The effects of neostigmine on the response of the rat anococcygeus muscle to field stimulation are not a consequence of Cholinesterase inhibition

Abstract

Abstract Neostigmine (5 times 10−7 to 5 times 10−6 M) and physostigmine (10−5 M) each augment the responses of the rat anococcygeus muscle to field stimulation whereas iso-OMPA (5 times 10−6 to 5 times 10−4 M) or BW 62c47 (5 times 10−7 to 5 times 10−5 M) do not. At a concentration of 10−5 M, neostigmine, BW 62c47 and iso-OMPA respectively produced a 48, 50 and 68% inhibition of cholinesterase activity in homogenates of anococcygeus muscle. The ED50 for cholinesterase inhibition by neostigmine (1.4 times 10−5 M) is approximately 15 fold greater than the ED50 for the augmentation of the response to field stimulation (9.5 times 10−7 M). It is concluded that the action of neostigmine in augmenting the response of the rat anococcygeus muscle to field stimulation is not a consequence of cholinesterase inhibition even though stimulation of muscarinic receptors is implicated.