Objectives: This study aimed to elucidate the effect of the extract of daikenchuto (DKT), a Japanese Kampo medicine, on the contractile activity of the internal anal sphincter in conscious dogs.

Methods: Force transducers were attached to the serosal surface of the rectum and the internal anal sphincter of male beagle dogs. In addition, the contractile activity of the rectum and the internal anal sphincter was continuously measured until 6 h after DKT administration via telemetry in the conscious state. The DKT dose was 1.5 g/body, and the administration route was intrarectal in the expectation of a direct effect on the rectoanal region. DKT was re-administered to the same animal after drug withdrawal, and the plasma concentrations of hydroxy-α-sanshool (HAS) and hydroxy-β-sanshool (HBS) before and after administration were measured.

Results: After DKT administration, the contractile activity of the internal anal sphincter immediately increased, peaked at 10 min, continued for ≥1 h, and had almost disappeared after 4 h. Rectal contraction differed from that of the internal anal sphincter, with no significant contraction observed. HAS and HBS were found in the plasma of animals administered with DKT and persisted up to 2 h after the administration.

Conclusions: This is the first report on in vivo telemetry demonstrating that DKT exhibited contractile effects on the dog's internal anal sphincter. The increased anal pressure and improvement of fecal incontinence symptoms observed in previous clinical studies may have been based on this sphincter contraction.