ACUTE EFFECTS OF L-TRYPTOPHAN ON BRAIN EXTRACELLULAR 5-HT AND 5-HIAA LEVELS IN CHRONIC EXPERIMENTAL PORTAL-SYSTEMIC ENCEPHALOPATHY

Portal-systemic encephalopathy (PSE) is associated with increased brai n turnover of serotonin (5-hydroxytryptamine; 5-HT). Despite this meta bolic increase, neuronal release of 5-HT is unaltered in neocortex of portacaval shunted (PCS) rats. In the present study, frontal neocortic al extracellular 5-HT and 5-hydroxyindole-3-acetic acid (5-HIAA) level s were determined in PCS rats and sham-operated controls prior to, as well as, after acute challenge with L-tryptophan (L-TRP; a bolus dose of 280 mg/kg i.p. followed by 5 consecutive hourly doses of 50 mg/kg). Neither basal 5-HT nor 5-HIAA extracellular levels were significantly altered in PCS rats compared to controls. L-TRP administration result ed in unaltered extracellular 5-HT but elevated 5-HIAA levels in PCS a nd sham rats. These findings do not suggest that changes in brain neur onal 5-HT release play any major functional role in the pathogenesis o f chronic PSE. The present data also emphasize the importance of disti nguishing between brain 5-HT metabolism and brain 5-HT release.