Deuterium enrichment in plasma, rumen fluid and urine of growing sheep dosed with D2O intravenously and intraruminally does not differ
The D2O method has been used in humans to measure fractional gluconeogenesis. The advantage of this method is that all contributions of gluconeogenic substrates are considered. In ruminants, we aimed to determine whether the route of D2O administration affects equilibration of deuterium with protons from water in various body water pools. Four sheep (23.5 ± 1 kg BW), equipped with a rumen fistula and a jugular vein catheter, were fed a pelleted ration (35 g/kg BW and d; 9 MJ ME/d) at 2-h intervals. Water was offered ad lib. To label body water, sheep were given two boli of 7 g D2O/kg BW (99.2 atom% D) at 800 and 1200 h either into the rumen (IR) or into the jugular vein (IV) in a balanced cross-over design. Two weeks separated each site of administration. Plasma was sampled prior to and hourly for 11 h following the first bolus whereas rumen fluid and urine were collected prior to and at 3, 6, 9 and 11 h. Samples were diluted and D2O enrichments were measured by isotope ratio mass spectrometry. Paired t-test was used to evaluate route effect. D2O enrichments did not differ with route of tracer administration. A quasi-plateau in D2O enrichment was reached 2 h after the first bolus (IR: 0.76; IV: 0.78 atom% excess (APE)) with a further increase to a second plateau 2 h after the second bolus (IR: 1.48; IV: 1.47 APE; P>0.1). Urine D2O enrichment 3 h after the initial IR dose tended (P = 0.09) to be lower than with the IV route (IR: 0.47; IV: 0.78 APE), however, both routes of dosing lead to a similar maximum enrichment 9 to 11 h after the initial bolus (IR: 1.51; IV: 1.52 APE; P>0.1). Rumen fluid D2O enrichment attained a plateau 6 h after the initial bolus (IR: 1.51; IV: 1.43 APE; P>0.1). This study verified that for measurement of fractional gluconeogenesis using the D2O method, the kinetics of D2O labelling are similar with the IR and IV routes of administration, and that either approach can be employed in ruminants.
Keywords: Gluconeogenesis, deuterium oxide, rumen