The metabolic fate of infused L-tryptophan in men: possible clinical implications of the accumulation of circulating tryptophan and tryptophan metabolites

L-Tryptophan (Trp) was widely used as a natural tool for the support of serotonin-mediated brain functions and as a challenge probe for the assessment of serotonin-mediated neuroendocrine responses. The metabolic fate of the administered Trp and the kinetics of the accumulation of Trp metabolites in the circulation, however, have never thoroughly been investigated. This study describes the time- and dose-dependent alterations in the plasma levels of various Trp metabolites and large neutral amino acids after the infusion of Trp to healthy young men (1, 3 and 5 g; placebo-controlled, double-blind, cross-over study during day- and night-time). The major Trp metabolites (kynurenine, indole acetic acid and indole lactic acid) in plasma increased dose-dependently but rather slowly after Trp administration to reach their maximal plasma levels (up to 10-fold after the 5 g dose) at about 3 h p.i., and remained at an elevated level (about 5-fold) for up to 8 h. N-acetyl-Trp and 5-hydroxy-Trp rose rapidly and massively after Trp infusions, at the 5 g dose more than 200- and 20-fold, respectively, and declined rapidly to about 5-fold baseline levels within 2 h. Whole blood serotonin levels were almost unaffected by the Trp infusions. A rather slow increase of 5-hydroxyindole acetic acid was seen, reaching maximum values (3-fold at the 5 g dose) at about 2 h after the infusion of Trp. Additionally, a dose-dependent rise of circulating melatonin was observed after L-Trp infusions. The administration of L-Trp caused a depletion of the concentrations of the other large neutral amino acids and a dose dependent decrease of the ratio between plasma tyrosine and the sum of the plasma concentrations of the other large neutral amino acids. Apparently, none of the existing pathways of peripheral Trp metabolism is saturated by its substrate, Trp in men. At least some of the central effects reported after L-Trp administration may be mediated by the Trp-stimulated formation of neuroactive metabolites or by the decreased availability of tyrosine for catecholamine synthesis.

The influence of intravenous L-tryptophan on plasma melatonin and sleep in men

The sleep-inducing mechanisms of L-Tryptophan (L-Trp) are generally thought to be mediated by a central serotonergic activation. Evidence is presented that some effects of L-Trp on sleep may be mediated by melatonin, a Trp-metabolite with sedative properties. Trp effects on vigilance, sleep, and plasma-melatonin concentrations were measured after double-blind application of 0, 1, 3, and 5 g L-Trp in nine and five healthy probands during daytime and nighttime, respectively. A significant sleep-inducing effect was observed after L-Trp administration during daytime and nighttime. The infusions of L-Trp caused a massive elevation of plasma melatonin levels. This effect was significant both during the night and the day, indicating that the increment of circulating melatonin may be of extrapineal origin.

[Radiation pneumonitis and radiation fibrosis following systemic irradiation of thoracic lymph nodes in Hodgkin's disease]

146 of 226 patients suffering from Hodgkin's disease were submitted to a high voltage therapy in the chest using the method of single fields. In order to be in a position to judge the appearance and the development of a modification of the pulmonary parenchyma induced by radiations, the authors evaluated the data of 69 patients who could be checked up in relatively small intervals during at least one year after the radiotherapy. Dilatations of interpleural and hilar lymphomas or pulmonary infiltrates have to be considered as one of the most important causes of atypical pneumonia and fibrosis induced by radiation. 12 patients out of 35 (i.e. 35,3%) with intrathoracic lymphomatosis granulomatosa presented atypical pneumonias which mostly were not very serious, and four patients (i.e. 11,8%) had fibroses. If the mediastine was irradiated systematically for the purpose of prophylaxis, no pulmonary reaction was observed that could be demonstrated by means of X-rays.