The changes of the number of beta-adrenergic receptors, the activity of cAMP-PDE and the level of cAMP were observed in the guinea pigs with allergic asthma with radioligand assay, radioenzyme assay and radioimu-noassay respectively. It was found that there were a 25% decrease of the number of beta-adrenergic receptors on the lung membrane, a 36% decrease of the level of cAMP in the lung tissue, and a 35% increase of cAMP-PDE activity in the asthmatic animals as compared with those of the control. A close positive correlation was observed between the number of beta-adrenergic receptors and cAMP level,but a negative correlation between cAMP-PDE activity and cAMP level in the asthmatic group.

An experimental model of asthma was established with ovalbumin sensitization in guinea-pigs and then the preventive effects of ketotifen on the terbutaline-induced down regulation of beta-adrenoceptors in lymphocytes were investigated with radioligand binding assay.It was found that terbutaline significantly reduced the density of beta-adrenoceptors in lymphocytes,ketotifen administered simultaneously with terbutaline prevented the density of beta-adrenoceptors in lymphocytes from reducing.and neither ketotifen nor terbutaline changed the Kd values in either group.These findings suggest that ketotifen is of value to provent asthmatic patients from the adverse effects of tschyphylactic therapy of beta-adrenoceptor stimulants.