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H Saiki

Publications and source records attributed to H Saiki.

44 records · Page 3Linked to original sources
PubMed1979

Changes in enzymes and potassium content of the neuromuscular systems of albino rats during prolonged exposure to simulated hypogravics.

With respect to neuromuscular function, aldosterone activity, enzymatic and potassium (K) metabolism of organ tissues were investigated during the stress and adaptation stabilized phases of hypodynamically stressed rats. During adaptation, muscle tissue enzymes, such as aldolase, showed no change until the 35th day. The decrease of succinic dehydrogenase (SDH) was evident at 7 days. Lactic dehydrogenase (LDH) and creatine phosphokinase (CPK) serum levels increased transiently on the 18th day; this implied the development of muscular atrophy. A decrease in the 42K uptake of muscle was found from the 18th day onward. In the brain, a progressive decrease of aldolase was observed. 42K uptake showed no change in the brain, but the K content increased at both 7 and 18 days of exposure. The increase of cholinesterase (ChE) was more remarkable in the brain than in muscle, although transient. We suggest that the brain plays an important part in the adaptation process, through increasing or maintaining the functions of the neuromuscular excitation system during the 7-18 days of hypodynamic exposure.

Adaptation, Physiological↗
PubMed1977

Dynamics of sleep patterns during prolonged simulated weightlessness.

Subjects immersed for 6 days in water, simulating weightlessness, exhibited marked changes in the total time spent in sleep and in the percentage of that time spent in each sleep stage. The length of time spent in Stage 4 deep sleep and in REM sleep decreased in the first half of the 6-day immersion period. During the latter half of the immersion period, a clear adaptive response was observed in the sleep patterns: the sequential appearance of the different stages of sleep and the percentage of time spent in the six stages of sleep showed a clear approach to the pre-immersion data. During the 3-day post-immersion period, the patterns approached the normal pre-immersion levels, although there was some overshoot or a negative phase period characterizing this approach. By the sixth day of immersion, the percentage of time spent in each stage of sleep had returned to near normal pre-immersion values, but the total time spent in sleep was still somewhat less than normal. This fact suggests that, once adapted to a condition of weightlessness, the sleep requirement may be less than during normal ambulatory life. During the post-immersion period, the pattern of Stage 4 sleep at early evening, midnight and dawn showed no special reactive characteristics, but rather a clear recovery towards the original pattern. On the other hand, at the duration of REM sleep, it overshot the pre-immersion values at the beginning of the post-immersion period, and then returned to the original pattern. These experiments suggest that some of the changes in sleep patterns which are observed under conditions simulating weightlessness may be adaptive.

Adaptation, Physiological↗
PubMed1976

Metabolic and hormonal mechanisms of mineral metabolic adaptation to induced hypokinetics in rats.

During simulated hypokinetics, many biological functions have a tendency to stabilize at different levels with the passing of time. In this experiment, hypokinetic exposure was induced in albino rats by the suspension method for 5 weeks. A new plateau in urinary K+ excretion was attained during the third week, after a transient decrease during the first week. Since the formation of this steady plateau is considered a manifestation of the adaptation of this function, the hypokinetic exposure period was divided into a prestabilized phase and a stabilized phase. To ascertain the biochemical mechanisms of this adaptation process, the effects of aldosterone and anti-aldosterone substances (e.g., tetracycline) on K+ and Na+ excretion patterns in each phase were investigated. Decreasing aldosterone activity in the prestabilized phase and increasing activity in the stabilized phase are recognized as one of the main factors in the renal adaptation process to hypokinetics.

Adaptation, Physiological↗
PubMedDate not supplied

Effect of physical fitness and training on physiological responses to hypogravity.

The studies on the orthostatic tolerance during the hypodynamics exposure seem to be significant in connection with the selection, training and health maintenance of astronauts. Using male human subjects of various physical fitness levels, fluctuations of their physical fitness through 2 weeks of vigorous athletic training were measured in many parameters. For some of the subjects, the effects of 6 hr thermal neutral water immersion exposure in head out supine position on the physical fitness parameters and orthostatic tolerability were compared before training with after training. The results obtained were as follows: (1) Before training, orthostatic tolerability before hypodynamics exposure increased, following the physical fitness levels; the value after the hypodynamics exposure decreased in all the cases, but no differences were observed between the physical fitness levels. (2) As a result of training an increase of the physical fitness capacity was observed. The increase of orthostatic tolerability before hypodynamics exposure was noticed except for athletes. (3) Before hypodynamics exposure the urinary excretion of noradrenaline on non-athlete subjects increased as the physicsl fitness level increased. The values were decreased by physical training, the more so the better the physical fitness. After hypodynamics exposure the same relation was observed. But for athletes the values remain more stable and the decrease by hypodynamics exposure was not so distinctive. Such decreased reaction to hypodynamic conditions seems to reveal the neuro hormonal mechanism for the detrimental adaptation of athletes to hypodynamics. These results suggest that stable athletes do not always have low orthostatic tolerability, but do not respond well to hypodynamic conditions, at least from the orthostatic point of view. The mechanism seems related to sympathetic nerve activity.

Adolescent↗