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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Response of rat body composition to simultaneous exercise and centrifugation at 3.14g

A study is described calling into question the hypothesis that an increased physical load during chronic centrifugation contributes to the body composition changes observed in centrifuged rats. Considering fat-free and fat-free dry masses of the total body and carcass, it is seen that centrifugation combined with either wheel running or restraint reduced these masses to approximately 85% of the respective 1-g values, that is, the same result with either sedentary rats or rats running several hundred meters per day. It is pointed out that if an effect of a centrifugation-induced load is present but hidden by opposing factors, an analysis of variance should reveal it as an interaction between acceleration and other variables; however, no such interactions are found here. Tables are included emphasizing the pervasive influence of chronic centrifugation after only 12 days exposure.

Pitts, G. C.↗
NASA NTRS1984

Simulating certain aspects of hypogravity: Effects on the mandibular incisors of suspended rats (PULEH model)

The effect of a hypogravity simulating model on the rate of mandibular incisor formation, dentinogenesis and, amelogenesis in laboratory rats was studied. The model is the partial unloading by elevating the hindquarters. In this system, rat hindquarters are elevated 30 to 40 deg from the cage floors to completely unload the hindlimbs, but the animals are free to move about using their forelimbs. This model replicates the fluid sift changes which occur during the weightlessness of spaceflight and produces an osteopenia in the weight bearing skeletons. The histogenesis and/or mineralization rates of the mandibular incisor during the first 19d of PULEH in young growing rats are recorded.

Simmons, D. J.↗
NASA NTRS1984

The effects of spaceflight on the mineralization of rat incisor dentin

Specific effects of space flight on dentin formation on the lower incisors of male rats were determined. Data were Fourier analyzed to determine the spectra of chemical growth rhythms. It was found that Calcium and P were more concentrated in the newly forming dentin of the Flight rats than in comparable regions of control tissues. There was no significant difference in the mean S-concentration between the two groups, but the pattern of S-distribution in the recently formed dentin from the Flight rats was different from that in the control group. Sulfur fluctuations in flight animals periodically peak above the irregular background fluctuations, but there are no comparable sulfur peaks across the dentin in the control. It is indicated that spaceflight has measurable effects on dentinogenesis, and may also bear on the problem of the regulatory role of proteoglycans in mineralization and the maturation of mineral and matrix moieties in skeletal tissue.

Simmons, D. J.↗
NASA NTRS1984

Influence of suspension hypokinesia on rat soleus muscle

Hindlimb hypokinesia was induced in rats by the Morey method to characterize the response of the soleus muscle. Rats suspended for 1-4 wk exhibited continuous and significant declines in soleus mass, function, and contractile duration. Soleus speeding was in part explained by an alteration in fiber type. The normal incidence of 70-90 percent type I fibers in the soleus muscle was reduced after 4 wk of suspension to 50 percent or less in 9 of 11 rats. A significant decline in type I myosin isozyme content occurred without a change in that of type II. Other observed histochemical changes were characteristic of denervation. Consistent with soleus atrophy, there was a significant increase in lysosomal (acid) protease activity. One week of recovery after a 2-wk suspension was characterized by a return to values not significantly different from control for muscle wet weights, peak contraction force, one-half relaxation time, and type I myosin. Persistent differences from control were observed in maximal rate of tension development, contraction time, and denervation-like changes.

Templeton, G. H.↗
NASA NTRS1983

Hematopoiesis in antiorthostatic, hypokinesic rats

Rats exposed to antiorthostatic, hypokinesia showed the following effects which are comparable to those seen in man during or after space flight: weight loss, reduced food and water consumption, transient increases in peripheral hematocrit and RBC count, decreasing MCV and reduced reticulocyte count. In addition, the hemoglobin P50 was shifted to the right. A significant shortening of RBC t1/2 was only seen after suspension. Changes in leukocyte and platelet numbers in suspended rats were also comparable to those in man during space flight, but leukocyte PHA sensitivity in rats showed no consistent alteration. The results demonstrate that this model reproduces many of the hematological effects of space flight and has potential as a tool in understanding the hematopoietic response to zero gravity.

Dunn, C. D. R.↗
NASA NTRS1983

The effects of hypergravity on the rate of antibody formation in the rat

This experiment was designed to measure the immune response in acutely stressed and chronically centrifuged hyper-G-adapted male rats. Rats were exposed to 2.1 and 3.1 G. Acutely stressed animals were injected with sheep red blood cells (SRBC) on the day of inital exposure to hyper-G, and were chronically centrifuged for 10 to 15 days after immunization. Hyper-G-adapted rats were chronically centrifuged for 28 days prior to antigen injection and for 21 days after injection. Booster injections were given and serum samples taken at intervals from 3 to 9 days after the initial and booster injections. Antigen dose, injected ip, ranged between 1.35 x 10 to the 6th and 1.38 x 10 to the 9th SRBC/100 g. body weight. Pair-fed and ad libitum fed noncentrifuged controls were used. No significant differences in anti-SRBC antibody titers were found between centrifuged and control animals, although there were some changes in WBC counts and a significant increase in adrenal-gland size in acutely stressed animals.

Scibetta, S. M.↗
NASA NTRS1984

Skeletal muscle metabolism in hypokinetic rats

Muscle growth, protein metabolism, and amino acid metabolism were studied in various groups of rats. Certain groups were adrenaliectomized; some rats were suspended while others (the controls) were weight bearing. Results show that: (1) metabolic changes in the extensor digitorum longus muscle of suspended rats are due primarily to increased circulating glucocorticoids; (2) metabolic changes in the soleus muscle due to higher steroid levels are probably potentiated by greater numbers of steroid receptors; and (3) not all metabolic responses of the soleus muscle to unloading are due to the elevated levels of glucocorticoids or the increased sensitivity of this muscle to these hormones.

Tischler, M. E.↗
NASA NTRS1985

The salutary effect of dietary calcium on bone mass in a rat model of simulated weightlessness

Whether supplementation of dietary calcium reduces the differences in bone mass of unweighed limbs and normally weighted limbs, and whether parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D (1,25(OH)2D) respond differently to dietary calcium in unweighted animals in comparison with pair-fed controls was studied. The hind limbs of rats were unweighted by a tail suspension method and diets containing 0.1% to 2.4% calcium. After 2 weeks serum calcium, phosphorus, PTH and 1,25(OH)2D intestinal calcium transport were determined and bone mass, ash weight, and calcium in the tibia, L-1 vertebra, and humerus were measured. No significant differences in body weights were observed among the various groups. Suspended rats maintained constant levels of serum calcium and phosphate over the wide range of dietary calcium. Serum PTH and 1,25(OH)2D and intestinal calcium transport fell as dietary calcium was increased. Bone calcium in the tibia and vertebra from suspended rats remained less than that from pair-fed control. It is suggested that although no striking difference between suspended and control animals was observed in response to dieteary calcium, increasing dietary calcium may reduce the negative impact of unloading on the calcium content of the unweighted bones. The salutary effect of high dietary calcium appears to be due to inhibition of bone resorption rather than to stimulation of bone formation.

Bikle, D. D.↗
NASA NTRS1985

Blood Pressure Responses and Mineral Ocorticoid Levels in the Suspended Rat Model for Weightlessness

Cardiovascular responses and fluid/electrolyte shifts seen during space flight are attributed to cephalad redistribution of vascular fluid. The antiorthostatic (AO) rat (suspended head down tilted, 15-20 deg) is used to model these responses. Current studies show that elevated blood pressures in A0 rats are sustained for periods up to seven days. Comparisons are made with presuspension rats. Increased blood pressure in head down tilted subjects suggests a specific response to A0 positioning, potentially relatable to cephalad fluid shift. To assess a role for hormonal regulation of sodium excretion, serum aldosterone levels were measured.

Musacchia, X. J.↗
NASA NTRS1984

Hypergravity effects on litter size, nursing activity, prolactin, TSH, T3, and T4 in the rat

In a recent study of the effects of hypergravity (HG) on the reproductive system of the rat, it was found that the estrous cycle is perturbed in a pseudopregnancy-like pattern upon first exposure of animals to HG. This can be prevented by previous exposure to HG or by administration of bromergo cryptin. Adapted rats can mate and deliver in HG. However, little is known of the condition of the individual pregnant rat, fetuses, and newborn pups in this environment. There are also questions regarding the effects of HG on the number of fetuses, the mortality rate in different HG levels, and the effects on production and secretion of PRL and TSH. The present investigation is concerned with such questions, taking into account possible approaches to avoid or minimize the lethal effects of HG. The obtained results suggest that peripartum plasma PRL levels and thyroid hormone levels are critical for the survival of the litter.

Megory, E.↗
NASA NTRS1985

Fatigue and contraction of slow and fast muscles in hypokinetic/hypodynamic rats

The effects of hypokinesia/hypodynamia (H/H) on the fatigability and contractile properties of the rat soleus (S) and gastrocnemius (G) muscles have been investigated experimentally. Whole body suspension for one week was used to induce H/H, and fatigue was brought on by train stimulation for periods of 45 and 16 minutes. Following stimulation, rapid rates of fatigue were observed in the G-muscles of the suspended rats, while minimal fatigue was observed in the S-muscles. The twitch and tetanic contractile properties of the muscles were measured before and after train stimulation. It is found that H/H suspension increased twitch tension in the G-muscles, but did not change any contractile properties in the S-muscles. The peak twitch, train, tetanic tensions and time to peak were unchanged in the S-muscles of the suspended rats. On the basis of the experimental results, it is concluded that 1 wk of muscle atropy induced by H/H significantly increases fatigability in G-muscles, but does not affect the contractile properties of fast-twitch and slow-twitch muscles.

Fell, R. D.↗
NASA NTRS1985

Hyper-G stress-induced hyperglycemia in rats mediated by glucoregulatory hormones

The present investigation is concerned with possible relations of the hyperglycemic response of rats exposed to hyper-G stress to (1) alterations in blood levels of the glucoregulatory hormones and gluconeogenic substrates, and (2) changes in insulin response on muscle glucose uptake. Male Sprague-Dawley rats weighing 250-300 g were used in the study. The results of the experiments indicate that the initial rapid rise in blood glucose of rats exposed to hyper-G stress is mediated by increases in circulating catecholamines and glucagon, both potent stimulators of hepatic gluconeogenesis. Lactate, derived from epinephrine stimulation of muscle glycogenolysis, appears to be a major precursor for the initial rise in blood glucose. The inhibition of the insulin-stimulated glucose uptake by muscle tissues may be a factor in the observed sustained hyperglycemia.

Daligcon, B. C.↗
NASA NTRS1984

Androgen-estrogen synergy in rat levator ani muscle Glucose-6-phosphate dehydrogenase

The effects of castration and hormone administration on the activity of glucose-6-phosphate dehydrogenase in the rat levator ani muscle were studied. Castration caused a decrease in enzyme activity and in wet weight of the levator ani muscle. Chronic administration of testosterone propionate increased glucose-6-phosphate dehydrogenase activity in the levator ani muscle of castrated rats; the magnitude of the recovery of enzyme activity was related to the length of time of exposure to testosterone propionate after castration as well as to the length of time the animals were castrated. The longer the period of castration before exposure to testosterone propionate, the greater the effect. This result may be related to previously reported castration-mediated increases in androgen receptor binding in muscle. Dihydrotestosterone was less effective than testosterone propionate in enhancing glucose-6-phosphate dehydrogenase activity in the levator ani muscle from castrated rats; estradiol-17-beta alone was ineffective. Combined treatment with estradiol-17-beta and dihydrotestosterone, however, was as effective as testosterone alone. Thus, androgens and estrogens may exert synergistic effects on levator ani muscle.

Max, S. R.↗
NASA NTRS1985

Regulation of hematopoiesis in rats exposed to antiorthostatic, hypokinetic/hypodynamia. I - Model description

The effect of a 7-day suspension in a jacket and harness with 20-deg head-down tilt on body weight, food and water consumption, and hematological parameters is investigated experimentally in male Sprague-Dawley rats weighing 150-175 g. The results are presented in graphs and compared with those for unsuspended controls and with published data on rats and humans exposed to microgravity in space flight. Suspended rats are found to have reduced red-blood-cell mass, erythropoiesis, plasma volume (leading to temporarily increased hematocrit), body weight, and food and water consumption; rightward-shifted oxyhemoglobin-dissociation curves; and unchanged platelet count, leucocyte count or PHA reactivity, and red-blood-cell shape distribution. Since many of these effects are also seen in space flight, the present experimental model is considered a promising technique for simulating the hematopoietic effects of microgravity at 1 g.

Dunn, C. D. R.↗
NASA NTRS1984

Cardiovascular and hormonal (aldosterone) responses in a rat model which mimics responses to weightlessness

Cardiovascular responses and fluid/electrolyte shifts seen during spaceflight have been attributed to cephalad redistribution of vascular fluid. The antiorthostatic (AO) rat (suspended, head-down tilt of 15-20 deg) is used to model these responses. This study documents that elevated blood pressures in AO rats are sustained for periods of up to seven days, compared with presuspension values. Increased blood pressures in AO rats suggests a specific response to AO positioning, potentially relatable to a cephalad fluid shift. To assess a role for hormonal regulation of sodium excretion, serum aldosterone levels were measured. Circulating aldosterone concentrations were seen to increase approximately 100 percent during seven days of AO suspension, concurrently with a pronounced natriuresis. These results suggest that aldosterone may not be involved in the long term regulation of increased Na(+) excretion in AO animals. These studies continue to show the usefulness of models for the development of animal protocols for space flight.

Musacchia, X. J.↗
NASA NTRS1985

A possible role for endogenous glucocorticoids in orchiectomy-induced atrophy of the rat levator ani muscle: Studies with RU38486, a potent and selective antiglucocorticoid

RU38486, a potent and selective antiglucocorticoid, was employed to study a possible role for endogenous glucocorticoids in atrophy of the levator ani muscle secondary to castration of male rats. RU38486 was shown to block (3H) triamcinolone acetonide binding to cytosol from levator ani muscle. Daily oral administration of RU38486 to castrated rats partially prevented atrophy of the levator ani muscle, as well as a decrease in RNA concentration. In a control group receiving RU38486 alone, the levator ani underwent significant (20%) hypertrophy. Administration of exogenous dexamethasone also caused pronounced atrophy of the levator ani muscle. This atrophy was prevented, to a significant degree, by simultaneous oral administration of RU38486. It is concluded that endogenous glucocorticoids, the actions of which are blocked by RU38486, may be involved in regulation of the mass of the levator ani muscle in intact rats.

Konagaya, M.↗
NASA NTRS1986

Regulation of hematopoiesis in rats exposed to antiorthostatic hypokinetic/hypodynamia. II - Mechanisms of the 'anemia'

The cause of the red cell mass (RCM) deficit, which occurs in rats during suspenion, is investigated. The experimental conditions and procedures, in which male Sprague-Dawley rats are subjected to antiorthostatic hyypokinetic/hypodynamia and changes in RCM are monitored, are described. The influences of stress, reduced food and water consumption, and antiorhostatic posture on RCM are analyzed. Changes in body weight, RCM, radioiron incorporation, red blood cells (RBC), and reticulocytes, for the rats after head-down suspension are graphically presented; only the changes in RBC are related to the antiorthostatic posture. The data reveal that anemia is primarily caused by reduced food and water consumption and secondly by restricted movements.

Dunn, C. D. R.↗
NASA NTRS1985

Increased gluconeogenesis in rats exposed to hyper-G stress

The effect of gluconeogenesis on the levels of plasma glucose and liver glycogen was studied in rats exposed to hyper-G stress. Incorporation of lactate, alanine, or glycerol, labeled with C-14, into plasma glucose and liver glycogen was measured in rats centrifuged at 3.1 G for 0.25, 0.50, and 1.0-hr periods, and was compared to noncentrifuged controls injected with appropriate glycogen precursors. It was found that exposure to G-stress leads to increased incorporation from all three substrates into both plasma glucose and liver glycogen. These early incorporation increases were blocked upon pre-G administration of 5-methoxyindole-2-carboxylic acid, a gluconeogenesis inhibitor, or propanolol, a beta-adrenergic blocker, as well as by adrenodemedullation. Results indicate that the rapid rise in plasma glucose, as well as in liver glycogen in rats exposed to hyper-G stress is due to an increased rate of gluconeogenesis, and that epinephrine, released in response to hyper-G-induced activation of the sympathetic-adrenal system, plays a dominant role during the early stages of hyper-G stress.

Daligcon, B. C.↗