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 brain turnover of serotonin (5-hydroxytryptamine; 5-HT). Despite this metabolic increase, neuronal release of 5-HT is unaltered in neocortex of portacaval shunted (PCS) rats. In the present study, frontal neocortical extracellular 5-HT and 5-hydroxyindole-3-acetic acid (5-HIAA) levels 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 resulted in unaltered extracellular 5-HT but elevated 5-HIAA levels in PCS and sham rats. These findings do not suggest that changes in brain neuronal 5-HT release play any major functional role in the pathogenesis of chronic PSE. The present data also emphasize the importance of distinguishing between brain 5-HT metabolism and brain 5-HT release.
Bergqvist
P B
PB
Department of Clinical Pharmacology, Lund University, Sweden.
Hjorth
S
S
Apelqvist
G
G
Bengtsson
F
F
D000818:Animals; D001923:Brain Chemistry / Q000187:drug effects*; D002908:Chronic Disease; D005110:Extracellular Space / Q000187:drug effects / Q000378:metabolism*; D006501:Hepatic Encephalopathy / Q000378:metabolism*; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism*; D008297:Male; D017551:Microdialysis; D011167:Portacaval Shunt, Surgical; D011168:Portal System / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000378:metabolism*; D014364:Tryptophan / Q000494:pharmacology*
D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D014364:Tryptophan