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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Propranolol and pyrogen effects on shivering and nonshivering thermogenesis in rats

The influence of pyrogen and propranolol (a beta-adrenergic antagonist) on shivering and nonshivering thermogenesis (NST) in male rats exposed to 24-25 C and 17-18 C is studied. It is found that intavenous injection of an exogenous pyrogen into rats exposed to 24-25 C elicited a thermogenic response manifested by elevated body temperature, rate of oxygen consumption, and shivering activity, and that propranolol markedly diminished the pyrogen-induced increases in oxygen consumption and colonic temperature, with little changes in shivering activity. In contrast, in cold-exposed rats, propranolol did nor significantly affect the pyrogen-evoked thermogenesis; shivering rather tended to increase when NST was blocked. It is suggested that the fibrile responses evoked by exogenous pyrogen involve differential effects on the two modes of heat production. The assumption that pyrogen acts at a site common to both shivering and nonshivering pathways or that it uniformly alters the individual set points and/or thresholds for both thermogenic effectors is therefore unlikely in the light of the data presented.

Horwitz, B. A.↗
NASA NTRS1979

Weight control and restraint of laboratory rats

The use of restrained and confined rats in some procedures used in combustion toxicology introduces the problems of obtaining rats of the appropriate size for the apparatus, and of identifying any artifacts resulting from the use of restraint alone. Feeding studies indicate that controlled feeding of fast-growing strains such as the Sprague-Dawley can hold rat size essentially constant for significant periods of time. The undesirable aspects are the need to cage the animals individually, with resultant psychological as well as metabolic effects. Restraint studies of slow-growing strains such as the Fischer 344 indicate that denying access to food and water for periods of several hours at a time interrupts normal gain only temporarily.

Hilado, C. J.↗
NASA NTRS1979

Spaceflight and bone turnover - Correlation with a new rat model of weightlessness

Earlier manned spaceflight studies have revealed that the near-weightless environment of orbital flight produce certain biological effects in humans, including abnormalities in mineral metabolism. The data collected were compatible with bone mineral loss. Cosmos 782 and 936 experiments have shown a decrease in rat bone formation rate. In this paper, a rat model of weightlessness is described, which is unique in that the animal is free to move about a 360-deg arc. The model meets the requirements for an acceptable system. Data from the model and spaceflight are presented. Many of the responses noted in suspended animals indicate that the model closely mimics results from rats and man exposed to near-weightlessness during orbital spaceflight.

Morey, E. R.↗
NASA NTRS1980

Dynamics of change in rat arterial pressure under conditions of immobilization

Emotional stress developed in immobilized rats was shown to be accompanied by changes in the regulation of arterial pressure and the frequency of cardiac contractions. A group of adapting rats displayed definite resistance to emotional stress, while a group of rats incapable of adapting to acute emotional stress died with characteristics of cardiovascular insufficiency. The mechanisms providing resistance to emotional stress in numerous conflict situations were analyzed.

Yumatov, Y. A.↗
NASA NTRS1980

Adrenocortical response in rats subjected to a stress of restraint by immobilization whether accompanied by hypothermia or not

The restraint associated with hypothermia which increases the adrenal activity in rats was investigated. In rats with nomothermia or light hypothermia, the plasma and adrenal corticosterone levels increase at least threefold whatever the duration of restraint. Their return to normal values depends on the duration of the restraint. Exposure to cold produces in free rats a light hypothermia with an increase of the plasma and adrenal corticosterone levels, and in restraint animals an important hypothermia which does not potentiate the stimulation of adrenocortical activity induced by the restraint alone.

Buchel, L.↗
NASA NTRS1980

Thermoregulation in rats: Effects of varying duration of hypergravic fields

The effects of hypergravitational fields on the thermoregulatory system of the rat are examined. The question underlying the investigation was whether the response of the rat to the one hour cold exposure depends only upon the amplitude of the hypergravic field during the period of cold exposure or whether the response is also dependent on the amplitude and duration of the hypergravic field prior to cold exposure. One hour of cold exposure applied over the last hour of either a 1, 4, 7, 13, 19, 25, or 37 hr period of 3G evoked a decrease in core temperature (T sub c) of about 3 C. However, when rats were subjected concurrently to cold and acceleration following 8 days at 3G, they exhibited a smaller fall in T sub c, suggesting partial recovery of the acceleration induced impairment of temperature regulation. In another series of experiments, the gravitational field profile was changed in amplitude in 3 different ways. Despite the different gravitational field profiles used prior to cold, the magnitude of the fall in T sub c over the 1 hr period of cold exposure was the same in all cases. These results suggest that the thermoregulatory impairment has a rapid onset, is a manifestation of an ongoing effect of hypergravity, and is not dependent upon the prior G profile.

Horowitz, J. M.↗
NASA NTRS1980

Change in energy expenditure and brain and adrenal content of catecholamines in rats during muscular loading and hypokinesia

In male 1-7 month old rats, the growth and the protein content of skeletal muscles were higher than in female rats while the O2 consumption and the heart rate were lower. This is combined with reduction of the thyroid gland weight and of catecholamine content in adrenals at the age of 7 months. The development of male and female rats (1-7 month) under conditions of systematic muscular loads increases the growth tempo and protein of skeletal muscles and intensifies the degree of reduction of energy expenditure and the heart rate. This is accomplished by the greater reduction of relative weight of the thyroid gland and, at the age of 7 months, by reduction of the noradrenaline content in the brainstem. Hypodynamic conditions have the exact opposite effect.

Rozanova, V. D.↗
NASA NTRS1982

Body composition data from the rat subjects of Cosmos 1129 experiment K-316

The effects of 18.5 days of weightlessness on the body composition of young, growing, male laboratory rats were examined. Three groups of 5 rats each were examined. It is indicated that exposure of young, growing, male rats to 18.5 days of weightlessness produces: (1) no effect on the quantity of fat stored by the body; (2) a slight reduction in the quantity of fat free tissue laid down by the body; (3) a small reduction in the fraction of water contained by the fat free body mass; (4) a similar reduction in the fraction of water contained by the fat free skin and fat free carcass; (5) a shift in relative distribution of the total body water from skin to viscera; (6) a diminution in the fraction of extracellular water contained by the fat free body; (7) no effect on the fraction of total skeletal musculature contained by the fat free body, as indicated by body creatine content; (8) a sizeable reduction in the fraction of bone mineral contained by the fat free body, as calculated from body calcium content. The nature of the physiological changes induced by unloading from Earth gravity in the mammalian organism are illustrated.

Pace, N.↗
NASA NTRS1982

The efficiency coefficient of the rat heart and muscular system after physical training and hypokinesia

The efficiency of an isolated heart did not change after prolonged physical training of rats for an extreme load. The increase in oxygen consumption by the entire organism in 'uphill' running as compared to the resting level in the trained rats was 14% lower than in the control animals. Prolonged hypokinesia of the rats did not elicit a change in the efficiency of the isolated heart.

Alyukhin, Y. S.↗
NASA NTRS1982

Conditioned feeding suppression in rats produced by cross-coupled and simple motions

Results are presented of an experiment on the induction of motion sickness in rats by the use of cross-coupled accelerations of magnitudes similar to those used in human experiments. Accelerations were produced in a seesaw apparatus with rotating disks supporting the animal cages mounted on each seesaw arm, and motion sickness was assessed according to the consumption of a sweet food previously offered to the animals immediately before the motion treatment. During a 1-hour test session 72 h after motion treatment and after a 24-h fast, rats having undergone cross-coupled vertical sinusoidal and rotational motion are observed to consume less food than those having experienced either type of motion alone, or no motion. The ordering of the conditioned suppressive feeding effects is consistent with the amounts of vestibular stimulation produced by the respective motions. The results support the existence of motion sickness effects in rats, even though they are unable to vomit.

Fox, R. A.↗
NASA NTRS1982

Morphometric analysis of rat muscle fibers following space flight and hypogravity

The effect of hypogravity on striate muscles, containing both fast twitch glycolytic and slow twitch oxidative fibers, was studied in rats aboard two Cosmos biosatellites. Results of a computer-assisted image analysis of extensor digitorum muscles from five rats, exposed to 18.5 days of hypogravity and processed for the alkaline ATPase reaction, showed a reduction of the mean fiber diameter (41.32 + or - 0.55 microns), compared to synchronous (46.32 + or - 0.55 microns) and vivarium (49 + or - 0.5 microns) controls. A further experiment studied the ratio of fast to slow twitch fibers in 25 rats exposed to 18.5 days of hypogravity and analyzed at four different periods of recovery following the space flight. Using the previous techniques, the gastrocnemius muscle showed a reduction of the total muscle fiber area in square microns and a reduction in the percentage of slow fibers of flight animals compared to the control animals.

Chui, L. A.↗
NASA NTRS1982

A new rat model for studies of hypokinesia and antiorthostasis

A new rat model (suspension and immobilization) is described for induction of hypokinesia and orthostatic manipulations. Hypokinetic responses were comparable to those in prolonged bed rest and weightlessness in humans, body or limb casted and small cage restrained animals. Responses to antiorthostasis (15 to 20 deg head down tilt) in rats were similar to those in neutral bouyancy tests in humans and animals and to those in prolonged bed rest in humans. During seven days of hypokinesia there was an atrophy of the gastrocnemius and increased excretion of urinary nitrogeneous end products. The antiorthostatic (AOH) 15 to 20 deg head down tilt resulted in diuresis, natriuresis and kaliuresis. No comparable responses were observed in orthostatic hypokinetic (OH) rats. Readaptation from AOH and OH occurred during one week recovery in metabolic cage conditions.

Musacchia, X. J.↗
NASA NTRS1982

Atrophy of rat skeletal muscles in simulated weightlessness

A hypokinetic rat model was used for elucidation of the mechanism of skeletal muscle wasting which occurs in weightlessness. Rats were suspended from a back-harness with the head tilted downward and the hind limbs totally unloaded. A progressive decrease in the size of the soleus muscle from suspended rats was observed as a function of time. The rate of protein degradation of the homogenates from the soleus muscles of suspended and control animals was not significantly different. The rate of cell-free protein synthesis was severely repressed in the atrophied muscle. An initial rise in the levels of plasma glucose and corticosterone was observed on the second day of suspension, but they subsequently returned to normal values.

Feller, D. D.↗
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.↗