Activity of the sympathetic-adrenomedullary system in rats after space flight on the Cosmos biosatellites.

The indicators of adrenomedullary activity (catecholamine content (CA) and the activity of the catecholamine-synthesizing enzymes tyrosine hydrozylase (TH) and dopamine-beta-hydrozylase (DBH) were measured in the adrenal glands of rats living in a state of weightlessness for 18.5-19.5 days on board the biosatellites COSMOS 936 and COSMOS 1129. None of these indicators was significantly changed by space flight, neither in the group living in a state of weightlessness nor in the group living in a centrifuge on board the spacecraft and exposed to artificial gravity of 1 g (COSMOS 936). Animals exposed after space flight to repeated immobilization stress on Earth showed a significant decrease of adrenal adrenaline and an appreciable increase in adrenal TH activity compared to stressed animals which were not in space. These results suggest that a prolonged state of weightlessness during space flight does not by itself represent an intensive stressful stimulus for the adrenomedullary system but potentiates the response of cosmonauts to stress after return to Earth.

The effect of artificial gravity on plasma and tissue lipids in rats: the Cosmos 936 experiment.

Plasma and tissue lipids in male SPF Wistar rats flown for 18.5 days aboard the Cosmos 936 biosatellite were analyzed. One group of rats was subjected to artificial gravity by use of a centrifuge during the flight. An experiment simulating known space flight factors other than weightlessness was done on Earth. An increase of total cholesterol in plasma, of nonesterified fatty acids in plasma and brown adipose tissue, of triacylglycerols in plasma, liver, thymus and bone marrow was noted several hours after biosatellite landing. Smaller changes were observed in the terrestrial control experiment. With the exception of triacylglycerol accumulation in bone marrow, these increases disappeared 25 days after biosatellite landing. Exposing the rats aboard the biosatellite to artificial gravity was beneficial in the sense that such exposure inhibited the phospholipid and triacylglycerol increase in plasma and inhibited the increase of triacylglycerol in liver and especially in bone marrow.

Metabolic changes in rats subjected to space flight for 18.5 days in the biosatellite Cosmos 936.

From an investigation of the activity of six glucocorticoid dependent liver enzymes, the existence of chronic, transient, stress-induced hypercorticosteronaemia during flight is probable. This hypercorticosteronaemia arises from weightlessness and induces gluconeogenesis. Weightlessness also caused substantial increases in liver glycogen level. The increased lipolytic activity and that of lipoprotein lipase in several groups of animals could be interpreted as enhancement of fat mobilization and utilization under the influence of stress. As this latter enhancement was also found in ground-based controls, it may have been due to the stress of handling rather than to space flight per se.

Changes of deoxyribonucleoprotein in the spleen, thymus and liver of rats exposed to weightlessness and artificial gravity aboard the Cosmos biosatellites.

Changes of deoxyribonucleoprotein in the spleen, thymus and liver of rats exposed to weightlessness or artificial gravity on board biosatellites Cosmos 782 and Cosmos 936 after 20 days of flight were investigated. The level of polydeoxyribonucleotides in the spleen and thymus of rats exposed during the flight to weightlessness increased 4-11 hours after landing, suggesting breakdown of a part of the deoxyribonucleoprotein present. The use of artificial gravity prevented this breakdown in the thymus but not in the spleen. The breakdown was accompanied in the majority of cases by a decrease in the deoxyribonucleoprotein content. We believe the breakdown of deoxyribonucleoprotein is due to a nonspecific stress reaction to the change from the weightless state to that of terrestrial gravity during landing. The polydeoxyribonucleotide level and amount of deoxyribonucleoprotein in the majority of cases returned to normal values during the 25 days of readaptation. No substantial change of deoxyribonucleoprotein was found in the liver. The different findings in the three organs are due to the fact that breakdown of deoxyribonucleoprotein takes place in sensitive cells underlying pycnosis. These cells are found in the spleen and thymus, but not in the liver.

Physiological mechanisms of adaptation to weightlessness. Data from experiments with animals in earth-orbit biosatellites.

Four experiments were carried out with mammals (white laboratory rats) in Kosmos biosatellites. The experimental results indicate that rather prolonged weightlessness does not cause pathological changes in internal organs. Changes were discovered in the metabolic and hormonal status of the organisms, allowing us to consider an 18-22-day space flight as a moderately stressful activity. Changes in the musculoskeletal system involved atrophy of particular muscle groups, adaptive transformation of the contractile properties of some of them, osteoporosis, and decreased durability of bony tissue. There was a decrease in the ATPase activity of myocardial myosin, and there were changes in the erythrocytic system: decreased erythrocytic hemopoietic activity, increased levels of spontaneous hemolysis of erythrocytes, etc. All the described changes were reversible, and examination of the animals 25 days after their return to Earth showed practically complete normalization of the parameters studied.

Physiological reactions during acute adaptation to reduced gravity.

Experiments were carried out on healthy volunteers exposed to a 7-day water immersion. The subjects were kept dry by use of a water proof, highly elastic cloth. During the experiment different cardiovascular, fluid-electrolyte and biochemical parameters were recorded. During the 7-day immersion, physiological parameters changed on a phasic basis. An acute period of adaptation began within the first minutes of immersion and ended by the third day. Later some of the parameters showed relative normalization. The experimental results suggest that the hypophyseal-adrenal system and renal function are closely coupled regulatory mechanisms for adaptive reactions of the cardiovascular system and for fluid-electrolyte metabolism during acute adaptation of the human body to reduced gravity.

Biochemical changes in rats flown on board the Cosmos 690 biosatellite.

Male rats of the Wistar strain were examined one day and 26 days after the 20-day space flight on board the Cosmos 690 biosatellite. On the 10th flight day the animals were exposed to 24-hour gamma irradiation: some animals were irradiated at a dose of 220 rad and the others at a dose of 800 rad. The data were compared with the results obtained from two control groups one day and 26 days after the experiment: (i) rats kept in the vivarium and fed with a special diet, and (ii) rats from a synchronous experiment (which simulated the flight profile with the exception only of weightlessness). The studies showed the following changes one day after flight: an increase in the concentration of total cholesterol, glucose, urea and corticosterone in the blood plasma, an increase in the concentration of triglycerides in the plasma, liver and bone marrow, a decrease in the concentration of total cholesterol in the adrenals, a reduction in the DNA and RNA content in the spleen and bone marrow, a decline in the potassium concentration together with an increase in the sodium concentration in soleus muscle. The degree and pattern of the changes depended largely on the dose of irradiation. The parameters returned to normal 26 days post-flight.

Preliminary results of examinations of rats after a 22-day flight aboard the Cosmos-605 biosatellite.

The results of biomedical investigations carried out in flights of the Salyut and Skylab orbital stations give evidence that during prolonged weightlessness cosmonauts and astronauts remain in a good physical and mental condition. They fill specialists with optimism in regards to a further increase of the duration of manned space flights. In order to make reliable plans for such missions, it is necessary to accumulate detailed knowledge about the mechanism of the effect of weightlessness on different functions of the human body. In addition to manned experiments, of great interest are animal experiments. They may yield data that cannot be obtained in human studies, which is obviously very important from the point of view of space medicine. This was the purpose of the experiment carried out in November 1973 on the biosatellite Cosmos-605; 45 rats aboard the biosatellite flew for 22 d. Preliminary results of examinations of rats after a 22-d space flight in the Cosmos-605 satellite demonstrated not only physiological and biochemical but also morphological changes in the animal body due to prolonged weightlessness. These changes were reversible.

Characteristics of metabolism during prolonged water immersion.

The effect on the organism of a 12-day stay in a water immersion medium (head on the water surface) was studied on 10 subjects. The condition of the metabolic processes in the subjects was judged from the investigation of the parameters of protein and carbohydrate metabolism, acid-base equilibrium, the activity of a number of enzymes and steroid hormones. The venous blood and diurnal urine served as the material for conducting the corresponding biochemical determinations. The stay in an immersion medium is accompanied by a significant increase in the content of residual nitrogen in the blood, by a reduction of the creatinine content in the blood and by an increase of the creatine content of the blood with the simultaneous increase of the excretion of creatinine and creatine with the urine, by a significant increase of the glucose and lactate content in the blood, by the development of acidosis of a respiratory and metabolic character, as well as by a significant increase of the activity of creatine phosphokinase and the isoenzyme fraction of lactate dehydrogenase3. In all the subjects, an expressed intensification of the glucocorticoid and androgenic functions of the adrenal cortex is noted during the experimental period.