MODIFICATION OF BRONCHIAL REACTIVITY BY PHYSIOLOGICAL CONCENTRATIONS OF PLASMA EPINEPHRINE

Circulating epinephrine concentrations are altered in certain pathophysiological states, but whether such changes in epinephrine concentrations can alter bronchial responsiveness in subjects with asthma has not been studied. We studied 10 subjects with asthma in a double-blind crossover study on 4 nonconsecutive days. After measurement of baseline forced expiratory volume in 1 s (FEV1) and plasma epinephrine concentration, subjects were given placebo or 4, 16, or 64 ng.kg-1.min-1 epinephrine by intravenous infusion for 45 min. Blood was taken for plasma epinephrine concentration before the infusion and at 30 min, when a histamine challenge test was performed. Mean plasma epinephrine concentrations ranged from 0.37 nmol/I on placebo to 3.76 nmol/I with the 64-ng/kg infusion. FEV, increased progressively with increasing concentrations of infused epinephrine, the mean change ranging from -0.051 on placebo to 0.331 after the highest concentration of epinephrine. The provocative dose of histamine causing a 20% fall in FEV1 increased progressively with increasing concentrations of infused epinephrine, geometric mean values ranging from 0.61 mumol with placebo to 1.7 mumol after the highest dose of epinephrine. Thus epinephrine, at physiological plasma concentrations, can modify bronchial reactivity.