Influence of infused adenosine on bronchial tone and bronchial reactivity in asthma

Adenosine has been found to contract human bronchial smooth muscle in vitro and to induce bronchoconstriction in asthmatic patients when administered by inhalation. The aim of the present study was to investigate if elevation of circulating levels of adenosine influence bronchial tone or bronchial reactivity. Seven patients with bronchial asthma in whom bronchial hyperreactivity had been confirmed in a pretrial bronchial histamine challenge (PC20 FEV1 0.064 to 2.45 mg/ml) received intravenous infusions of adenosine in increasing doses (10, 30 and 50 micrograms/kg/min, 6 min on each dose step) or placebo (saline solution) on two different days in a randomized, single-blind manner. Heart rate, blood pressure and lung function (lung volumes, flow-volume loops and airway conductance) were measured on each dose step. Infusion rate was held constant (at 50 micrograms/kg/min) throughout the trial and a bronchial methacholine challenge was performed during the infusion of adenosine or placebo. Infusions of adenosine and placebo did not influence heart rate, blood pressure or bronchial tone on either day and bronchial reactivity was similar on both days. We conclude that bronchial tone and bronchial reactivity in asthmatic patients are not increased by intravenously administered adenosine at a dose level which, in other studies, has been shown to induce regional effects in the systemic arterial circulation.