Isotopic tracer techniques for assessing calcium absorption in rats

Abstract

The femur uptake and whole body retention methods (two isotopic tracer techniques for assessing calcium absorption) were compared using CaCl 2 as the salt. The two methods gave identical values for calcium absorption. Tricalcium phosphate, doubly labeled with 45Ca and 47Ca, was used to evaluate extrinsic labeling techniques for determination of calcium bioavailability. The extrinsic 47Ca to instrinsic 45Ca absorption ratio from a test meal ranged from 1.139±0.097 to 1.183±0.087 (mean ± SD), depending on the procedure for extrinsic labeling. For the femur uptake method, intraperitoneal and intravenous injections of 45Ca were accumulated identically by femurs. We conclude that calcium absorption can be conveniently measured by either whole body retention or femur uptake methods, and that comparisons of oral uptake can be made to either intraperitoneally or intraveneously administered calcium tracers. However, care should be taken in using the extrinsic labeling approach, which tends to overestimate calcium absorption.