Increased level of serum vascular endothelial growth factor by long-term exposure to hypergravity.
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We have previously demonstrated that short-term exposure to hypergravity at 2G for 4 h induces expression of cyclooxygenase-2 (COX-2) in the mouse heart. Moreover, expression of vascular endothelial growth factor (VEGF) is also induced in the heart in a COX-2-dependent manner. Here, we demonstrate that long-term exposure of mice to 2G for 24 h resulted in a significant increase of serum VEGF level, although expression of COX-2 and VEGF in the heart decreased to the 1G-control level. Moreover, increase of serum VEGF was not suppressed by treatment with COX-2 inhibitor, indicating that VEGF was induced in a COX-2-independent manner. These results suggest that gravitational force contributes to maintenance of the serum VEGF level. (+info)
Hypergravity resistance exercise: the use of artificial gravity as potential countermeasure to microgravity.
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The aims of this study were to 1) determine if hypergravity (HG) squats can produce foot forces similar to those measured during 10-repetition maximum (10RM) squats using weights under normal 1-G(z) condition, and 2) compare the kinematics (duration and goniometry) and EMG activities of selected joints and muscles between 10RM and HG squats of similar total foot forces. Eight men and six women [27 yr (SD 4), 66 kg (SD 10)] completed ten 10RM [83 kg (SD 23)] and 10 HG squats (2.25-3.75 G(z)). HG squats were performed on a human-powered short-arm centrifuge. Foot forces were measured using insole force sensors. Hip, knee, and ankle angles were measured using electrogoniometers. EMG activities of the erector spinae, biceps femoris, rectus femoris, and gastrocnemius were also recorded during both squats. All subjects were able to achieve similar or higher average total foot forces during HG squats compared with those obtained during 10RM squats. There were no differences in total duration per set, average duration per repetition, and goniometry and EMG activities of the selected joints and muscles, respectively, between 10RM and HG squats. These results demonstrate that HG squats can produce very high foot forces that are comparable to those produced during 10RM squats at 1 G(z). In addition, the technique and muscle activation are similar between the two types of squats. This observation supports the view that HG resistance training may represent an important countermeasure to microgravity. (+info)
Histological assessments on the abnormalities of mouse epiphyseal chondrocytes with short term centrifugal loading.
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We have examined the morphological changes in chondrocytes after exposure to experimental hypergravity. Tibial epiphyseal cartilages of 17-days-old mouse fetuses were exposed to centrifugation at 3G for 16 h mimicking hypergravitational environment (experimental group), or subjected to stationary cultures (control group). Centrifugation did not affect the sizes of epiphyseal cartilage, chondrocyte proliferation, type X collagen-positive hypertrophic zone, and the mRNA expressions of parathyroid hormone-related peptide and fibroblast growth factor receptor III. However, centrifuged chondrocytes showed abnormal morphology and aberrant spatial arrangements, resulting in disrupted chondrocytic columns. Through histochemical assessments, actin filaments were shown to distribute evenly along cell membranes of control proliferative chondrocytes, while chondrocytes subjected to centrifugal force developed a thicker layer of actin filaments. Transmission electron microscopic observations revealed spotty electron-dense materials underlying control chondrocytes' cell membranes, while experimental chondrocytes showed their thick layer. In the intracolumnar regions of the control cartilage, longitudinal electron-dense fibrils were associated with short cytoplasmic processes of normal chondrocytes, indicating assumed cell-tomatrix interactions. These extracellular fibrils were disrupted in the centrifuged samples. Summarizing, altered actin filaments associated with cell membranes, irregular cell shape and disappearance of intracolumnar extracellular fibrils suggest that hypergravity disturbs cell-to-matrix interactions in our cartilage model. (+info)
Strong galvanic vestibular stimulation obscures arterial pressure response to gravitational change in conscious rats.
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Galvanic vestibular stimulation (GVS) is known to create an imbalance in the vestibular inputs; thus it is possible that the simultaneously applied GVS obscures adequate gravity-based inputs to the vestibular organs or modifies an input-output relationship of the vestibular system and then impairs the vestibular-mediated response. To examine this, arterial pressure (AP) response to gravitational change was examined in conscious rats with and without GVS. Free drop-induced microgravity and centrifugation-induced hypergravity were employed to elicit vestibular-mediated AP response. GVS itself induced pressor response in an intensity-dependent manner. This pressor response was completely abolished by vestibular lesion, suggesting that the GVS-induced response was mediated by the vestibular system. The pressor response to microgravity (35 +/- 3 mmHg) was significantly reduced by simultaneously applied GVS (19 +/- 1 mmHg), and pressor response to 3-G load was also significantly reduced by GVS. However, GVS had no effect on air jet-induced pressor response. The effects of GVS on pressor response to gravitational change were qualitatively and quantitatively similar to that caused by the vestibular lesion, effects of which were demonstrated in our previous studies (Gotoh TM, Fujiki N, Matsuda T, Gao S, Morita H. Am J Physiol Regul Integr Comp Physiol 286: R25-R30, 2004; Matsuda T, Gotoh TM, Tanaka K, Gao S, Morita H. Brain Res 1028: 140-147, 2004; Tanaka K, Gotoh TM, Awazu C, Morita H. Neurosci Lett 397: 40-43, 2006). These results indicate that GVS reduced the vestibular-mediated pressor response to gravitational change but has no effect on the non-vestibular-mediated pressor response. Thus GVS might be employed for the acute interruption of the AP response to gravitational change. (+info)
Time-course of changes in amounts of specific proteins upon exposure to hyper-g, 2-D clinorotation, and 3-D random positioning of Arabidopsis cell cultures.
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