Abstract: Objective To investigate the role of capsaicin in regulating permeation of P-gp substrate rhodamine 123 (R123)
across the jejunum, ileum and colon membranes of rats. Methods The permeability of R123 or fluorescein sodium (CF) across
the jejunum, ileum and colon membranes of male SD rats was evaluated using a Ussing chamber. The concentration of R123 or
CF in the receptor was determined using fluorospectrophotometry to calculate the apparent permeability coefficient (Papp).
Results Compared with the blank control group, capsaicin increased the permeability of R123 across jejunal membranes in the
mucosal-to-serosal (M-S) direction and decreased its permeability in the serosal-to-mucosal (S-M) direction, but produced no
obvious effect on R123 transport across the ileum or colon membranes. Capsaicin caused a regional increase in the
permeability of CF across the jejunal membranes compared with the control group, but CF transport across the ileum and
colon membranes was not affected. Conclusion Capsaicin can affect the transport of R123 and CF across rat jejunal
membranes, and this effect is shows an obvious intestine segment-related difference probably because of the different
distribution of P-gp or tight junction in the intestines. This finding suggests that capsaicin is a weak P-gp inhibitor and an
improver of mucous membrane channels.