Effect of Weightlessness on Tissue Regeneration in Rodents

Bone and calcium physiology

Rattus norvegicus (Fischer 344 rat)
Flight: 12 Male

Basal: 8, Delayed synchronous: 12, Vivarium: 24 (28 and 22 °C)

Ambient Temperature Recorder, Animal Enclosure Module

Little is currently known about the effects of microgravity on tissue repair. In the era of a long-term human presence in space, the probability of minor injury requiring on-orbit treatment will increase. This experiment aims to evaluate the effects of space flight on the histological and tensiometric properties of full thickness abdominal incisional skin wounds in the rat. A second experimental objective was to evaluate the effectiveness of basic fibroblast growth factor (FGF) and platelet-derived growth factor (bb-homodimer, PDGF) in promoting granulation tissue formation and collagen deposition.

Flight and control rats received preflight abdominal implants of polyvinyl acetal sponge disks containing either recombinant human bFGF, recombinant PDGF-BB, or a placebo. Postflight, animals received an injection of hypothalamic-releasing hormones. After sacrifice, the sponges were removed and prepared for biochemical and histological analysis of DNA, protein, and collagen content. Histological organization, amount of visible collagen, and the resolution of hemorrhage at the infiltrating interface were also examined.

Histological analysis showed that both bFGF and PDGF showed positive effects in the ground-control rats, but only immediate-release bFGF and delayed-release PDGF had significant, positive effects in the flight rats. This may be due to the 2-day launch delay of the Shuttle mission, which caused the growth factor to be released earlier during space flight than planned. Although cellular influx into the tissue space of placebo-treated sponges was unaffected by space flight, there was a significantly blunted response to either bFGF or PDGF-BB in flight animals. Microgravity significantly reduced wound collagen concentration regardless of the treatment group. The collagen concentration of granulation tissue in flight animals treated with bFGF was significantly less than in those treated with PDGF, but not significantly less than in the placebo treated group. These results show that a highly standardized wound repair process in young rats is significantly altered by space flight.

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