An Exploratory Study on the Contractile Effects of Hydroxy-α-Sanshool and Hydroxy-β-Sanshool, the Active Ingredients of Daikenchuto, on the Internal Anal Sphincter.

Objectives: Daikenchuto (DKT) enhances the contraction of the internal anal sphincter (IAS) in patients with constipation and fecal incontinence; however, the mechanism of its action is unknown. We investigated the effects of the active ingredients of DKT (hydroxy-α-sanshool (HAS) and hydroxy-β-sanshool (HBS)) on the contractile activity of the canine rectum and IAS. Methods: Three male beagle dogs were prepared for each of the HAS, HBS, and control groups. Force transducers were attached to the rectal and IAS surfaces of the dogs, and the contractile responses were measured by telemetry under conscious conditions. HAS (10 mg/body) and HBS (2.5 mg/body) were administered intrarectally at doses previously identified from an effective dose of DKT extract (1.5 g/body), and contractile responses were recorded up to 6 h after administration. Contractile activity of the rectum and IAS was evaluated by observing the area under the curve (AUC) of the recorded contraction waveform. Plasma concentrations of HAS and HBS were measured before and after administration to confirm IAS exposure to both ingredients. Results: The mean AUC values of the IAS for the control, HAS, and HBS groups at 10 min after administration were 115, 87, and 220 (g-min), respectively, indicating a higher contraction in the HBS group, which was maintained for approximately 3 h. As for the rectum, no contractile response was observed in either the HAS or HBS groups. Plasma concentrations of both ingredients peaked at 20 min after administration. Conclusions: HBS could be involved in the contractile action of DKT on the IAS.