Consumo esplácnico de O2 durante la infusión de amonio en la vena mesentérica en ovinos

RECAVARREN, MARIANA INÉS; DEL SOLE, MARÍA JOSÉ; MILANO, GUILLERMO DANIEL

Mar del Plata

Congreso; 37° Reunión Anual de la Sociedad Argentina de Farmacología Experimental; 2005

Sociedad Argentina de Farmacología Experimental

Metabolism of ammonium (NH4+) absorbed from the gut increases liver O2 consumption, thus reducing energy available for body tissues. Short lasting episodes of high NH4+ absorption, frequently associated with the intake of diets rich in non-protein N or rapidly rumen degradable protein, were simulated in 5 wethers (42±3.4 kg BW), fitted with chronic indwelling catheters in aorta and splanchnic veins, via infusion of 340 µmol NH4+HCO3-/min into the mesenteric vein for 3 h, over 7 d. On the last day, portal and hepatic blood flows, and arterial, portal and hepatic concentrations of NH4+ and O2 were measured during the last 90 min of the NH4+ infusion to calculate net mass transfers of NH4+ and O2 across portal-drained viscera (PDV), liver and splanchnic tissues. Measurements were repeated on the following day, after withdrawal of the NH4+ infusion (control period). NH4+ infusion increased PDV NH4+ absorption (232 vs. 669 µmol/min; sed, 36; P=0.001), liver NH4+ uptake (276 vs. 698 µmol/min; sed, 64; P=0.007) and O2 consumption by the liver (1169 vs. 1347 µmol/min; sed, 26,6; P=0.007), the PDV (1082 vs. 1355µmol/min; sed, 75; P=0.04) and the splanchnic tissues (2509 vs. 2926 µmol/min; sed, 88; P=0.006). Liver O2 consumption equated 0.42 mol per mol of extra NH4+ removed, a value somewhat larger than the standard 0.3 mol O2/ mol N predicted by the stoichometry of the ornithine cycle. Overall, incremental splanchnic energy expenditure was 455 kJ / mol NH4+ removed by the liver (based on 460 kJ/ mol O2 consumed).