The effect of insulin on elder phenylketonuric patients

The effect of insulin on blood phenylalanine, tyrosine and catecholamine levels was investigated in six phenylketonuric patients and eight normal controls. The plasma phenylalanine-tyrosine ratio was lower after insulin injection in five of six patients. In four patients the plasma catecholamine concentrations increased. The tyramine level was remarkably high one hour after insulin injection. Urinary homovanillic acid was elevated in four patients. It appeared that insulin treatment produced some therapeutic effects in patients with smaller phenylalanine-tyrosine ratios or elevated catecholamine levels.