A selective radioenzymatic assay for the determination of octopamine and phenylethanolamine in plasma and cerebrospinal fluid. Preliminary results in human and experimental hepatic encephalopathy.

A sensitive radioenzymatic assay for the simultaneous determination of phenylethanolamine and octopamine in biological fluids is described. It is derived from the radioenzymatic assay originally described by Molinoff et al. (1969) and subsequently modified by Saavedra (1974). The enzymatic reaction is based upon the methylation of phenylethanolamine and octopamine by phenylethanolamine-N-methyl transferase using 14C-S-adenosylmethionine as the methyl donor. The N-methyl derivatives of the two amines are separately extracted and estimated. Selectivity is increased by optimization of extraction and evaporation and by subsequent extraction of the two compounds. Phenylethanolamine and octopamine levels were determined in plasma of human subjects and in plasma and CSF of dogs. The levels were found significantly elevated both in human and experimental hepatic encephalopathy.