Oxygen Consumption and Metabolite Flux of Bovine Portal-Drained Viscera and Liver

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Abstract
Oxygen (O2) uptake and net metabolite flux by portal-drained viscera (PDV) and hepatic (HEP) tissues have been quantitated in vivo by measuring blood flow and arteriovenous concentration differences in cattle with chronic indwelling catheters in appropriate blood vessels. Results from use of this technique show that PDV of cattle account for 8–10% of body tissue, but 18–25% of whole animal O2 consumption. Similarly, HEP tissues account for 1–2% of body tissues, but more of whole animal O2 consumption than PDV. Glucose, volatile fatty acids (VFA), glutamate and glutamine are used as substrates by PDV; ketones, alanine and glycine are major products of PDV metabolism that are transported to HEP tissues along with absorbed VFA, ammonia, amino acids and other products of digestion. Most amino acids, l-lactate, propionate and butyrate and ammonia in blood from PDV are removed by HEP tissues, which in turn release glucose, glutamate, branched-chain amino acids, ketones, acetate and urea to peripheral blood. Net HEP flux of glucose measured by this technique is compatible with glucose requirements for lactation and other metabolism; similarly, HEP uptake of ammonia and α-amino N can account for 95% of HEP release of urea N. The technique is a powerful tool for quantitation of intermediary metabolism.