Abstract
In the previous papers (1-3) it has been reported that some partial agonists accelerate the liberation of acetylcholine from the isolated guinea pig and rat ilea to contract them, yet also antagonize the action of the released acetylcholine and that the intrinsic activity (4) or efficacy (5) of a drug is decided by two factors: acetylcholine liberating activity and inhibitory activity to acetylcholine. In this paper, the receptor mechanisms for partial agonists were studied on the ganglion free taenia caecum from the guinea pig, of which the acetylcholine liberation mechanisms are poor. Some of this work has already been briefly reported (6, 7).
