Oxygen consumption by splanchnic tissues of sheep under mesenteric load of N compounds

Abstract

Four Corriedale castrated male sheep (42 ± 3.4 kg body weight (BW)) surgically implanted with chronic indwelling catheters into the mesenteric, portal and hepatic veins, housed in metabolism cages and fed oat-ryegrass hay at maintenance level were used in a trial conducted to evaluate the effect of the mesenteric load of N compounds on oxygen consumption by the liver. After 17 days of a pre-experimental period, treatments were applied throughout four days following a 4 × 4 Latin Square design, which consisted of mesenteric vein infusion of either NaCl (0.15 M, Control), NH4HCO3 (0.25 M), alanine (0.25 M) or arginine (0.125 M) solution. All solutions were infused continuously at a rate of 2 ml/min during six hours in each experimental period, as to provide a mesenteric N load of 500 umol/min. Blood flow across portal and hepatic veins were estimated through downstream dilution of p-aminohippurate also continuously infused into the mesenteric vein. The blood flow across the portal vein was not affected by treatments whereas the blood flow across the hepatic vein tended (P = 0.09) to be higher in the control treatment. Oxygen consumption by the portal-drained viscera was similar for all treatments whereas oxygen consumption by the liver was higher (P < 0.05) in the control treatment. In conclusion, energy expenditure by the liver was not directly impacted by ammonia or amino acids load. Instead, the blood flow across the liver seems to have a key role in its oxidative metabolism.