1 The psychotropic effects of a single oral dose of (‐)‐tryptophan (5 g) in human volunteers were investigated using a series of physiological and psychological tests. 2 Self‐ratings of mood showed increase in drowsiness but no euphoria was detected. 3 Severe initial nausea occurred and headache increased; other bodily symptoms were unaffected. 4 Trptophan caused increased activity in the slow wavebands of the EEG but did not alter the other physiological measures. 5 The levels of total and free tryptophan in the plasma increased 8 and 20 fold respectively to peak levels 2 h after ingestion.

The effects of intravenous infusion of L‐tryptophan at doses of 75 and 100 mg/kg were compared with that of normal saline in healthy volunteers by means of a series of psychological and physiological measures. The 100 mg/kg infusion produced a 40 fold increase in free tryptophan and an 8 fold increase in the bound form. Few of the objective tests showed any differences. The electroencephalogram showed a significant increase in slow‐wave activity (4.0 to 7.5 Hz) and a trend toward decreased fast‐wave activity (13.5 to 26.0 Hz). Some impairment of a motor speed task was also noted. Reduction of arousal and increased drowsiness (but no euphoria) were shown by the subjective ratings.

Platelet monoamine oxidase (MAO) activity was determined before and after the subcutaneous administration of adrenaline to nine healthy volunteers. Significant increases were found 15 min and 1 hr after adrenaline in the enzymatic activity with benzylamine acting as substrate. Increases were also found in all but two samples in the activity towards tyramine. Such increases may be part of a general response to "stress", and, if so, need to be taken into account when interpreting changes in platelet MAO activity in psychiatric patients.

SynopsisNon-esterified fatty acid and total and free tryptophan were determined in the plasma of psychiatric patients unselected with respect to psychiatric diagnosis and in the plasma of normal subjects before and after physiological and psychiatric tests. Retarded patients had significantly low total and free tryptophan values which correlated negatively with agitation. Total tryptophan fell significantly after testing in the non-retarded subjects. The only biochemical abnormality significantly associated with a diagnosis of primary depression was the rise of plasma non-esterified fatty acid after testing. Thus, tryptophan abnormalities were associated more with psychiatric rating scores than with diagnoses.