Hepatic Capacity for Ammonia Removal in Sheep

Abstract

S u rn rn a r yTwo steps of infusion with NH4C1 (20 or 30 pmol' min-' . kg-') were employed in four sheep by continuous infusion into the mesenteric vein within 120 minutes. Hepatic ammonia uptake was limited and reached 1.45 prnol . min-' . g-' of fresh wet hepatic tissue at the end of infusion. Blood ammonia levels rose in peripheral arterial blood up to 500 pmol.l-' with the higher dose. Urea synthesis increased during NH,C1 infusion and was higher than needed for ammonia removal, particularly during the second hour of ammonia load. Even one hour after the experimental treatment, liver urea was continually being synthesized at a similar intensity, whereas ammonia uptake had declined. Portal and hepatic blood flow decreased in conditions of local portal hyperammonaemia and increased when the peripheral ammonia level was elevated.

Experimental Soybean Meal Intoxication in Cattle

“…It is consistent with high correlations between R-ammonia and PUN concentrations (R = 0.78-0.72) before H [8][9][10][11][12] and between R-ammonia and P-ammonia concentrations (R = 0.90-0.92) after H 16 (experiment 1) and H 24 (experiment 2).…”

“…The pKa of ammonia is high (9.2) and ammonia is absorbed in the nonionized form (NH 3 ) across the ruminal wall, but is in the ionized form (NH 4 + ) in blood. 2,4 This conclusion is consistent with high positive correlation between the P-ammonia concentration and blood pH until H [10][11][12] and with the high P-ammonia concentrations from H [10][11][12] to H 24-26. Terminal acidosis was described during urea intoxication and attributed to severe muscle tremors inducing a production of lactic acid. 2 These findings were not observed here, probably because of the moderate clinical signs.…”

“…In experiment 1 ( Fig 3), P-ammonia concentration increased (P < 0.01) between H 10 and H 18 , with a peak at H [12][13][14] . The PUN concentration increased (P < .01) from H 8 to H 30 .…”

“…2 Saturation of hepatic capacity for ammonia removal as early as H [8][9][10][11][12] is suggested by the increased P-ammonia concentration in both experiments, and by a high peak P-ammonia concentration at H [14][15][16] in experiment 2. It is consistent with high correlations between R-ammonia and PUN concentrations (R = 0.78-0.72) before H [8][9][10][11][12] and between R-ammonia and P-ammonia concentrations (R = 0.90-0.92) after H 16 (experiment 1) and H 24 (experiment 2).…”

“…The marked peak of P-ammonia concentration was only observed in experiment 2 at H [14][15][16] First, the amount of SBM and R-ammonia absorption (because of increased ruminal pH 12 ) differed between experiments. Second, utilization of ammonia by the liver could be decreased because of a reduction in citrullogenesis during a severe increase in the propionate concentration in rumen.…”