AJP - Gastrointestinal and Liver Physiology, Vol 251, Issue 3 326-G331, Copyright © 1986 by American Physiological Society
Postnatal development of protein absorption in conventional and germ-free mice
M. Heyman, A. M. Crain-Denoyelle, G. Corthier, J. L. Morgat and J. F. Desjeux
In the jejunal epithelium of adult animals, horseradish peroxidase (HRP) is
transported via two functional pathways: a major route involving lysosomal
degradation and a minor route allowing transport of the intact protein. The
postnatal development of HRP absorption and the influence of conventional
microflora were studied in vitro, using jejunal epithelium of conventional
and germ-free suckling mice mounted in Ussing chambers. In conventional
mice, tritiated peroxidase ([3H]HRP) transport from mucosa to serosa did
not change with age except during days 3 and 4, when it increased fivefold.
This increase was entirely due to the rise in intact HRP transport and was
not related to a decrease in lysosomal cathepsin B and D activities. In
germ-free mice, HRP transport developed similarly but decreased by 75%
along both pathways. This reduced absorption was associated with lower
cathepsin B and D activities. These results strengthen the existence of two
transcellular pathways in nonimmunoglobulin protein absorption by the
proximal gut with a limiting step situated before the lysosomal system,
presumably at the brush-border membrane. Their development is not parallel
and does not correlate with gut closure to immunoglobulin transfer.
