Potentiation of isoprenaline-induced plasma cyclic AMP response by aminophylline in normal and asthmatic subjects.

1 The effect of intravenous aminophylline infusion (6 mg-1 kg in 20 min, then 0.9 mg-1 kg-1 h thereafter) and its interaction with inhaled isoprenaline (800 microgram ex inhaler) on plasma cyclic AMP levels was studied in five normal and five asthmatic subjects. 2 Aminophylline infusion alone did not significantly change plasma cyclic AMP levels in either group. 3 In both groups, the plasma cyclic AMP response to isoprenaline aerosol inhalation was enhanced by aminophylline, although to a lesser degree in the asthmatic subjects. 4 The results provide in vivo evidence consistent with the hypothesis that in man, therapeutic doses of aminophylline may exert their clinical effects by inhibition of cyclic AMP phosphodiesterase.