Absorption of Chromium Across the Rat Small Intestine

Abstract

Chromium is an essential element in trace quantities, but
toxic at high concentrations, particularly in the hexavalent form.
In this study the transport of physiological non-toxic amounts of
trivalent chromium across different regions of rat small intestine
was investigated using the everted sac technique.
A very small percentage of chromium was transported to the
serosal compartment, and a larger percentage of chromium was rapidly
taken up by the intestinal tissue. There was no specific site of
absorption for chromium in the rat small intestine. The amount of
chromium both transported to the serosal compartment and taken up by
the tissue was dependent upon the initial concentration of chromium
and no evidence of saturation was observed. There was however a
good correlation between water and chromium transport across the
jejunum and ileum.
Changes in glucose concentration, temperature, or anoxic
conditions appeared to have no affect on chromium transport to the
serosal compartment. However transport was increased in the presence
of decreased concentration of calcium ions and also in the presence
of increased concentration of hydrogen ions. Bile salts and E.D.T.A.
did not affect the serosal transport of chromium, however, the
interaction of chromium with citric acid increased the amount of
chromium transported to the serosal compartment.
There was strong and tenacious interaction between the
intestinal tissue and chromium ions which displayed characteristics
of covalent bonding. Variations in glucose concentration and pH, as
well as anoxic condition and high concentration of bile salts, markedly
influence the interaction of chromium with the intestinal tissue.
Lowered luminal volumes resulted in an increase in the tissue-chromium
interaction.
From the observations a model was developed to describe the
transport mechanism for chromium, and factors which influence chromium
absorption. Chromium crosses the intestinal epithelium by passive
diffusion via the zonulae occludentes. Interaction of chromium with a
dietary agent may increase the amount transported to the serosal
compartment and result in the complex using an intracellular route.
The tenacious binding of chromium to the intestinal tissue,
possibly to phosphate groups, suggests that the intestinal barrier
acts as a controlling factor for the amount of chromium entering the
body pool, and also predicts other conditions that might affect the
absorption of chromium.

Date of Award	1979
Original language	English
Awarding Institution	Aston University