organ Zn were simulated for growing rats
receiving adequate (Fig. 8.12) or deficient
(Fig. 8.13) dietary Zn. Rats fed a deficient
Zn diet accumulated less Zn overall in
tissues, but muscle accumulated relatively
more zinc than the other tissues, mainly at
the expense of bone. The tissue distribu-
tion of Zn shown at day 28 in Figs 8.12 and
8.13 is from Giugliano and Millward
(1984). The redistribution of Zn was
simulated using modelling techniques for
regulating Zn tissue mass as described
above. The rate of redistribution was
assumed to take about one-half of the 28-
day period simulated, which is consistent
with the time course of^65 Zn redistribution
observed in another study with marginally
deficient rats.
Copper
Copper metabolism has been the subject of
extensive reviews (e.g. Linder, 1991).
Copper absorption is quite variable
depending on species and dietary factors.
Absorption by humans varies from about
12 to 55%, whereas absorption by
ruminants varies from about 1 to 13%. At
low absorption percentages, changes of a
few percent can double or triple absolute
Cu absorption, which can have profound
affects on Cu nutrition. Absorbed Cu is
bound mainly to plasma albumin, and
possibly transcuprein and amino acids. It
is transported to the liver where it is
removed efficiently from circulation.
Within the liver, Cu is incorporated into
the protein ceruloplasmin and released
into the general circulation. Ceruloplasmin
Cu is tightly bound, does not exchange
readily with ionic Cu in plasma and com-
prises 80–97% of plasma Cu in species
surveyed. Tissue Cu turnover leads to
release of Cu to the bloodstream, where it
is assumed to travel in association with
plasma albumin, transcuprein and amino
acids. Excretion of Cu is mainly via the bileTrace Element Dynamics 173Fig. 8.12.Tissue Zn accumulation of young growing male rats fed adequate dietary Zn (12 μg g^1 ) in a
semi-synthetic diet. The figure is a simulation based on a kinetic model of Zn metabolism (Fig. 8.1) and
published data as described in the text.