (one-dimensional aggregate) formation in diluted autologous plasma exposed to gas mixtures with different Po(2) and Pco(2). RBC indexes and RBC suspension pH were measured for the oxygenated or the deoxygenated condition, and the cell shape was observed with a scanning electron microscope. In the oxygenation-deoxygenation process, the rate of rouleaux formation increased with rising pH of the RBC suspension, which was lowered in the presence of CO(2). The rate increased with increasing mean corpuscular hemoglobin concentration (thus the cells shrank), which increased with rising pH and decreased in the presence of CO(2). With rising pH, cell diameter increased and cell thickness decreased (thus the cell flattened). In addition, slight echinocytosis was induced in the presence of CO(2), and the aggregation was reduced by the morphological change. In conclusion, RBC aggregation in the oxygenation-deoxygenation process is mainly influenced by the pH-dependent change in the surface area-to-volume ratio of the cells, and the aggregation is modified by CO(2)-induced acidification and the accompanying changes in mean corpuscular hemoglobin concentration and cell shape.

Adult↗

PubMed2002

Effects of rapid saline infusion on orthostatic intolerance and autonomic tone after 20 days bed rest.

To test whether acute volume expansion can normalize orthostatic intolerance and autonomic tone after prolonged bed rest (BR), 23 men were subjected to 20 days BR. Left ventricular (LV) echocardiography was performed during the lower body negative pressure (LBNP) test before and after BR with and without preceding rapid infusion of saline (1,500 ml/30 min). Saline infusion restored heart rate, LV dimension, and stroke volume during LBNP, increased cardiac output (from 4.1 +/- 1 to 5.3 +/- 1 L/min), and normalized LBNP tolerance time (from 11 +/- 4 to 23 +/- 6 minutes). In 9 men, a Holter electrocardiogram was recorded on the day before BR, the fourth and twentieth days of BR, and the day after BR. The high-frequency component of heart rate variability during sleep gradually decreased and reached the lowest level on the day after BR (100%, 66 +/- 16%, 39 +/- 18%, 10 +/- 8%). Thus, restoring decreased blood volume is an effective countermeasure for orthostatic intolerance after BR. However, decreased vagal tone persisted, suggesting reset autonomic tone.

Adult↗

PubMed2002

Reduced oxygen release from erythrocytes by the acceleration-induced flow shift, observed in an oxygen-permeable narrow tube.

The oxygen release from flowing erythrocytes under accelerational force (0-4 g) was examined using an oxygen-permeable, fluorinated ethylenepropylene copolymer tube (25 microm in inner diameter). The narrow tube was fixed vertically on the rotating disk of a new centrifuge apparatus, and erythrocyte suspension was perfused in the direction of Earth gravity. The accelerational force was applied perpendicularly to the flow direction of cells by centrifugation. The microscopic images of the flowing cells obtained at five different wavelengths were analyzed, and marginal cell-free layer and oxygen saturation of the cells were measured. By lowering oxygen tension around the narrow tube, erythrocytes were deoxygenated in proportion to their traveling distance, and the deoxygenation was enhanced with decreasing flow velocity and hematocrit. With increase of the g-value, the shift of flowing erythrocyte column to the centrifugal side was increased, the column was compressed, and the oxygen release from the cells was suppressed. Qualitatively, similar results were obtained by inducing erythrocyte aggregation with Dextran T-70 (MW = 70,400), without accelerational force. These results conclude that both the accumulation of erythrocytes under accelerational force and the enhancement of erythrocyte aggregation by macromolecules lead to the reduction of oxygen release from the flowing cells.

Acceleration↗

PubMed2002

Changes in mood status and neurotic levels during a 20-day bed rest.

This study evaluated changes of mood status and depressive and neurotic levels in nine young male subjects during a 20-day 6 degrees head-down tilting bed rest and examined whether exercise training modified these changes. Participants were asked to complete psychometrical inventories on before, during, and after the bed rest experiment. Depressive and neurotic levels were enhanced during bed rest period according to the Japanese version of Zung's Self-rating Depression Scale and the Japanese version of the General Health Questionnaire. Mood state "vigor" was impaired and "confusion" was increased during bed rest and recumbent control periods compared to pre-bed rest and ambulatory control periods according to the Japanese version of Profiles of Mood State, whereas the mood "tension-anxiety", "depression-dejection", "anger-hostility" and "fatigue" were relatively stable during experiment. Isometric exercise training did not modify these results. Microgravity, along with confinement to bed and isolation from familiar environments, induced impairment of mental status.

Adaptation, Psychological↗

PubMed2002

Glucose and oxygen hypometabolism in aceruloplasminemia brains.

OBJECTIVE: Aceruloplasminemia is an iron metabolic disorder caused by mutations in the ceruloplasmin gene. It is characterized by progressive neurodegeneration in association with iron accumulation. Excess iron functions as a potent catalyst of biologic oxidation. Previously we showed that an increased iron concentration is associated with the products of lipid peroxidation in the serum, cerebrospinal fluid, and brain tissues. To clarify the free radical-mediated tissue injury caused by intracellular iron accumulation through mitochondrial dysfunction. PATIENTS AND METHODS: We have measure brain oxygen and glucose metabolisms using positron emission tomography (PET) and examined brains at autopsy for iron contents and activities of the mitochondrial respiratory chain in two affected patients who had different truncation mutations of the ceruloplasmin gene. RESULTS: PET showed a marked decrease in glucose and oxygen consumption in the entire brain of aceruloplasminemia patients, with a preponderance of metabolic reduction in basal ganglia. Enzyme activities in the mitochondrial respiratory chain of the basal ganglia were reduced to approximately 45% and 42% respectively for complexes I and IV. An inverse relationship was shown between the amounts of iron accumulated and the levels of mitochondrial enzyme activities in all the brain regions examined. CONCLUSION: Iron-mediated free radicals may contribute to the impairment of mitochondrial energy metabolism in aceruloplasminemia.

Aged↗

PubMed2002

Comparing cardiovascular responses during exercise between head-down tilt pedaling with lower body negative pressure and upright cycling in man.

If lower body negative pressure (LBNP) loaded on exercise in weightlessness environment is able to derive a comparable cardiovascular responses to these in the ground, it should be identified as an optimal LBNP for exercise in space. To investigate the LBNP, 7 young subjects were exercised 4 work rates stepping up every 50 watts from 50 watts to 200 watts every 5 minutes in the upright position or 6 degree head down tilt position with each LBNP of 20, 40, 60, 80, and 100 mmHg. Oxygen uptake during tilt exercise with over 60 mmHg LBNP was not different from it in upright exercise. Heart rate and systolic arterial pressure responses to exercise were very similar between tilt exercise with 60 mmHg LBNP and upright exercise. In conclusion, the optimal LBNP loaded on exercise in space should be around 60 mmHg.

Comparative Study↗