Effect of L-5-HTP on the Release of Growth Hormone, TSH and Insulin

Abstract

Effect of L-5-HTP (L-5-hydroxytryptophane) on the release of human growth hormone (HGH), thyroid stimulating hormone (TSH) and immunoreactive insulin (IRI) was investigated in 7 normal subjects and 25 patients with endocrine disorders. A single oral dose of 200mg of L-5-HTP showed the elevation of HGH in plasma; however, no release of TSH and insulin in plasma of normal subjects. HGH response to L-5-HTP administration was less in quantity as compared with HGH respone to insulin hypoglycemia or arginine infusion. The timing of HGH respone to L-5-HTP was quite variable (between 30 and 120min) in an oral dose of L-5-HTP. No release of HGH by L-5-HTP administration was observed in each of the patients with primodial dwarfism, panhypopituitarism, pituitary dwarfism, and some cases of hypothyroidism. The effect of hyperglycemia or sedative on the release of HGH induced by L-5-HTP was observed. HGH release by L-5-HTP was not observed in these treatments of glucose or diazepam, therefore it might suggest that HGH release by L-5-HTP was inhibited by hyperglycemia or diazepam administration. Suppression of TSH release by L-5-HTP dose was noticed in some patients with hypothyroidism; however no effect in normal subjects. Neither elevation nor reduction of IRI was observed by the L-5-HTP oral dose in normal subjects. These findings suggested that L-5-HTP might induce the release of HGH from normal pituitary gland, that the release of TSH might be reduced by the dose of L-5-HTP in the patients with hypothyroidism, but not in normal subjects, and that IRI was not affected by the dose of L-5-HTP in normal subjects.

Central Serotoninergic Stimulation by Fenfluramine Challenge Does Not Affect Plasma Thyrotropin-Stimulating Hormone Levels in Man

“…These data are further consistent with the lack of effect of the 5-HT receptor antagonist metergoline on basal and TRH-stimulated TSH in normal men [10], However, they may not be inconsistent with data from 5-HTP studies which suggest an inhibitory effect of 5-HT on TSH in pa tients with primary hypothyroidism [16,40]. It is possible that central 5-HT receptors may be supersensitive in the hypothyroid state secondary to decreased 5-HT synthesis and turnover [35].…”

“…Transient stimulation, followed by prolonged suppression, of plasma TSH during 5-HTP infu sion has been reported in one study [21], Data from similar studies employing 5-HTP, however, suggest and inhibitory effect of 5-HT on TSH in patients with primary hypothyroiReceived; October 24. 1986 Accepted after revision: September 4, 1987 dism [16,40], Finally, no effect of 5-HT on TSH has been suggested by studies examining the effect of metergoline, a 5-HT receptor antagonist, on basal TSH and TSH induced by thyrotropin-releasing hormone (TRH) [10] or of acute or subchronic treatment with the 5-HT reuptake inhibitor zimelidine on basal levels of TSH [26].…”

Complex Role of 5-HT in the Regulation of TSH Secretion in the Male Rat

“…Most studies support the idea of the hypothalamic noradrenergic stimulation and dopaminergic inhibition of TSH secretion [19], The role of 5-hydroxytryptamine (5-HT) has been most controversial and the results published so far have suggested either no effect [32], a definite inhibition [5,14,18] or stimulation [4,9] of TSH secre tion.…”

Effect of Adrenergic-blocking Agents on Plasma Growth Hormone Response to L-5-Hydroxytryptophan (5-HTP) in Man

“…The reason for the discrepancy between our and their data is not readily apparent. However, the fact that both Yoshimura et al (1973) and Takahashi et al (1973) also observed stimulatory effect of 5-HTP on plasma hGH suggests that the discrepancy seems to be attributed at least partly to the differences of the races or the drugs used.…”