Plasma tryptophan tolerance curves in drug free normal controls, schizophrenic patients and prisoner volunteers.

A DISTURBANCE in indole metabolism, particularly 5-hydroxytryptamine (5-HT) and its metabolites, has been proposed in various psychiatric disorders. These include schizophreniale6 and mental depression.7-g Large oral tryptophan (TP) loads given with a monoamine oxidase inhibitor exacerbate some of the symptoms of schizophrenics but also produce central nervous system effects in non-psychotic patients.lO-l3 TP has also been used in the treatment of depressi0n.l”l5 In view of the fact that the primary source of brain indoles is ultimately TP, it was important to establish that fasting plasma levels of TP and those following oral loads were within normal limits in psychiatric patients. Fernstrom and Wurtman16 have shown that rat brain 5-HT levels are related to plasma TP. They have also shown that the ratio of TP to other plasma neutral amino acids such as tyrosine, phenylalanine, leucine, isoleucine and valine regulate brain TP and hence brain 5-HT.r7 In the present study venous blood samples from four different diagnostic groups were analyzed for plasma TP. The subjects were drug free chronic schizophrenics, acute schizophrenics, prisoner volunteers with personality disorders with and without depression, and normals consisting of staff personnel and medical students. This manuscript describes the changes in total plasma TP in these subjects before and after a 32 mg/kg oral TP load given in the morning and a standard meal containing 394.4 mg of TP and 1187 calories given in the evening. METHODS