Effect of L-tryptophan on apomorphine-induced growth hormone secretion in normal subjects.

Oral administration of the serotonin precursor, L-tryptophan, to normal male volunteers (n = 7) in a dose (3 g) sufficient to increase free plasma tryptophan concentrations more than 12-fold had no significant effect on basal growth hormone secretion or on apomorphine HCL-induced (0.75 mg sc) peak growth hormone concentrations. These data suggest that, in man, tryptophan administration has little effect on central dopaminergic function, at least in the hypothalamic-pituitary axis and that serotonergic mechanisms have no major modulatory effect on dopamine-mediated growth hormone secretion.