The effects of glucocorticoids on the availability of L-tryptophan and tyrosine in the plasma of depressed patients.
There is evidence that a functional deficit of serotonin/noradrenaline and/or of their precursors L-tryptophan (L-TRP)/tyrosine and disorders in the hypothalamic-pituitary-adrenal (HPA) axis are linked to the pathophysiology of severe depressions. Several reports suggest a reciprocal relationship between these neurotransmitters and HPA axis activity. In order to investigate the effect of glucocorticoid excess on the availability of L-TRP and tyrosine to the brain, we measured urinary cortisol (UC) excretion in 24-h urine, and the availability of both amino acids before and after treatment with 1 mg dexamethasone in 26 depressed patients. We found no relationship between UC excretion and the availability of either amino acid. Dexamethasone significantly suppressed the availability of L-TRP (P less than 10(-5] and of tyrosine (P = 0.005). Major depressed patients with melancholia exhibited a significantly lower availability of L-TRP than minor depressives (P = 0.007).
Maes
M
M
Department of Psychiatry, University of Antwerpen, Edegem, Belgium.
Schotte
C
C
Scharpé
S
S
Martin
M
M
Blockx
P
P
D000596:Amino Acids / Q000097:blood; D003866:Depressive Disorder / Q000097:blood / Q000175:diagnosis*; D003907:Dexamethasone; D006801:Humans; D006854:Hydrocortisone / Q000652:urine*; D007030:Hypothalamo-Hypophyseal System / Q000187:drug effects; D008875:Middle Aged; D010913:Pituitary-Adrenal System / Q000187:drug effects; D011446:Prospective Studies; D014364:Tryptophan / Q000097:blood*; D014443:Tyrosine / Q000097:blood*
D000596:Amino Acids; D014443:Tyrosine; D003907:Dexamethasone; D014364:Tryptophan; D006854:Hydrocortisone