Liberation of 14CO2 from 14C-fatty acids by riboflavin-deficient sucking rat pups: a study of 14C-Octanoate and 14C-palmitate oxidation in vivo.

To test the hypothesis that impaired fatty acid oxidation in the mitochondria of riboflavin-deficient rats may be reflected in impaired rates of fatty acid oxidation to carbon dioxide in vivo, the conversion of 14C-labelled fatty acids to 14CO2 was measured in rat pups. Sucking pups were selected, since whole body energy expenditure was reduced by riboflavin deficiency in this age group. A gas-flow apparatus was designed, to permit the collection of expired CO2 over a 4 hr period, in pups maintained at constant temperature. 14C-octanoate and 14C-palmitate, given by intraperitoneal injection, were oxidised to 14CO2, with peak production rates at 20 min and at 30 min respectively. Cumulative recoveries of the injected 14C were: ca. 50% of the dose for 14C-octanoate, and ca. 20% of the dose for 14C-palmitate, during 4 hr collection of expired air. Per unit of body weight, the rates and extents of oxidation of each fatty acid substrate in riboflavin-deficient pups were not significantly reduced in comparison with their pair-fed or ad-lib fed, riboflavin-sufficient controls. This study a) has confirmed the feasibility of the 14C-fatty acid-breath test assay for sucking rat pups; b) has excluded the possibility of massive reductions due to riboflavin deficiency in the oxidation of two fatty acid substrates, and c) has provided estimates of biological variation of these indices, which will assist future studies.