Slight Effect of<scp>l</scp>-Tryptophan on Growth Hormone Release in Normal Human Subjects¹

Abstract

Oral administration of 70 mg/kg of l-tryptophan (TP) induced a slight rise in plasma human growth hormone (hGH) in 21 normal women and 11 normal men. In 6 subjects, intravenous injection of insulin (0.1 IU/kg) or oral TP loading showed the latter stimulus to be by far less potent in eliciting hGH release. Combined treatment with TP and insulin (0.05 IU/kg iv) in 10 subjects blunted the hGH response which followed administration of insulin alone. Oral administration of 150 mg/kg of l-hydroxytryptophan in 7 women did not induce a significant increase in plasma hGH. These data suggest that the serotoninergic system does not play a stimulatory role in hGH secretion.