Neuroendocrine response to trihexyphenidyl in depressed patients.

: The effect of a single dose (10 mg P.O.) of trihexyphenidyl (THP) on plasma cortisol, growth hormone (GH), and immunoreactive beta-endorphin (ir-beta-EP) was studied in seven major depressed patients and seven controls. GH secretion was suppressed (34-41%) by THP in both groups. THP did not affect cortisol secretion in depressed patients and controls. An increase (18%; p less than 0.05) in plasma ir-beta-EP levels was detected in the healthy subjects only. The results of this study do not support the hypothesized altered responsiveness to anticholinergic provocation in major depression. The inhibitory activity of THP on GH secretion indicates the involvement of the cholinergic system in the regulation of GH release in humans.