A radioenzymatic method for determination of normetanephrine in blood plasma

A radioenzymatic assay for determination of normetanephrine in blood plasma is described. It was based on N-methylation of normetanephrine by phenylethanolamine-N-methyltransferase using S-adenosyl[methyl-3]methionine as the methyl donor. 2981 +/- 85 cpm (mean +/- s mean, n = 32) were obtained from 1 ng normetanephrine. Blank values corresponded to 27 +/- 3 pg (n = 7). Normetanephrine levels measured in the blood plasma of 12 persons ranged from 1.3 to 9.6 ng/ml.