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Thymic involution in the suspended rat model for weightlessness: decreased glucocorticoid receptor concentration. THE PHYSIOLOGIST 2001; 27:S39-40. [PMID: 11539011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 02/21/2023]
Abstract
Hindlimb muscle atrophy, thymic involution and adrenal hypertrophy in rats during spaceflight can be simulated using suspension models. Skeletal muscle and thymus are sensitive to glucocorticoids (GC) and previous studies have demonstrated that muscle atrophy in suspended rats is associated with increased GC receptor concentration. The objectives were to confirm thymic involution during suspension, and determine if involution correlated with increased GC receptor concentration. Seven days of antiorthostatic (AO) suspension of rats produced a significant (P<0.001) reduction in thymic wet weight not associated with an alteration of % water content. GC receptor concentration (pmol/mg protein) decreased 20% (P<0.025) in thymus glands from 7 day AO suspended rats. Suspension, therefore, is associated with involution of the thymus but this is not dependent upon AO positioning. Thymus GC receptor concentrations were depressed in 7 day suspended rats, in contrast with previous observations on skeletal muscle, suggesting that different mechanisms may underlie these responses.
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Abstract
Experimental hypothermia and natural hibernation are two forms of hypometabolism with recognized physiological changes, including depression of endocrine and metabolic functions. To better understand functional changes, helox (i.e., helium and oxygen (80:20) mixtures) and low ambient temperatures have been used to induce hypothermia in hamsters and rats. Both clinical and biological survival, i.e., survival without recovery and survival with recovery from hypothermia, respectively, are related to depth and length of hypothermia. In the rat, body temperatures of 15 degrees C for periods greater than 6-10 h greatly restrict biological survival. The role of glucocorticoids in enhancing thermogenic capacity of rats was assessed using triamcinolone [correction of triamcinalone] acetonide. In the hamster, treatment with cortisone acetate prolonged both clinical and biological survival. Hypothermic hamsters continue utilizing circulating glucose until they become hypoglycemic and die. Hypothermic rats do not utilize glucose and respond with a significant hypoinsulinema. The role of endocrines in the regulation of carbohydrate homeostasis and metabolism differs in hibernation and hypothermia. Glucocorticoids influence the hypothermic response in both species, specifically by prolonging induction of hypothermia in rats and by prolonging survival in hypothermic hamsters.
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The use of suspension models and comparison with true weightlessness: "a resumé". THE PHYSIOLOGIST 2001; 28:S237-40. [PMID: 11539736] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/21/2023]
Abstract
The topics for this workshop were selected to illustrate the manner in which particular physiological and biochemical phenomena can be assessed using specific animal model systems. Our speakers presented data which offer comparisons of experiments in earthside laboratories with experiments using subjects which have experienced weightlessness in response to orbital flight. In addition, there have been speculative assertions that the earthside experiments mimic or simulate responses which one may expect to see with exposure to micro or zero gravity conditions. The topics focused on at least three areas that appear to be amenable to earthside investigations; in addition, they serve as primary areas for flight experimentation. As the result of animal and human exposures to microgravity experienced during orbital space flight, there is ample evidence of pathophysiological functional and structural alterations in muscle, bone, cardiovascular and related body fluid shift responses. This Animal Model Workshop represents the first of a series of sessions planned for further meetings of the IUPS Commission on Gravitational Physiology.
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Weightlessness simulations for cardiovascular and muscle systems: validity of rat models. JOURNAL OF GRAVITATIONAL PHYSIOLOGY : A JOURNAL OF THE INTERNATIONAL SOCIETY FOR GRAVITATIONAL PHYSIOLOGY 1997; 4:49-59. [PMID: 11541869] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/21/2023]
Abstract
Animal models are widely used to evoke responses comparable to those obtained during weightlessness. Two models are reviewed; one examines cardiovascular responses and cephalad fluid shifts in head down tilting (HDT), and the other examines atrophy in load bearing muscles by unloading the hind limbs. Cephalad fluid shifts result in diuresis, natriuresis, and kaliuresis. Reversals are rapid, within one week. Reports of cardiovascular responses are not similar among various laboratories, probably due to variations in protocols. Blood pressures (MAP, SP and DP) and heart rates measured with direct aorta cannulations become elevated as early as one and three days of HDT; recovery occurs within several hours; the response is a transient hypertension. The role of central and peripheral sympathetic nervous activity in flight and suspended rats is examined. Rats show little or no evidence of cardiac deconditioning. Direct blood pressures have not been made in flight rats, precluding direct comparisons with earth side experiments. Muscle atrophy and load bearing (slow twitch fibers) and non-load bearing (fast twitch fibers) muscle responses with hind limb unloading and recovery are compared with flight animal responses. Soleus muscle in response to whole body suspension (WBS), tail suspension (TS) or flight exposure consistently shows significant weight loss. In contrast, the extensor digitorum longus and vastus medialis show less marked responses. More specifically, slow twitch fibers in all these muscles show the greatest loss in mass (e.g. cross sectional areas). The conclusion is that both WBS or TS systems are useful in predicting and comparing changes due to weightless flight.
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Abstract
The rat whole body suspension technique mimics responses seen during exposure to microgravity and was evaluated as a model for cardiovascular responses with two series of experiments. In one series, changes were monitored in chronically catheterized rats during 7 days of head-down tilt (HDT) or non-head-down tilt (N-HDT) and after several hours of recovery. Elevations of mean arterial (MAP), systolic, and diastolic pressures of approximately 20% (P < 0.05) in HDT rats began as early as day 1 and were maintained for the duration of suspension. Pulse pressures were relatively unaffected, but heart rates were elevated approximately 10%. During postsuspension (2-7 h), most cardiovascular parameters returned to presuspension levels. N-HDT rats exhibited elevations chiefly on days 3 and 7. In the second series, blood pressure was monitored in 1- and 3-day HDT and N-HDT rats to evaluate responses to rapid head-up tilt. MAP, systolic and diastolic pressures, and HR were elevated (P < 0.05) in HDT and N-HDT rats during head-up tilt after 1 day of suspension, while pulse pressures remained unchanged. HDT rats exhibited elevated pretilt MAP and failed to respond to rapid head-up tilt with further increase of MAP on day 3, indicating some degree of deconditioning. The whole body suspended rat may be useful as a model to better understand responses of rats exposed to microgravity.
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Abstract
The vastus medialis (VM) from rats after 14 days of microgravity on COSMOS 2044 (F) was compared with VM from tail-suspended hindlimb-unloaded rats (T) and ground controls, including vivarium (V), synchronous (S), and basal (B) animals. The VM is composed chiefly of fast-twitch fibers; however, it contains a deep portion closer to the bone with mixed slow- and fast-twitch fibers. In the mixed-fiber portion, type I and II fiber areas were significantly reduced in F animals. In the homogeneous portion with chiefly fast-twitch fibers, F rats also showed reductions in cross-sectional areas compared with T, V, and B but not S rats. Fiber densities (fibers/mm2) were greatest in VM from F rats. Capillary density changes paralleled fiber density changes. F animals have significantly greater density of capillaries in the mixed-fiber portion. Concentrations of protein, RNA, and DNA were highest in V controls, whereas F rats had the lowest level of total RNA. Lactate dehydrogenase activity, one measure of anaerobic capacity, was greater in F than in S rats. Citrate synthase activity, a measure of oxidative capacity, showed no significant differences between groups. Although triglyceride stores of VM were greater in F than in T rats, there were no significant differences from any of the control groups. It was concluded that VM wet weights may be a less sensitive measure of atrophy than the fiber area measurements. Fiber area decreases and fiber density increases in F animals were quantitatively comparable to those in soleus and extensor digitorum longus after 7 days of weightless flight in Spacelab 3. Our results suggest that VM shows measurable responses to weightlessness.
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Effects of caudal elevation on testicular function in rats. Separation of effects on spermatogenesis and steroidogenesis. JOURNAL OF ANDROLOGY 1992; 13:224-31. [PMID: 1351049] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 03/25/2023]
Abstract
A variety of biologic processes are perturbed when exposed to microgravity (space flight) for more than 7 days, including testicular function. Suspension of rats in a special harness (caudal elevation) to induce thoracic pooling of blood fluids and remove the support function of the hind limbs is used to mimic, on earth, the effects of microgravity encountered during space flight. Typically, this induces cryptorchidism in male rats. Three experiments were conducted to differentiate the effects of caudal elevation (30 degrees angle) and anatomic location of testes on spermatogenesis and steroidogenesis. Rats were subjected to caudal elevation for 7 days using either a tail harness (experiments 1 and 2) or a whole-body harness (experiment 3). Testes of rats fell into the abdominal cavity when a tail harness was used, but ligation of the inguinal canal prevented this repositioning. For rats with abdominal testes, testicular weight was reduced (P less than 0.05) and histology of testes was abnormal; the number of spermatids per gram parenchyma was lower (P less than 0.05) in tail-suspended rats compared with control rats. In contrast, spermatogenesis was not affected by caudal elevation in most rats in which the inguinal canal was ligated or in rats elevated by whole-body harness. Concentrations of testosterone in serum and testicular interstitial fluid were lower (P less than 0.05) in suspended rats, regardless of the method used for caudal elevation or anatomic location of testes. Concentrations of luteinizing hormone in serum were elevated (P less than 0.05) in rats with intra-abdominal testes.(ABSTRACT TRUNCATED AT 250 WORDS)
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An assessment of suspension systems: models that reproduce responses to weightlessness. THE PHYSIOLOGIST 1992; 35:S92-5. [PMID: 1589551] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
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9
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Variations in recovery and readaptation to load bearing conditions after space flight and whole body suspension in the rat. THE PHYSIOLOGIST 1991; 34:S170-1. [PMID: 2047428] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
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10
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Morphometric and metabolic indices of disuse in muscles of hibernating ground squirrels. COMPARATIVE BIOCHEMISTRY AND PHYSIOLOGY. B, COMPARATIVE BIOCHEMISTRY 1991; 99:815-9. [PMID: 1790675 DOI: 10.1016/0305-0491(91)90147-6] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
1. Morphological, biochemical and metabolic characteristics of hindlimb muscles from summer-active (SA), winter-active (WA) and hibernating (H) golden-mantled ground squirrels (Spermophilus lateralis) were examined to identify alterations resulting from seasonal periods of inactivity. 2. Cross-sectional areas of fibers from the soleus were reduced in both WA and H, although only significantly (P less than 0.05) in WA. Fibers in the EDL exhibited significant reductions in cross-sectional areas in both H and WA groups. Muscle fiber and capillary densities were altered in quantitative agreement with changes in cross-sectional areas. 3. Protein content was reduced 20% (P less than 0.05) in EDL from H and WA groups, but reductions (10%) in the soleus were not statistically significant. RNA content in WA and H groups was significantly decreased in soleus (20%) and EDL (35%) compared with SA, but DNA content was unchanged. 4. In the plantaris, triglyceride content was unchanged, but citrate synthase activity in H (210 +/- 13 mumol min-1 g-1) was significantly greater than in SA (177 +/- 10). In contrast, LDH activity in H was reduced by 25% (P less than 0.05) compared with SA. 5. These results demonstrate atrophic effects associated with seasonal inactivity in hibernating ground squirrels, but suggest the existence of natural mechanisms which limit the response.
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Abstract
Comparisons of soleus and extensor digitorum longus (EDL) muscles from male Sprague-Dawley rats (350-400 g) after 7 days of weightlessness, 7 and 14 days of whole body suspension (WBS), and 7 days of recovery from WBS and from vivarium controls were made. Muscle mass loss of approximately 30% was observed in soleus after 7 and 14 days of WBS. Measurement of slow- and fast-twitch fibers showed significant alterations. Reductions in cross-sectional areas and increases in fiber densities in soleus after spaceflight and WBS were related to previous findings of muscle atrophy during unloading. Capillary density also showed a marked increase with unloading. Seven days of weightlessness were sufficient to effect a 20 and 15% loss in absolute muscle mass in soleus and EDL, respectively. However, the antigravity soleus was more responsive in terms of cross-sectional area reductions. After 7 days of recovery from WBS, with normal ambulatory loading, the parameters studied showed a reversal to control levels. Muscle plasticity, in terms of fiber and capillary responses, indicated differences in responses in the two types of muscles and further amplified that antigravity posture muscles are highly susceptible to unloading. Studies of recovery from spaceflight for both muscle metabolism and microvascular modifications are further justified.
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Abstract
Disuse can induce numerous adaptive alterations in skeletal muscle. In the present study the effects of hindlimb unloading on muscle mass and biochemical responses were examined and compared in adult (450 g) and juvenile (200 g) rats after 1, 7, or 14 days of whole body suspension. Quantitatively and qualitatively the soleus (S), gastrocnemius (G), plantaris (P), and extensor digitorum longus (EDL) muscles of the hindlimb exhibited a differential sensitivity to suspension and weightlessness unloading in both adults and juveniles. The red slow-twitch soleus exhibited the most pronounced atrophy under both conditions, with juvenile responses being greater than adult. In contrast, the fast-twitch EDL hypertrophied during suspension and atrophied during weightlessness, with no significant difference between adults and juveniles. Determination of biochemical parameters (total protein, RNA, and DNA) indicated a less rapid rate of response in adult muscles. This was corroborated by assessment of muscle alpha-actin mRNA levels, which indicated a rapid (within 1 day) and significant (P less than 0.05) effect in juveniles but not in adults. The results of this investigation indicate 1) a qualitatively similar differential effect of unloading on muscles of adults and juveniles, 2) a quantitatively reduced and less rapid effect of suspension on adult muscles, and 3) a close similarity of adult and juvenile muscle responses during suspension and spaceflight, suggesting that this ground-based model simulates many of the unloading effects of weightlessness.
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13
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Fluid/electrolyte balance and cardiovascular responses: head-down tilted rats. THE PHYSIOLOGIST 1990; 33:S46-7. [PMID: 2371344] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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14
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Biochemical and histochemical observations of vastus medialis from rats flown in Cosmos 1887 (experiment K608). THE PHYSIOLOGIST 1989; 32:S21-2. [PMID: 2727096] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
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Comparative morphometry of fibers and capillaries in soleus following weightlessness (SL-3) and suspension. THE PHYSIOLOGIST 1988; 31:S28-9. [PMID: 11538245] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 04/16/2023]
Abstract
This work is a continuation of efforts to assess responses of rat skeletal muscle to weightlessness and earthside laboratory experiments with unloading of hind limbs. The soleus is a slow twitch, load bearing (antigravity) muscle. Both exposure to weightlessness (W) and to the hypokinesia/hypodynamia of whole body suspension (WBS) results in soleus atrophy. Cross sectional areas of both slow and fast twitch fibers decrease during 7 days of W, and 7 or 14 days of WBS. Density and area changes tended to reverse to control levels during 7 days of recovery (R) following WBS. Capillary density was increased with 7 days of W, and 7 or 14 days of WBS. During 7 days of R the capillary density returned toward control levels. In summary, the reduction in fiber cross sectional areas and increase in fiber and capillary densities support the hypothesis that in both forms of disuse, i.e., W and WBS, there is a loss in soleus muscle cell mass and not in fiber numbers.
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Disuse atrophy, plasma corticosterone, and muscle glucocorticoid receptor levels. AVIATION, SPACE, AND ENVIRONMENTAL MEDICINE 1987; 58:996-1000. [PMID: 3675473] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
A suspension model, characterized by differential atrophy of disused hindlimb skeletal muscles, was utilized to investigate plasma levels of and tissue sensitivity to glucocorticoids. The three objectives were determination of time course and extent of plasma corticosterone changes during 1 week of whole-body suspension; comparison of glucocorticoid receptor site concentrations in muscles differing in morphology and antigravity function; and investigation of the effect of disuse on tissue glucocorticoid receptor site concentrations. Plasma corticosterone increased significantly (p less than 0.01) on the first and third days of suspension, but returned to control levels by day 7. Muscle glucocorticoid receptors exhibited a characteristic hormonal specificity. In controls, receptor site concentration in the slow-twitch soleus (48 +/- 5 fmol/mg prot.) was comparable to that in the fast-twitch gastrocnemius (47 +/- 6) and plantaris (58 +/- 4) muscles but significantly (p less than 0.02) less than the extensor digitorum longus (66 +/- 5). Seven days of suspension resulted in significant differential effects on muscle receptor levels, with a large increase in the soleus (140%), lesser increments in the gastrocnemius (55%) and plantaris (45%), and only a small, statistically insignificant alteration in the EDL (10%). Receptor levels in the soleus remained elevated following 14 d of suspension, but levels in other muscles returned to control values. These results suggest that circulating glucocorticoids, as well as increased tissue hormonal sensitivity, may be related to muscle responses in this model of disuse.
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296. Med Sci Sports Exerc 1987. [DOI: 10.1249/00005768-198704001-00296] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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18
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Introduction. Am J Physiol Regul Integr Comp Physiol 1987. [DOI: 10.1152/ajpregu.1987.252.2.r207] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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Physiological comparison of rat muscle in body suspension and weightlessness. THE PHYSIOLOGIST 1987; 30:S102-5. [PMID: 3562600] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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20
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Physiological responses during whole body suspension of adult rats. THE PHYSIOLOGIST 1987; 30:S94-5. [PMID: 3562638] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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21
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Spaceflight effects on adult rat muscle protein, nucleic acids, and amino acids. THE AMERICAN JOURNAL OF PHYSIOLOGY 1986; 251:R1059-63. [PMID: 2431627 DOI: 10.1152/ajpregu.1986.251.6.r1059] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Exposure to conditions of weightlessness has been associated with decrements in muscle mass and strength. The present studies were undertaken to determine muscle responses at the cellular level. Male Sprague-Dawley rats (360-410 g) were exposed to 7 days of weightlessness during the Spacelab-3 shuttle flight (May 1985). Animals were killed 12 h postflight, and soleus (S), gastrocnemius (G), and extensor digitorum longus (EDL) muscles were excised. Muscle protein, RNA, and DNA were extracted and quantified. Differential muscle atrophy was accompanied by a significant (P less than 0.05) reduction in total protein only in S muscles. There were no significant changes in protein concentration (mg/g) in the muscles examined. In S muscles from flight animals, sarcoplasmic protein accounted for a significantly greater proportion of total protein that in ground controls (37.5 vs. 32.5%). Tissue concentrations (nmol/g) of asparagine-aspartate, glutamine-glutamate, glycine, histidine, and lysine were significantly reduced (from 17 to 63%) in S muscles from flight animals, but only glutamine-glutamate levels were decreased in the G and EDL. Muscle DNA content (microgram) was unchanged in the tissues examined, but S muscle DNA concentration (micrograms/mg) increased 27%. RNA content (micrograms) was significantly (P less than 0.025) reduced in S (-28%) and G(-22%) muscles following spaceflight. These results identify specific alterations in rat skeletal muscle during short term (7-day) exposure to weightlessness and compare favorably with observations previously obtained from ground-based suspension simulations.
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Thymic involution in the suspended rat: adrenal hypertrophy and glucocorticoid receptor content. AVIATION, SPACE, AND ENVIRONMENTAL MEDICINE 1986; 57:162-7. [PMID: 3954705] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The thymus gland and skeletal muscle are sensitive to the catabolic effects of glucocorticoids (GC). Previous studies using suspended rats demonstrated that muscle disuse atrophy resulting from hindlimb unloading was associated with an increase in glucocorticoid receptor site concentration. The objectives of the current studies were: to assess the temporal relationship between adrenal hypertrophy and thymic involution in suspended rats, to evaluate the role of positioning--antiorthostatic, (AO) vs. orthostatic (O)--in the thymic and adrenal responses, and to determine whether or thymic involution, like muscle disuse atrophy, was associated with an increase in GC receptor site concentration. The wet weight of the thymus was reduced by 50% (p less than 0.001) during 7 d of AO suspension. Suspended (AO) rats exhibited a significant (p less than 0.001) hypertrophy of the adrenal glands (33%), primarily on the initial day of suspension. Recovery for 7 d was associated with a return of thymus weight to control levels, but adrenal hypertrophy was not completely reversed. Rats suspended in an O position exhibited thymic and adrenal responses comparable to those of AO rats. Thymic involution in both AO and O rats was associated with a 20% (p less than 0.001) decrease in glucocorticoid receptor site concentration (pmol X mg-1 protein). However, when expressed relative to tissue weight, receptor site concentrations were not significantly different from control values. These results suggest a temporal correlation between adrenal hypertrophy and thymic involution in the suspended rat, but neither of these responses were dependent upon AO positioning.(ABSTRACT TRUNCATED AT 250 WORDS)
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Effect of seven days of spaceflight on hindlimb muscle protein, RNA and DNA in adult rats. THE PHYSIOLOGIST 1985; 28:S221-2. [PMID: 2422671] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
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Altered carbohydrate metabolism in the whole body suspended rat. THE PHYSIOLOGIST 1985; 28:S139-40. [PMID: 3834435] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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Effect of hypokinesia-hypodynamia on rat muscle oxidative capacity and glucose uptake. THE AMERICAN JOURNAL OF PHYSIOLOGY 1985; 249:R308-12. [PMID: 2994497 DOI: 10.1152/ajpregu.1985.249.3.r308] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
Whole-body hypokinetic-hypodynamic (H/H) suspension, unlike other models of muscle disuse, allows voluntary contractile activity. This study examined the oxidative capacity and insulin sensitivity of rat hindlimb muscles subjected to 7 days of suspension H/H conditions. Oxidative capacity was determined by measuring citrate synthase activity and cytochrome c concentration in soleus and gastrocnemius muscles. A perfused hindquarter preparation was used to measure glucose uptake rates at rest with physiological and supramaximal concentrations of insulin in the perfusate. Citrate synthase activity was 17% lower in soleus and 23% lower in gastrocnemius muscles from H/H rats. Similarly, a 29% decrease in H/H rat gastrocnemius cytochrome c concentration was observed. Rates of glucose uptake were lower in muscles from H/H rats compared with controls at physiological levels of insulin and did not increase in response to a further increase in insulin concentration. Muscles undergoing a significant loss in mass after 7 days suspension were found to have increased glycogen concentrations. In conclusion, data presented in this study suggest that hindlimb muscle disuse, brought about by whole-body suspension, results in a decreased aerobic capacity in load bearing muscles and a lowered insulin sensitivity in perfused rat hindlimb muscles.
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Abstract
Glucocorticoids (GC) are important for thermoregulatory responses to low environmental temperatures. Pretreatment of hamsters, which are capable of natural hibernation, with cortisone acetate has been demonstrated to improve carbohydrate homeostasis during hypothermia. The objectives of the current studies were to evaluate the effects of GC pretreatment of a nonhibernator, the rat, on (i) cooling time, (ii) carbohydrate homeostasis (in terms of liver and cardiac glycogen concentrations and plasma glucose concentration), and (iii) duration of survival in hypothermia. In addition, the effects of liver glycogen depletion on cooling times and survival were examined. Hypothermia was induced in rats by exposure to a helium:oxygen (80:20, Helox) atmosphere at 0 degree C. Pretreatment of rats with triamcinolone acetonide (1.5 mg/kg/day, sc, 48, 24, and 1 hr prior to induction) significantly (P less than 0.05) lengthened induction time, while fasting was associated with a significant decrement (25%). While liver and cardiac glycogen levels in control and GC-treated rats fell approximately 45% during cooling, this reduction occurred over a significantly greater period of time in treated rats and suggests a sparing of glycogen or increased capacity for its production in response to GC. Glycogen utilization was accompanied by a hyperglycemia in control, GC-treated, and fasted groups. Survival in hypothermia at a rectal temperature of 14-15 degrees C in GC-treated (9.5 +/- 1.2 hr) and fasted (10.9 +/- 0.9 hr) rats was not significantly different from control (10.5 +/- 1.1 hr) values. These findings suggest that treatment with GC can increase the thermogenic capacity of the rat (as evidenced by an increased induction time) and promote carbohydrate homeostasis, but does not contribute to an enhancement of survival in the hypothermic nonhibernator.
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Senile amyloidosis and neuron binding antibody in the aging Syrian hamster. JOURNAL OF GERONTOLOGY 1985; 40:261-7. [PMID: 3989238 DOI: 10.1093/geronj/40.3.261] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
The effects of age, sex, and irradiation on the genesis of amyloidosis, neuron-binding antibody (NBA), and the concomitant appearance of these two phenomena were studied in a colony of Syrian hamsters. In nonirradiated controls amyloidosis increased in prevalence with age after 12 months, and prevalence was higher in females than in males. Irradiation had the effect of advancing the appearance of amyloidosis to the 7-12 months group but did not intensify the amyloidotic process. IgG binding to the nucleus or cytoplasm of neurons was rare, and, despite the fact that IgM and IgA binding to these structures was present in about one-third of the animals, there was neither an aging nor an irradiation effect. The only statistically significant findings with respect to the concomitant occurrence of amyloid and NBA were negative correlations between nuclear IgM and IgA binding and amyloidosis. Of the various species thus far studied, the hamster is the first in which there has been no aging effect in respect to NBA.
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Abstract
This investigation examined the effects of hypokinesia/hypodynamia (H/H) on fatigability and contractile properties of rat soleus (S) and gastrocnemius (G) muscles. Whole-body suspension for 1 wk was used to eliminate hindlimb load-bearing functions and simultaneously permit voluntary isotonic contractions. Train stimulations (45/min, 16 min) resulted in significantly (P less than 0.05) faster rates of fatigue to lower asymptotes in G from H/H rats. Fatigue in the S was minimal at this stimulation frequency and differences between H/H and control animals were not significant. Contractile properties (twitch and tetanic) were measured before and after train stimulations. H/H suspension resulted in an increased twitch tension in G. However, H/H did not change train or tetanic tensions per gram or other G contractile properties. Peak twitch, train, and tetanic tensions, time to peak tension, one-half relaxation time, and twitch and tetanic peak rates of tension development and decline were unchanged by H/H in S muscles. These results indicate that 1 wk of H/H-induced muscle atrophy significantly increases fatigability in G but does not effect contractile properties of fast-twitch (G) or slow-twitch (S) muscles.
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Abstract
It is obvious that research is far from the last chapter in developing a model for natural hibernation. The relationships and comparative mechanisms for thermogenesis and survival in hibernation and experimental hypothermia are still unclear. Yet, two primary areas appear to be most promising, namely, the control of thermogenesis via the glucocorticoids and the specific role of the central nervous system (CNS) in survival of hypothermic subjects and arousal of hibernating subjects. Although there have been several approaches to understanding the role of the CNS in terms of circulation, integrity of the blood-brain barrier (BBB) system, and CNS sites of activity, it may appear that more questions have been raised than have been answered. However, a more optimistic view can also be taken. The development of a laboratory model, using experimental hypothermia for natural hibernation, is progressing. This view is justified in terms of results from the use of glucocorticoids in metabolic regulation of available carbohydrates, i.e., available glucose in hypothermia, and the continued promising parallel studies of physiological and biochemical integrity of areas of the CNS in hypothermic and hibernating subjects.
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Analysis of 1- and 3-methylhistidines, aromatic and basic amino acids in rat and human urine. JOURNAL OF CHROMATOGRAPHY 1984; 311:267-76. [PMID: 6520174 DOI: 10.1016/s0378-4347(00)84720-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
A procedure based on automated amino acid analysis has been developed to simultaneously quantify 1-methylhistidine (1-MH), 3-methylhistidine (3-MH), tyrosine, phenylalanine, tryptophan, lysine, histidine and arginine levels in human and rat urines. Deproteinized urine samples containing amino acids in the range 1-10 nmol were analyzed using single-column methodology with ninhydrin detection. Standard curves produced correlation coefficients greater than or equal to 0.99 with duplicate analyses agreeing to within +/- 1.9%. Quantitative recovery was ensured by using L-alpha-amino-beta-guanidinopropionic acid as an internal standard. Elution was accomplished in less than 90 min at pH 5.7 with sodium citrate buffers at 45 degrees C and 65 degrees C. Since 3-MH in the rat is acetylated at the alpha-amino group, rat, but not human, urine ultrafiltrates required acid hydrolysis prior to analysis. The utility of the technique of analysis of 1-MH and 3-MH in human urine was demonstrated for an adult male on a meat-free diet for 21 days; urinary excretion rates for 3-MH and 1-MH were determined to be 3.06 +/- 0.10 and 0.72 +/- 0.07 mumol/kg body mass/day, respectively. The technique was also used to measure the effect of disuse atrophy of rat skeletal muscle which induced a 40-60% increase in 3-MH. The procedure is also highly suited for measurement of urinary aromatic and/or basic amino acids.
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Effect of antiorthostatic suspension on interferon-alpha/beta production by the mouse. PROCEEDINGS OF THE SOCIETY FOR EXPERIMENTAL BIOLOGY AND MEDICINE. SOCIETY FOR EXPERIMENTAL BIOLOGY AND MEDICINE (NEW YORK, N.Y.) 1984; 177:253-6. [PMID: 6483860 DOI: 10.3181/00379727-177-41939] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Mice were suspended in a model that simulates weightlessness that occurs during prolonged space flight. After 1 and 2 weeks of suspension in an antiorthostatic (head-down tilt) position, the mice were challenged with polyriboinosinic-polyribocytidylic acid to induce interferon-alpha/beta. Interferon production was severely reduced in mice that had been suspended. When mice were allowed to recover in cages for a week following removal from suspension, they recovered their full interferon-production capacity. Mice suspended in an orthostatic (horizontal) position did not have their interferon production capabilities affected, which indicates that stress per se was not a major component in the effects of antiorthostatic suspension on interferon induction.
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Effect of hypokinesia and hypodynamia on protein, RNA, and DNA in rat hindlimb muscles. THE AMERICAN JOURNAL OF PHYSIOLOGY 1984; 247:R728-32. [PMID: 6208790 DOI: 10.1152/ajpregu.1984.247.4.r728] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Weightlessness is associated with a differential atrophic effect on skeletal muscle that has been attributed to both hypokinesia and hypodynamia. A suspension technique was developed to simulate this atrophic effect by inducing hypokinesia/hypodynamia (H/H) in the rat hindlimb. The purpose of the present studies was to assess the effects of H/H on protein, RNA, and DNA contents in hindlimb skeletal muscles. Suspended animals exhibited a differential reduction in absolute muscle protein content with some alterations in protein concentration. Absolute DNA levels did not change in atrophic muscles. There were pronounced effects of suspension on DNA concentration and on protein/DNA, which suggests that muscle atrophy was accompanied by a reduction in muscle cell size. Hindlimb H/H was associated with a decreased absolute content of RNA in atrophic muscles as well as reductions in RNA/DNA. RNA concentration was reduced 16-21% in atrophic muscles. These findings document a pronounced and differential effect of suspension on hindlimb muscle protein and suggest the potential for effects on the capacity for protein synthesis in muscles from suspended animals.
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33
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A suspension model for hypokinetic/hypodynamic and antiorthostatic responses in the mouse. AVIATION, SPACE, AND ENVIRONMENTAL MEDICINE 1984; 55:612-6. [PMID: 6466257] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Hypokinetic/hypodynamic and antiorthostatic responses to weightlessness and bedrest were simulated in mice using a suspension technique. Animals were suspended for 1 or 2 weeks in an antiorthostatic posture and positioned to permit freedom of movement but eliminate load bearing by the hindlimbs. Suspended mice exhibited reduced food and water intakes and rapid 10% decrease in body weight to a level which was maintained for the remainder of the suspension period. Diuresis was evident in suspended mice, but the natriuresis and kaliuresis previously observed in the suspended rat were not evident. Differential hindlimb muscle atrophy (soleus greater than plantaris = gastrocnemius greater than EDL) and increased excretion of urea and ammonia were also noted in suspended mice. Postsuspension recovery studies indicated that the recovery process was highly effective. These results document specific responses to hypokinesia/hypodynamia and antiorthostasis in the mouse and demonstrate similarities in the responses of mice and rats to suspension. These studies expand the utility of the suspension model and suggest that the mouse may be useful in future studies simulating both weightlessness and bedrest.
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Cardiovascular and hormonal (aldosterone) responses in a rat model which mimics responses to weightlessness. THE PHYSIOLOGIST 1984; 27:S41-2. [PMID: 11539012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 04/16/2023]
Abstract
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 degrees) 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% during seven days of AO suspension concurrently with a pronounced natriuresis. These results suggest that aldosterone many 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.
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Rat hindlimb muscle responses to suspension hypokinesia/hypodynamia. AVIATION, SPACE, AND ENVIRONMENTAL MEDICINE 1983; 54:1015-20. [PMID: 6651726] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Hypokinetic/hypodynamic (H/H) whole body suspension of rats eliminates hindlimb load bearing functions while permitting continued use of the forelimbs. Responses of hindlimb muscles were assessed in terms of absolute and relative weights during 1 and 2 weeks of H/H suspension. Muscle mass loss was in the order soleus greater than gastrocnemius = plantaris greater than extensor digitorum longus (EDL). The soleus, a postural antigravity muscle composed mainly of slow twitch fibers, was most sensitive, losing 35% and 45% of its weight during the first and second weeks, respectively. The gastrocnemius and plantaris showed losses during the first week but no significant loss during the second week. The EDL showed little or no weight loss. During post suspension recovery all muscles showed a weight gain. H/H suspended rats failed to grow; following removal from suspension they gained weight linearly, comparable to controls. Products of muscle metabolism including urea, ammonia, and 3-methylhistidine increased in the urine during H/H suspension and were significantly reduced approaching control levels during recovery. This suspension model offers considerable promise for comparison with H/H responses during weightlessness.
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Introduction. Am J Physiol Regul Integr Comp Physiol 1983. [DOI: 10.1152/ajpregu.1983.244.3.r303] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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A new rat model for studies of hypokinesia and antiorthostasis. THE PHYSIOLOGIST 1980; 23:S91-2. [PMID: 7243948] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
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39
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Water metabolism and renal function during hibernation and hypothermia. FEDERATION PROCEEDINGS 1980; 39:2969-73. [PMID: 6998740] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Total water turnover in normothermic, cold-exposed 13-lined ground squirrels was about half that predicted from allometric relationships of water loss and body weight. During hibernation pulmocutaneous water loss and oxygen consumption were 1/77th and 1/52nd of values during normothermia, respectively, in this species. Renal function during deep torpor with body temperatures of 8 C or lower has also been assessed in ground squirrels and hamsters. The weight of evidence suggests that glomerular filtration and urine formation are absent of undetectable in these animals. We feel that the reduction in arterial blood pressure may be the primary adaptation for eliminating filtration. If filtration (which is not thermally vulnerable, being dependent on hydrostatic pressure) occurred, it is difficult to imagine how reabsorption (which has critical metabolic steps such as ion transport that would be thermally vulnerable) could keep pace. Filtration and hypertonic urine formation occur at body temperatures of 20 to 30 C during the arousal process. Marmots differ from other hibernating rodents in that measurable filtration and hypertonic urine formation occurs during hibernation.
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Model for antiorthostatic hypokinesia: head-down tilt effects on water and salt excretion. JOURNAL OF APPLIED PHYSIOLOGY: RESPIRATORY, ENVIRONMENTAL AND EXERCISE PHYSIOLOGY 1980; 49:576-82. [PMID: 7440274 DOI: 10.1152/jappl.1980.49.4.576] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Water and electrolyte excretion was investigated in antiorthostatic hypokinetic and orthostatic hypokinetic and control rats in metabolic cages. Significant (t test, P < 0.05), diuresis, natriuresis, and kaliuresis occurred in the antiorthostatic hypokinetic subjects but did not occur in either the orthostatic hypokinetic or controls. Recovery from antiorthostatic hypokinesia was characterized by retention of water, sodium, and potassium. Patterns of changes in body weight and food and water orthostatic hypokinetic rats and thus could not account for the differences in renal handling of water and electrolytes. Also, differences in ingestion of food and water in controls could not account for differences in excretion of water and electrolytes between these and antiorthostatic hypokinetic rats. It was concluded that the antiorthostatic position was responsible for the diuresis and natriuresis and that the antiorthostatic hypokinetic rat appears to be a good model for the study of water and electrolyte excretion during conditions such as bed rest, water immersion, and exposure to weightlessness.
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A model for hypokinesia: effects on muscle atrophy in the rat. JOURNAL OF APPLIED PHYSIOLOGY: RESPIRATORY, ENVIRONMENTAL AND EXERCISE PHYSIOLOGY 1980; 48:479-86. [PMID: 7372517 DOI: 10.1152/jappl.1980.48.3.479] [Citation(s) in RCA: 100] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Hypokinesia in the hindlimbs of rats were induced by suspension; a newly developed harness system was used. The animal was able to use its forelimbs to maneuver, within a 140 degrees arc, to obtain food and water and to permit limited grooming of the forequarters. The hindlimbs were nonload bearing for 7 days; following a 7-day period of hypodynamia, selected animals were placed in metabolic cages for 7 days to study recovery from hypokinesia. During the 7-day period of hypokinesia there was evidence of muscle atrophy. Gastrocnemius weight decreased, renal papillary urea content increased, and daily urinary losses of urea, NH3, and 3-methylhistidine increased. During the 7-day recovery period muscle mass and excretion rate of urea, NH3 and 3-methylhistidine returned to control levels. Calcium balance was positive throughout the 7-day period of hypokinesia. Hypertrophy of the adrenals suggested the occurrence of some level of stress despite the apparent behavioral adjustment to the suspension harness. It was concluded that significant muscle atrophy and parallel changes in nitrogen metabolism occur in suspended rats and these changes are readily reversible.
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42
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The function of glucocorticoids in thermogenesis. FEDERATION PROCEEDINGS 1979; 38:2177-81. [PMID: 446769] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Studies both in vivo and in vitro implicate glucocorticoids in various aspects of thermogenesis and prevention of heat loss. Many or most of these effects are probably permissive. Adrenalectomized, cold-exposed rats require glucocorticoids for catecholamine-mediated mobilization of free fatty acids, for shivering responses, and for vasoconstriction and piloerection. Glucocorticoid pretreatment of hypothermic hamsters results in a physiological state more similar bioenergetically to hibernation than to hypothermia. For example, such hamsters can arouse to normothermia from a body temperature of 8 C in a 7--8 C cold room. Lipolytic, gluconeogenic, glycogenolic, and pressor actions resulting from several hormone interactions that require glucocorticoids for optimum responses may account for the enhanced thermogenic ability shown by glucocorticoid-pretreated hamsters. Glucocorticoid treatment also results in enhanced blood and liver carbohydrate levels during hypothermia, a condition similar to that occurring in naturally hibernating animals as opposed to the depleted carbohydrate reserves generally seen in hypothermic animals.
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43
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Intestinal transport of hexoses in the rat following chronic heat exposure. JOURNAL OF APPLIED PHYSIOLOGY: RESPIRATORY, ENVIRONMENTAL AND EXERCISE PHYSIOLOGY 1979; 47:87-90. [PMID: 468678 DOI: 10.1152/jappl.1979.47.1.87] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The effect of 3 wk heat exposure (Ta 34 degrees C) on intestinal weight and intestinal absorption of D-glucose and D-galactose in vitro was examined in the rat. Intestinal dry weight was reduced with heat exposure compared to both ad libitum and pair-fed animals at Ta 22 degrees C. Intestinal tissue water was elevated after pair feeding but not heat exposure; extracellular (inulin) space was similar in the three groups. Mucosal uptake of glucose per gram wet weight in an everted sac preparation was unchanged compared to pair-fed animals, but serosal transfer was increased. Intestinal metabolism of glucose was decreased with heat exposure. Galactose accumulation with 30 min incubation was increased in intestinal rings from both heat-exposed and pair-fed animals. This increase is likely to be related to the reduction in ring size present in the groups with reduced food intake. Vmax and apparent Km for galactose transport were unchanged. Our results indicate that despite a reduction in intestinal weight following heat exposure, the ability of the intestine to transport hexoses per gram remains relatively stable. Alterations of hexose transport appear to be related to altered glucose metabolism and not altered transport capacity. Differences in intestinal weight and glucose utilization between pair-fed and heat-exposed animals suggest that the intestinal response to chronic heat exposure is not solely a function at the amount of food consumed. However, the alteration of more than one variable in pair feeding makes interpretation complex.
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Fever and hyperthermia: introduction. FEDERATION PROCEEDINGS 1979; 38:27-9. [PMID: 759234] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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45
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Glucocorticoids and carbohydrate metabolism in hypothermic and hibernating hamsters. EXPERIENTIA. SUPPLEMENTUM 1978; 32:247-58. [PMID: 274310 DOI: 10.1007/978-3-0348-5559-4_28] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
In hibernating hamsters carbohydrate reserves are regulated and are in dynamic equilibrium. During "deep" hypothermia (Tb 7-8 degrees C) hamsters undergo a progressive hypoglycemia, depletion of liver glycogen, and death within 24 hours. Glucocorticoid treatment results in enhanced blood and liver carbohydrates, prolonged survival at Tb 7-8 degrees C, and enhanced thermogenic capacity leading to arousal.
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46
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Diabetes mellitus in the 13-lined ground squirrel (Citellus tridecemlineatus). LABORATORY ANIMAL SCIENCE 1977; 27:477-81. [PMID: 333178] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Spontaneous diabetes mellitus was diagnosed in six of 126, 13-lined ground squirrels, Citellus tridecemlineatus. Serum glucose values were significantly higher in the diabetic ground squirrels than in the non-diabetic ground squirrels, while serum insulin values of fasted diabetic squirrels were significantly lower than fasted nondiabetic ground squirrels. In addition, the classic diabetic signs of poly-dipsia, polyuria, glycosuria, ketonuria, polyphasia, and weight loss were present. The proportion of islet tissue to total pancreatic area in diabetic ground squirrels was less than 25% of that in the nondiabetic ground squirrels. Both the number and size of the islets of Langerhans in diabetic ground squirrels were less than those in nondiabetic ground squirrels.
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Mechanisms responsible for decreased glomerular filtration in hibernation and hypothermia. JOURNAL OF APPLIED PHYSIOLOGY: RESPIRATORY, ENVIRONMENTAL AND EXERCISE PHYSIOLOGY 1977; 42:420-5. [PMID: 838661 DOI: 10.1152/jappl.1977.42.3.420] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Mechanisms underlying the elimination or marked depression of renal function in hibernation and hypothermia were investigated through measurements of blood pressure, heart rate, red blood cell and plasma volumes, and relative distribution of cardiac output. Hamsters (Mesocricetus auratus) were made hypothermic (rectal temperature (Tre), 7 degrees C) by exposure to helox and cold, or permitted to hibernate with several weeks of cold exposure (Ta approximately 5 degrees C). Mean arterial pressure, 120 Torr in normothermic control animals, demonstrated a 55% and 60% decrease during hibernation and hypothermia, respectively. As the animals rewarmed from hypothermia or aroused from hibernation, blood pressure increased rapidly at 8-12 degrees C, more gradually at 12-17 degrees C, and plateaued thereafter. Blood pressure rapidly returned to near control levels whereas heart rate remained at less than one-half control value at the highest temperature examined. Red blood cell volume, 26.2 +/- 0.6 ml/kg body wt in the control animals appeared unaffected by hypothermia. Plasma volume, by contrast, decreased from control values of 33.0 +/- 0.8 to 21.3 +/- 0.6 ml/kg body wt in hypothermia, a decrease of approximately 35%. Distribution of cardiac output to various organs in hibernation and hypothermia followed a similar pattern. Relative flow to the heart, lung, diaphragm, and brown fat increased while the fraction distributed to the visceral organs appeared to decrease. The normothermic control kidney received approximately 16% of the cardiac output while the hibernating and hypothermic kidneys received approximately 10% and 6%, respectively. The data are discussed in terms of the determinants of glomarular filtration rate and explain, in part, the elimination or marked reduction in renal function observed in depressed metabolic states.
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Abstract
Hamsters undergo hypothermia when exposed to a mixture of 80% helium and 20% oxygen at low ambient temperatures. The hypothermic hamster, rectal temperature (Tre) 7 degrees C, becomes hypoglycemic, and reversal of hypoglycemia is effected with glucose infusion. Hypothermic hamsters at Tre 7 degrees C showed a fivefold increase in survival times from 20 to 100.5 h when infused with glucose which maintained a blood level at about 45 mg/100 ml. A potential role for osmotic effects of the infusion was tested and eliminated. There was no improvement in survival of 3-O-methylglucose or dextran 40-infused animals. The fact that death eventually occurs even in the glucose-infused animal after about 4 days and that VO2 undergoes a slow decrement in that period suggests that hypothermic survival is not wholly substrate limited. Radioactive tracer, [U-14C]glucose, showed that localization of the 14C, was greatest in brain tissue and diaphragm, intermediate in heart and kidney, and lowest in skeletal muscle and liver. The significance of the label at sites important to respiration and circulation was presented.
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Mechanisms of temperature regulation in heat-acclimated hamsters. THE AMERICAN JOURNAL OF PHYSIOLOGY 1976; 231:707-12. [PMID: 970452 DOI: 10.1152/ajplegacy.1976.231.3.707] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Mechanisms of temperature regulation were assessed by measurements of oxygen consumption (VO2), body temperature (Rre = rectal, Tsk = skin), evaporative water loss (EWL), regional distribution of blood flow, and blood volume. Hamsters (Mesocricetus auratus) were acclimated to ambient temperatures of 34 or 22 degrees C. VO2 of 34 degrees C-exposed animals was reduced to 50% of that of controls at 22 degrees C, whereas EWL with heat exposure was almost double that of controls. Heat-acclimated animals had a slightly elevated Tre in comparison to 22 degrees C-acclimated animals, whereas there was a marked elevation in Tsk with heat exposure, in contrast to control animals at 22 degrees C. Blood flow distribution measurements indicated that with 34 degrees C exposure there was a decreased flow in liver, kidney, and intestine, whereas there was an increase to the carcass. Red cell and plasma volumes in heat-acclimated hamsters were decreased belwo the values of the 22 degrees C controls. Heat acclimation of the fhamster appears to involve reduced VO2 and increased WEL. Convective and radiative heat loss appear to be maintained by increased Tsk with heat exposure. Nonevaporative heat dissipation mechanisms are of primary importance in thermoregulation of the heat-acclimated hamster, and it is suggested that this is mediated by increased peripheral blood flow with reduced flow to the viscera.
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Hypothermia induction and survival in hamsters: the role of temperature acclimation and an anesthetic (Holothane). Cryobiology 1976; 13:361-7. [PMID: 1277875 DOI: 10.1016/0011-2240(76)90119-x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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