Interindividual variation in kinetics of infused epinephrine

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Abstract
1‐Norepinephrine was infused continuously for 10 hr into 5 normotensive, male laboratory subjects (mean age, 32.4 ± 1.9 yr) at a mean rate of 0.06 µg/kg/min. Mean plasma norepinephrine (NE) rose from the preinfusion level of 0.19 ± 0.02 µ/l to a steady state level of 1.22 ± 0.29 µ/l. The mean increase in blood pressure was 21.8 ± 0.9 mm Hg systolic and 14.1 ± 1.0 mm Hg diastolic. The mean depression in heart rate was 12.7 ± 1.7 beats/min. The clearance of norepinephrine ranged front 27.9 to 100.0 ml/kg/min (mean, 58.0 ± 13.8) and was little influenced by acute hemodynamic changes. The volume of distribution ranged widely (0.09 to 0.40 Mkg), the mean value being 13.51 1. The mean norepinephrine half‐life was brief, ranging from 1.45 to 2.9 min (mean, 2.09 ± 0.34 min). There was no evidence of a slowly accumulating high‐capacity low‐affinity pool of norepinephrine. These results support the use of plasma norepinephrine as an index of sympathetic activity within an individual but not its validity in interindividual comparisons.