Abstract
Eserine and mipafox have often been used as anticholinesterases to allow measurement of spontaneous release of acetylcholine from the ileum (1-4). Mipafox was chosen because of its apparent inability to release acetylcholine from smooth muscle (5). It has also been reported that values for acetylcholine release in the presence of mipafox (1) were much lower than those obtained by other workers using eserine (2, 3). It, therefore, follows that the choice of a particular anticholinesterase may influence the release of acetylcholine from smooth muscle. In order to experimentally test this possibility, we examined the effect of four cholinesterase inhibitors—eserine, prostigmine, phosphamidon and mipafox, on the spontaneous release of acetylcholine from isolated guineapig ileum.
PAM (2-pyridyl-aldoxime methiodide) reactivates the phosphorylated (inhibited) cholinesterase (6, 7); At certain concentrations, it induces the release of acetylcholine while at others, it inhibits the acetylcholine release from rat phrenic nerve diaphragm preparation (8). The effect of PAM on the release of acetylcholine from smooth muscle has so far not been studied. The effect of PAM, if any, on the acetylcholine output from isolated guineapig ileum, in the presence of anticholinesterases, has also been examined in the present study.
