QUANTIFICATION OF IN-VITRO AND IN-VIVO ENERGY-METABOLISM OF THE GASTROINTESTINAL-TRACT OF FED OR FASTED SHEEP

The effect of level of nutrition on in vitro and in vivo O2 consumption by the gastrointestinal tract in four nonlactating, nonpregnant ewes catheterized in the anterior mesenteric vein, hepatic portal vein and mesenteric artery with duodenal cannulae was investigated. Animals were fed a pelleted ration at maintenance (M) or twice maintenance (2M) or fasted (F) subsequent to the M measurement. Duodenal in vitro O2, ouabain-sensitive O2 (OSO2) and cycloheximide-sensitive O2 (CSO2) consumption was determined polarographically using a YSI O2 monitor; whole-gut O2 consumption was determined as (arterio-venous difference of O2 concentration) x (blood flow through the PV). Whole-body O2 consumption was determined using indirect calorimetry. Ewes fed 2M exhibited higher (P < 0.10) whole-body O2 consumption than either M or F ewes. Ewes fed M and 2M had higher (P < 0.10) duodenal in vitro O2 and ouabain-insensitive O2 (OIO2) consumption than F ewes. Hepatic portal blood flow was directly proportional to level of intake (P < 0.10): it was lowest for F ewes (81.0 L h-1), intermediate for M ewes (97.7 L h-1) and highest for 2M ewes (122.5 L h-1). Ouabain inhibition of O2 consumption by portal-drained viscera (PDV) was highest in M ewes and lowest in 2M ewes (P < 0.10). CSO2 consumption by the entire PDV was not affected by level of intake, corresponding to no change in OIO2 consumption by the PDV. As a proportion of whole-body O2 consumption, total O2, OSO2 and cycloheximide-insensitive O2 consumption by the PDV was higher in F ewes than in 2M ewes (P < 0.10). Fasted ewes expended a greater proportion of whole-body O2 consumption on gastrointestinal energetics than did 2M ewes.