Characteristics of beta-adrenoceptors in tracheal smooth muscle of guinea pig sensitized by egg albumin.

The effect of pretreatment with egg albumin was examined on the beta-adrenoceptors in guinea pig isolated trachea. Befunolol and carteolol acted as partial agonists and their pA2 values were significantly larger than their corresponding pD2 values in tracheae from both untreated guinea pigs and those treated with egg albumin, suggesting that the beta-adrenoceptors contain two different affinity sites. The Scatchard plot of specific [3H]befunolol binding showed two affinity sites of the receptor (high and low affinity sites) in tracheae from both untreated animals and those treated with egg albumin. The pKD values of befunolol for both low and high affinity sites were in agreement with their respective pD2 and pA2 values. The intrinsic activities of befunolol and carteolol and the pD2 values of the test drugs were decreased by the treatment with egg albumin. The treatment with egg albumin also decreased the total amount of the two affinity sites of the receptor without any change in affinity. The present results support the partial blockade of beta-adrenoceptors in asthma proposed by Szentivanyi.