Original Articles

Desensitization to ephedrine on isolated guinea pig trachea in relation to beta-adrenoceptor

Authors: Duan-Zheng Xu, Qin-Yan Gong, Zao-Chen Yang

Abstract

Log concentration-effect curves (Lcec) for isoproternol (Iso), ephedrin (Eph) and aminophylline (Am) are generated on isolated guinea pig tracheal spirals contracted by histamine. The pD2 values, as the indices of affinity to receptors, were derived repeatedly from Lcec in the same preparations. The experiments uncovered that the tracheal preparations that were desensitized to the spasmolytic action of Iso also exhibited a reduction in sensitivity to ephedrine, but did not to the spasmolytic action of aminophylline. A cross desensitization occurred to Iso and Eph, but not to Am and Eph. It supports the concept that the beta receptor may play a major role in the process leading to a reduced sensitivity to Eph.
Pretreatment of the trachea with propranolol, the entire Lcec of Iso was shifted to the right and the set of curves was essentially parallel. However, the Lcec of Eph were not the case. The maximal heights decreased as compared with the control curve. The phenomena suggest that propranolol is a competitive antagonist to Iso and is a non-competitive antagonist to ephedrine.
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