Decrease in rat internal anal pressure with the use of a topical ointment containing a killed E. coli culture suspension.
OBJECTIVES: The present study aimed to clarify the mechanisms of a topical ointment containing an Escherichia coli culture suspension and hydrocortisone (Posterisan forte, BCS+HC) in lowering internal anal pressure in conscious rats. MATERIALS AND METHODS: Internal anal pressure was measured using a water-filled balloon system for consecutive 10-min periods. The changes in pressure were evaluated by the number of peaks above 20 mmH2O between 1 and 8 min of recording. RESULTS: Topical intra-anal application of BCS+HC ointment (160 mg/kg) significantly decreased the internal anal pressure at 3 h after the application. Thereafter, this effect reached a maximum decrease at 4 h and lasted until 6 h. BCS+HC ointment (40, 80, and 160 mg/kg) lowered the internal anal pressure at 4-5 h in a dose-dependent manner. The maximum decrease ratios of the ointment and corresponding hydrocortisone-free ointment (Posterisan, BCS) were 32.6+/-12.7 and 25.7+/-9.0%, respectively, revealing significant pressure-lowering effects compared with a placebo (P<0.05). In contrast, the same ointment containing hydrocortisone alone and other ointments containing steroids or local anesthetics had no effects. DISCUSSION: Treatment with 1 mg/kg NG-nitro-L-arginine methyl ester HCl (L-NAME), a non-selective nitric oxide synthase inhibitor, significantly suppressed the effect of BCS+HC ointment (160 mg/kg) in lowering the internal anal pressure. Furthermore, BCS+HC ointment (160 mg/kg) significantly lowered capsaicin-induced high internal anal pressure compared to a placebo. CONCLUSION: These findings suggest that BCS+HC and BCS ointments containing an E. coli culture suspension significantly lowered the internal anal pressure due to endogenous nitric oxide production in conscious rats.