NEOCORTICAL DIALYSATE MONOAMINES OF RATS AFTER ACUTE, SUBACUTE, AND CHRONIC LIVER SHUNT

Intracerebral microdialysis was applied to monitor the neocortical ext racellular levels of the aromatic amino acids phenylalanine, tyrosine, and tryptophan, the neurotransmitters dopamine (DA), noradrenaline (N A), and serotonin (5-HT), and the metabolites 3,4-dihydroxyphenylaceti c acid (DO PAC) and 5-hydroxyindole-3-acetic acid (5-HIAA) in rats wit h various forms of experimental hepatic encephalopathy (HE). The extra cellular aromatic amino acid levels were clearly increased in acute, s ubacute, and chronic HE. No changes compared with controls in the neoc ortical DA release could be detected in the three experimental HE rat models investigated. The NA release showed a significant increase only in the subacute HE group. These data suggest that HE may not be assoc iated with any major reduction of neocortical DA or NA release as prev iously suggested. In acute and subacute HE, decreased extracellular DO PAC but elevated 5-HIAA concentrations were seen. In chronic HE, eleva tions of both DOPAC and 5-HIAA were observed. Neocortical 5-HT release did not change in subacute and chronic HE, whereas it decreased in ac ute HE compared with control values. Significant increase in extracell ular concentrations of 5-HIAA and of the 5-HIAA/5-HT ratio in the pres ent study are in agreement with previously reported increases in 5-HT turnover in experimental HE. However, a substantially increased 5-HT t urnover in experimental HE does not appear to be related to an increas e in neuronal neocortical 5-HT release.