A. Study design with injection regimen (color coded). B. Oral contrast- enhanced CT scans before (day 3, drug naive) and after (day 8) repeated dosing of vehicle (0.5% DMSO s.c., N=5), NFEPP (0.4 mg/kg s.c., N=5) or fentanyl (0.4 mg/kg s.c., N=6) BID. Arrows denote the cecum. C. Effects of NFEPP and fentanyl on CT-based GI transit. D. Effects of NFEPP and fentanyl administration (each opioid at 0.4 mg/kg s.c.) on defaecation. E-F. Effects of NFEPP and fentanyl on colon diameter (E) and cecum diameter (F). Abbreviations: BID, bis in die (twice daily). DMSO, dimethyl sulfoxide. DSS, dextran sulphate sodium. * p<0.05. *** p<0.001. Two-way ANOVA, Bonferroni test.