Journal of Applied Physiology, Vol 79, Issue 4 1361-1369, Copyright © 1995 by American Physiological Society
Elimination rate of 65Zn as a measure of food intake: a validation study in the mouse (Mus sp.)
J. A. McLean and J. R. Speakman
Department of Zoology, University of Aberdeen, Scotland, United Kingdom.
We measured elimination of 65Zn in white mice (Mus musculus) using daily
whole body counting. Thirteen male mice were randomly divided into three
groups, each maintained at a different temperature. Each animal was labeled
with 65Zn on day 0 and monitored over days 0-48 postinjection. Daily food
intake and body masses of all the animals were measured. We evaluated the
ability of derived components of the 65Zn elimination curves to predict
food intake over different phases of the measurement period. Food intake
was significantly different between temperature groups; temporal variation
in food intake was not intercorrelated between groups. Whole body
elimination of 65Zn involved a rapid decline over days 0-1, followed by a
biexponential decline in counts over days 1-48. Components of the first
phase of the biexponential elimination curve were not significantly related
to food intake. The rate (k2) of isotope elimination in the second phase
was significantly related to mean food intake over days 25-48, 13-24, and
37-48. Rate of turnover in the second phase of elimination, incorporating
the variation in zinc body pool size (k2 x 1/N2), where N2 is the constant
of the second phase of elimination, was the best predictor of food intake
and accounted for 60% of the variability over days 37-48.
