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 of¹³N activity in blood and for coincidence positron imaging of the liver and heart.¹³N activity over the head was also recorded. Chromatographic analysis of¹³N-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, and¹³N 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 of¹³N and¹³N over the head were correlated with various indices of portal hypertension. The relative proportion of nonammonia¹³N 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.