[Dehydrogenase activity in skeletal muscles of rats after long-term exposure to weightlessness]. / Aktivnost' degidrogenaz v skeletnykh myshtsakh krys posle dlitel'nogo deistviia nebesomosti.

Malate- and isocytratedehydrogenase activity in mitochondrial and cytoplasmic fractions and lactate dehydrogenase activity in hindlimb muscles have been studied at different stages after 18.5-day flight on a biosatellite "Cosmos-1129" and after 20-day hypokinesia. A decrease in dehydrogenase activity has been found on the first postflight day. The enzyme activities returned to the control values in mitochondria, and in the cytoplasm they were greater by day 6 postflight. It was concluded that hypokinesia did not reveal all the effects of microgravity on the whole system but some enzyme alterations in the muscle resembled those observed during the flight. The effects may be caused by the inhibition of both aerobic and anaerobic metabolic pathways under the effect of microgravity.

[Energy reactions in the skeletal muscles of rats after short-term space flight on Kosmos-1514]. / Energeticheskie reaktsii v skeletnykh myshtsakh krys posle kratkovremennogo kosmicheskogo poleta na biosputnike "Kosmos-1514".

Ten hours after the 5-day space flight on Cosmos-1514 rats were examined for oxidative phosphorylation in mitochondria isolated from the posterior femoral muscles as well as for Krebs cycle enzymes and glycolysis in the mitochondrial and cytoplasmic fractions of the muscles. The mitochondrial respiration rate in various metabolic states was similar in flight rats and vivarium controls. After flight calculated parameters of energy efficacy of respiration as well as activity of malate dehydrogenase, isocitrate dehydrogenase and total lactate dehydrogenase remained unchanged. Unlike the flight rats, the synchronous controls showed signs of the stress-reaction: uncoupling of oxidative phosphorylation and oxalacetate inhibition of succinate dehydrogenase. Comparison of these findings with those from prolonged space flights indicates that inhibition of oxidative metabolism and glycolysis in mixed muscles which was demonstrated in the 20-day space flight does not develop immediately after launch but occurs within the time interval between mission days 6 and 18.

[Energy reactions in the skeletal muscles of rats after a flight on the Kosmos-1129 biosatellite]. / Energeticheskie reaktsii v skeletnykh myshtsakh krys posle poleta na biosputnike "Kosmos-1129".

The polarographic analysis of biological oxidation in rat skeletal muscles after the 18.5-day flight revealed changes specific for the flight animals: oxidative phosphorylation uncoupling, distinct inertness of energy accumulation 10 hrs after recovery. Tissue respiration inhibition occurred in both flight and synchronous rats suggesting the effect of other than weightlessness factors. In the flight animals the parameters of energy metabolism returned to the prelaunch level within a longer (29 days) time than in the synchronous rats (6 days). Muscles of different function (predominance of fast or slow fibers) showed similar responses of energy metabolism to weightlessness, i. e. inhibition of the intensity and decrease of the energy efficiency of oxidative processes.

[Energy reactions in the skeletal muscles of rats following space flight on the Kosmos-936 biosatellite]. / Energeticheskie reaktsii v skeletnykh myshtsakh krys posle kosmicheskogo poleta na biosputnike "Kosmos-936".

The respiration of mitochondria isolated from mixed skeletal muscles of hindlimbs of rats flown for 18.5 days on Cosmos-936 was investigated polarographically. At R + 10 hours the rate of mitochondrial respiration in different metabolic states during the oxidation of succinic acid and NAD-dependent substrates declined. The enzyme activity of mitochondrial cytochrome oxidase and cytosol lactate dehydrogenase diminished. At R + 25 days both aerobic and anaerobic oxidative processes increased, thus leading to the recovery of the parameters (sometimes they not only returned to the norm but exceeded it).

[Skeletal muscle capillary bed during hypokinesia]. / Kapilliarnoe ruslo skeletnykh myshts pri gipokinezii.

The functioning capillaries (containing red cells) of the gastrocnomius, soleus and tibial muscles as well as biceps femoris were subjected to quantitative histological study in rats exposed to 20-day hypokinesia. During hypokinesia the rats showed atrophy of and reduced blood supply to hind limb muscles as indicated by the decreased number of the functioning capillaries, the number of the capillaries supplying red muscular fiber being lowered in the first turn. The only exception was the soleus muscle where the number of the functioning capillaries remained unchanged, and blood congestion developed. It is suggested that the microcirculatory disorders in the soleus muscle and concomitant tissue hypoxia are responsible for severe dystrophic changes seen in the muscle of the hypokinetic rats.