Highly sensitive and specific HPLC with fluorometric detection for determination of plasma epinephrine and norepinephrine applied to kinetic studies in humans

Abstract

An HPLC separation method combined with fluorometric detection was extended to enable simultaneous assessment of plasma 3H-labeled and endogenous epinephrine (E) and norepinephrine (NE). Forearm fractional extraction (FFE) of 3H-labeled E and NE and of endogenous E was measured in 40 healthy volunteers who were receiving a continuous infusion of 3H- 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. Arterial 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 and 11.3 ± 0.70 ng/L for DA. The FFE of 3H-labeled E was slightly but significantly higher (0.790 ± 0.016) than the that of either 3H-labeled NE or endogenous E (0.748 ± 0.0146 and 0.745 ± 0.0185, respectively; 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 3H-labeled E allows the calculation of the apparent spillover 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. The high sensitivity of this measurement of venous E widens the possibilities for studying E kinetics under physiological conditions.