Oxygen uptake and net flux of metabolites by splanchnic tissues of sheep in response to short-term mesenteric infusion of nitrogenous compounds.

This study was conducted in an attempt to quantify the impact of N load on splanchnic tissues metabolism of sheep. The trial was conducted with four male sheep (45 ± 2.5 kg body weight (BW)) surgically implanted with chronic indwelling catheters into the portal, hepatic and mesenteric veins. Blood flow and metabolic flux through portal-drained viscera (PDV), liver and total splanchnic tissues (ST) were measured daily following a 4 × 4 Latin Square experimental design, where sheep were continually infused into the mesenteric vein with a physiological saline (0.15 m NaCl) solution during 90 min followed by the infusion, during more 120 min, of either solution: physiological saline (control), 0.250 mNH4 HCO3 , 0.250 m L-alanine or 0.125 m L-arginine, all of them infused at a rate of 1.5 ml/min to provide 375 µmol N/min. During the treatment infusion period, the net removal of ammonia N and the net production of urea N by liver were higher (p < .05) in NH4 HCO3 infused sheep. Based on oxygen consumption, and on average of all treatments, the heat produced by liver and ST was on average 6 and 14 kcal/kg BW representing 16% and 38% of the metabolizable energy intake respectively. Linear relationships between variables indicated that gluconeogenesis and ureagenesis occurred concomitantly and both processes accounted for approximately 50% of total liver energy expenditure, two-thirds of it associated with gluconeogenesis. The results of the current study did not present clear evidence of the expected energy costs associated with ammonia N, alanine or arginine metabolism by liver. However, they indicated that gluconeogenesis is on average a more energy expensive process than ureagenesis.

Relationship between level of forage intake, blood flow and oxygen consumption by splanchnic tissues of sheep fed a tropical grass forage.

Four Polwarth castrated male sheep (42 ± 4.4 kg live weight (LW) surgically implanted with chronic indwelling catheters into the mesenteric, portal and hepatic veins, housed in metabolism cages and offered Cynodon sp. hay at rates (g of dry matter (DM)/kg LW) of 7, 14, 21 or ad libitum, were used in a 4 × 4 Latin square experiment to evaluate the effect of the level of forage intake on blood flow and oxygen consumption by the portal-drained viscera (PDV), liver and total splanchnic tissues (ST). The portal blood flow and the oxygen consumption by PDV linearly increased at increased organic matter (OM) intake. No effect of level of OM intake was obtained for the hepatic artery blood flow and oxygen consumption by liver. As a consequence, the level of OM intake only tended to directly affect hepatic blood flow and oxygen consumption by total ST. Oxygen consumption was linearly and positively related to blood flow across PDV, liver and total ST. The heat production by PDV and total ST, as proportion of metabolizable energy (ME) intake, decreased curvilinearly at increased ME intake. In conclusion, the oxygen consumption by PDV, but not by liver, was directly related to the level of forage intake by sheep. Moreover, when ingested at levels below maintenance, most of ME was spent as heat produced by ST.