Abstract #W255

# W255
Comparison of fractional gluconeogenesis estimates in sheep determined with D2O administered via vein or rumen and by intravenous infusion of 13C6-glucose.
Cornelia C. Metges*1, Solvig Görs1, Gürbüz Das1, Umang Agarwal2, Brian J. Bequette2, 1Institute of Nutritional Physiology, Leibniz Institute for Farm Animal Biology, Dummerstorf, Germany, 2Dpt. Animal and Avian Sciences, University of Maryland, College Park, MD.

In ruminants, the main precursor for GNG is ruminal propionate which fundamentally differs from gluconeogenic precursors of monogastrics. The D2O method has been used to measure fractional gluconeogenesis (GNG) in humans. We aimed to determine whether the route of D2O administration (rumen (IR) or jugular vein (IV)) affects D enrichment of rumen fluid, ruminal propionate and estimates of fractional GNG. In addition, we compared these GNG estimates with estimates derived from 13C6-glucose infusion. 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. Sheep were given 2 boli of 7 g D2O (99.2 atom% (AP) D/kg BW) at 0800 and 1200 h either IR (method 1) or IV (method 2), or received continuous IV infusion of 13C6-glucose (0.15 g/h) for 10 h (method 3) in a crossover design with 1 wk separating tracer administrations. Ruminal D enrichments were measured by isotope ratio mass spectrometry whereas ruminal propionate and plasma glucose D enrichment was measured by GC-MS. Fractional GNG was calculated from the ratio of D enrichment at C-5 of glucose (labeling via GNG only) to that at C-2 (labeling during GNG and glycogenolysis). The 13C-mass isotopomer enrichment of plasma glucose was determined by GC-MS and GNG was calculated. Statistical comparison of GNG estimates was made with repeated measures ANOVA using PROC MIXED of SAS. Rumen fluid D enrichment attained a plateau 6 h after the first bolus (IR: 1.51; IV: 1.43 APE; P > 0.1). The D enrichment of ruminal propionate as a precursor for GNG showed faster labeling with the IR route (3 h: P < 0.10; 6 h: P < 0.05). However, the plateau enrichments of rumen fluid D and propionate D did not differ (P > 0.10). GNG estimates derived from IR and IV routes of D2O administration did not differ (P = 0.83) which resulted in an overall GNG estimate of 58.8%. In contrast, GNG estimate derived from 13C6 glucose dilution was at 72.8%, which did not differ from the other 2 methods (P > 0.13). Thus all 3 methods yield similar estimates of GNG in ruminants.

Key Words: ruminants, gluconeogenesis, stable isotope-labeled tracer