No influence of circulating noradrenaline on bronchial reactivity to histamine in asthmatic patients.

The influence of circulating noradrenaline on bronchial reactivity to histamine was investigated in eight asthmatic patients. Bronchial hyperreactivity was confirmed by a pretrial bronchial histamine challenge which was positive at a concentration below 6 mg/ml in all patients. On two separate occasions bronchial challenge tests were performed during infusions of placebo (saline) or noradrenaline (0.25 micrograms X kg-1 X min-1). The latter infusion elevated venous plasma noradrenaline concentrations from 2.5 +/- 0.3 to 27.4 +/- 3.3 nmol/l and increased blood pressure by 30/17 mm Hg. The effects of noradrenaline and placebo did not differ with regard to any lung function parameter. Histamine inhalations induced bronchoconstriction (greater than 60% reduction of Sgaw) and elevated heart rate by 11 beats/min, but did not alter venous plasma adrenaline concentrations. The bronchial reactivity to histamine was similar during placebo and noradrenaline infusions. High levels of circulating noradrenaline do not alter basal airway calibre or the bronchial reactivity to histamine in asthmatic patients.