Bd. Sheehan et al., USE OF A DIETARY MANIPULATION TO DEPLETE PLASMA TYROSINE AND PHENYLALANINE IN HEALTHY-SUBJECTS, J PSYCHOPH, 10(3), 1996, pp. 231-234
The aim of the present study was to lower plasma concentrations of tyr
osine, the amino acid precursor of noradrenaline and to determine whet
her this manipulation impaired noradrenergic function as measured by t
he evening rise in concentrations of plasma melatonin. Eight healthy v
olunteers received three drinks: (i) an essential amino acid load with
tyrosine, (ii) the same load without tyrosine and its precursor, phen
ylalanine and (iii) tap water. The tyrosine- and phenylalanine-deficie
nt drink lowered plasma tyrosine by approximately 50% over 5 h. Howeve
r, this did not alter the evening plasma melatonin levels compared to
the other two drinks. The results suggest that amino acid loading prod
uces a modest decline in plasma tyrosine levels but this does not lowe
r noradrenergic neurotransmission in the pineal gland.