Metabolism of an ingested serine load in psychotic and nonpsychotic subjects

Our previous studies have shown that in psychotics, the plasma serine level is abnormally high and that plasma serine hydroxymethyltransferase (which cleaves serine to glycine) activity is abnormally low as compared with that in nonpsychotic subjects. In this study, psychotic and nonpsychotic subjects ingested a large bolus of L-serine (4 mM/kg) at breakfast and blood was drawn before breakfast, 2 hr, 4 hr, and 6 hr after serine ingestion. Baseline serine and SHMT activity differentiated between psychotics and nonpsychotics with high degrees of significance (p less than 0.0001) and p less than 0.01, respectively). Plasma serine levels 2 hr after serine ingestion were significantly higher (p less than 0.01) in nonpsychotics as compared with psychotics. Elimination of serine in psychotics was bimodal and was significantly different from that of nonpsychotics (p less than 0.0079, Moses test). These findings provide additional evidence for abnormal serine metabolism in psychotic patients.