A dynamic study of rectally absorbed ammonia in liver cirrhosis using [13N]ammonia and a positron camera

[13N]Ammonia produced by the cyclotron was instilled intrarectally in patients with cirrhosis and other liver diseases to study the turnover of rectally absorbed [13N]ammonia. A positron camera connected to an on-line computer system was used for the measurement of sequential changes of 13N activity in blood and for coincidence positron imaging of the liver and heart. 13N activity over the head was also recorded. Chromatographic analysis of 13N-labeled substances in blood was carried out using a Dowex 50Wx8 column at varying times after the administration. In the control, [13N]ammonia was absorbed quickly and visualized the liver, whereas in patients with cirrhosis, the lungs and heart were first visualized, and 13N activity over the head was also higher. It was suggested that a large proportion of absorbed [13N]ammonia bypassed hepatocytes and reached peripheral tissues in cirrhosis. The heart/liver ratio of 13N and 13N over the head were correlated with various indices of portal hypertension. The relative proportion of nonammonia 13N metabolites in blood was lower at 5 and 15 min after administration in cirrhosis, suggesting a reduced capacity of the liver to remove and metabolize ammonia.