HIGHLY SENSITIVE AND SPECIFIC HPLC WITH FLUOROMETRIC DETECTION FOR DETERMINATION OF PLASMA EPINEPHRINE AND NOREPINEPHRINE APPLIED TO KINETIC-STUDIES IN HUMANS

An HPLC separation method combined with fluorometric detection was ext ended to enable simultaneous assessment of plasma H-3-labeled acid end ogenous epinephrine (E) and norepinephrine (NE). Forearm fractional ex traction (FFE) of H-3-labeled E and NE and of endogenous E was measure d in 40 healthy volunteers who were receiving a continuous infusion of H-3-labeled E and NE. Concentrations of arterial and venous E were 26 .8 +/- 1.95 (mean +/- SE) and 6.8 +/- 0.75 ng/L, respectively. Arteria l and venous NE and dopamine (DA) were also measured, with respective values of 140.7 +/- 8.5 and 192.1 +/- 15.1 for NE, and 13.1 +/- 0.78 a nd 11.3 +/- 0.70 ng/L for DA. The FFE of H-3-labeled E was slightly bu t significantly higher (0.790 +/- 0.016) than the that of either H-3-l abeled NE or endogenous E (0.748 +/- 0.0146 and 0.745 +/- 0.0185, resp ectively; P < 0.001), the correlations being highly significant (r = 0 .80, P < 0.001) in both cases. The small difference between the FFE of E and of H-3-labeled E allows the calculation of the apparent spillov er of E. However, this spillover was negligible compared with forearm NE spillover (0.0112 +/- 0.0031 vs 1.369 +/- 0.128 ng/L per minute. Th e high sensitivity of this measurement of venous E widens the possibil ities for studying E kinetics under physiological conditions.