L-Tryptophan injection enhances pulsatile growth hormone secretion in the rat

Endocrinology. 1981 Jan;108(1):331-5. doi: 10.1210/endo-108-1-331.


The effect of injecting L-tryptophan or a serotonin receptor agonist [6-Cl-2-[1-piperazinyl]pyrazine ((MK0212)] on pulsatile GH secretion was studied in male rats bearing right atrial cannulae. After injection, blood samples were drawn at 15-min intervals for periods up to 4 h. L-Tryptophan administration (50 or 100 mg/kg, ip) significantly enhanced mean plasma GH levels measured over a 3.5-h period. Injection of another large neutral amino acid, L-valine (100 mg/kg, ip), did not influence plasma GH levels. However, when administered with tryptophan, valine blocked the tryptophan-induced enhancement of GH secretion and blunted the increases in brain tryptophan and serotonin levels that normally accompany tryptophan injection. Injection of MK-212 (2 mg/kg, ip) elicited an immediate rise in plasma GH levels; this effect was completely blocked by pretreatment with metergoline (2 mg/kg, ip), a serotonin receptor antagonist. Taken together, these data support the notion that treatments which increase serotonin receptor stimulation enhance or induce pulsatile GH secretion.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Brain Chemistry / drug effects
  • Growth Hormone / metabolism*
  • Male
  • Piperazines / pharmacology
  • Pituitary Gland / drug effects
  • Pituitary Gland / metabolism*
  • Pyrazines / pharmacology
  • Rats
  • Receptors, Serotonin / drug effects
  • Serotonin / metabolism
  • Tryptophan / metabolism
  • Tryptophan / pharmacology*
  • Valine / pharmacology


  • Piperazines
  • Pyrazines
  • Receptors, Serotonin
  • Serotonin
  • 6-chloro-2-(1-piperazinyl)pyrazine
  • Tryptophan
  • Growth Hormone
  • Valine