ELIMINATION RATE OF ZN-65 AS A MEASURE OF FOOD-INTAKE - A VALIDATION-STUDY IN THE MOUSE (MUS SP)

We measured elimination of Zn-65 in white mice (Mus musculus) using da ily whole body counting. Thirteen male mice were randomly divided into three groups, each maintained at a different temperature. Each animal was labeled with Zn-65 on day 0 and monitored over days 0-48 postinje ction. Daily food intake and body masses of all the animals were measu red. We evaluated the ability of derived components of the Zn-65 elimi nation curves to predict food intake over different phases of the meas urement period. Food intake was significantly different between temper ature groups; temporal variation in food intake was not intercorrelate d between groups. Whole body elimination of Zn-65 involved a rapid dec line over days 0-1, followed by a biexponential decline in counts over days 1-48. Components of the first phase of the biexponential elimina tion curve were not significantly related to food intake. The rate (k( 2)) of isotope elimination in the second phase was significantly relat ed to mean food intake over days 25-48, 13-24, and 37-48. Rate of turn over in the second phase of elimination, incorporating the variation i n zinc body pool size (k(2) x 1/N-2), where N-2 is the constant of the second phase of elimination, was the best predictor of food intake an d accounted for 60% of the variability over days 37-48.