Plasma catecholamines via an improved fluorimetric assay: comparison with an enzymatic method.

The fluorimetric method of Renzini and Valori, utilizing alumina and ion exchange chromatography, was modified to include dl-3H norepinephrine (3H-NE) for individual plasma NE recoveries and mercaptoethanol as a stabilizing agent for the fluorescent lutines. Plasma NE and epinephrine (E) were measured in hypertensive patients, and results were compared with those of the enzymatic method of Engelman in duplicate plasma specimens. The correlations of the NE and the total plasma catecholamine concentrations determined by the two methods were both r = 0.98 (p less than 0.001) and that of the E concentrations was r = 0.79 (p less than 0.01). The reproducibility of the method for measuring 10 ml. aliquots of pooled plasma yielded a standard deviation of less than 10 per cent of the mean. The fluorimetric method was more economical, less time-consuming, and as reliable as the enzymatic method for quantitating plasma catecholamines.