Can the effects of meptazinol on the guinea-pig isolated ileum be explained by inhibition of acetylcholinesterase?

Abstract

It has previously been shown that there is a cholinergic component in the antinociceptive action of the opioid analgesic drug meptazinol. In the present study meptazinol was shown to be an inhibitor of acetylcholinesterase in-vitro with a potency one hundredth that of physostigmine. This activity was found to reside only in the (-)-enantiomer of meptazinol. The anticholinesterase activity of meptazinol may explain the increase in the size of the electrically-evoked contraction of the guinea-pig isolated ileum preparation since by using a long pulse width (5 ms) it was found that the (-)-enantiomer of meptazinol modified only the component of the response due to neuronally released acetylcholine and had no direct effect on the smooth muscle. This property of meptazinol may also be responsible for the cholinergic effects of the drug in-vivo.