Effect of L-Tryptophan on Growth Hormone and Prolactin Release in Normal Volunteers and Patients with Secretory Pituitary Tumors

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Abstract
L-tryptophan (a serotonin precursor) 5 g. was administered to 20 normal volunteers (5 males, 10 females on no medications and 9 females on oral contraceptives). Fourteen patients with secretory pituitary tumors were similarly studied. The tumor group consisted of 8 patients with pure prolactin secreting tumors, 3 with pure growth hormone secreting tumors and 3 whose tumors secreted both GH and PRL. In the normal subjects, L-tryptophan caused a significant GH elevation in both groups of females, on or off birth control medication. Although L-tryptophan administration was associated with a slight rise in plasma GH levels in males, this elevation was not statistically significant. Six of 8 pure prolactin secreting tumor patients exhibited a substantial GH response to L-tryptophan. Early detection undoubtedly was responsible for the high percentage responders. The two patients with PRL secreting tumors failing to respond to L-tryptophan with a GH rise were 2 of the 3 patients in the group who had previously been operated on and had residual tumor. L-tryptophan administration altered plasma GH concentrations minimally in patients with GH secreting tumors, 2 of 6 showing modest declines in plasma GH concentration. Prolactin responses to L-tryptophan were unimpressive. Only approximately half of the normal volunteers exhibited a positive response. Similarly L-tryptophan had little influence on plasma PRL concentrations in patients with PRL secreting tumors.

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