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.


METHODS
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.


RESULTS
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.


CONCLUSIONS
These data contrast with a previous study using hydrocortisone in the same paradigm and demonstrate important functional differences between dexamethasone and hydrocortisone.
Porter
R J
RJ
Department of Neuroscience and Psychiatry, University of Newcastle, Royal Victoria Infirmary, UK.
McAllister-Williams
R H
RH
Jones
S
S
Young
A H
AH
D000293:Adolescent; D000328:Adult; D000893:Anti-Inflammatory Agents / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology*; D004644:Emotions / Q000187:drug effects*; D005938:Glucocorticoids / Q000494:pharmacology*; D019382:Human Growth Hormone / Q000097:blood; D006801:Humans; D006854:Hydrocortisone / Q000097:blood / Q000494:pharmacology; D007262:Infusions, Intravenous; D008297:Male; D009490:Neurosecretory Systems / Q000187:drug effects*; D011388:Prolactin / Q000097:blood; D011985:Receptors, Serotonin / Q000187:drug effects; D044263:Receptors, Serotonin, 5-HT1; D014364:Tryptophan / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*
D000893:Anti-Inflammatory Agents; D005938:Glucocorticoids; D011985:Receptors, Serotonin; D044263:Receptors, Serotonin, 5-HT1; D019382:Human Growth Hormone; D003907:Dexamethasone; D014364:Tryptophan; D011388:Prolactin; D006854:Hydrocortisone