# Analgesic Effect of the Kampo Formula Yokukansan via the Suppression of Substance P in an Experimental Rat Model of Hunner-Type Interstitial Cystitis

## TL;DR

This study shows that Yokukansan, a traditional Japanese medicine, reduces bladder pain in rats with interstitial cystitis by suppressing substance P.

## Contribution

The novel finding is that Yokukansan's analgesic effect in Hunner-type interstitial cystitis is linked to the suppression of substance P expression.

## Key findings

- Yokukansan administration increased pain thresholds in rats with Hunner-type interstitial cystitis.
- Yokukansan suppressed the increased expression of substance P in the bladder and spinal cord of affected rats.

## Abstract

Introduction: Yokukansan (YKS), a Kampo formula used in traditional Japanese medicine, has an analgesic effect, and is used for various pain disorders. This study investigated its analgesic effects on Hunner-type interstitial cystitis (HIC) and its mechanism of action in animal models.

Methods: Rats with toll-like receptor-7 agonist (loxoribine)-induced HIC were used. Eight-week-old female Wistar rats were divided into three groups: control, HIC, and HIC-administered YKS (YKS + HIC). Bladder pain was assessed based on escape behavior using the von Frey test. Three days after HIC induction, the bladder and spinal cord were excised, and the expression of substance P (SP) was examined.

Results: The pain threshold decreased significantly in the HIC group compared to that in the control group, but this decrease was suppressed by further YKS administration. The expression of SP in the bladder wall and spinal cord increased significantly in the HIC group compared to that in the control group; however, this increase was suppressed by YKS administration.
Conclusion: SP is involved in the onset of bladder pain via neurokinin 1 receptors in bladder tissue. YKS may be useful for managing HIC-induced pain, and the suppression of SP secretion is one of its mechanisms of action.