L-Tryptophan injection enhances pulsatile growth hormone secretion in the rat.
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.
D000818:Animals; D001923:Brain Chemistry / Q000187:drug effects; D013006:Growth Hormone / Q000378:metabolism*; D008297:Male; D010879:Piperazines / Q000494:pharmacology; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism*; D011719:Pyrazines / Q000494:pharmacology; D051381:Rats; D011985:Receptors, Serotonin / Q000187:drug effects; D012701:Serotonin / Q000378:metabolism; D014364:Tryptophan / Q000378:metabolism / Q000494:pharmacology*; D014633:Valine / Q000494:pharmacology
D010879:Piperazines; D011719:Pyrazines; D011985:Receptors, Serotonin; D012701:Serotonin; C014896:6-chloro-2-(1-piperazinyl)pyrazine; D014364:Tryptophan; D013006:Growth Hormone; D014633:Valine