Two Principles for Absorption Determinations using Isotope-labelled Nutrients

Abstract

LABELLED nutrients have become indispensable in research since they facilitate investigations which otherwise would be impossible or extremely difficult. As an example may be mentioned Hoekstra's¹ investigations of zinc metabolism, in which he used the general method suggested by Cotzias et al.². Zinc-65 retention in rats was determined by whole-body counting. Once the zinc-65 had been absorbed from the digestive tract it was handled similarly to injected zinc-65. The percentage absorption of orally-given zinc-65 was calculated by extrapolating the linear part of the retention curves (plotted on a logarithmic scale versus time) back to zero time and adding the increment representing the non-linear portion of the injected zinc-65 curve.