Hepatic origin of hyperammonemia induced by shock in normal rats

This study was undertaken in order to see whether instability in blood ammonia levels frequently observed in the anaesthesized rat could be explained by variations in blood pressure. In normal Wistar rats, anaesthesized with sodium pentobarbital, a bleeding of 1 ml/100 g body weigth produced in a few minutes a significant decrease in blood pressure and a significant increase in arterial blood ammonia level. With the blood pressure normalization following the blood reinfusion this hyperammonemia decreased but reappeared at high levels after a second and a third bleeding. The shock produced by an occlusion of the inferior vena cava above the renal veins gave similar results. The arterial hyperammonemia induced by shock did not result from muscle or renal ammonia production but is related to impaired hepatic uptake of portal ammonia. These results indicate that in the rat the blood pressure stability is a necessary precondition in any experiment on ammonia metabolism.