Abstract— Phenylalanine ammmonia‐lyase (PAL), an enzyme which converts phenylalanine (Phe) and tyrosine (Tyr) to trans‐p‐cinnamic acid and trans‐p‐coumaric acid, respectively, was administered to mice and its effect on the conversion of [3H]tryptophan to 5‐[3H]HT in the brain was measured. Although PAL significantly depleted plasma Tyr, it has little or no effect on either brain Tyr or catecholamine concentrations. Endogenous brain tryptophan levels were significantly increased 2 h after PAL administration, brain 5‐HT was dramatically increased 4 h following PAL and each returned to baseline levels by 8 h. This return to baseline was accompanied by a marked decrease in the fraction of tryptophan converted to 5‐HT during a 20 min pulse period preceding death, suggesting the activation of a compensatory decrease in 5‐HT synthesis in response to increased 5‐HT concentration. These data suggest that PAL administration readily produces reversible alterations in 5‐HT synthesis and that this may be a fruitful approach to studying brain 5‐HT function.
|Number of pages
|Journal of neurochemistry
|Published - Nov 1979
ASJC Scopus subject areas
- Cellular and Molecular Neuroscience