Octopamine and ammonia plasma levels in hepatic encephalopathy.

It has been recently proposed that hepatic encephalopathy could be due to the accumulation of octopamine acting as a false neurotransmitter, and the increase of ammonia might reflect this accumulation. The simultaneous determination of octopamine and ammonia was performed in 88 cases with or without encephalopathy. The correlation between the two substances appeared to be good (P less than 0.01; r = 0.5), except in shunted patients. All the cases with low octopamine and high ammonia were patients who had been submitted to surgical portal-systemic anastomosis. This finding does not seem to be coincidental; in this type of patients, the mechanism of hepatic encephalopathy could involve other beta-hydroxyphenylethanolamines in addition to octopamine. The presence of the inhibition of the reaction of transmethylation constantly observed during octopamine plasma assay is in favour of this hypothesis.