AJP - Gastrointestinal and Liver Physiology, Vol 249, Issue 4 439-G448, Copyright © 1985 by American Physiological Society
Iron absorption in normal and iron-deficient beagle dogs: mucosal iron kinetics
M. H. Nathanson, A. Muir and G. D. McLaren
Absorption of dietary iron requires uptake of iron by the brush border of
the intestinal epithelial cells, intracellular transport, and transfer to
the systemic circulation. In iron-deficiency anemia, iron absorption is
greatly increased, but the individual steps responsible for this increase
have not been identified. We have developed a method to evaluate the rate
constants for each of these steps, and we report here our results in beagle
dogs a) under normal conditions and b) after phlebotomy to produce
iron-deficiency anemia. Simultaneous administration of oral 59Fe3+-citrate
and intravenous 55Fe-transferrin was used to investigate the kinetics of
mucosal iron transport. Plasma levels of both isotopes and the whole-body
excretion pattern of 59Fe were monitored sequentially, and the fractional
mucosal transport rates were estimated by nonlinear least-squares fit of a
physiologically based mathematical model to these data. Under normal
conditions the fractional rate of mucosal iron uptake from the intestinal
lumen was rate limiting, being less than 1% of the fractional rate of
either iron incorporation into the mucosal storage pool or transfer of iron
from the mucosa to the plasma. After induction of iron-deficiency anemia,
the fractional mucosal iron uptake rate increased sixfold (P less than
0.005), while the rate of incorporation into the mucosal storage pool
decreased ninefold (P less than 0.02); in contrast, the fractional rate of
iron transfer to the plasma did not change. These results indicate that the
enhanced iron absorption in iron-deficiency anemia is attributable to an
increase in mucosal iron available for transfer to the plasma, leading in
turn to a net increase in iron absorption, despite a normal fractional
transfer rate.
