The effect of meptazinol on the guinea-pig sphincter of Oddi in-vitro.

Meptazinol causes a dose-dependent contraction of the guinea-pig sphincter of Oddi in-vitro. This was antagonized by atropine in concentrations which blocked the contractile response to acetylcholine but not that to KCl. Naloxone was unable to block the response of the tissue to meptazinol, and other opioid drugs had inconsistent effects. Although meptazinol has significant anticholinesterase activity on this preparation, comparison with neostigmine suggests that this is irrelevant to its contractile action.