Effects of spaceflight on the spermatogonial population of rat seminiferous epithelium

Testes from rats flown on Cosmos 1887 were compared with vivarium control and synchronous control samples. The mean weights of flight testes, normalized for weight per 100 g, were 6.4% less when compared with the vivarium controls. Counts of spermatogonia from tissue sections (seminiferous tubules in maturation stage 6) from five animals in each group revealed 4% fewer spermatogonia in flight testes compared with synchronous controls and 11% fewer spermatogonia in flight samples compared with vivarium controls.     

Effects of spaceflight on rat humerus geometry, biomechanics, and biochemistry

The effects of a 12.5-day spaceflight (Cosmos 1887 biosatellite) on the geometric, biomechanical, and biochemical characteristics of humeri of male specific pathogen-free rats were examined. Humeri of age-matched basal control, synchronous control, and vivarium control rats were contrasted with the flight bones to examine the influence of growth and space environment on bone development. Lack of humerus longitudinal growth occurred during the 12.5 days in spaceflight. In addition, the normal mid-diaphysial periosteal appositional growth was affected; compared with their controls, the spaceflight humeri had less cortical cross-sectional area, smaller periosteal circumferences, smaller anterior-posterior periosteal diameters, and smaller second moments of area with respect to the bending and nonbending axes. The flexural rigidity of the flight humeri was comparable to that of the younger basal control rats and significantly less than that of the synchronous and vivarium controls; the elastic moduli of all four groups, nonetheless, were not significantly different. Generally, the matrix biochemistry of the mid-diaphysial cross sections showed no differences among groups. Thus, the spaceflight differences in humeral mechanical strength and flexural rigidity were probably a result of the differences in humeral geometry rather than material properties.     

Effect of short-term microgravity and long-term hindlimb unloading on rat cardiac mass and function.

The purpose of this study was to test the hypothesis that exposure to short-term microgravity or long-term hindlimb unloading induces cardiac atrophy in male Sprague-Dawley rats. For the microgravity study, rats were subdivided into four groups: preflight (PF, n = 12); flight (Fl, n = 7); flight cage simulation (Sim, n = 6), and vivarium control (Viv, n = 7). Animals in the Fl group were exposed to 7 days of microgravity during the Spacelab 3 mission. Animals in the hindlimb-unloading study were subdivided into three groups: control (Con, n = 20), 7-day hindlimb-unloaded (7HU, n = 10), and 28-day hindlimb-unloaded (28HU, n = 19). Heart mass was unchanged in adult animals exposed to 7 days of actual microgravity (PF 1.33 +/- 0.03 g; Fl 1.32 +/- 0.02 g; Sim 1.28 +/- 0.04 g; Viv 1.35 +/- 0.04 g). Similarly, heart mass was unaltered with hindlimb unloading (Con 1.40 +/- 0.04 g; 7HU 1.35 +/- 0.06 g; 28HU 1.42 +/- 0.03 g). Hindlimb unloading also had no effect on the peak rate of rise in left ventricular pressure, an estimate of myocardial contractility (Con 8,055 +/- 385 mmHg/s; 28HU 8,545 +/- 755 mmHg/s). These data suggest that cardiac atrophy does not occur after short-term exposure to microgravity and that neither short- nor long-term simulated microgravity alters cardiac mass or function.     

Morphological and biochemical examination of Cosmos 1887 rat heart tissue: Part I--Ultrastructure

Morphological changes were observed in the left ventricle of rat heart tissue from animals flown on the Cosmos 1887 biosatellite for 12.5 days. These tissues were compared to the synchronous and vivarium control hearts. While many normal myofibrils were observed, others exhibited ultrastructural alterations, i.e., damaged and irregular-shaped mitochondria and generalized myofibrillar edema. Analysis of variance (ANOVA) of the volume density data revealed a statistically significant increase in glycogen and a significant decrease in mitochondria compared to the synchronous and vivarium controls. Point counting indicated an increase in lipid and myeloid bodies and a decrease in microtubules, but these changes were not statistically significant. In addition, the flight animals exhibited some patchy loss of protofibrils (actin and myosin filaments) and some abnormal supercontracted myofibrils that were not seen in the controls. This study was undertaken to gain insight into the mechanistic aspects of cardiac changes in both animals and human beings as a consequence of space travel (1). Cardiac hypotrophy and fluid shifts have been observed after actual or simulated weightlessness and raise concerns about the functioning of the heart and circulatory system during and after travel in space (2-4).     

The Effects of Radiation and Hindlimb Unloading on Rat Bone Marrow Progenitor Cells

Bone marrow cells of mesenchymal origin play an important role in adaptation of physiological systems to space flight. Hematopoiesis, immunity, and homeostasis of bone tissue depend on their functional activity. An investigation that was carried out in the framework of the Bion and Bion-M programs showed a decrease of the number of rat bone marrow hematopoietic progenitors and the inhibition of lympho- and erythropoiesis when the granulocyte-macrophage linage was activated. A negative influence on nonhematopoietic bone marrow cells was also revealed. The pathogenetic influence of radiation and microgravity on the bone marrow progenitor cells has remained unclear so far. The goal of this research was to study the effect of a 30-day unloading and 6 days of γ-irradiation on rat bone marrow progenitor cells. The study was conducted on male rats of four groups: vivarium control (VC), hindlimb unloading (HU), irradiation (IR), and combined action (HU + IR). The following parameters have been examined: the number of bone marrow mononuclear cells, proliferative activity of marrow mononuclear cells, immunophenotype, number of hematopoietic CFU and CFU-f, and differentiation potency of hematopoietic and stromal bone marrow precursors. It was found that the cellularity and proliferation activity of rat bone marrow cells did not change under simulation of space flight. The number of CFU-f was decreased. Irradiation was accompanied by an increase in the hematopoietic cell share among total bone marrow mononuclear cells, while their activity was attenuated. The osteopotential of the stromal precursors was unchanged. Adipogenic differentiation was stimulated with irradiation. The functional activity of bone marrow progenitor cells was restored after 2 weeks of recovery. Thus, 30-day simulation of space flight factors negatively affected the morphofunctional properties of rat bone marrow progenitor cells. These effects were reversible upon 2 weeks of recovery.     

Effects of space flight on bone formation and resorption.

Samples of femurs and tibiae of male Wistar rats subjected to a 13 day space-flight on the biosatellite Cosmos 1887--were investigated and compared with vivarium and synchronous controls or immobilized rats, using histological and histomorphometric methods. 1. After flight in the metaphysis of bones the density and volume of the spongious trabeculae diminished significantly indicated by the Sv and Vv histomorphometric values and histological data comparing to the controls. In the diaphysis, the density of trabeculae decreased too. 2. In the flight group significant suppression of bone formation was determined by histological and histomorphometric (decrease of the OS, OB and OBI values) methods. 3. In the flight group according to the histological pictures the signs of bone resorption (increase of Hoswship's lacunae, osteoclastic activity, structural rarefication of spongious and cortical bones, osteon disintegration, osteocytic osteolysis) were revealed, which was substantiated by the histomorphometric results (increase of osteoclastic index: OCI). 4. Significant differences between flight and immobilized groups were not determined, except the osteoid value, which was increased in the case of immobilization. 5. Some histomorphometric values related to bone formation of synchronous control group showed close relationship rather to the flight group than to the vivarium control group.     

Variable lymphocyte responses in rats after space flight.

Most studies of human blood lymphocyte function following space flight have indicated that microgravity suppresses T cell proliferation. However, several other postflight experiments with animals have shown no decrease in proliferation of lymphocytes from peripheral lymphatic tissues, suggesting that different tissues may be variably affected by microgravity. Therefore, we examined the proliferation of lymphocytes from both spleen and lymph nodes of rats following a 4-day flight aboard the Space Shuttle. The experiments were designed to investigate tissue variability as well as potential mechanisms involved in suppressing proliferation. We found that proliferation of lymph node lymphocytes (LNL) from flight (FLT) animals stimulated with the antigen receptor-dependent T cell mitogen concanavalin A was depressed and could not be restored by supplementing cultures with interleukin 1 or interleukin 2 (IL-2). Response to another receptor-dependent mitogen, phytohemagglutinin, was not decreased. However, proliferation of FLT LNL following stimulation with the receptor-independent, mitogenic combination of phorbol ester and ionomycin was depressed. LNL IL-2 activity, cell surface marker expression, and B cell responses to mitogen were normal. Thus, deficits in antigen receptor/ligand interactions, cell surface marker expression, or IL-2 did not account for the suppressed lymphocyte proliferation observed postflight. In contrast to LNL, FLT splenocyte proliferation was not depressed. Assayable IL-2, IL-2 receptor expression, and cell surface marker expression likewise were unaffected by space flight. The differences between lymph node and splenic responses demonstrate the tissue-specific nature of microgravity effects on individual lymphatic tissues.     

Alterations In Gastrointestinal Steady-State Kinetics Associated With the Growth of Experimental Tumours

Changes in the growth kinetics of the intestinal epithelium were observed in mice bearing the Lewis lung carcinoma and the T1699 mammary adenocarcinoma and in rats bearing the H-4-II-E₂ hepatoma. Proliferative activity in the jejunal tissue was markedly depressed with increasing tumour burden. Simultaneously, a significant reduction in total crypt cellularity occurred, followed by a reduction in villus height. While the total number of proliferative cells per crypt decreased, the relative proliferative compartment within the shrinking crypt increased. the rate of mucosal DNA synthesis remained constant during the initial cytokinetic changes, falling only after proliferative activity of the intestine was reduced to less than 50% of control levels. No general correlation could be drawn from the three tumour models studied between the level of gastrointestinal proliferation and tumour size, tumour growth rate or loss of weight by the tumour-bearing animals. However, intestinal proliferation was reduced by 50% when the tumour burden for each of the three tumours reached 6–8% of the host animal weight.     

Protective effects of N-acetylcysteine on intestinal functions of piglets challenged with lipopolysaccharide

The neonatal small intestine is susceptible to damage by endotoxin, but effective methods for prevention and treatment are lacking. N-acetylcysteine (NAC) is a widely used precursor of L: -cysteine for animal cells and plays an important role in protecting cells against oxidative stress. This study was conducted with the lipopolysaccharide (LPS)-challenged piglet model to determine the effects of NAC on intestinal function. Eighteen piglets were randomly allocated into control, LPS and LPS?+?NAC groups. The control and LPS groups were fed a corn- and soybean meal-based diet, and the LPS?+?NAC group was fed the basal diet +500?mg/kg NAC. On days 10, 13 and 20 of the trial, the LPS and LPS?+?NAC groups received intraperitoneal administration of LPS (100?μg/kg BW), whereas the control piglets received saline. On day 20 of the trial, D-: xylose (0.1?g/kg BW) was orally administrated to all piglets 2?h after LPS or saline injection, and blood samples were collected 1?h thereafter. One hour blood xylose test was used to measure intestinal absorption capacity and mucosal integrity, and diamine oxidase (DAO) was used as a marker of intestinal injury. On day 21 of the trial, pigs were killed to obtain the intestinal mucosa. Compared to the control, LPS challenge reduced (P?相似文献   

Bone biochemistry in rat femoral diaphysis after space flight

The aim of this experiment was to identify the location of the biochemical changes associated with depressed mineralization during space flight. We carried out biochemical analysis of 4 sections of the femoral diaphyses from 107 day old male rats flown aboard Cosmos 2044 Biosatellite for 16 days. Control femurs were preflight, vivarium, synchronous for feed, cage and temperature exposure, and a flight simulation model. Distal sections in both the flight and synchronous femurs showed mineral deficits associated with reduced levels of the reducible cross-link product of type I collagen, dehydro-dihydroxylysinonorleucine (deH-DHLNL) (p<.05). Unloaded bones in the ground based flight simulation model showed changes in cross-links similar to flight and synchronous controls, but were not associated with the mineral deficit. Mean values of elements measured in each section of all groups revealed significant associations (p<.005) between the non-collagenous protein, osteocalcin and calcium (r=0.774), phosphorus (r=-.624) and deH-DHLNL/deH-HLNL (r=.883). The ratio of the nonreducible cross-link, pyridinoline, to its lysl analogue, deoxypyridinoline, was consistently lower in the distal than proximal sections of the groups tested. None of the changes during space flight were unique to flight bone. The most significant and extensive changes in bone composition, i.e. mineral deficits associated with changes in both osteocalcin and reducible cross-links, were located in the distal section of the diaphysis of the femur.     

Differential jejunal and colonic adaptation due to resection and IGF-I in parenterally fed rats

Patients with severe short-bowel syndrome (SBS) often require long-term total parenteral nutrition (TPN) to maintain their nutritional status because of limited intestinal adaptation. Growth factors, including insulin-like growth factor I (IGF-I), are under investigation to promote intestinal adaptation and tolerance to oral feeding. We investigated structural and functional adaptation of the jejunum and colon in four groups of rats maintained with TPN for 7 days after a 60% jejunoileal resection and cecectomy or sham surgery and treatment with IGF-I or vehicle. Resection alone did not stimulate jejunal growth. IGF-I significantly increased jejunal mucosal mass, enterocyte proliferation, and migration rates. IGF-I decreased jejunal sucrase specific activity and reduced active ion transport and ionic permeability; resection alone had no effect. In contrast, resection significantly increased colonic mass and crypt depth but had no effect on active ion transport or ionic permeability. IGF-I had minimal effects on colonic structure. IGF-I but not resection stimulates jejunal adaptation, whereas resection but not IGF-I stimulates colonic growth in rats subjected to a model for human SBS. IGF-I treatment may improve intestinal adaptation in humans with SBS.     

Histomorphometric and electron microscopic analyses of tibial epiphyseal plates from Cosmos 1887 rats

Previous studies have shown that the changes seen in the bones of growing rats exposed to microgravity are due in part to changes that occur in the growth plate during spaceflight. In this study, growth plates of rats flown aboard Cosmos 1887 (12.5-day flight plus 53.5-h recovery at 1 g) were analyzed using light and electron microscopy and computerized planimetry. The proliferative zone of flight animals was found to be significantly (P less than or equal to 0.01) larger than that of controls, while the reserve and hypertrophic/calcification zones were significantly reduced. Flight animals also had more cells per column in the proliferative zone than did controls and less in the hypertrophic/calcification region. The total number of cells, however, was significantly greater in flight animals. No difference was found in perimeter or in shape factor, but area was significantly less in flight animals. Electron microscopy showed that collagen fibrils in flight animals were wider than in controls. Since the time required for a cell to cycle through the growth plate is 2-3 days at 1 g, the results reported here represent both the effects of exposure to microgravity and the initial stages of recovery from that exposure.     

Structural and metabolic properties of rat muscle exposed to weightlessness aboard Cosmos 1887.

Male Wistar rats were subjected to 12.5 days of weightlessness aboard Cosmos 1887. Histomorphometric and biochemical analyses were investigated in soleus (SOL), plantaris (PL) and extensor digitorum longus (EDL) muscles of flight rats (group F) and compared with data from two groups of terrestrial controls: one group living free in a vivarium (group V) and another subjected to a flight simulation except for the state of weightlessness (group S). Relative to groups V and S, no alteration in the percentage distribution of fibres had occurred in SOL, PL or EDL, after the flight. In SOL muscles from group F animals, cross-sectional areas of all fibre types were reduced to a greater extent (-40%) than capillary to fibre ratio (-24%) leading to a higher capillary density (+33%) than in V and S groups. In PL, type I, IIA and IIB fibre cross-sectional areas were less decreased (-25%). In EDL, only fast-twitch fibre cross-sectional areas showed an average decrease of 30%. Capillary per fibre ratio was reduced by 15% and 28% respectively in PT and EDL muscles from group F rats compared to control groups V and S. Citrate synthase and 3-hydroxyacyl-coenzyme A dehydrogenase activities remained unchanged in SOL, PL and EDL following spaceflight. These findings indicate greater atrophy and functional alterations (capillarity) compared to those observed after 7 days of microgravity on Cosmos 1667.     

Microgravity effect on testicular functions

In mammals spaceflight influences spermatogenesis since spermatogonial germ cell proliferation, compared to synchronous controls, is lightly decreased in irradiated or flown rats. Moreover, changes of the plasmatic testosterone production was described either in flight rats, or in rats maintained in simulated microgravity conditions. The hormonal levels of the astronauts change as it has been previously described, including hormones involved in the regulation of spermatogenesis such as testosterone and luteinizing hormone (LH). In microgravity conditions, human testosterone levels decreased whereas circulating LH levels increased. To study the effect of simulated microgravity on mammalian spermatogenesis we have utilized the Rotary Cell Culture System (RCCS) and we have cultured testicular fragments isolated from prepuberal rats in a chemically defined medium for three days under microgravity conditions. As control we have cultured the same amount of fragments at unit gravity. The morphology of the samples has been studied and the number of proliferating cells has been counted in control samples and in samples maintained in RCCS. The results indicate that the number of duplicating cells in the tubules was significantly increased in the microgravity-cultured fragments. The amount of testosterone secreted in the culture medium has been also evaluated and in RCCS samples the amount of the hormone was higher respect to the control samples.     

Effects of space flight on GLUT-4 content in rat plantaris muscle

 The effects of 14 days of space flight on the glucose transporter protein (GLUT-4) were studied in the plantaris muscle of growing 9-week-old, male Sprague Dawley rats. The rats were randomly separated into five groups: pre-flight vivarium ground controls (PF-VC) sacrificed approximately 2 h after launch; flight groups sacrificed either approximately 5 h (F-R0) or 9 days (F-R9) after the return from space; and synchronous ground controls (SC-R0 and SC-R9) sacrificed at the same time as the respective flight groups. The flight groups F-R0 and F-R9 were exposed to micro-gravity for 14 days in the Spacelab module located in the cargo bay of the shuttle transport system – 58 of the manned Space Shuttle for the NASA mission named ”Spacelab Life Sciences 2”. Body weight and plantaris weight of SC-R0 and F-R0 were significantly higher than those of PF-VC. Neither body weight nor plantaris muscle weight in either group had changed 9 days after the return from space. As a result, body weight and plantaris muscle weight did not differ between the flight and synchronous control groups at any of the time points investigated. The GLUT-4 content (cpm/μg membrane protein) in the plantaris muscle did not show any significant change in response to 14 days of space flight or 9 days after return. Similarly, citrate synthase activity did not change during the course of the space flight or the recovery period. These results suggest that 14 days of space flight does not affect muscle mass or GLUT-4 content of the fast-twitch plantaris muscle in the rat. Received: 25 March 1997 / Accepted: 18 August 1997     

The Role of Wnt/β-Catenin Signaling in Enterocyte Turnover during Methotrexate-Induced Intestinal Mucositis in a Rat

Background/Aims

Intestinal mucositis is a common side-effect in patients who receive aggressive chemotherapy. The Wnt signaling pathway is critical for establishing and maintaining the proliferative compartment of the intestine. In the present study, we tested whether Wnt/β-catenin signaling is involved in methotrexate (MTX)-induced intestinal damage in a rat model.

Methods

Non-pretreated and pretreated with MTX Caco-2 cells were evaluated for cell proliferation and apoptosis using FACS analysis. Adult rats were divided into three experimental groups: Control rats; MTX-2 animals were treated with a single dose of MTX given IP and were sacrificed on day 2, and MTX-4 rats were treated with MTX similar to group B and were sacrificed on day 4. Intestinal mucosal damage, mucosal structural changes, enterocyte proliferation, and enterocyte apoptosis were measured at sacrifice. Real Time PCR and Western blot was used to determine the level of Wnt/β-catenin related genes and protein expression.

Results

In the vitro experiment, treatment with MTX resulted in marked decrease in early cell proliferation rates following by a 17-fold increase in late cell proliferation rates compared to early proliferation. Treatment with MTX resulted in a significant increase in early and late apoptosis compared to Caco-2 untreated cells. In the vivo experiment, MTX-2 and MTX-4 rats demonstrated intestinal mucosal hypoplasia. MTX-2 rats demonstrated a significant decrease in FRZ-2, Wnt 3A Wnt 5A, β-catenin, c-myc mRNA expression and a significant decrease in β-catenin and Akt protein levels compared to control animals. Four days following MTX administration, rats demonstrated a trend toward a restoration of Wnt/β-catenin signaling especially in ileum.

Conclusions

Wnt/β-catenin signaling is involved in enterocyte turnover during MTX-induced intestinal mucositis in a rat.     

Histological analysis of the aortic nerve in the rat raised in space (Rapid communication on Neurolab Project).

To study development of the aortic nerve baroreflex under conditions of microgravity, we examined the cross section of the left aortic nerve (LAN), which is the afferent of the baroreflex, in the neonate rats aged 25 days raised in microgravity on the space shuttle Columbia (flight:FLT group) for 16 days. In this paper, we report a part of the result obtained from the data of the myelinated fibers of LAN analyzed with an electron microscope. Two kind of ground control groups were compared to the FLT group; one was asynchronous ground control (AGC) group where the rats were housed in the same cage as that on the shuttle, and the other was vivarium(VIV) group where the rats were housed in a commercial cage. The LANs in each group were extirpated the from rats perfused with a fixative and embedded for histological analysis. We observed the transverse sections of LAN and took pictures of several areas (magnified to x 2K to x 200K). No irregular myelination was found in all fibers of FLT group when they were compared with two control groups. The thickness of myelin of the maximally myelinated fibers were 0.55 +/- 0.17 micrometer in FLT(n=5), 0.45 +/- 0.10 micrometer in AGC(n=5), and O.47 +/- 0.06 micrometer meter in VIV(n=5). There was no significant difference among three groups (unpared t-test). The results suggest that there is no effect of space environment on the myelin formation of each nerve fiber in the aortic nerve.     

Intestinal epithelial cell proliferation and migration in Atlantic salmon, Salmo salar L.: effects of temperature and inflammation

A 28-day feeding trial was carried out to characterise intestinal epithelial cell (IEC) turnover in Atlantic salmon (Salmo salar L.) post-smolts in seawater. Four groups of fish raised at two temperatures of 8°C or 12°C and fed two different diets were investigated. The diets included a reference maize gluten and fishmeal-based diet (FM) and an experimental enteropathy-causing diet containing 20% extracted soybean meal (SBM). IEC proliferation and migration were investigated by labelling cells with the in vivo proliferation marker 5-bromo-2′-deoxyuridine (BrdU). Proliferating cell nuclear antigen (PCNA) labelling was used as a control for identifying proliferating cells. Samples of the proximal (PI), mid (MI) and distal (DI) intestinal regions were collected at five time points (3 h–28 days) over the experimental period. Histologically, FM-fed fish had normal mucosa, whereas the SBM-fed fish developed DI enteropathy. Major zones of cell proliferation were observed in the mucosal fold bases for all intestinal regions. Over time, BrdU-labelled cells migrated up mucosal folds to the tips before being lost. Migration rates were dependent on intestinal region, temperature and diet. Highest migration rates were observed in the PI followed by the MI and DI for FM-fed fish. Diet and temperature barely affected migration in the PI and MI. Migration in the DI was most sensitive to diet and temperature, with both SBM and the higher water temperature increasing proliferation and migration rates. The slow IEC turnover in the DI might help to explain the sensitivity of this region to dietary SBM-induced enteropathy.     

The role of curcumin on intestinal oxidative stress,cell proliferation and apoptosis after ischemia/reperfusion injury in rats

The aim of this study was to demonstrate the role of curcumin on oxidative stress, cell proliferation and apoptosis in the rat intestinal mucosa after ischemia/reperfusion (I/R). A total of 30 male Wistar albino rats were divided into three groups: sham, I/R and I/R+ curcumin; each group contain 10 animals. Sham group animals underwent laparotomy without I/R injury. After I/R groups animals underwent laparotomy, 1 h of superior mesenteric artery ligation were followed by 1 h of reperfusion. In the curcumin group, 3 days before I/R, curcumin (100 mg/kg) was administered by gastric gavage. All animals were sacrificed at the end of reperfusion and intestinal tissues samples were obtained for biochemical and histopathological investigation in all groups. Curcumin treatment significantly decreased the elevated tissue malondialdehyde levels and increased of reduced superoxide dismutase, and glutathione peroxidase enzyme activities in intestinal tissues samples. I/R caused severe histopathological injury including mucosal erosions and villous congestion and hemorrhage. Curcumin treatment significantly attenuated the severity of intestinal I/R injury, with inhibiting of I/R-induced apoptosis and cell proliferation. These results suggest that curcumin treatment has a protective effect against intestinal damage induced by intestinal I/R. This protective effect is possibly due to its ability to inhibit I/R-induced oxidative stress, apoptosis and cell proliferation.     

Oxidative phosphorylation in rat skeletal muscles after space flight on board biosatellites

Polarographic analysis of biological oxidation in rat's skeletal muscles after the 18- and 22-day flights revealed changes specific for the flight animals: oxidative phosphorylation uncoupling, distinct inertness of energy accumulation after 10 hrs of landing. Tissue respiration's inhibition was observed in both flight and synchronous rats suggesting the effect of other than microgravity factors. Energy metabolism in muscles of flight animals returned to the pre-flight level later (29 d) compared to the synchronous rats (6 d). Muscles of different functions (predominance of fast or slow fibers) showed similar responses of energy metabolism to weightlessness, i.e. inhibition of the intensity and decline of the energy efficiency of oxidative processes. A decrease in dehydrogenase activity has been found in the first day of recovery. The effects may be caused by the inhibition of both aerobic and anaerobic metabolism after space flight.