The maximum capacity of the liver of the adult dairy cow to metabolize ammonia

Abstract

1. Three adult dairy cows were fitted with cannulas in a mesenteric, portal, hepatic and jugular vein and a carotid artery. They received infusions of step-wise increasing amounts of ammonia as ammonium acetate via a mesenteric vein until NH₃ intoxication occurred. Sodium acetate was used in control infusions. The maximum rate of uptake of NH₃ by the liver and the concentrations of glucose, urea, lactate, acetate and bilirubin in blood were measured.2. During the infusions of ammonium acetate the liver extracted almost all the NH₃ present in the portal vein until an infusion rate of approximately 15·0 mmol/min was reached. The maximum capacity of the liver to remove NH₃ during its first pass was on average 1·84 mmol/min per kg wet weight. The cows became intoxicated when arterial plasma ammonia concentrations reached 0·8 mmol/1. Concentrations of NH₃ in jugular venous blood were between 66 and 74% of those in the carotid.