Ammonia metabolism in dogs with portacaval shunts.

Plasma ammonia, arginine, citrulline and urine ammonia, total nitrogen, and orotic acid were measured in shunted and control dogs. The progressive rise in plasma ammonia in the experimental group could not be explained solely by shunt hemodynamics. Similarity of control and experimental urinary nitrogen does not implicate nitrogen load. Urea synthesis was similar in experimental and control liver slices and was augmented by ornithine only in the experimental slices. Additionally, elevated urine orotic acid suggests urea cycle compromise at the ornithine transcarbamylase step.