IN VIVO DETERMINATION OF PHENYLALANINE HYDROXYLASE ACTIVITY IN CIRRHOTIC PATIENTS WITH ~2H-PHENYLALANINE

The phenylalanine hydroxylase activities of 23 cirrhotic patients (8 compensated and 15 decompensated) and 8 normal adults were measured with a deuterated phenylalanine loading test. After a single iv injection of 10mg/kg labeled L-phenylalanine or 20 mg/kg labeled DL Phe,the abundances of plasma Phe and Tyrosine were analysed with GC-MS. The activities of phenylalanine hydroxylase were estimated by ①the slope of Tyr abundance curve, ②the slope of Tyr/Phe abundance ratio curve, ③the area under Tyr abundance curve, and ④the area under Tye/Phe abundance ratiocurve. The results revealed that the activity of phenylalanine hydroxylase was impaired in cirrhotic patients and the impairment was more severe in decompensated than in compensated cirrhosis.