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At least 847 records · Page 47Linked to original sources
PubMedDate not supplied

[Energy-metabolism enzymes during combined exposure of the body to simulated weightlessness and gravitational overloads].

Exposure to simulated weightlessness (7-day water immersion and 7-day head-down tilt) caused a decrease in the activity of malate (MDH) and isocitrate dehydrogenase (ICDH), and creatine phosphokinase dehydrogenase (ICDH), and creatine phosphokinase (CPK) at the expense of its MM isoform whereas the activity of alanine (ALT) and aspartate aminotransferase (AST) and pattern of distribution of MDH isoforms remained unchanged. Exposure to acceleration of +3 Gz before and after simulated weightlessness revealed similar changes in the activity of MDH, ICDH, ALT, AST and MDH cytoplasmic fractions. However, the higher increase in the enzyme activity after simulated weightlessness may give evidence for a greater change in cell membrane permeability during acceleration effects that followed simulated weightlessness.

Bed Rest↗
PubMedDate not supplied

[Modeling of human movements under conditions of varying gravitational force].

The control of man's movements during adaptation to an altered gravity field was modelled by mathematical methods. Two types of movements were investigated: forearm displacements with various loads and repulsions from a support in zero-g and at high g's. It has been shown that movement coordination in altered gravity fields can be maintained due to a rearrangement of the control over muscle contraction which includes changes in the amplitude and pattern of joint momenta in harmony with the gravity changes.

Gravitation↗
PubMedDate not supplied

[Effect of weightlessness and an artificial gravitational force on the ion-regulating function of the kidney in rats].

Weightless rats showed greater changes in the fluidelectrolyte metabolism and ion regulatory function of the kidneys than centrifuged rats. During water loads they exhibited an increased sodium excretion. During potassium loads they displayed a higher potassium excretion. The study of electrolyte composition of different kidney segments demonstrated a reduced potassium content in the wet cortical and medullary matter due to elevated tissue hydration. Kidney microdissection did not reveal any structural differences in nephrons of the weightless and centrifuged rats.

Animals↗
PubMed1980

[Vascular-neurocytic interrelations in the ganglionic layer of the dog retina exposed to gravitational overloading].

By means of anatomical and histological methods and a morphometric analysis, microcirculatory vessels of the reticular ganglionary layer in the dog eye were studied within Scharrer's zone with special reference to the reciprocal arrangement of the vessels and opticoganglionary cells under normal conditions and at overloadings (9 units for 10 min) applied in the direction head--pelvis (I series) and pelvis--head (II series). It was stated that immediately after the overloading in the direction head--pelvis the microcirculatory vessels grew narrow and the area of the vascular-neurocytic contacts decreased. At the overloading applied in the direction pelvis--head, the diameter of the vascular-neurocytic contacts sharply increased. In both series of the experiment the vessels became deformed and twisted and the vascular wall permeability was disturbed.

Animals↗
PubMedDate not supplied

[Effect of simulated gravitational loading on chick embryo myocardium].

Daily centrifugation of 5--8-day embryos at 7 G for 20 min by means of a specially designed attachment to dlHP-1 decreased the amplitude and increased the rate of rhythmic activity of ventricular myocytes, the automatic activity of atrial pacemakers remaining unaltered. These changes were accompanied by a decrease of Ca2+-sensitivity of myocytes. Daily centrifugation of 11--20-day chick embryos led to myocardial hypertrophy and increase in the diameter of myocardiocytes as well as to decrease in the content of actin, troponin-T and the second light chain of myosin, increase in the content of tropomyosin and emergence of the third light chain of myosin in the electrophoregrams. It appears that the changes in the composition of protein subunits of the contractile system are induced by selective activation of proteolytic enzymes in the muscle tissue.

Animals↗
PubMed1980

[Directional sensitivity of neurons of the cercal system of crickets in different body positions in a gravitational field].

The giant interneurons in the terminal abdominal ganglion of cricket (Acheta domesticus) were studied using sound signals with special interest to the effect of the body tilt on the directional sensitivity diagrams. The neurons under study receive their inputs from the cerci which have receptors sensitive to mechanic and acoustic stimulation and receptors sensitive to the cricket orientation in the gravity field. Directional sensitivity diagrams of the neurons were estimated by counting the numbers of impulses in their responses to sound signals of various directions for various body tilt. A detailed experimental investigation and corresponding calculation have demonstrated that the sound directional sensitivity diagrams of the neurons always turn as being fixed to the body when the cricket is tilted. This result indicates that cercal gravity receptors do not exert any specific influence on directional sensitivity of the abdominal ganglion neurons.

Acoustic Stimulation↗
PubMedDate not supplied

[The role of gravitational tidal changes in regulating the systemic response of circulation and respiration to orthostasis].

The transient reply parameters of passive postural changes (lying-sitting) were evaluated. The most important 8 variables of circulation and respiration were analysed during 20-30 min of orthostatic test. The findings were based on 552 tests performed on 237 volunteers. It was shown that the adaptation of a human organism to the postural hydrostatic factor is formed by the systemic cooperation of circulation and respiration like a hydraulic homeostat. Influence of some physical factors (physiotherapy) changed this cooperation. The same data is discovered in orthostatic responses as a result of the different phases of lunar-semidiurnal gravity waves. That confirmed the gravity tidal variations have influence on human regulation systems.

Adolescent↗
PubMedDate not supplied

[Effect of gravitational tidal changes on the periodicity of T-lymphocyte receptor expression in vitro].

The hourly registration of the expression of the human s T-lymphocytes subpopulations receptors in vitro during 6 hours demonstrated the existence of the periodicity from 2 to 4 hours. There is high degree of T-lymphocytes expressions coincidence from different individuals depending of the date. For most of daily average individual chronograms, there were described back linear and valid correlations with a character of heterogeneity of the gravity force changes. The results are in according to suggestion about the time field geometric effect to structural-functional cells periodicity.

Adolescent↗
PubMed1994

[The interaction of vestibular inputs with differing orientations of the otoliths in a gravitational field].

In alert pigeons Columba livia effects of static tilts about fore-aft and binaural axes (angles of tilts: 30-40 deg) on neck and ocular nystagmus elicited by monaural galvanic stimulation of the lateral semicircular canals with sinusoidal currents (peak amplitudes: 20-100 microA; period: 35 sec) were investigated. It was shown that the same angles of the tilts elicited different changes of horizontal nystagmus parameters in different animals. In some of them changes of quantitative characteristics of opposite-directed nystagmus differed with signs. Data support the correctness of recently (Stolbkov, 1989) proposed scheme of forming vestibulomotor reactions, according to which signals from heterolateral vestibular nuclei, during nystagmus, which are integrated, contain both canal and otolith components independent of stimulus mode addressed to canals or otoliths (separately or jointly). Results suggest also that caloric test may be a source of incorrect conclusions concerning state of vestibular system during static tilts the responses of functionally asymmetric semicircular canals may be symmetric ones. Moreover data suggest that sensitivity of convergent vestibular neurons to the canal signals is different depending on separated or combined canal and otolith stimulations.

Animals↗