Effects of long-term hypergravity on muscle, heart and lung structure of mice

Abstract

Quantitative changes in lung, heart and muscle structure were assessed in mice exposed for 14 weeks to a gravitational field of 3 G since the age of 4 weeks; matched controls were kept at normal gravity (1 G). The body mass of 3-G-exposed mice was significantly reduced by 9%, while total skeletal muscle mass remained the same fraction of body mass. The mass of the soleus muscle was found to be significantly larger in 3-G-exposed mice both in absolute (+27%) and body mass specific terms (+42%). Capillary density was significantly reduced by 22% because of a relatively larger increase of fiber cross-sectional area (+47%) than of capillary to fiber ratio (+16%). Other morphometric variables remained unchanged with hypergravity. Heart mass and mitochondrial volume were both larger in 3-G-exposed mice (+15% and +27%, respectively). This difference reached statistical significance when normalized to body mass. The only significant difference in lung structure detectable by morphometric methods were a smaller volume (-9%), that paralleled lower body mass, and thinner alveolar septa (-12%). From these results it is concluded that the lung's support structures in mice are sufficiently strong to withstand the stress of long-term hypergravity; however, 3-G exposure leads to a selective hypertrophy of soleus muscle fibers while absolute capillary length in this muscle remains unaltered.

Ground-Based Researches on the Effects of Altered Gravity on Mice Development

“…A reduction of body mass was consistently observed in weanling or mature animals as long as they remain under the acceleration field (Pitts et al 1972;Oyama et al 1985;Frey et al 1997;Smith 1973), but the animals generally recovered almost completely the control weight after 2 months at 1G (Pitts and Oyama 1979;Oyama et al 1985;Thorling and Fredens 1995;Wade et al 1997). In the present study, a slight decrease of 6.4%, in males, and 10.9%, in females, persisted in the average body mass of HG mice at the age of 9 months.…”

“…Overall, centrifuged adults showed an increased relative mass of antigravity muscles, and no change or a slight increase of non weightspecific muscles (Frey et al 1997;Stevens et al 2003;Roy et al 1996), whereas animals born and grown in HG showed a stable relative mass of postural muscles and a stable or decreasing relative mass of non postural muscles (Picquet et al 2002;Oyama et al 1985). In the present study, HG mice showed a significantly smaller force in the grip strength test, in relation with the reduction of their body mass, but they did not differ from control when the force was normalized relative to the body mass.…”

“…The loss of body mass, in relation with an increase of lean mass and a decrease of fat mass (Oyama and Platt 1965;Oyama et al 1985;Frey et al 1997;Wade 2005), is a prominent finding of studies on hypergravity. A reduction of body mass was consistently observed in weanling or mature animals as long as they remain under the acceleration field (Pitts et al 1972;Oyama et al 1985;Frey et al 1997;Smith 1973), but the animals generally recovered almost completely the control weight after 2 months at 1G (Pitts and Oyama 1979;Oyama et al 1985;Thorling and Fredens 1995;Wade et al 1997).…”

Divergent Anabolic Signalling responses of Murine Soleus and Tibialis Anterior Muscles to Chronic 2G Hypergravity

“…This increase in Sol weight is more likely associated with an increase in connective tissue 33 or complexes of the extracellular matrix 34, 35 . There are reports showing that an exposure to greater levels of gravitational field (3G) for 4 or 14 weeks can result in a significant increase in mouse Sol weight as well as CSA of Sol muscle fibres 36, 37 .…”

Effects of Static Load on the Weight and Protein Content in the Leg Muscles of the Mouse: a Simulation of Prolonged Standing in the Workplace

“…We did not have to stimulate directly or do any operations. Although such a stress as blood flow change and dullness of sense of balance were thought to be involved in centrifugation, they did not lead to a large amount of weight loss if the gravity was not so strong 7) .…”