A radioenzymatic assay for free and conjugated normetanephrine and octopamine excretion in man.

A radioenzymatic method for the measurement of free and conjugated normetanephrine (NMN) and octopamine (OCT) is described for human urine. The assay is based on the conversion of NMN or OCT to radiolabeled metanephrine (MN) or synephrine (SYN) by phenylethanolamine-N-methyl transferase (PNMT), using tritium-labeled S-adenosyl-methionine [3H]SAM as methyl donor. Thin-layer chromatographic separation yields an assay of high specificity. The sensitivity of the assay is 5 and 2.5 pg of NMN or OCT, respectively. The normal value of free and conjugated NMN was found to be 23 +/- 13 and 102 +/- 49 ng/mg creatinine. Four patients with pheochromocytoma had highly increased levels of free and conjugated NMN. The urinary excretions of free and total octopamine were 5.7 +/- 2.8 and 34.8 +/- 16.6 ng/mg of creatinine, respectively, in normal patients.