Elimination rate of 65Zn as a measure of food intake: a validation study in the mouse (Mus sp.)

Abstract

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.