Circulating serum phenylalanine concentrations and the effect of arginine infusion on plasma levels of growth hormone and insulin in treated phenylketonuric children.

According to desired phenylalanine (Phe) levels of 50-80 mg/l during treatment, three groups of patients with classical phenylketonuria (PKU) (5.3-17.1 years) were formed. They were investigated for their growth hormone (GH) and insulin response to arginine infusion: Group I (N = 5) had Phe levels below (22 +/- 4 mg/l), group II (N = 3) within (61 +/- 6 mg/l), and group III (N = 3) above therapeutic limits (156 +/- 3 mg/l). Nine children (5.2-14.5 years) with short stature served as controls. Whereas group I and II PKU children showed normal GH response to arginine infusion, group III children exhibited impaired GH response expressed as integrated GH response (218 +/- 38.6 micrograms X 1(-1) X 2 h vs 911 +/- 145 micrograms X 1(-1) X 2 h; P less than 0.01) or peak GH response (6.6 +/- 1.2 micrograms/l vs 18.7 +/- 2.3 micrograms/l; P less than 0.05). Integrated insulin responses did not differ between the three PKU groups but were significantly higher in all PKU patients compared with controls (4903 +/- 421 mU/l vs 2750 +/- 378 mU/l; P less than 0.01). However, this reflects impaired insulin secretion in children with constitutional delay of growth and adolescence rather than hyperinsulinism in PKU patients.