Response to pentagastrin after acute phenylalanine and tyrosine depletion in healthy men: a pilot study

Abstract

Objective: To assess the effects of the acute depletion of the catecholamine precursors phenylalanine and tyrosine on mood and pentagastrin-induced anxiety.

Design: Randomized, double-blind controlled multiple crossover study.

Setting: University department of psychiatry.

Participants: 6 healthy male volunteers.

Interventions: 3 treatments were compared: pretreatment with a nutritionally balanced amino acid mixture, followed 5 hours later by a bolus injection of normal saline placebo; pretreatment with a balanced amino acid mixture, followed by a bolus injection of pentagastrin (0.6 microgram/kg); and pretreatment with an amino acid mixture without the catecholamine precursors phenylalanine or tyrosine, followed by pentagastrin (0.6 microgram/kg).

Outcome measures: Scores on the panic symptom scale, a visual analogue scale for anxiety, the Borg scale of respiratory exertion and the Profile of Mood States Elation-Depression Scale.

Results: Pentagastrin produced the expected increases in anxiety symptoms, but there was no significant or discernible influence of acute phenylalanine and tyrosine depletion on anxiety or mood.

Conclusions: These pilot data do not support further study using the same design in healthy men. Under these study conditions, phenylalanine and tyrosine depletion may have larger effects on dopamine than noradrenaline. Alternative protocols to assess the role of catecholamines in mood and anxiety are proposed.