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PubMed2001

Influence of vestibulo-sympathetic reflex on muscle sympathetic outflow during head-down tilt.

To clarify the response of muscle sympathetic nerve activity (MSNA) to static stimulation of otolith organs in a craniocaudal direction (+Gz) in humans, we examined the effect of otolith stimulation on MSNA without changing the effect of cardiopulmonary baroreceptors using a 6-8.5 degrees head-down tilt (HDT) and lower body negative pressure (LBNP) device. Before the study, we established that 6-8.5 degrees HDT with 10 mmHg LBNP caused a fluid shift to the degree that the thoracic impedance was the same as the supine position without LBNP. Subjects were young male volunteers aged 22.1 +/- 3.8 years who gave informed consent. MSNA was recorded from the tibial nerve by microneurography simultaneously with heart rate (ECG), thoracic fluid volume (impedance method), and blood pressure (tonometric method). During 6-8.5 degrees HDT with 10 mmHg LBNP, MSNA was suppressed slightly without significantly changing heart rate, thoracic impedance, or mean arterial blood pressure. The results suggest that the sympathosuppression was related not to the result of cardiopulmonary [correction of cardioplumonary] loading but to the -Gz change (caudocranial direction [correction of dirction]) of 0.1 G. It is estimated that the vestibulo-sympathetic reflex may suppress sympathetic outflow to muscles in humans.

Adult↗
PubMed2001

Effect of spaceflight on isoflavonoid accumulation in etiolated soybean seedlings.

In order to explore the potential impact of microgravity on flavonoid biosynthesis, we examined isoflavonoid levels in soybean (Glycine max) tissues generated under both spaceflight and clinorotation conditions. A 6-day Space Shuttle-based microgravity exposure resulted in enhanced accumulation of isoflavone glycosides (daidzin, 6"-O-malonyl-7-O-glucosyl daidzein, genistin, 6"-O-malonyl-7-O-glucosyl genistein) in hypocotyl and root tissues, but reduced levels in cotyledons (relative to 1g controls on Earth). Soybean seedlings grown on a horizontally rotating clinostat for 3, 4 and 5 days exhibited (relative to a vertical clinorotation control) an isoflavonoid accumulation pattern similar to the space-grown tissues. Elevated isoflavonoid levels attributable to the clinorotation treatment were transient, with the greatest increase observed in the three-day-treated tissues and smaller increases in the four- and five-day-treated tissues. Differences between stresses presented by spaceflight and clinorotation and the resulting biochemical adaptations are discussed, as is whether the increase in isoflavonoid concentrations were due to differential rates of development under the "gravity" treatments employed. Results suggest that spaceflight exposure does not impair isoflavonoid accumulation in developing soybean tissues and that isoflavonoids respond positively to microgravity as a biochemical strategy of adaptation.

Adaptation, Physiological↗
PubMed2001

Indomethacin attenuates post-suspension hypotension in Sprague-Dawley rats.

Orthostatic hypotension is a serious condition that is sometimes manifested in astronauts during standing postflight. These observations may be related to impairment of autonomic function and/or excessive production of endothelium-dependent relaxing factors. To evaluate the role of the cyclooxygenase inhibitor indomethacin as a countermeasure against the post-suspension reduction in mean arterial pressure (MAP), we examined the cardiovascular responses to 7-day 30 degrees tail-suspension and a subsequent 6-hr post-suspension period in conscious male Sprague-Dawley rats. Indomethacin (2 mg/kg) or saline were administered intravenously prior to release from suspension and at 2 and 4 hrs post-suspension. Direct MAP and heart rate were determined prior to suspension, daily and every 2 hrs post-suspension. During suspension, MAP did not change, in contrast, during post-suspension; it decreased compared to parallel non-suspended, untreated animals. There were no significant changes in heart rate. The reduction in MAP post-suspension was associated with significant increases in plasma prostacyclin. Indomethacin attenuated the observed post-suspension reduction in MAP and reduced plasma prostacyclin levels. Also, the baroreflex sensitivity for heart rate was modified by indomethacin--the MAP threshold for baroreflex activation was raised and the effective MAP range expanded. Thus, the post suspension reduction in mean arterial pressure may be due to overproduction of vasodilatory prostaglandins and/or other endothelium-dependent relaxing factors and alteration in baroreflex activity.

Animals↗
PubMed2002

[Preliminary study on protecting effect of two kinds of Chinese medical herbs on changes of three physiology systems in suspended rats].

Objective. To observe the protecting effect of two kinds of Chinese medical herbs on changes of blood circulation, muscle and skeletal systems in tail suspended rats. Method. Changes of blood circulation, muscle and skeletal systems in tail suspended rats (n=15), Chinese medical herb group 1 (n=15) and Chinese medical herb group 2 (n=15) after 30 d tail suspension were compared with those in control group rats (n=15). Result. Two kinds of Chinese medical herbs have obvious effect on improving the condition of blood circulation, and have some effects on improving the muscle and skeletal systems in tail suspended rats. Conclusion. Chinese medical herbs have a good prospect of being used in space flight, and further studies are needed.

Animals↗
PubMed2002

[Decrease in tetanic tension in 4-week tail-suspended rat soleus and analysis of its underlying mechanisms].

Objective. To observe the dynamic changes in tetanic tension in 4-week tail-suspended rat soleus (SOL) and extensor digitorum longus muscle (EDL) and to elucidate its underlying mechanisms. Method. After 4 weeks of tail suspension SOL and EDL of the rats were isolated and perfused. Their isometric twitch and tetanic tensions were recorded. Result. Atrophy occurred in the SOL, but not in the EDL. The maximum twitch tension (Pt) decreased significantly and was more dependent on stimulation voltage in SOL of tail-suspended rat. Time to maximum twitch tension (TPT) and time from maximum twitch tension to half relaxation (TR50) were reduced in the SOL. Pt also decreased in the EDL, but TPT and TR50 did not change in the EDL. The maximum tetanic tension reduced in SOL and EDL of tail-suspended rats. The decline rate of tetanic tension in SOL was faster than the control. The profile of tetanic contraction curve in atrophic SOL approached that in EDL. Conclusion. The above results suggested that the underlying mechanisms of reduced maximum twitch and tetanic tension in 4-week tail-suspended rat SOL may involve the reduction in number of cross-bridge per cross-section area or force produced per cross-bridge. The rapid decline rate in atrophic SOL may be related to the shift in myosin heavy chain and troponin I isoforms or to decrease in excitability.

Animals↗
PubMed2002

[Two types of event-related brain slow potentials in auditory location discrimination (correction of dicrimination) task].

Objective. To study the difference between two types of event-related brain potentials (ERPs) in auditory location discrimination task. Method. Event-related potentials (ERPs) in auditory location discrimination task were recorded in 14 normal subjects and were compared with head-down tilt (HDT) and head-up tilt (HUT) conditions. Result. 1) The subjects could be divided into group I (n=7) and group II (n =7) according to the feature of the target ERPs component (P3). The difference between the two groups was mainly that there was a negative slow wave after 150 ms in the ERPs of group II subjects, and that the reaction time and error rate in II group was higher than in I group. These data indicated that the psychological load on group II was larger than that on group I. 2) The reduction of mean slow potential amplitude during HDT was more significant in group II than in group I. Conclusion. The slow potential amplitude of ERPs may reflect the psychological load and the brain function state. Attention should be paid to the feature of auditory ERPs in space medical practice.

Acoustic Stimulation↗
PubMed1999

[Countermeasuring effect of lower body negative pressure against orthostatic intolerance induced by 21 d -6 degrees head down tilt in humans].

Objective. To investigate whether LBNP during 21 d -6 degrees head-down tilt (HDT) would modify orthostatic tolerance. Method. 12 healthy males, age 23.7 +/- 5.0, were exposed to -6 degrees HDT for 21 d. 6 of them received -4.0 kPa LBNP sessions for 1 h/d from 15th day to 21st day of HDT. The other 6 served as control. HUT + 75 degrees, 20 min orthostatic tolerance test were done before, on day 10 and on day 21 of HDT. Result. During HUT + 75 degrees, 20 min orthostatic tolerance test on day 10 of HDT, 5 subjects of the control group and 4 of the LBNP group presented presyncopal or syncopal signs and symptoms, the average standing time of both groups were shorter than those of the pre-HDT (p<0.05). During HUT + 75 degrees, 20 min orthostatic tolerance test on day 21 of HDT, 5 subjects of the control group and one subject of the LBNP group presented presyncopal or syncopal signs and symptoms, the average standing time of control group reduced significantly as compared with those of pre-HDT(P<0.05), also significantly shorter than those of LBNP group (P<0.05). Conclusion. The present study clearly shows that the use of LBNP could alleviate the bed rest-induced orthostatic intolerance.

Adult↗
PubMed1999

[Effects of 7 d head down tilt on cardiopulmonary circulation during orthostasis].

Objective. To accumulate data for further studies on the mechanisms of the decrease of cardiovascular function after weightlessness. Method. Cardiopulmonary circulatory function under supine position and head up tilting (HUT) for 20 min before and after exposure to 7 d 6 degrees head down tilt (HDT) in 6 healthy adults who aged 19-21 were measured with a XXH-2000 lesser (pulmonary) circulation and cardiac function instrument. Result. The 7 d HDT resulted in orthostatic intolerance of the subjects; the reduction of RVET (j-z) and the elevation of RPEP [RVET(Q-j)/(j - z)] indicated a decrease of the right heart function. An obvious decrease of the right heart reserves was also observed under HUT after HDT. Conclusion. hc and hc/hz were demonstrated to be useful parameters to evaluate orthostatic tolerance or to forecast orthostatic syncope. The lesser (pulmonary) circulation and cardiac function testing methods are valuable in evaluating the cardiopulmonary circulatory function during HUT.

Adult↗
PubMed1999

[Effects of 24 h -6 degrees head-down tilt bed-rest on cardiovascular function and response to orthostatic stress].

Objective. To investigate the effects of 24 h -6 degrees head-down tilt bed-rest (HDT) on cardiovascular function and response to orthostatic stress. Method. -6 degrees head-down tilt bed rest for 24 h in 6 healthy males, aged 22-23, were observed. The changes of cardiac function were observed by electrical impedance instrument before and at 0th, 6th, 12th, 18th and 24th hour of HDT, and blood pressure were recorded and urine were collected. The changes of cardiovascular response to head up tilt (HUT 90 degrees, 10 min) before and post HDT were recorded. Result. During HDT, HR reduced significantly than that of pre-HDT (standing). HR at 6th, 12th, and 18th hour of HDT reduced significantly than that at 0th hour of HDT. Stroke output (SO) and stroke index (SI) [correction of CI] at 0th, 6th, 12th, and 24th hour of HDT were higher than pre-HDT value. Cardiac output (CO) and cardiac index (CI) at 18th hour of HDT were significantly lower than those at 0 h of HDT. Total peripheral resistance (TPR) at 18th hour of HDT were higher than that at 0th of HDT. During HUT before and post HDT, HR, MBP, TPR were significantly increased, SO, [correction of SV] SI, CO and CI were significantly reduced. DBP were significantly increased and PP were reduced significantly during HUT post-HDT. Hourly average value of urine during 0-4 h were higher than those during 4-12 h and 12-24 h. Conclusion. 24 h -6 degrees head-down tilt bed rest has significant effects on cardiovascular function and response to HUT in humans.

Adaptation, Physiological↗
PubMed2002

[Research progress [correction of progresses] of cell culture apparatus].

Cell culture apparatus (CCA) is necessary to space medicine research and space life-science research. With development of technology, CCA has been fully developed. Nowadays, CCA has been used in scientific research and production widely. In addition, space cell culture apparatus has become an indispensable tool in correlative space research. In this paper, a variety of apparatus used on ground and in space are summarized.

Aerospace Medicine↗
PubMed2002

Effect of head-out water immersion on neuromuscular function of the plantarflexor muscles.

INTRODUCTION: Electromyograms (EMGs) recorded during head-out immersion have demonstrated reduced signal amplitudes and decreased EMG/force ratios for both maximal and submaximal isometric contractions compared with measurements on dry land. Similar EMG changes have been found in spaceflight. HYPOTHESIS: This study was designed to examine neuromuscular function in the legs during immersion with special reference to reflex sensitivity. METHODS: Recordings were made during plantarflexion in air and water. EMGs were recorded from surface and/or internal electrodes on the soleus (SOL) and medial gastrocnemius (MG) muscles during maximal voluntary contraction (MVC). Hoffman and Achilles tendon reflexes were measured during submaximal plantarflexion (50% MVC) in air and water. RESULTS: During immersion, MVC decreased 13% while EMG amplitude of the plantarflexor muscles decreased by 29% and 35% for SOL and MG, respectively. A similar trend was observed in measurements of Hofman and Achilles tendon reflexes. CONCLUSIONS: Head-out immersion induced a deterioration of neuromuscular function, perhaps by triggering inhibitory mechanisms. The origin of these mechanisms seems to be related mainly to effects of partial weightlessness, but hydrostatic pressure should also be considered.

Adult↗
PubMed1997

Effect of bisphosphonate administration on the excretion of stress hormones in tail-suspended rats.

We demonstrated that administration of a bisphosphonate, YH529, prevents the development of disuse atrophy of the hind limbs induced by tail-suspension in rats. Since tail suspension is accompanied by an increase in the secretion of stress hormones, we studied whether administration of bisphosphonate affects the secretion of stress hormones during that procedure. Tail suspension was carried out in a metabolic cage by connecting a wire inserted through tail bone to the ceiling of the cage. The control rat received the same treatment but was not suspended. YH529 or a vehicle (PBS=phosphate buffered saline) was administered daily starting 3 days before the commencement of tail suspension. Urine samples were collected before the wire was inserted (day 0), on the day of insertion (day 1) and 3, 5 and 7 days after. In the control rats receiving PBS, urinary excretion of corticosterone and epinephrine did not change throughout the 7-day experimental period. In the control rats receiving YH529, urinary excretion of corticosterone increased significantly on the day of tail-piercing and wiring but then returned to the prior level. This increase was not observed in the control group receiving PBS. In the tail suspended rats, excretion of corticosterone and epinephrine increased significantly in both PBS and YH529 groups, the highest level being observed on the first day of tail suspension. Although statistically not significant, corticosterone excretion on day 1 of tail suspension was higher in the YH529 groups than that in the PBS group. It is thus suggested that administration of YH529 causes an augmented response to stress load.

Animals↗
PubMed1997

Administration of bisphosphonate prevents disuse bone atrophy induced by tail suspension.

We recently demonstrated that osteopenia induced by rat tail-suspension was associated with an initial increase in bone resorption. To study the significance of the increase in early bone resorption for osteopenia, we investigated whether administration of YH529, a third-generation bisphosphonate, prevents the development of osteopenia as evidenced by increased wet weight of the femur, together with its calcium and phosphorus contents, when compared with those of tail-suspended rats treated with the vehicle alone. These results suggested that the initial increase in bone resorption plays an important role in the development of osteopenia induced by tail suspension.

Animals↗