Brain tryptophan metabolism remained unaltered in restraint stressed rats following fluoxetine administration

Effects of two hours immobilization stress on tryptophan (Tp) metabolism in rats was studied following fluoxetine-HCl (20 mg/kg) administration. After 2 hr immobilization stress there was no effect on peripheral liver Tp metabolism but there was marked increase in brain Tp metabolism leading to increases in 5-HT (5-Hydroxy tryptamine) synthesis and turn over. Rats subjected to 2 hrs immobilization stress immediately after fluoxetine-HCl (20 mg/kg) administrations show significant increases in holo and total Tp pyrrolase enzyme activities leading to decreased serum total Tp concentrations. Brain Tp and 5-HT remain unchanged but 5-hydroxy indole acetic acid (5-HIAA) concentration was significantly increased when compared to fluoxetine injected non-immobilized rats. Administration of fluoxetine-HCl (20 mg/kg) inhibited holo and total Tp pyrrolase enzyme activities when compared to saline injected rats and ultimately increases liver Tp concentrations. Although serum total Tp remained unchanged but brain Tp and 5-HT concentrations were significantly increased. It is therefore concluded that pre-treatment of rats with fluoxetine-HCl did not alter conditioned stress induced change in brain Tp metabolism. Future studies on chronic administration of the drug will be fruitful to investigate its effects on Tp metabolism in conditioned stress.