Effects of Buscopan on human gastrointestinal smooth muscle activity in an ex vivo model: Are there any differences for various sections?

Hyoscine butylbromide (Buscopan ®) is clinically used as an anticholinergic antispasmodic for the treatment of abdominal cramping or visceral pain associated with cramps. However, the spasmolytic efficacy on contractile activity of human gastrointestinal smooth muscle from various sections remains unclear. We aimed to investigate the potentially selective actions of Buscopan on different bowel segments, as well as muscular layers and contractile states. Human smooth muscle tissues of the esophagus, gastric corpus and antrum, jejunum, ileum and colon were obtained. Isometric measurements of circular and longitudinal muscle strips were performed to determine effects of Buscopan on spontaneous activity and induced-contractions by 30 mM KCl, 10 μM bethanechol and electrical field stimulation (EFS). Buscopan concentration-dependently (10−9–10−5 M) inhibited smooth muscle activity, particularly in spasticity evoked by bethanechol and EFS but not high K+. The inhibiting effects were mainly responsible for the antagonism on muscarinic M2 and M3 receptors (IC50 values: 3.1×10−5 M vs. 0.9×10−5 M). The sensitivity toward Buscopan revealed a tendency of increasing from the esophagus, gastric corpus and antrum to the colon, jejunum and ileum. There was a reversed gradient of mRNA and protein expression of muscarinic M2 and M3 receptors from the blocking effects of Buscopan, which could be ascribed to the fact that a higher concentration of Buscopan was needed to antagonize the spastic contraction to reach the equipotent inhibitory rate in the region with higher muscarinic receptor activity. The findings of different inhibitory effectiveness on various parts of the gastrointestinal tract provide a potential guideline for the clinical application.