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Biomedical subjects

M Miyamura

Publications and source records attributed to M Miyamura.

At least 37 records · Page 2Linked to original sources
PubMed1998

The effects of intermittent exposure to hypoxia during endurance exercise training on the ventilatory responses to hypoxia and hypercapnia in humans.

The present study was performed to investigate the effects of a combination of intermittent exposure to hypoxia during exercise training for short periods on ventilatory responses to hypoxia and hypercapnia (HVR and HCVR respectively) in humans. In a hypobaric chamber at a simulated altitude of 4,500 m (barometric pressure 432 mmHg), seven subjects (training group) performed exercise training for 6 consecutive days (30 min x day(-1)), while six subjects (control group) were inactive during the same period. The HVR, HCVR and maximal oxygen uptake (VO2max) for each subject were measured at sea level before (pre) and after exposure to intermittent hypoxia. The post exposure test was carried out twice, i.e. on the 1st day and 1 week post exposure. It was found that HVR, as an index of peripheral chemosensitivity to hypoxia, was increased significantly (P < 0.05) in the control group after intermittent exposure to hypoxia. In contrast, there was no significant increase in HVR in the training group after exposure. The HCVR in both groups was not changed by intermittent exposure to hypoxia, while VO2max increased significantly in the training group. These results would suggest that endurance training during intermittent exposure to hypoxia depresses the increment of chemosensitivity to hypoxia, and that intermittent exposure to hypoxia in the presence or absence of exercise training does not induce an increase in the chemosensitivity to hypercapnia in humans.

Adult↗
PubMed1998

Effects of endurance physical training on hydroxyl radical generation in rat tissues.

Physical exercise is known to increase oxygen consumption to compensate for enhanced ATP consumption and thus to induce oxidative stress in tissues. Our previous data indicate that training significantly increased the hydroxyl radical level in rat tissues after physical exercise, but reduced the basal level in aged rats. This result suggests the paradoxical effect of physical training, which may be to increase or scavenge reactive oxygen species (ROS) generated by physical exercise. In this paper, the effects of training on the levels of hydroxyl radicals and the anti-oxidative glutathione system, were examined in rats. After 3 weeks' training, rats were sacrificed at rest or after treadmill running, and the levels of hydroxyl radicals trapped with salicylic acid, reduced (GSH); and oxidized glutathione (GSSG) in tissues were quantified by high-performance liquid chromatography-electrochemical detection (HPLC-ECD). Endurance training reduced the basal level of hydroxyl radicals significantly in plasma and soleus muscle. In liver and brain a similar tendency was observed, but the difference was not statistically significant. In liver the basal level of GSH increased significantly after training. Slower training with longer duration reduced the basal levels of hydroxyl radical in plasma more markedly than more intense training. These results suggest that endurance exercise can increase the anti-oxidative capacity in rats.

Animals↗
PubMed1998

Initiation of increase in muscle sympathetic nerve activity delay during maximal voluntary contraction.

To investigate the effects of maximal voluntary exercise on sympathetic nerve activity, contraction force and muscle sympathetic nerve activity (MSNA) were recorded during maximal (MVG) and submaximal voluntary isometric handgrip (SVG) for 2 min in eight healthy subjects. MSNA was determined by a microneurographic technique, and handgrip force, heart rate (HR) and arterial blood pressure (ABP) were measured by a non-invasive method during exercise. Grip force decayed rapidly to 58% of maximal grip force (MGF) at 10 s after commencement of exercise and was almost constant (approximately 30% of MGF) 40 s after exercise. MSNA increase was delayed by 20 s during MVG, followed by a gradual increase. HR was elevated immediately after onset of exercise, while mean ABP rise showed a 20 s lag from initiation of MVG exercise. During SVG increases in MSNA, HR and mean ABP were delayed by 50, 40 and 20 s, respectively, relative to commencement of exercise. Thereafter, these parameters increased time-dependently. These results suggested that the MSNA increase during MVG may be predominantly because of the metaboreflex.

Adult↗
PubMed1998

Effects of sho-saiko-to extract on fibrosis and regeneration of the liver in rats.

Sho-saiko-to, one of the most widely used Chinese herbal preparations, has long been used for the treatment of chronic liver diseases. We have investigated its effect in retarding the process of liver fibrosis and accelerating liver regeneration, especially its effect on Ito cells that are thought to be deeply involved with liver fibrosis. Sho-saiko-to extract and its active constituents were orally administered to rats with dimethylnitrosamine-induced liver-injury. After treatment with sho-saiko-to extract hepatic function improved, histopathological results confirmed repair of liver tissue, and retinoid levels increased. On the other hand, when active constituents of sho-saiko-to extract were administered alone, liver retinoid levels remained low, implying that interaction among active constituents of the extract was suppressing Ito cell activation. When sho-saiko-to extract was administered to 70% hepatectomized normal and liver-injured rats, liver weight, the number of S-phase-cells and retinoid levels increased with time. However, these changes were different for normal and liver-injured rats, suggesting that the site of action of sho-saiko-to extract in regenerating liver is different for normal and liver-injured rats. These results show that sho-saiko-to extract was useful for suppressing the activation of Ito cells.

Animals↗
PubMed1998

Expression of growth factor ligand and their receptor mRNAs in bovine ova during in vitro maturation and after fertilization in vitro.

We analyzed the expression of mRNAs for growth factor [epidermal growth factor (EGF), insulin-like growth factor-I (IGF-I), basic fibroblast growth factor (bFGF) and platelet-derived growth factor A chain (PDGF-A)] and their receptor (R) by reverse transcription-polymerase chain reaction in bovine ova during oocyte maturation in vitro (0-21 hr) and after fertilization in vitro (6-144 hr: zygotes to blastocysts). Transcripts for EGF were not found before fertilization. Transcripts for IGF-I were present in immature oocytes immediately after collection and in embryos from the 2-cell stage onward. Transcripts for bFGF were present in all stages of oocyte maturation and after fertilization up to the 16-cell stage. Transcripts for PDGF-A were present in all stages of oocyte maturation and after fertilization up to the 2-cell stage. Transcripts for ErbB3 (a member of the EGF-R subfamily), and bFGF-R were present in all stages of oocyte maturation, after fertilization up to the 2-cell stage, and the blastocyst stage. Transcripts for IGF-I-R and PDGF-Ralpha were present in all stages of oocyte maturation and embryo development. The results of this study showed that eight different messages for growth factor and their receptor were detectable in bovine ova during oocyte maturation and/or after fertilization in vitro and their expression patterns were the gene-specific rather than the developmental stage of bovine ova.

Animals↗
PubMed1998

Relationship between maximal pulmonary ventilation and arterialized venous blood potassium and dopamine concentrations obtained at exhaustion in man.

This study was performed to test the hypothesis that potassium concentration in arterialized blood may be closely related to maximal pulmonary ventilation (V.Emax) obtained at exhaustion during maximal exercise in man. Eleven healthy men performed bicycle exercise with incremental loading at 60 rpm until exhaustion. Pulmonary ventilation (V.E), oxygen uptake (V.O2), and heart rate (HR) were determined continuously throughout the experiment. Arterialized venous blood samples were collected to measure potassium ([K+]), lactate ([La]), hydrogen ion (pH), catecholamine ([CA]), and dopamine ([DA]) concentrations. A significant correlation (r = 0.98-0.88) between V.E and [K+], [La], and pH during exercise was observed in all subjects. Furthermore, a close relationship was found in this study between dopamine concentration measured at exhaustion ([DA]0) and maximal pulmonary ventilation per kilogram of body weight (V.Emax/W) (r = -0.668, p < 0.05) or maximum oxygen uptake per kilogram of body weight (VO2MAX/W) (r = 0.720, p < 0.05). However, no significant correlation was found between V. Emax/W and [K+]0 (r = 0.202, NS), [La]0 (r = -0.096, NS), and pH0 (r = 0.344, NS). These results suggest that dopamine may play a more important role in the determination of maximal pulmonary ventilation during exercise in man than K+ or pH.

Adolescent↗
PubMed1997

Effect of aging on the concentrations of nitrous oxide in exhaled air.

Trace gases in exhaled air have been used as a simple means of assessing metabolic reactions. The investigations of trace gases derived from bacteria in human exhalation are usually hydrogen (H2) or methane (CH4). On the other hand, nitrous oxide (N2O) is also derived from microorganisms, especially denitrifying bacteria. Although many kinds of denitrifying bacteria have been isolated on and in the human body, there has been few concerning N2O. We studied 222 healthy people from the age of 5 to 85 years. The analysis of N2O in exhaled air was carried out by a infrared-photoacoustic (IR-PAS) analyzer. It was found that N2O ranged from 0 to 1670 ppbv in exhaled air and that 59% (131) of the subjects were producers of N2O. A highly significant relationship was observed between age and concentrations of N2O (r = 0.40, P < 0.01). The rate of production in young children and in the aged was significantly higher than that in adults aged 20-39 years (P < 0.01), and less than 30% were producers during puberty. The change of normal microflora on and in human body with aging may have caused the significant relationship between age and emissions of N2O.

Adolescent↗
PubMed1997

Ventilatory response at the onset of voluntary exercise and passive movement in endurance runners.

The present study was performed to examine whether or not the ventilatory response at the onset of voluntary exercise and passive movement in endurance runners is the same as in untrained subjects. Twelve long-distance runners belonging to the varsity athletic club and 13 untrained subjects of our university participated as subjects in this study. Maximum oxygen uptake was significantly higher in the endurance runner group [mean (SD) 70.8 (4.7) ml.kg-1.min-1] than in the untrained group [49.8 (6.3) ml.kg-1.min-1]. Cardiorespiratory responses during voluntary exercise and passive movement of alternate flexion-extension of the right and left legs for about 15 s at a frequency of about 60 rpm, were determined by means of breath-by-breath techniques. Minute inspiratory ventilation (VI), tidal volume (VT), respiratory frequency (fb), cardiac output (Qc), stroke volume (SV) and heart rate (HR) increased significantly immediately at the onset of voluntary exercise and passive movement. The incremental rate for VI was greater than that for Qc. Average values and standard deviations of changes in VI were calculated as the difference between the mean of the first and second breath and the mean of five breaths preceding the exercise or movement. The rates obtained in voluntary exercise and passive movement in the endurance runner group [2.34 (0.82) and 1.72 (0.71 l.min-1), respectively] were significantly (P < 0.05) lower than those in the untrained group [4.16 (2.66) and 2.71 (1.56 l.min-1), respectively]. Also changes in VT and HR were significantly lower in the endurance group than in the untrained group with regard to both voluntary exercise and passive movement. The results suggest that the magnitude of cardiorespiratory responses at the onset of voluntary exercise and passive movement in humans is influenced by chronic endurance training for long periods.

Adult↗
PubMed1997

Effects of combined beta-adrenergic and cholinergic blockade on the initial ventilatory response to exercise in humans.

To elucidate whether combined adrenergic and parasympathetic blockade would affect the ventilatory response to exercise, especially at the initial stage (phase I), six healthy subjects performed a brief and light voluntary bilateral leg extension exercise and passive movements under the conditions of control (before the blockade) and after intravenous administration of combined beta-adrenergic (propranolol, 0.2 mg.kg-1) and muscarinic (atropine, 0.04 mg.kg-1) receptor antagonists. The movements were continued only within two breaths after the onset of the motion. Ventilation increased immediately and significantly (P < 0.05) within the first breath at the onset of voluntary exercise in all conditions as compared with at rest. However, the magnitude of increase in mean ventilation within two breaths at the start of exercise as against the resting value (delta ventilation) was significantly less (P < 0.05) after the combined blockades (2.5 l.min-1) than in the control condition (3.7 l.min-1). Passive movements showed a similar but smaller change as compared with voluntary exercise. The heart rate response to exercise was attenuated by the combined blockade while cardiac output showed a slight change at the onset of exercise. It is concluded that phase I should occur despite the inhibited activity of the beta-adrenergic and the cholinergic systems; nevertheless, the response was attenuated by the combined blockade. These results suggest a possible role of the beta-adrenergic and/or cholinergic systems in the rapid increase in ventilation that occurs at the start of exercise.

Adrenergic beta-Antagonists↗
PubMed1997

Comparison of exhaled nitric oxide and cardiorespiratory indices between nasal and oral breathing during submaximal exercise in humans.

In order to examine the origin and role of nitric oxide (NO) in exhaled air during exercise, exhaled NO outputs of 8 healthy human subjects were compared using different breathing methods, through the mouth or nose, at two intensities of bicycle exercise. The concentration of NO in the exhaled air and ventilatory gas exchange variables were measured by a chemiluminescence analyzer and a mixing chamber method, respectively. The concentration and total output of NO in the expired air was significantly higher under nasal breathing than under oral breathing for both exercise intensities, whereas no significant difference was observed in cardiorespiratory variables between them. NO output increased significantly when exercise intensity was increased from unloaded (0 W) to 60 W under nasal breathing, but not under oral breathing. A negative correlation among subjects was found between NO output and minute ventilation in both breathing methods only for unloaded exercise. Data indicate that nasal airways have a large contribution, at least 50% of total NO output in the exhaled air during nasal breathing, but this nasal NO may have no further modulation on respiratory function during submaximal exercise by healthy humans.

Adolescent↗
PubMed1997

[A study of the association between HLA phenotype and serum concentration of soluble HLA class I].

We investigated the association between the phenotypes of human leucocyte antigens (HLA) class I on the surface of lymphocytes and serum concentrations of soluble HLA (sHLA) in normal and Human immunodeficiency virus (HIV) infected subjects. Serum concentrations of sHLA inn normal subjects with HLA-A 24 were significantly higher than those in such subject without HLA-A 24. The similar relation was found in HIV infected subjects whose levels of sHLA significantly increased compared with that of normal subjects. These results might suggest that the mechanism which causes the increase in secretion of sHLA in HIV infected subjects does not change the association between HLA phenotype and serum concentration of sHLA.

Adult↗
PubMed1997

[Metamorphopsia and transient increase in the cerebral blood flow of the left occipital pole on 123I-IMP SPECT: a case report].

A 55-year-old right-handed man suddenly developed unformed visual hallucination of rainbow-colored balls coming out from the lower quadrant of the right visual field. Visual field examination revealed a right lower quadrant homonymous hemianopia. Metamorphopsia of the hand or face appeared 6 days later when he looked at his hands or at the face in the mirror, and persisted for about 10 minutes. 123I-IMP SPECT demonstrated a marked increase in CBF of the left occipital pole while the patient realized the visual symptoms, and a marked decrease in CBF after the symptoms disappeared. T1 and T2-weighted MRIs of the brain were unremarkable, but the Gd-DTPA-enhanced T1-weighted MRI showed high signal in the subcortical white matter of the left occipital pole. The metamorphopsia was induced probably by the activation of the left occipital lesion by the epileptogenic mechanism although the nature of the lesion remained unclarified.

Amphetamines↗
PubMed1996

[Properties of glycyrrhizin in Kampo extracts including licorice root and changes in the blood concentration of glycyrrhetic acid after oral administration of Kampo extracts].

We investigated in vitro the properties of glycyrrhizin (GL), such as dissolution, absorption and resolution, using a Sho-Seiryu-To extract, a Sho-Saiko-To extract, both including a licorice root, and licorice extract. The dissolution of GL differed with the pH of the solvent. The absorption (partition coefficient) of GL decreased with an increase in pH, and increased in the presence of other active constituents, such as baicalin, baicalein, and ephedrine. In the case of the Sho-Saiko-To extract, the conversion from GL to glycyrrhetic acid (GA) by beta-glucuronidase originated from E. coli occurred slowly. It was also suppressed by adding baicalin. We determined in vivo the pharmacokinetics of GA after oral administration of Kampo extracts in healthy volunteers. In each Kampo extract, the time of administration had no influence on the mean maximum blood concentration (Cmax) and the area under the blood concentration-time curve (AUC). Tmax was delayed in the case of the administration after meal (p < 0.05).

Administration, Oral↗
PubMed1996

Human blood lactate and ammonia levels after supramaximal uphill and downhill running.

The purposes of this study were 1) to confirm whether there is a difference in the levels of blood lactate and ammonia after supramaximal uphill and downhill running for the same short duration and 2) to examine the relationship between peak blood lactate levels and work/lean body mass (LBM), as well as the relationship between peak blood ammonia levels and work/LBM following supramaximal uphill and downhill running. Eight healthy, untrained male subjects performed supramaximal uphill and downhill running on a motor-driven treadmill for about 70 sec. Though there was a significant difference (p < 0.05) in running speed and work/LBM between supramaximal uphill and downhill running, no significant difference was found in exhaustion time or heart rate. Both the peak blood lactate and ammonia concentrations were significantly lower after downhill running than after uphill running (p < 0.05). Although there was no significant relationship between peak blood ammonia levels and work/LBM following either uphill or downhill running, significant linear relationships between the peak blood lactate levels and work/LBM were observed following uphill running (r = 0.74, p < 0.05) and downhill running (r = 0.72, p < 0.05). These results suggest that the differences in the blood lactate and ammonia concentration between supramaximal downhill and uphill running of the same duration may be due to the total recruitable muscle mass during exercise, and that peak blood lactate can be used as an index of anaerobic work capacity for untrained subjects under these running conditions.

Adult↗
PubMed1994

Ventilatory responses at the onset of passive movement and voluntary exercise with arms and legs.

This study was undertaken to elucidate whether phase I appeared at the onset of voluntary and passive arm movements and to compare these results with those of similar leg movements. Instead of the conventional cranking exercise, seven male subjects performed alternately flexion-relaxation of both arms, extension-relaxation of both legs, and combined arm and leg exercise at the rate of about 60 min-1 for four breaths in a sitting position. Similar movements were accomplished passively by the experimenters. In all experiments, minute ventilation increased rapidly within the first breath after the onset of exercise. The difference of ventilation (delta value) between the mean of the first two breaths at the onset of voluntary exercise and that of five breaths during rest was significantly (P < 0.05) greater in arm (7.75 l min-1) than in leg (5.19 l min-1). Passive movement showed a similar tendency. Arm delta ventilation correlated highly (r = 0.74-0.91) with leg delta ventilation and the slope of the regression lines was about 1.2. Heart rate increased abruptly while cardiac output did not always increase rapidly at the onset of locomotion. Oxygen uptake in the voluntary leg exercise continued for 3 min was slightly but nonsignificantly higher than in the arm exercise, indicating the equality of the exercise intensity. In conclusion, ventilatory responses at the onset of the arm exercise are larger than those of the leg in both voluntary and passive conditions regardless of the muscle mass, suggesting the different neurogenic mechanism between arm and leg.

Adult↗
PubMed1994

Relationship between maximal pulmonary ventilation during exhaustive exercise and postexercise plasma potassium concentration in man.

The present study was undertaken to examine the relationship between maximal pulmonary ventilation (VEmax) and potassium concentration ([K+]) or lactate concentration ([La]) of venous blood in man. Nine healthy men performed exercise on a bicycle ergometer at a constant rate of 60 rpm until volitional fatigue. VEmax ranged from 100.4 to 153.2 l/min. In all subjects, potassium concentration measured at 1 min ([K+]1.0) after maximal exhaustive exercise was the highest, and it returned quickly to the resting level within a few minutes during recovery. VEmax was significantly correlated (r = 0.750, p < 0.05) to [K+]1.0, but not to lactate concentration determined at 1 min ([La]1.0) during recovery. These results suggest that a higher increase in blood [K+] may, at least partly, contribute to a greater augmentation of VE during exhaustive exercise.

Adult↗
PubMed1994

Control of ventilation during exercise in man with special reference to the feature at the onset.

When exercise starts, various cardiorespiratory adjustments take place for accommodating the greatly increased metabolic requirements. A rapid response in ventilation (Phase I) may be at least useful for preventing oxygen deficiency and for increasing alveolar ventilation, oxygen tension, and oxygen uptake even if it is minimal. But why is the increasing tidal volume and respiratory frequency elicited so quickly just at the onset of exercise? Dose rapid ventilatory response play an important role as a trigger for surviving in exercising man? It has hitherto been reported that phase I response is observed during not only voluntary and passive movement, but also during electrically induced muscle contraction in man. In addition, it was observed that ventilation in phase I is not affected by hypoxia and is not causally linked to cardiac output. Although these mechanisms have extensively been explored by many investigators, they have still remained obscure until now. At present, the causal factors of phase I are classified as central (descending) and peripheral (ascending) neurogenic stimulus, or as both. In the awake condition, abrupt ventilatory increment immediately after voluntary and passive exercise in man could be attributed to the drives from the central command including cortical and hypothalamic activities as well as some peripheral afferent information mainly through group III and IV fibers. However, further investigations to clarify many unsolved problems should be advanced in future.

Animals↗