The Effects of Intravenous Urea Infusions on Portal and Arterial Plasma Ammonia and Urea Enrichment of Jejunal and Colonic Infusions: Acute Experiments with Growing Pigs

Abstract

Malmlöf K, Simoes Nunes C. The effects of intravenous urea infusions on portal and arterial plasma ammonia and urea enrichment of jejunal and colonic infusions. Scand J Gastroenterol 1992;27:620-624.

Six pigs (49-69 kg) were anaesthetized and fitted with cannulas in the brachiocephalic artery and portal and jugular veins. In addition, inlet-outlet perfusion cannulas were placed in segments of the small and large intestine. Intravenous infusion of urea for 2 h increased arterial plasma urea from a base-line level of 176 (SE, 51) mg/1 up to 292 (SE, 67) mg/1 after 5 h. During this rise portal ammonia levels remained fairly constant, with minimum and maximum values of 1.2 (SE, 03) and 1.7 (SE, 0.6) mg/1, respectively. The average amount of urea recovered in perfusates from small- and large-intestinal segments were 141.4 and 43.8, respectively (P; < 0.001), when expressed as ug/g tissue/30 min. It thus appears as if the portal blood is not an important carrier of ammonia liberated from the hydrolysis of urea and that the gastrointestinal tract is differentially permeable to urea at different levels.

Key Words:

• Ammonia
• colon
• portal vein
• small intestine
• urea