Serotonin and noradrenaline concentrations and serotonin uptake in platelets from hyperphenylalaninaemic patients.

In three untreated patients with phenylketonuria (PKU), three PKU and six hyperphenylalaninaemic (HPA) patients in good metabolic control, the kinetic constants of platelet in vitro uptake of [14C]serotonin (5HT) did not significantly differ from those in 12 control subjects matched for age. The platelet concentrations of endogenous 5HT and noradrenaline (NA), taken as long-term indices of the amount of these amines circulating in plasma, were lower than normal in PKU and HPA patients, whether or not they were kept on a diet. However, a reduction in plasma NA concentrations at the moment of blood collection was seen only in untreated PKU patients. These data indicate that there may be a chronic inhibition of 5HT and possibly of NA synthesis even in PKU or HPA subjects in good metabolic control, with normal psychomotor development and only slightly raised plasma phenylalanine levels.