Proliferation of jejunal mucosal cells in rats flown in space.

To examine the effects of spaceflight on the proliferation and turnover of jejunal mucosal cells, we compared the percentages of mitotic cells present in the crypts of Lieberkühn in the proximal, middle, and distal jejunum in each of five rats flown on the COSMOS 2044 mission and in rats included in the vivarium, synchronous, and caudal-elevated groups. On the basis of the data obtained, there was no difference in mitotic indexes between animals in the flight and vivarium (ground control) groups. Thus it appears that the ability of jejunal mucosal cells to proliferate is not affected by microgravity conditions associated with spaceflight. Although the length of villi and depth of crypts were reduced in flight animals compared with those in the vivarium group, the observed reduction is probably attributable to changes in the connective tissue core of villi and is not likely due to an impairment of the proliferation and migration of jejunal mucosal cells.

Effects of spaceflight on the proliferation of jejunal mucosal cells.

The mitotic indices, villus heights, and crypt depths were determined in each of three jejunal regions (proximal, middle, and distal) for five animals each in the flight, vivarium, and synchronous groups. Because of the rapid turnover of intestinal mucosal cells and the delay in recovering the flight animals, it is not known whether the proliferation of jejunal mucosal cells is affected by microgravity conditions associated with spaceflight. However, since there were no consistent differences between animals in the flight group and those in the synchronous and vivarium control groups, it appears that any effects of microgravity on the turnover of jejunal mucosal cells are short-lived. Thus, this study represents an initial step in determining the effects of microgravity on the proliferation and turnover of intestinal mucosal cells.