Estimation of material balance of totally fasted rats by doubly labeled water

Abstract

A test has been carried out of the possibility of estimating, with the aid of D₂O¹⁸, the CO₂ and water output of six rats in a severely nonsteady state, that resulting from complete deprivation of food and water. The data used for the estimation were a) isotopic concentrations in initial and final blood water, b) initial and final body weights and c) final percentage body water. In addition, O₂ consumption was calculated from the CO₂ output and the R.Q. The isotopically computed values were compared with those observed in an open-circuit metabolic train which were taken to be correct. Despite a number of simplifying assumptions, the average errors under the conditions of the test were 4, 3 and 5% for CO₂ output, water output and O₂ consumption, respectively.