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 consumptio n 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 we re fed a pelleted ration at maintenance (M) or twice maintenance (2M) or fasted (F) subsequent to the M measurement. Duodenal in vitro O2, o uabain-sensitive O2 (OSO2) and cycloheximide-sensitive O2 (CSO2) consu mption 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 consumptio n was determined using indirect calorimetry. Ewes fed 2M exhibited hig her (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-i nsensitive O2 (OIO2) consumption than F ewes. Hepatic portal blood flo w was directly proportional to level of intake (P < 0.10): it was lowe st for F ewes (81.0 L h-1), intermediate for M ewes (97.7 L h-1) and h ighest 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 2 M 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 pro portion of whole-body O2 consumption on gastrointestinal energetics th an did 2M ewes.