title: Absent growth hormone response to L-tryptophan in acromegaly.
abstract: In acromegaly, regulation of GH secretion by dopamine pathways appears to be qualitatively abnormal. To determine whether regulation of GH secretion by serotonin pathways is also abnormal in acromegaly, we administered L-tryptophan (5 g orally), the initial precursor of serotonin, to 10 patients with active acromegaly (9 treated and 1 untreated), 3 patients with cured acromegaly, and 8 normal subjects. The normal group showed a significant (P less than 0.05) increase in serum GH after L-tryptophan [peak value, 12.3 +/- 4.0 (se) ng/ml], though the magnitude of the response was highly variable. In contrast, subjects with active acromegaly did not show an increase in serum GH after L-tryptophan [mean integrated percentage change in serum GH, -25 +/- 25% (SE); P = NS]. One patient whose acromegaly had been surgically cured did show a GH rise after L-tryptophan. In acromegaly, the GH response to L-tryptophan is absent, suggesting that regulation of GH secretion by serotonin pathways might be qualitatively abnormal.
mesh_terms: D000172:Acromegaly / Q000097:blood*; D000328:Adult; D005260:Female; D013006:Growth Hormone / Q000097:blood*; D006801:Humans; D007700:Kinetics; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D014364:Tryptophan
chemical_list: D014364:Tryptophan; D013006:Growth Hormone