Model Of Microgravity Research Articles

Animal Model of Simulated Microgravity: A comparative study of hindlimb unloading via tail vs. pelvic suspension

The aim of this study is to compare the effects of simulated microgravity in tail suspended (TS) as well as in pelvic suspended (PS) rats mimicking aspects of prolonged bed rest and sub‐clinical insulinopenia.Materials and MethodsAdult male Sprague‐Dawley rats divided into suspended and control‐non‐suspended groups (6 each per group), were subjected to two separate methods of suspension and maintained with regular food and water for two weeks. Body weights, food and water consumption, soleus muscle weights, malodialdehyde levels of soleus muscle and brain tissues were measured. Pressure‐pain threshold (PPT) was measured using Randall‐Selitto technique at regular 2–3 days intervals during one week before and 2 weeks after HLS.ResultsBody weights in suspended rats from day 10 are significantly different between groups. Food and water intakes are not different between control and suspended groups. Suspended rats had smaller soleus muscle weights and increased MDA levels (p <0.05). PPT were decreased below control after 5 days of PS and 10 days of TS and continued to drop till day 14. X‐ray images show less spinal deformity in PS rats as compared to TS rats.ConclusionsThese data suggest that both procedures develop peripheral neuropathy. Pelvic suspension appears to provide a suitable alternative to tail suspension for chronic hindlimb unloading alleviating excess stress.

Fundamental and applied objectives of investigation in dry immersion

The results of extended comparative research in the effect of hypogravity on the motor system in space flights and ground-based experiments have shown that “dry” immersion (DI) is the most adequate model of microgravity—the time of development, and the volume and depth of structural and functional motor disorders in DI are very close to what is observed in real microgravity. The high intensity and speed of development of hypogravity effects during immersion hypokinesia in comparison with bed rest hypokinesia, differing from DI only by the level of support deafferentation, promoted an insight into the leading (triggering) role of support lessness in the genesis of microgravity-induced syndromes of muscular deconditioning and hypogravitational ataxia. The involvement and pathways of support afferentation within the muscular system were experimentally studied and verified. The mechanisms of the development of changes in the activity of the system mechanisms remain much less investigated. These issues, as well as some new approaches for the elimination of the negative effects of hypogravity, were the subjects of investigation in the program of a complex dry immersion experiment, the results of which are presented in this issue of the journal.

Early changes in vasoreactivity after simulated microgravity are due to an upregulation of the endothelium-dependent nitric oxide/cGMP pathway

Emerging evidence suggests that nitric oxide (NO) plays a pivotal role in the mechanism of vascular hyporesponsiveness contributing to microgravity-induced orthostatic intolerance. The cellular and enzymatic source of the NO, however, remains controversial. In addition, the time course of the endothelial-dependent contribution remains unstudied. We tested the hypotheses that the change in vasoresponsiveness seen in acute (3-day) hindlimb unweighted (HLU) animals is due to an endothelium-dependent mechanism and that endothelial-dependent attenuation in vasoreactivity is due to endothelial nitric oxide synthase (NOS-3) dependent activation. Vasoreactivity was investigated in rat aortic rings following acute HLU treatment. Dose responsiveness to norepinepherine (NE) was depressed after 3-day HLU [1,338 +/- 54 vs. 2,325 +/- 58 mg at max (NE), HLU vs. C, P < 0.001]. However, removal of the endothelium restored the vascular contractility to that of C. In addition, 1H-oxadiazole quinoxalin-1-one (ODQ), a soluble guanylyl cyclase inhibitor, restored the reduced vasoconstrictor responses to phenylephrine (PE) seen in 3-day HLU rings (1.30 +/- 0.10 vs. 0.53 +/- 0.07 g, HLU + ODQ vs. HLU, P = 0.0001). Ca(+) dependent nitric oxide synthase (NOS) activity was increased, as was vascular NO products as a result of HLU. While NOS-3 expression was not increased in HLU rats, phosphorylation of NOS-3 at serine-1177 (an activator of NOS-3) was increased while phosphorylation of serine-495 (an inactivator of NOS-3) was decreased. These findings demonstrate that changes in vasoresponsiveness in the acute HLU model of microgravity are due to an upregulation of the endothelial-dependent NO/cGMP pathway through NOS phosphorylation.

Effects of a Simulated Microgravity Model on cell structure and function in mouse testis

Decreased testicular blood flow shift occurring under microgravity conditions causes impaired spermatogenesis in males. The tail suspended model has been used mainly in studies of muscle atrophy/osteoporosis and of body fluid shift in few studies aimed at spermatogenesis. We examined serum testosterone levels, testis morphology and apoptotic phenomena in tail suspended mice, a model used to reproduce some of the effects of the absence of gravity. Male C57BL mice (6months old) were divided into two groups: tail suspended (TS) and controls (C). After 14 days of treatment testosterone levels were determined. On fixed sections histological stain (HE) was performed; DNA fragmentation was visualized using TUNEL technique. On the frozen samples immunoblotting for BAX, Bcl2, Caspase 39 and p53 was carried out. Testosterone levels were 0.18±0.09 and 3.74±2.2 ng/ml (mean±DS) in suspended and control animals, respectively. HE staining showed disturbed cell arrangement and a markedly decreased number of spermatozoa in the testes, TUNEL revealed an increased apoptotic index and immunoblotting provided evidence of apoptotic markers in TS animals. These data support results previously obtained by other groups showing a significant influence of short duration microgravity conditions on testicular function.

Rat Pancreatic Response to Simulated Microgravity by Hindlimb Suspension

Hindlimb suspension (HLS) of rats is a validated model of simulated microgravity representing weightlessness. This study examines the stress response induced by HLS on the structural integrity of endocrine and exocrine pancreas in rats. The influence of a dietary soyprotein meal was also examined. Four groups of animals were used: two unsuspended control having each group fed with either Purina chow or a meal containing 100% custom made soyprotein meal and two suspended groups with the same feeding schedule but suspended for one week by their tail. After one week, the animals were sacrificed to collect pancreatic tissues for measurements of malondialdyde (MDA) and histopathological changes. The results show that HLS significantly increased MDA levels in addition to marked structural changes in the exocrine and endocrine pancreas as determined by vacuolation, vacuolar fusion, pyknosis and increased size and number of islets. These effects by HLS have been significantly reversed with dietary soyprotein meal. The results suggest that pancreatic response to one week suspension by HLS is induced by oxidative stress and soyprotein appeared to have the protective effect on this organ (Supported by a grant from Arkansas Space Grant Consortium).

Removal of the N-terminal Extension of Cardiac Troponin I as a Functional Compensation for Impaired Myocardial β-Adrenergic Signaling

Although beta-adrenergic stimuli are essential for myocardial contractility, beta-blockers have a proven beneficial effect on the treatment of heart failure, but the mechanism is not fully understood. The stimulatory G protein alpha-subunit (Gsalpha) couples the beta-adrenoreceptor to adenylyl cyclase and the intracellular cAMP response. In a mouse model of conditional Gsalpha deficiency in the cardiac muscle (Gsalpha-DF), we demonstrated heart failure phenotypes accompanied by increases in the level of a truncated cardiac troponin I (cTnI-ND) from restricted removal of the cTnI-specific N-terminal extension. To investigate the functional significance of the increase of cTnI-ND in Gsalpha-DF cardiac muscle, we generated double transgenic mice to overexpress cTnI-ND in Gsalpha-DF hearts. The overexpression of cTnI-ND in Gsalpha-DF failing hearts increased relaxation velocity and left ventricular end diastolic volume to produce higher left ventricle maximum pressure and stroke volume. Supporting the hypothesis that up-regulation of cTnI-ND is a compensatory rather than a destructive myocardial response to impaired beta-adrenergic signaling, the aberrant expression of beta-myosin heavy chain in adult Gsalpha-DF but not control mouse hearts was reversed by cTnI overexpression. These data indicate that the up-regulation of cTnI-ND may partially compensate for the cardiac inefficiency in impaired beta-adrenergic signaling.

Simulated weightlessness alters biological characteristics of human breast cancer cell line MCF-7

The aim of this study is to investigate the effects of the clinostat-simulated microgravity on MCF-7 cells (a breast cancer cell line) biological characteristics. MCF-7 cells were incubated for 24 h in an incubator and then rotated in a clinostat as a model of simulated microgravity for 24, 48 and 72 h, respectively. The effects of the clinostat-simulated microgravity on MCF-7 cells proliferation, invasion, migration, gelatinase production, adhesion, cell cycle, apoptosis and vinculin expression were detected. The results showed that the clinostat-simulated microgravity affected breast cancer cell invasion, migration, adhesion, cell cycle, cell apoptosis and vinculin expression. These results may explore a new field of vision to study tumor metastasis in future.

Geophysical characterization of derelict coalmine workings and mineshaft detection: a case study from Shrewsbury, United Kingdom

ABSTRACTA study site of derelict coalmine workings near Shrewsbury, United Kingdom was the focus for multi‐phase, near‐surface geophysical investigations. Investigation objectives were: 1) site characterization for remaining relict infrastructure foundations, 2) locate an abandoned coalmine shaft, 3) determine if the shaft was open, filled or partially filled and 4) determine if the shaft was capped (and if possible characterize the capping material).Phase one included a desktop study and 3D microgravity modelling of the relict coalmine shaft thought to be on site. In phase two, electrical and electromagnetic surveys to determine site resistivity and conductivity were acquired together with fluxgate gradiometry and an initial microgravity survey. Phase three targeted the phase two geophysical anomalies and acquired high‐resolution self potential and ground penetrating radar datasets. The phased‐survey approach minimised site activity and survey costs.Geophysical results were compared and interpreted to characterize the site, the microgravity models were used to validate interpretations. Relict buildings, railway track remains with associated gravel and a partially filled coalmine shaft were located. Microgravity proved optimal to locate the mineshaft with radar profiles showing ‘side‐swipe’ effects from the mineshaft that did not directly underlie survey lines.Geophysical interpretations were then verified with subsequent geotechnical intrusive investigations. Comparisons of historical map records with intrusive geotechnical site investigations show care must be taken using map data alone, as the latter mineshaft locations was found to be inaccurate.

A potential application of dietary soy protein, aminoguanidine and L‐carnitine as anti‐oxidants in an animal model of simulated microgravity.

The objective of the current study was to determine the effect of antioxidants in rats under simulated microgravity induced by hind‐limb suspension (HLS). Methods: A NASA validated model was used with five groups of rats. L‐carnitine and aminoguanidine were used in the drinking water in rats on Purina chow. A separate group was maintained on a soybean diet. Group 1 was hindlimb loaded control; Group 2 was hindlimb unloaded control, Group 3 was hindlimb unloaded on L‐carnitine (LC), Group 4 was hindlimb unloaded on aminoguanidine (AG), and Group 5 was hindlimb unloaded on 9.6% soybean protein diet. The animals were primed and suspended for fourteen days (total 21 days). At term, the animals were sacrificed. Tissues from brain, heart, lung, liver, stomach, pancreas, small intestine, kidney and testes were harvested. Harvested tissues were extracted for measurements of malondialdehyde (MDA) and glutathione levels. Results: MDA levels in tissues were elevated by suspension (p &lt; 0.05). MDA levels were lower (p&lt; 0.05) in the animals on LC, AG, and the soybean diet, when compared to the hindlimb unloaded control group. Glutathione levels varied between the tissues. Conclusions: Results suggest that LC, AG, and a soybean diet decrease peroxide formation, while tail suspension increases it. Data indicate that LC, AG, and a soybean diet may have a protective role in the reduction of lipid peroxidation damage produced by stress.

Impaired but reversible vascular reactivity in a rat model of microgravity

Background: The hindlimb unweighting (HLU) rat model mimics cardiovascular deconditioning following microgravity or human bed rest, particularly for the development of orthostatic intolerance. We have examined vascular responses to α1 adrenergic and non-α1 adrenergic agonists in vitro. We have also explored the reversibility of the contractile abnormalities observed. Methods: Dose-response curves were generated to phenylephrine (PE) and norepinephrine (NE) (10 −9 to 10 −4 M), U46619 (U4) (10 −10 to 10 −6 M) at one-half log order intervals in controls (n = 6), HLU (n = 6), or recovered rats (n = 6). EC50s and maximal responses (Emax) were calculated by nonlinear logistic regression analysis with PRIZM software (Graphpad, Mountain View, CA). Results: Simulated microgravity results in attenuated contractile responses to both α1 adrenergic and non-α1 adrenergic agonists, but the impaired contractile phenomenon reverses with time. Conclusions: The decreased vascular reactivity after microgravity and prolonged bed rest could cause attenuated baroreflex function and produce orthostatic intolerance, but that problem resolved with time. (Korean J Anesthesiol 2008; 55: 602～6)

Cardiovascular Effects of Hind-limb Unweighing in Mice

Background: Orthostatic intolerance is a debilitating problem that can occur after prolonged bed-rest, exposure to microgravity, and in the elderly. This study examined the integrated cardiovascular response to baroreceptor activation in a hind-limb unweighing (HLU) mouse model of microgravity to test the hypothesis that both the pressor and contractility response are attenuated in HLU mice. Methods: C57BL/6 mice (25-30 g body wt, 8-10 wk old) were exposed to HLU for 2 weeks. A bilateral carotid artery occlusion and open-loop baroreceptor stimulus was performed to measure the myocardial contractile responses using a left ventricular micromanometer-conductance catheter in the mice. In isolated myocytes simultaneous sarcomere shortening and calcium transient were measured in response to increasing concentrations of the β-agonist isoproterenol. Results: In the controls, bilateral carotid artery occlusion increased the heart rate and mean arterial pressure. These responses were markedly attenuated in the HLU mice. A bilateral carotid artery occlusion also increased the slope of the end-systolic pressure volume relationship (Ees) by 70 ± 11% and the slope was markedly attenuated to 10 ± 8% in the HLU mice. Isoproterenol increased the sarcomere shortening in both control and HLU mice in a dose-dependent manner. However the contractile response to isoproterenol was significantly attenuated in the HLU mice than the controls. Conclusions: Both the pressor and myocardial contractile responses appear to be impaired in a mouse model of microgravity. (Korean J Anesthesiol 2007; 53: 222～8)

Physiologically adaptive changes of the L5 afferent neurogram and of the rat soleus EMG activity during 14 days of hindlimb unloading and recovery

The hindlimb unloading rat model (HU, Morey's model) is usually used to mimic and study neuromuscular changes that develop during spaceflights. This Earth-based model of microgravity induces a muscular atrophy of the slow postural muscle of hindlimbs, such as the soleus, a loss of strength, modifications of contraction kinetics, changes in histochemical and electrophoretical profiles and modifications of the tonic EMG activity. It has been suggested in the literature that some of these neuromuscular effects were due to a reduction of afferent feedback during HU. However, no direct data have confirmed this hypothesis. The aim of this study was to clearly establish if changes of the L5 afferent neurogram are closely related to the soleus EMG activity during and after 14 days of HU. Immediately after HU, the EMG activity of the soleus muscle disappeared and was associated with a decrease in the afferent neurogram. The soleus electromyographic and afferent activities remained lower than the pre-suspension levels until the sixth day of HU and were recovered between the sixth and the ninth day. On the twelfth and fourteenth days, they were increased beyond the pre-suspension levels. During the first recovery day, these activities were significantly higher than those on the fourteenth HU day and returned to the pre-suspension levels between the third and sixth recovery days. To conclude, our study directly demonstrates that the HU conditions cannot be considered as a functional deafferentation, as suggested in the literature, but only as a reduction of afferent information at the beginning of the HU period.

Transcriptional Regulation Of Apoptosis In Atrophied Fast Twitch Plantaris Muscles Of Young Adult And Aged Rats

Hindlimb suspension in rats is a model of simulated microgravity that has been used to investigate skeletal muscle adaptations during non-weight-bearing conditions. The loss of muscle mass occurs quickly in hindlimb muscles that contain a high percentage of slow myosin; however, muscles with a high percentage of fast myosin containing fibers usually have less severe atrophy during unloading. Although apoptosis appears to explain part of the atrophy in slow muscles (e.g., soleus muscles), it is not known if pro-apoptotic markers are elevated in fast muscles (e.g., plantaris muscles) where atrophy is less severe. PURPOSE Because inhibitor of differentiation protein-2 (Id2) has been implicated in apoptosis and muscle atrophy during aging, we examined if Id2 and pro-apoptotic gene levels were increased during hypokinesia in the rat plantaris after hindlimb suspension. METHODS Young adult (n=8, 9 mo.) and aged (n=8, 33 mo.) Fischer Brown Norway rats were hindlimb suspended for 2 weeks to allow atrophy of the hindlimb musculature. Following suspension, rats were euthanized, the plantaris muscles were excised, and total RNA was isolated. RT-PCR for AIF, Apaf-1, Bax, Caspase-9, and Id2 genes was performed with the amplification products normalized to the 18S gene. The young adult and aged animals were compared to aged-matched controls using ANOVA with significance set at p<0.05 RESULTS Muscle wet weight significantly decreased by 17.1% in the aged animals, compared to only 7.8% in young animals. Compared to young adult rats, aged rats had significantly elevated mRNA levels of Apaf-1 (53%) in response to HS, with similar increases in AIF mRNA (52% vs. 53%) in both young and aged animals following HS. The increases in the mRNA for Caspase-9 or Bax were similar in muscles from young and aged rats following HS. When normalized to control muscles, the change in Id2 mRNA was less in unloaded muscles from young adult rats (30%) as compared with aged rats (52%), suggesting that an elevation of Id2 transcripts might contribute to the exaggerated muscle atrophy observed in response to HS in aged plantaris muscle. Significant positive correlations were observed between Id2 and Apaf-1 (p<0.01), Id2 and Caspase-9 (p<0.05), Bax and AIF (p<0.01) Bax and Caspase-9 (p<0.05). CONCLUSIONS These data suggest that unloading induced muscle atrophy involves an altered gene expression for pro-apoptotic transcripts even in muscles where atrophy is less severe, but aging exacerbates the increase in expression of these transcripts. Supported by NIH R01AG021530.

ACTIVATION OF NUCLEAR TRANSCRIPTION FACTOR–κB IN MOUSE BRAIN INDUCED BY A SIMULATED MICROGRAVITY ENVIRONMENT

Microgravity induces inflammatory responses and modulates immune functions that may increase oxidative stress. Exposure to a microgravity environment induces adverse neurological effects; however, there is little research exploring the etiology of these effects resulting from exposure to such an environment. It is also known that spaceflight is associated with increase in oxidative stress; however, this phenomenon has not been reproduced in land-based simulated microgravity models. In this study, an attempt has been made to show the induction of reactive oxygen species (ROS) in mice brain, using ground-based microgravity simulator. Increased ROS was observed in brain stem and frontal cortex with concomitant decrease in glutathione, on exposing mice to simulated microgravity for 7 d. Oxidative stress-induced activation of nuclear factor-kappaB was observed in all the regions of the brain. Moreover, mitogen-activated protein kinase kinase was phosphorylated equally in all regions of the brain exposed to simulated microgravity. These results suggest that exposure of brain to simulated microgravity can induce expression of certain transcription factors, and these have been earlier argued to be oxidative stress dependent.

Rats exhibit aldosterone-dependent sodium appetite during 24 h hindlimb unloading.

Hindlimb unloading (HU) is an animal model of microgravity and bed rest. In these studies, we examined the role of ingestive behaviours in regulating body fluid balance during 24 h HU. In the first experiment, all rats were given distilled water to drink while two groups were also given access to a sodium chloride solution (0.9% or 1.8%). Water and saline intakes were measured before, during and after 24 h of HU. Rats reduced water intake during 24 h HU in all conditions. During HU, rats increased their intakes of both saline solutions (0.9% NaCl (n= 11): control 7.8 +/- 3 ml; HU 18.2 +/- 4 ml; recovery 8.9 +/- 2.5 ml; 1.8% NaCl (n= 7): control 1.0 +/- 0.4 ml; HU 3.8 +/- 0.3 ml; recovery 1.2 +/- 0.5 ml). Although water intake decreased there was no reduction in total fluid intake when saline was available. Plasma volumes were reduced during HU compared to rats in a normal posture when only water was available to drink (control (n= 11) versus HU (n= 11): 4.0 +/- 0.2 versus 3.4 +/- 0.2 ml (100 g body weight)(-1)). When 0.9% saline was available in addition to water, plasma volumes after 24 h HU were not different from rats in a normal posture (control (n= 11) versus HU (n= 12): 4.3 +/- 0.4 versus 4.3 +/- 0.1 ml (100 g body weight)(-1)). Plasma aldosterone but not plasma renin activity was significantly elevated after 24 h HU. Central infusions of spironolactone blocked the increased intake of 1.8% saline that was associated with 24 h HU. Thus, HU results in an aldosterone-dependent sodium appetite and the ingestion of sodium may help maintain plasma volume.

Blood pressure variability during 120–day head-down bed rest in humans

Influence of physical inactivity and microgravity to periodic structure of blood pressure was studied. Six healthy males were kept under head-down bed rest (HDBR) for 120 days. Blood pressure and heart rate (HR) were recorded by a portable sphygmomanometer and a Holter electrocardiogram, respectively. The results were analyzed by spectrum analysis. Phase, amplitude and acrophase of systolic blood pressure (SBP) by approximately 24, 12 and 8 h were measured before, 60, 120 day and after HDBR. The phase at 24, 12 and 8 h did not show significant changes during HDBR, and acrophase showed a tendency to shift to 14:00 after HDBR. Amplitude for 24 h tended to attenuate during bed rest (BR), and significantly increased after BR. The results of this study suggest that the circadian rhythm of SBP and HR were maintained by strict control of sleep, awakening and food intake in microgravity model of a long-term BR state. However, the tendency to decrease 24–h cyclic amplitude of SBP appeared to be the rhythmic modulation related to cardiovascular deconditioning.

Gender differences in organ density in a rat simulated microgravity model

Research investigating the physiological effects of microgravity on the human body has demonstrated a shift of body fluids in actual spaceflight and in simulated Earth-based microgravity models in both males and females, possibly causing many deleterious physiological effects. Twenty-five anatomically normal female (NF) and 20 ovariectomized (OE) Fischer 344 rats were randomly selected to be in an experimental ( 1 h of 45° head-down tilt, 45HDT) or control ( 1 h of prone position) group. At the end of the hour experimental period, the density of the brain, lungs, heart, liver, and left and right kidneys were measured using spiral computed tomography (SCT) while the rats remained in their experimental positions. A sub-group of OE rats ( N=6) was administered estrogen replacement therapy on a daily basis ( 5 μg/kg body weight, s.c.) for 4 days and then underwent 1 h of 45HDT and SCT analysis at one day, 2 days, and 5 days to determine if estrogen replacement therapy would alter organ densities. Our data demonstrate that 1 h of 45HDT produced significant increases ( p<0.05) in the organ densities of the brain, liver, left kidney, and lung of the OE female group compared to their prone controls. However, only the brain density was significantly increased in the NF group. Estrogen replacement therapy caused a significant decrease in brain organ density at the 5 day time point compared to the 24 h time point. We conclude that estrogen plays a role in fluid distribution in a rat 45HDT model.

A rat resistance exercise regimen attenuates losses of musculoskeletal mass during hindlimb suspension.

Exposure to microgravity and/or spaceflight causes dramatic losses in both muscle and bone mass. In normal gravity, resistance exercise has been effectively used to increase muscle and bone mass. We tested a novel form of resistance exercise training using flywheel technology as a countermeasure to offset the loss of musculoskeletal mass during 4 weeks of adult rat hindlimb suspension (HS), an unloading model of microgravity. Male, Sprague-Dawley rats (6-month old) were operantly conditioned to perform resistance exercise, and then randomly assigned to groups of sedentary control (CON), HS, and HS with resistance exercise training (HSRT; 2 sets of approximately 21 repetitions, 3 days week(-1) for 4 weeks during suspension). In soleus, HS resulted in lower (P < 0.05) muscle mass to body mass ratio (approximately 50% of controls) and rates of protein synthesis. HSRT significantly attenuated the loss of muscle mass in soleus muscle, and rates of protein synthesis for soleus were similar for HSRT and controls. There were no differences among groups for mass or rates of protein synthesis in extensor digitorum longus. In cancellous regions of the distal femur, HS resulted in significant reductions of bone mineral density (BMD), but this was restored to control levels with HSRT. Cortical regions of the femur were not different among HS, HSRT or control groups. Together, these data suggest that resistance training using flywheel technology may be a promising tool to attenuate losses of the musculoskeletal system during periods of hindlimb unloading.

Simulated microgravity suppresses osteoblast phenotype, Runx2 levels and AP-1 transactivation.

Conditions of disuse such as bed rest, space flight, and immobilization result in decreased mechanical loading of bone, which is associated with reduced bone mineral density and increased fracture risk. Mechanisms involved in this process are not well understood but involve the suppression of osteoblast function. To elucidate the influence of mechanical unloading on osteoblasts, a rotating wall vessel (RWV) was employed as a ground based model of simulated microgravity. Mouse MC3T3-E1 osteoblasts were grown on microcarrier beads for 14 days and then placed in the RWV for 24 h. Consistent with decreased bone formation during actual spaceflight conditions, alkaline phosphatase and osteocalcin expression were decreased by 80 and 50%, respectively. In addition, runx2 expression and AP-1 transactivation, key regulators of osteoblast differentiation and bone formation, were reduced by more than 60%. This finding suggests that simulated microgravity could promote dedifferentiation and/or transdifferentiation to alternative cell types; however, markers of adipocyte, chondrocyte, and myocyte lineages were not induced by RWV exposure. Taken together, our results indicate that simulated microgravity may suppress osteoblast differentiation through decreased runx2 and AP-1 activities.

Effects of hindlimb unweighting on the mechanical and structure properties of the rat abdominal aorta.

Previous studies have shown that hindlimb unweighting of rats, a model of microgravity, reduces evoked contractile tension of peripheral conduit arteries. It has been hypothesized that this diminished contractile tension is the result of alterations in the mechanical properties of these arteries (e.g., active and passive mechanics). Therefore, the purpose of this study was to determine whether the reduced contractile force of the abdominal aorta from 2-wk hindlimb-unweighted (HU) rats results from a mechanical function deficit resulting from structural vascular alterations or material property changes. Aortas were isolated from control (C) and HU rats, and vasoconstrictor responses to norepinephrine (10(-9)-10(-4) M) and AVP (10(-9)-10(-5) M) were tested in vitro. In a second series of tests, the active and passive Cauchy stress-stretch relations were determined by incrementally increasing the uniaxial displacement of the aortic rings. Maximal Cauchy stress in response to norepinephrine and AVP were less in aortic rings from HU rats. The active Cauchy stress-stretch response indicated that, although maximum stress was lower in aortas from HU rats (C, 8.1 +/- 0.2 kPa; HU, 7.0 +/- 0.4 kPa), it was achieved at a similar hoop stretch. There were also no differences in the passive Cauchy stress-stretch response or the gross vascular morphology (e.g., medial cross-sectional area: C, 0.30 +/- 0.02 mm(2); HU, 0.32 +/- 0.01 mm(2)) between groups and no differences in resting or basal vascular tone at the displacement that elicits peak developed tension between groups (resting tension: C, 1.71 +/- 0.06 g; HU, 1.78 +/- 0.14 g). These results indicate that HU does not alter the functional mechanical properties of conduit arteries. However, the significantly lower active Cauchy stress of aortas from HU rats demonstrates a true contractile deficit in these arteries.