Effects of dexamethasone on neuroendocrine and psychological responses to L-tryptophan infusion

5-Hydroxytryptamine1A (5-HT1A) receptors have been shown to be suppressed by corticosteroid hormones in a variety of animal experimental paradigms. This effect may be central to the pathophysiology of severe clinical depressive illness, a condition in which 5-HT1A receptor function is reduced and corticosteroid hormones are elevated. Evidence suggests that the growth hormone (GH) response to L-tryptophan (L-TRP) is mediated by 5-HT1A receptors. This response has been shown to be reduced following acute administration of hydrocortisone. The purpose of this study was to examine the effects of acute administration of dexamethasone, in normal volunteers, on hormonal and psychological responses to L-TRP infusion.

Sixteen healthy male volunteers took part in a random order, double blind study, in which 5 mg dexamethasone or placebo was administered 11 h before infusion of L-TRP.

Pretreatment with dexamethasone had no effect on the GH response to the infusion. However, baseline prolactin (PRL) was significantly reduced, as was the prolactin response to the infusion.

These data contrast with a previous study using hydrocortisone in the same paradigm and demonstrate important functional differences between dexamethasone and hydrocortisone.