TISSUE-REPAIR IN-SPACE

Extended habitation of astronauts aboard the space station increases t he probability that minor cuts and lacerations will require treatment; however, little is known about the effects of microgravity on tissue repair. In this study, we evaluate the effects of temperature and spac eflight on the histological and tensiometric properties of full-thickn ess abdominal incisional skin wounds in Fischer 344 rats housed for te n days aboard space shuttle Endeavour. The incisions of half of the gr ound control and flight animals were treated with a protective barrier wipe in order to evaluate the efficacy of this partial barrier on tis sue repair. Animals caged in flight hardware or vivarium cages on Eart h served as controls. Twelve days post-operatively, the flight animals were returned to the Kennedy Space Center and found to be in good hea lth. Based on visual examination, the incisions appeared to have heale d normally. Post-flight histological evaluation revealed that the inci sions had closed by active re-epithelialization. However, a moderate t o marked inflammatory response and fibroplasia were observed in 67 per cent of the flight animals compared to only a 29 percent incident rate in ground controls. Dermal collagen fibers were nonremarkable in skin sections from vivarium ground controls while collagen fibers from the flight animals were often loosely arranged with clefts and associated with an inflammatory cellular infiltrate. Skin samples prepared from the flight animals were also significantly larger (P < 0.05) than cont rol samples that were harvested and stored in an identical manner. Ten siometric measurements based on tissue dimensions at the time of analy sis revealed that Stress at Maximum Load and Young's Modulus of elasti city were significantly reduced (P < 0.05) in the flight group compare d to the ground controls. Collectively, these results are consistent w ith the hypothesis that the inflammatory response occurring during wou nd healing is sustained in a larger percentage of animals exposed to s pace flight. We speculate that an enhanced release of proinflammatory cytokines may contribute to this response. Although ''normal'' tissue repair can apparently proceed within a microgravity environment, some aspects of the wound healing process may be impaired, prolonged, or de layed. More detailed biochemical studies are required to critically ev aluate the physiological mechanisms that may be contributing to these effects and their long term consequences to wound healing in humans in space.