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At least 937 records · Page 52
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Morphologic and histochemical studies of bone cells from SL-3 rats

Previous studies of rat bone following space flight indicate a significant reduction in new bone formation as a result of hypogravity. In the present study of animals from SL-3 flight, the cellular activity of the bone forming cells, the osteoblasts, was investigated. Measurements of alkaline and acid phosphatase, Golgi activity, secretory granule size, and lysosomal activity, all indicated very little difference between flight and flight-simulated controls. However, there was a tendency for osteoblasts in compact bone of flight animals to show a smaller cytoplasmic volume compared to non-flight controls. If, as in previous studies, a significant reduction in bone formation occurred, it could be due to a normal level of procollagen degradation within these smaller osteoblasts, resulting in less collagen secretion per cell.

Doty, S. B.↗
NASA NTRS1986

Effect of inactivity and passive stretch on protein turnover in phasic and postural rat muscles

Muscle atrophy in humans can occur during prolonged bed rest, plaster cast immobilization, and space flight. In the present study, the suspension model used by Musacchia et al. (1983) is employed to investigate changes in protein synthesis and degradation in fast-twitch phasic (extensor digitorum longus) and slow-twitch postural (soleus) muscles in the rat, following hypokinesia and hypodynamia. In addition, the use of passive stretch was examined as a means of preventing atrophy. The obtained results suggest that the mechanisms controlling the processes of protein synthesis and protein breakdown during muscle disuse atrophy may be independent of each other. It appears, however, that the muscle atrophy due to hypokinesia and hypodynamia can be temporarily prevented by passively stretching a muscle.

Loughna, P.↗
NASA NTRS1986

Increased response to insulin of glucose metabolism in the 6-day unloaded rat soleus muscle

Hind leg muscles of female rats were unloaded by tail cast suspension for 6 days. In the fresh-frozen unloaded soleus, the significantly greater concentration of glycogen correlated with a lower activity ratio of glycogen phosphorylase (p less than 0.02). The activity ratio of glycogen synthase also was lower (p less than 0.001), possibly due to the higher concentration of glycogen. In isolated unloaded soleus, insulin (0.1 milliunit/ml) increased the oxidation of D(U-C-14) glucose, release of lactate and pyruvate, incorporation of D-(U-C-14) glucose into glycogen, and the concentration of glucose 6-phosphate more (p less than 0.05) than in the weight-bearing soleus. At physiological doses of insulin, the percent of maximal uptake of 2-deoxy-D-(1,2-H-3) glucose/muscle also was greater in the unloaded soleus. Unloading of the soleus increased, by 50 percent the concentration of insuling receptors, due to no decrease in total receptor number during muscle atrophy. This increase may account for the greater response of glucose metabolism to insulin in this muscle. The extensor digitorum longus, which generally shows little response to unloading, displayed no differential response of glucose metabolism to insulin.

Henriksen, Erik J.↗
NASA NTRS1986

Reduction-oxidation state and protein degradation in skeletal muscles of growing rats

The relationship between the NAD redox state and protein degradation during growth was studied in isolated soleus and extensor digitorum longus muscles of 4- to 14-week-old rats. As muscle size increased with age, protein breakdown slowed and the muscles became progressively more reduced as shown by higher ratios of lactate/pyruvate in incubated and fresh-frozen muscle. Correlations were strong between redox state of protein degradation, and muscle mass, and between redox state and protein degradation. This relationship may be important in the slowing of muscle breakdown that occurs with age.

Fagan, Julie M.↗
NASA NTRS1986

Role of glucocorticoids in the response of rat leg muscles to reduced activity

Adrenalectomy did not prevent atrophy of rat soleus muscle during 6 days of tail cast suspension. Cortisol treatment enhanced the atrophy and caused atrophy of the weight-bearing soleus and both extensor digitorum longus (EDL) muscles. Unloading led to increased sarcoplasmic protein concentration in the soleus but cortisol administration increased the myhofibrillar (+stromal) protein concentration in both muscles. Suspension of hindlimbs of adrenalectomized animals led to faster protein degradation, slower sarcoplasmic protein degradation, and faster myofibrillar protein synthesis in the isolated soleus, whereas with cortisol-treated animals, the difference in synthesis of myofibrillar proteins was enhanced and that of sarcoplasmic proteins was abolished. Both soleus and EDL of suspended, cortisol-treated animals showed faster protein degradation. It is unlikely that any elevation in circulating glucocorticoids was solely responsible for atrophy of the soleus in this model, but catabolic amounts of glucocorticoids could alter the response of muscle to unloading.

Jaspers, Stephen R.↗
NASA NTRS1987

Size and metabolic properties of fibers in rat fast-twitch muscles after hindlimb suspension

The effect of hind-limb suspension (HS) on single fibers of the medial gastrocnemius (MG) and the tibialis anterior (TA) muscles were studied in rats. Fiber area and the activities of succinate dehydrogenase (SDH) and alpha-glycerophosphate dehydrogenase (GPD) were determined in tissue sections using an image analysis system. After 28 days of HS, the MG atrophied 28 percent, whereas the TA weight was maintained. Both dark- and light-ATPase fibers in the deep region of the MG had decreased cross-sectional areas following HS, with the atrophic response being twice as great in the light-ATPase fibers than in the dark-ATPase fibers. Following HS, mean SDH activities of both fiber types were significantly lower in the MG and TA than in the CON; by contrast, mean GPD activities were either maintained at the CON level or were higher in both MG and TA muscles. The data suggest an independence of the mechanisms determining the muscle fiber size and the metabolic adaptations associated with HS.

Roy, Roland R.↗
NASA NTRS1987

An enzyme immunoassay for rat growth hormone - Applications to the study of growth hormone variants

A sensitive and specific competitive enzyme immunoassay for rat growth hormone (GH) is described and its use in the detection of GH variants is demonstrated. In the present assay, soluble GH and GH adsorbed to a solid-phase support compete for monkey anti-GH antibody binding sites. The immobilized antibody-GH complex is detected and quantified using goat antimonkey immunoglobin G covalently conjugated to horseradish peroxidase. It is noted that the assay can be performed in 27 hours and that sensitivities in the range of 0.19 to 25 ng can be obtained in the region of 10 to 90 percent binding.

Farrington, Marianne A.↗
NASA NTRS1988

Use of diphosphonates to correct disorders in calcium metabolism and mineral composition of bone tissue with 60-day hypokinesia in rats

Compounds of the diphosphonate group suppress bone resorption and bone tissue metabolism, from which it was assumed that they can be used for the prevention of osteoporosis and disorders of calcium homeostasis in humans during space flight. Two compounds of this group were used for preventive purposes in 60 day hypokinesia in rats. The results showed that diphosphonates have a marked effect on calcium metabolism and the condition of the bone tissues under conditions of long term hypokinesia: they reduce the content of ionized calcium in blood, delay the loss of calcium and phosphorus by the bone tissue, and to a considerable degree prevent reduction of bone density. This confirms the possibility of using compounds of this group for correcting and preventing changes of bone tissue and mineral metabolism during long term hypokinesia.

Morukov, B. V.↗
NASA NTRS1984

Separation of cells from the rat anterior pituitary gland

Data concerned with analyzing the cellular organization of the rat anterior pituitary gland are examined. The preparation of the cell suspensions and the methods used to separate pituitary cell types are described. Particular emphasis is given to velocity sedimentation at unit gravity, density gradient centrifugation, affinity methods, fluorescence activated cell sorting, and density gradient and continuous-flow electrophoresis. The difficulties encountered when attempting to compare data from different pituitary cell separation studies are discussed, and results from various experiments are presented. The functional capabilities of the separated cell populations can be tested in various culture systems.

Hymer, W. C.↗
NASA NTRS1987

Effects of hypokinesia and hypodynamia upon protein turnover in hindlimb muscles of the rat

Hypokinesia/hypodynamia was induced in the hindlimb muscles of the rat, using a suspension technique. This caused differing degrees of atrophy in different muscles. However, this atrophy was reduced in muscles held in a lenghthened position. The greatest degree of wasting was observed in the unstretched soleus, a slow postural muscle, where both Type 1 and Type 2a fibers atrophied to the same degree. However, wasting of the gastrocnemius muscle was associated with a reduction in the size of the Type 2b fibers. In both slow-postural and fast-phasic hindlimb muscles, atrophy was brought about by a reduction in the rate of protein synthesis in conjunction with an elevation in the rate of protein degradation. When inactive muscles were passively stretched, both protein synthesis and degradation were dramatically elevated. Even periods of stretch of as little as 0.5 h/d were found to significantly decrease atrophy in inactive muscles.

Loughna, Paul T.↗
NASA NTRS1987

Femur-bending properties as influenced by gravity. V - Strength vs. calcium and gravity in rats exposed for 2 weeks

The dependence of gravitationally related changes in femur bone strength on the comparable changes in calcium content was investigated in rats exposed to chronic simulations of altered gravity from the 28th to 42nd day of age. Zero G was simulated by harness suspension and 3 G by centrifugation. Bone strength (S) was determined by bending (using modified quasi-static cantilever bending methods and equipment described by Wunder et al., 1977 and 1979) and Ca content (C, by mass pct) determined by atomic absorption spectrometry; results were compared with data obtained on both normal and harnessed control animals at 1 G. Multiple regression showed significant dependence of S upon earth's gravity, independent from C, for which there was no significant coefficient of partial regression. It is suggested that the lack of S/C correlation might have been due to the fact that considerable fraction of the calcium in these young, developing bones has not yet crystallized into the hydroxyapatite which provides strength.

Wunder, Charles C.↗
NASA NTRS1988

Glucose uptake in rat soleus - Effect of acute unloading and subsequent reloading

The effect of acutely reduced weight bearing (unloading) on the in vitro uptake of 2-1,2-H-3-deoxy-D-glucose was studied in the soleus muscle by tail casting and suspending rats. After just 4 h, the uptake of 2-deoxy-D-glucose fell (-19 percent) and declined further after an additional 20 h of unloading. This diminution at 24 h was associated with slower oxidation of C-14-glucose and incorporation of C-14-glucose into glycogen. At 3 days of unloading, basal uptake of 2-deoxy-D-glucose did not differ from control. Reloading of the soleus after 1 or 3 days of unloading increased uptake of 2-deoxy-D-glucose above control and returned it to normal within 6 h and 4 days, respectively. These effects of unloading and recovery were caused by local changes in the soleus, because the extensor digitorum longus from the same hindlimbs did not display any alterations in uptake of 2-deoxy-D-glucose or metabolism of glucose.

Henriksen, Eric J.↗
NASA NTRS1988

Problems in analysis of data from muscles of rats flow in space

Comparison of hind-limb muscles of rats flown on Spacelab-3 or tail-traction-suspended showed that 11-17 h reloading postflight might have altered the results. Soleus atrophied; plantaris, gastrocnemius, and extensor digitorum longus grew slower; and tibialis anteiror grew normally. In both flight and simulated soleus and plantaris, higher tyrosine and greater glutamine/glutamate ratio indicated negative protein balance and increased glutamine production, respectively, relative to controls. Aspartate was lower in these muscles. Reloading generally decreased tyrosine, but increased aspartate and glutamine/glutamate. These data showed that 12 h of reloading after flight is characterized by reversal, to varying extents, of the effects of unloading.

Tischler, Marc E.↗
NASA NTRS1988

Changes in fiber composition of soleus muscle during rat hindlimb suspension

A technique in which the gravitational load in the rear limbs of rats was chronically reduced is used to study soleus muscle atrophy in near-zero-gravity conditions. The results show a decline in the number of fibers in groups that contained the slow isoenzyme of myosin and which were classified as type I. The total number of fibers did not change, and fibers containing the intermediate isoenzyme and those classified as type IIa increased. The results are consistent with either a change in the composition within existing fibers or a simultaneous loss of slow fibers accompanied by de novo synthesis of intermediate and fast fibers.

Templeton, G. H.↗
NASA NTRS1988

Periodic weight support effects on rat soleus fibers after hindlimb suspension

The morphological and histochemical properties of rat soleus muscles were investigated following one week of hindlimb suspension. Short-duration daily weight support activity is shown to ameliorate, but not prevent, soleus atrophy induced by hindlimb suspension. The results indicate that fiber cross-sectional area is more responsive to periodic weight support in dark than light ATPas fibers, and that muscle fiber atrophy need not be associated with a loss in succinate dehydrogenase activity.

Hauschka, Edward O.↗
NASA NTRS1988

Effects of immobilization on rat hind limb muscles under non-weight-bearing conditions

The effect of stretched and unstretched immobilization of a hind limb on the concentration and the metabolism of proteins in the hind-limb muscles of rats was investigated. The animals were divided into three groups: (1) weight-bearing controls, (2) tail-cast-suspended, and (3) suspended, with one hind limb immobilized with the ankle in dorsiflexion (30-40 deg angle) and the other freely moving. It was found that unloading the hind limbs for 6 days by tail cast suspension caused soleus to atrophy and reduced growth of the gastrocnemius and plantaris muscles; unloading resulted in a higher degradation rate and lower synthesis rate in both in vitro and in vivo. Chronic stretch of the unloaded soleus not only prevented its atrophy but led to significant hypertrophy, relative to weight-bearing controls, with increases in both the sarcoplasmic and myofibrillar protein fractions. Immobilizing one ankle in dorsiflexion prevented the inhibition of growth in the plantaris and gastrocnemius muscles due to unloading.

Jaspers, Stephen R.↗
NASA NTRS1988

Coexistence of twitch potentiation and tetanic force decline in rat hindlimb muscle

The effect of whole-muscle fatigue on the isometric twitch was investigated in various hindlimb muscles of anesthetized rats, using an experimental protocol designed to assess the levels of fatigability in motor units. The results of EMG and force measurements revealed the existence of a linear relationship between fatigability and the magnitude of the twitch force following the fatigue test in both soleus and extensor digitorum longus muscles.

Rankin, Lucinda L.↗
NASA NTRS1989

Glycogen supercompensation in rat soleus muscle during recovery from nonweight bearing

Events leading to the normalization of the glycogen metabolism in the soleus muscle of rat, altered by 72-h three days of hind-limb suspension, were investigated during the 72-h recovery period when the animals were allowed to bear weight on all four limbs. Relative importance of the factors affecting glycogen metabolism in skeletal muscle during the recovery period was also examined. Glycogen concentration was found to decrease within 15 min and up to 2 h of recovery, while muscle glucose 6-phosphate, and the fractional activities of glycogen phosphorylase and glycogen synthase increased. From 2 to 4 h, when the glycogen synthase activity remained elevated and the phosphorylase activity declined, glycogen concentration increased, until it reached maximum values at about 24 h, after which it started to decrease, reaching control values by 72 h. At 12 and 24 h, the inverse relationship between glycogen concentration and the synthase activity ratio was lost, indicating that the reloading transiently uncoupled glycogen control of this enzyme.

Henriksen, Erik J.↗