We measured the plasma concentration of a centrally derived noradrenaline (NA) metabolite, 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG), in 20 cirrhotic patients (eight with (group A) and 12 without (group B) hepatic encephalopathy (HE] and in 14 age matched healthy subjects to study if the central NA metabolism would be altered in liver cirrhosis patients, particularly in those with HE. The mean (SEM) plasma MHPG concentrations in the patient groups, group A (74.9 (8.6) pmol/l) and B (54.8 (7.2) pmol/l), were significantly (p less than 0.01) greater than in the control group (22.3 (2.0) pmol/l), and that in group A was significantly (p less than 0.05) greater than in group B. The plasma concentration of MHPG observed in these study subjects (n = 34) correlated (rs = 0.77, p less than 0.01) more strongly with the ratio of plasma catecholamine precursor amino acids (tyrosine and phenylalanine) to other neutral amino acids (tryptophan, leucine, isoleucine, and valine) known to compete with catecholamine precursor amino acids for uptake into the brain than with plasma concentration of tyrosine plus phenylalanine alone (rs = 0.63, p less than 0.01). In addition, the mean plasma MHPG concentrations measured in another group of eight cirrhotic patients (group C) during HE (79.3 (10.6) pmol/l) was significantly (p less than 0.01) greater than that measured after the recovery from HE (47.2 (5.2) pmol/l). The results suggest that the central NA metabolism may be altered in patients with liver cirrhosis, particularly in those with HE, and that the derangement in the central NA metabolism may be associated not only with an increase in plasma catecholamine precursor amino acids but also with a decrease in branched chain amino acids.
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