Abstract
A rapid and sensitive single-isotope radioenzymatic assay for norepinephrine has been developed. This method is based on the conversion of norepinephrine to tritiated epinephrine by the enzyme phenylethanolamine-N-methyltransferase (PNMT) and 3H-S-adenosylmethionine (3H-SAM).
100 μl of untreated plasma were added directly to the reaction mixture. After incubation, labelled epinephrine was extracted with alumina and separated from 3H-SAM by precipitation of 3H-SAM with tungstate and adenosine. Adenosine could be substituted for S-adenosylmethionine (SAM) to coprecipitate the remaining radioactive SAM. In order to eliminate the effects of other plasma components, catecholamine-free plasma and an internal standard had to be assayed in parallel with a sample. 400 μl of plasma was sufficient for duplicate determinations of norepinephrine.
This method is simple and 25 plasma samples (100 test tubes) can be processed within 4 hours.
