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Biomedical subjects

C Sekiguchi

Publications and source records attributed to C Sekiguchi.

At least 37 records · Page 2Linked to original sources
PubMed1997

Effect of bed rest immobilization on metabolic turnover of bone and bone mineral density.

Immobilization induces abnormal bone metabolism and severe decalcification of bone. To investigate the effect of middle-term immobilization on bone metabolism, we studied 10 young healthy males and females during bed rest for 20 days. Bone mineral density (BMD) rapidly decreased in both lumbar and metacarpal bones. No bone showed consistent BMD alterations, partial increase and partial decrease, and both lumbar and metacarpal bone showed similar rapid BMD change. Urinary excretion of pyridinoline tended to slightly increase by day 10, and to decline by day 20 (mean +/-SE: 34.2 +/-7.4, 26.3+/-4.6 nmol day-1, respectively). Neither alkaline phosphatase (isoform III) nor tartrate-resistant acid phosphatase, changed, suggesting that in the early stage of immobilization bone matrix in some part might increase or be resorbed without any activation of osteoblast or osteoclast, resulting in rapid calcification or decalcification, respectively.

Absorptiometry, Photon↗
PubMed1997

The effects of 20 days bed rest on serum lipids and lipoprotein concentrations in healthy young subjects.

The effects of 20 days bed rest (BR) on serum lipids and lipoprotein concentrations were investigated in 23 healthy young subjects (13 males and 10 females, aged 19 to 25 yr.). After 20 days BR, VO2max was reduced in both genders, but body composition did not change. The ratio of glucose area to insulin area during an oral glucose tolerance test decreased gradually throughout BR, which suggested a decrease in insulin sensitivity. Estimated changes in plasma volume from the beginning of BR were largest at day 3 of BR (-9.1% in females and -3.4% in males) and seemed to return the initial level at the end of BR in both genders. The increase in serum triglycerides and the decrease in high density lipoprotein (HDL) cholesterol, and apolipoprotein AI were observed in both genders during BR. In a smaller study of 4 males and 5 females, 20 days BR was associated with a decrease in HDL, cholesterol, a decrease in apolipoprotein AI and apolipoprotein AII, decrease in a plasma postheparin lipoprotein lipase activity and an increase in very low density lipoprotein triglyceride. Overall, the data suggested that the decrease in lipoprotein lipase activity and insulin sensitivity may contribute to the impairment in HDL metabolism.

Adult↗
PubMed1996

Myonuclear number and myosin heavy chain expression in rat soleus single muscle fibers after spaceflight.

The effects of 14 days of spaceflight on myonuclear number, fiber size, and myosin heavy chain (MHC) expression in isolated rat soleus muscle fiber segments were studied. Single soleus muscle fibers from rats flown on the Spacelab Life Sciences-2 14-day mission were compared with those from age-matched ground-based control rats by using confocal microscopy and gel electrophoresis. Spaceflight resulted in a significant reduction in the number of fibers expressing type I MHC and an increase in the number of fibers expressing type IIx or IIa MHC. Space-flight also resulted in an increase in the percentage of fibers coexpressing more than one MHC and in the reexpression of the neonatal isoform of MHC in some fibers. Fiber cross-sectional area was significantly reduced in pure type I MHC-expressing fibers and in fibers coexpressing type I+II MHC but not in fibers expressing one or more type II MHC in the flight rats. The number of myonuclei per millimeter was significantly reduced in type I MHC-expressing fibers from the flight rats but was not significantly different in type I+II and type II MHC-coexpressing fibers. Fibers expressing neonatal MHC were similar in size to control fibers but had significantly fewer myonuclei per millimeter than flight fibers not expressing neonatal MHC. In type I MHC-expressing fibers, the reduction in fiber cross-sectional area was greater than the reduction in myonuclear number; thus the average cytoplasmic volume per myonucleus was significantly lower in flight than in control fibers. The reduction in both myonuclear number and fiber size of fibers expressing type I MHC after 14 days of spaceflight supports the hypothesis that changes in the number of myonuclei may be a contributing factor to the reduction in fiber size associated with chronic unloading of the musculature.

Animals↗
PubMed1996

Spaceflight effects on beta-adrenoceptor and metabolic properties in rat plantaris.

Effects of 14 days of spaceflight on beta-adrenoceptor (beta-AR), mitochondrial enzyme activities, and fiber type composition were studied in plantaris muscles of male adult Sprague-Dawley rats. The beta-AR was analyzed in cross sections by quantitative autoradiography. The maximum binding capacity (Bmax) of beta-AR was significantly lowered (approximately 29%) after flight, but the recovery was not completed within 9 days in 1-G environment. Because the dissociation constant remained unchanged, it is suggested that the changes in the Bmax were caused by the alteration of receptor number. The activities of succinate dehydrogenase (SDH) measured in whole homogenates were subnormal (approximately -24%) in muscles sampled approximately 5 h after flight but they were normalized during 9 days of recovery. The percent composition of fiber types and beta-hydroxyacyl CoA dehydrogenase (HAD) activity did not change significantly due to spaceflight. It is suggested that the spaceflight-induced decrease of the Bmax of beta-AR in plantaris was accompanied by a lowered activity of a mitochondrial inner-membrane enzyme SDH but not a matrix enzyme HAD.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1996

Influence of spaceflight on succinate dehydrogenase activity and soma size of rat ventral horn neurons.

Succinate dehydrogenase (SDH) activities and soma cross-sectional areas (CSA) of neurons in the dorsolateral region of the ventral horn at the L5 segmental level of the spinal cord in the rat were determined after 14 days of spaceflight and after 9 days of recovery on earth. The results were compared to those in age-matched ground-based control rats. Spinal cords were quick-frozen, and the SDH activity and CSA of a sample of neurons with a visible nucleus were determined using a digitizer and a computer-assisted image analysis system. An inverse relationship between CSA and SDH activity of neurons was observed in all groups of rats. No change in mean CSA or mean SDH activity or in the size distribution of neurons was observed following spaceflight or recovery. However, there was a selective decrease in the SDH activity of neurons with soma CSA between 500 and 800 microns2 in the flight rats, and this effect persisted for at least 9 days following return to 1 g. It remains to be determined whether the selected population of motoneurons or the specific motor pools affected by spaceflight may be restricted to specific muscles.

Animals↗
PubMed1995

Imaginary gaze effects on eye movements induced by linear acceleration: involvement of vestibular induced smooth pursuit eye movement.

We investigated smooth eye movements elicited i) by linear acceleration in a space-fixed imaginary gaze condition (smooth component of eye movement induced by linear motion: LSEM) and ii) during acoustic pursuit of a moving sound source (smooth component of eye movement induced by acoustic pursuit of a sound source: SSPEM). The two conditions were examined using the same test subjects. LSEM and SSPEM performance was found to be positively correlated across the subject population. From the comparison of LSEM and SSPEM we propose the following hypothesis: LSEM consists not only of a pure translational vestibular-ocular reflex (tVOR) component but also of a component based on the perception of otolithic information. Accordingly, this second component is instrumental in the pursuit of an imaginary visual target during linear self-motion.

Acceleration↗
PubMed1994

Visual otolith-ocular reflex in normal subjects. A preliminary report.

The influence of the otolith-ocular reflex (OOR) induced by the linear (along Y-axis) acceleration was evaluated 12 healthy subjects. The elicited maximum eye velocity (MV) was comparatively analyzed under three stimulus conditions; (1) sinusoidal linear acceleration with eyes covered, (2) sinusoidal optokinetic stimulus and (3) sinusoidal linear acceleration with eyes open (visual-vestibular interaction). By the linear acceleration level of 78 cm2, i.e. 0.08 G, the MV of the optokinetic response (OKR) showed no change in spite of the existence of the OOR.

Acceleration↗
PubMed1994

Effect of head up tilt on cerebral circulation.

This study was performed to study the effect of the head up tilt (HUT) on cerebral circulation across the time course (60 degrees HUT for 15 minutes) and across the different angles of HUT (15, 30, 45, 60 degrees HUT for 15 minutes). Cerebral circulation was continuously monitored during 15 minutes of HUT by the carotid Doppler flow meter, the transcranial Doppler flow meter, and the near infra-red spectrophotometer. The results show that the cerebral blood flow decreased during HUT and that the cerebral blood volume decreased initially and then gradually increased. And the magnitude of the effect may have the relationship with the angles of the HUT.

Blood Pressure↗
PubMed1994

Individual differences of cerebrovascular responses to gravitational stress--prediction of orthostatic intolerance.

This experiment was designed to investigate the individual differences in the cerebrovascular responses to orthostatic stress. Seven male volunteers were exposed to head-up tilt (HUT) at 60 degrees for 15 min and to lower body negative pressure (LBNP) at 30 mmHg for 25 min. We measured the flow velocity of the middle cerebral artery and the quantity of the oxygenated and deoxygenated hemoglobin (oxy-Hb and deoxy-Hb) in the brain. Based upon oxy-Hb change during exposure to HUT, we classified the subjects into two groups: 1) the "good responder" group in which the oxy-Hb gradually increased from the 5th to 10th minute of HUT; 2) the "bad responder" group in which the oxy-Hb stabilized at lower levels after the initial decrease. The oxy-Hb changes between the two groups were significantly different during exposure to LBNP. During exposure to HUT and LBNP, no significant difference was observed in blood pressure and heart rate between the two groups. Our results suggest that there might be an individual difference in the cerebrovascular responses to orthostatic stress.

Adult↗
PubMed1994

Astronaut psychiatric selection procedures: a Japanese experience.

This paper presents the results of the first application of a structured NASA psychiatric interview for Japanese astronaut selection. We undertook a semi-structured, diagnostic, clinical psychiatric interview with 45 Japanese astronaut applicants for the position of mission specialist-astronaut, and performed "select-out" psychiatric evaluations according to DSM-III-R psychiatric diagnostic criteria. Two applicants (4.4%) who met Axis I or Axis II disorder criteria in DSM-III-R were evaluated as "Disqualified." There were 13 applicants "Qualified with Reservation"; the majority of their diagnoses were "hypomania." Those applicants "Qualified with Reservation" and "Disqualified" were not finally selected to be astronauts. This structured interview was not only useful for "select-out" psychiatric screening of Japanese astronauts, but also made clear the Japanese characteristics of this selection procedure.

Adult↗
PubMed1994

Psychological evaluation of Japanese astronaut applicants.

In 1991, a new psychological selection procedure was employed during the selection of Japanese Space Station astronauts. It was based on international selection criteria developed by an international psychological/psychiatric working group. A total of 372 individuals--fewer than expected--submitted applications for Space Station astronaut in Japan. Of the applicants, 233 were given several psychological written tests [Anxiety Scale, Performance Test, General Aptitude Test Battery, and Environmental Adjustment Test Battery (EATB)] in Phase I of the selection. Forty-five applicants went on to take the General Aptitude Test Battery (GATB), Human Assessment Method (a group test), a semi-structured psychological interview and an intelligence test in Phase II of the selection. All applicants were found to be highly intelligent. Interestingly, an unexpectedly large number of candidates were disqualified by the newly developed EATB. Assessment of individual functioning in a group (the Human Assessment Method) resulted in no applicant being ranked in either the "qualified with reservation" (QR) or "disqualified" (DQ) category. Much has been learned from this initial application of psychological "select-in" testing, but further efforts are needed to improve both psychological criteria and evaluation methods and to determine their reliability and validity.

Adaptation, Psychological↗
PubMed1994

Issues of health care under weightlessness.

This review will address issues of effects of space flights on the body. Cardiovascular deconditioning often induce symptoms like orthostatic intolerance after flight, and during flight there will be space motion sickness during the first few days with headache, malaise, nausea and eventually vomiting. These symptoms disappear and do not interfere with the performance of the astronauts after several days. During long-term flights, effects will be muscle atrophy and calcium loss from the skeleton. Radiation effects will be a significant issue, increasing with the length of the space flight. Also during long-term flights, psychological problems will become of increasing importance. Astronaut health care will be discussed related to Space Shuttle missions and Space Station missions. Furthermore, countermeasures for long-term space flights (up to 6 months) will be outlined. The NASA health care programme is reviewed, and the frequency of illnesses and injuries encountered in the NASA programme is discussed. There will be a need for setting up an international health care programme in view of the upcoming international cooperation in the Space Station era. It is emphasized that the Space Station is an international platform. Therefore, the health care team will be composed of international personnel, mainly from NASA with participation of Europe, Canada, Russia, and Japan. Specialized medical doctors will form the team and support the crew members from the ground. Some issues, such as medical licensing and responsibility, remain to be solved.

Aerospace Medicine↗
PubMed1993

Effect of transdermally administered scopolamine on the vestibular system in humans.

In order to elucidate the effect of scopolamine on the vestibular system in humans, various experimentally-induced forms of nystagmus, i.e. caloric nystagmus, rotational nystagmus, optokinetic nystagmus, visual-vestibular interaction and optokinetic after nystagmus, were evaluated before and after the administration of two pieces of Scopoderm-TTS or placebo patches retro-auricularly. Scopolamine reduced the responses of both the caloric and optokinetic after nystagmus compared with the placebo. The possible action site of this drug is discussed.

Administration, Cutaneous↗
PubMed1993

Effect of lower body negative pressure on cerebral circulation.

This experiment was performed to study the effects of lower body negative pressure (LBNP) on cerebral circulation. Cerebral hemodynamics were monitored continuously and noninvasively in eight subjects at 30 mmHg of LBNP for 25 minutes by following items: 1) the carotid Doppler flowmeter which measures the carotid blood flow, 2) the transcranial Doppler sonography which measures the flow velocity of the middle cerebral artery, 3) the near infrared spectrophotometer which measures the oxygenated and deoxygenated hemoglobin in the brain. The mean flow velocity of the middle cerebral artery and the blood flow of the common carotid artery significantly decreased during LBNP, even though the mean arterial blood pressure was well maintained. The oxygenated hemoglobin was significantly increased during LBNP, while the deoxygenated hemoglobin was not changed significantly. Our results suggest that exposure to moderate LBNP (30 mmHg) decreased the cerebral blood flow with the vasodilation on the arterial side of the brain.

Adult↗
PubMed1993

Hemodynamic and hormonal correlates with exposure to lower body negative pressure after 12 hours head-down tilt.

Hemodynamic and hormonal responses to lower body negative pressure (LBNP) after 12-h head-down tilt (HDT) were examined to investigate the mechanism of orthostatic intolerance following spaceflight. Ten young healthy male volunteers participated in the experiment. After 6 degrees HDT for 12 h, the tolerance to 1 h continuous -30 mm Hg LBNP was tested. Variables were measured before and after HDT, during LBNP, and 1 and 10 min after LBNP. Significant reduction in leg volume and plasma volume were observed at the end of 12-h HDT (500 ml and 5.5%, respectively). In the tolerant group, stroke volume index (SI) was decreased by 35% after 15 min LBNP, and carotid arterial blood flow (CBF), by 27% at the end of LBNP compared to the pre-LBNP value. Of the 10 subjects, 5 developed presyncope during LBNP; they exhibited remarkable reduction in SI, CBF, and heart rate, and increased secretion of ADH and adrenaline during or just prior to presyncope. This non-tolerant group tended to be hemo-concentrated from the start of the experiment. However, it will require a prospective study to determine if this variable is a reliable predictor of the outcome of the post-HDT LBNP test from data collected at the end of HDT.

Adaptation, Physiological↗
PubMed1991

Breast cancer developing after chemotherapy for osteosarcoma: a case report.

A 24-year-old patient who developed breast cancer 16 years after chemotherapy for osteosarcoma is presented. She had no family history of cancer. She had also not had radiotherapy. She had been given chemotherapy consisting of VAOMT (vincristine 10.2 mg, cyclophosphamide 900 mg, mitomycin C 15.2 mg, chromomycin A3 25.8 mg) pre- and post-operatively in the treatment of her osteosarcoma. Careful long-term follow-up is required after treatment of malignant neoplasms because there is a possibility of developing a second malignancy.

Adult↗
PubMed1988

Protective action of a calcium antagonist, nilvadipine, against aortic calcium deposition--a pathogenic factor in atherosclerosis.

Nilvadipine and other calcium antagonists were studied for their effect on 1-alpha-hydroxyvitamin D3 (1 - alpha (OH)D3)-induced aortic calcium deposition in rats. The animals were treated orally with 1-alpha (OH)D3 (10 micrograms/kg) for 2 weeks. Calcium antagonists were given orally twice a day during the same period. The aortic calcium content in 1-alpha (OH)D3-treated rats increased to about 100 times that in the control. Nilvadipine reduced the aortic calcium deposition dose-dependently, with percent inhibition of 6, 43, 72 and 92%, at doses of 0.1, 1, 10 and 100 mg/kg, respectively. Similar activities were obtained for the other calcium antagonists except diltiazem which had no effect even at the largest dose of 100 mg/kg. According to the ED50 values, nilvadipine (2.2 mg/kg) was more potent than nifedipine (23.2 mg/kg), nicardipine (12.4 mg/kg) and verapamil (32.0 mg/kg). Scanning and transmission electron microscopy showed clear-cut degenerative changes in the endothelial cells after 1-alpha (OH)D3 treatment. Nilvadipine exerted a protective effect against these degenerative changes but not against 1-alpha (OH)D3-induced hypercalcemia. Furthermore, the drug had only minimal effect on in vitro calcification of the aorta. Our findings suggest that nilvadipine inhibits aortic calcification by protecting the aortic wall cells.

Animals↗