Effects of anti-asthmatic drugs on airway resistance and plasma level of cyclic AMP in guinea pig.

Effects of anti-asthmatic drugs on airway resistance and plasma level of cyclic AMP were investigated in guinea pigs sensitized and non-sensitized with egg-albumin. Histamine increased airway resistance in the both groups of guinea pigs, and guinea pigs sensitized with egg-albumin were more sensitive to histamine. Anti-asthmatic drugs inhibited dose-dependently the increase of airway resistance caused by histamine. Sensitization with egg-albumin decreased the potencies of the beta-adrenoceptor stimulants, salbutamol and isoprenaline, but not that of aminophylline. The plasma level of cyclic AMP was increased by salbutamol and isoprenaline, but not by aminophylline. The increased plasma level of cyclic AMP by beta-adrenoceptor stimulants was not attenuated by sensitization with egg-albumin.