This study examined the effect of temperature and ischemia on permeation of fluorescently-labeled
dextran (M.W. = 4 kDa; FD4) across rat intestinal mucosa. Permeability was evaluated ex vivo using an
everted gut sac technique in both the mucosal-to-serosal (M→S) and serosal-to-mucosal (S→M) directions.
At baseline (B), 30-min of ischemia (I-30) and 60-min of ischemia (I-60), intestinal segments were prepared
and incubated at 37°C, 15°C and 4°C for 30 min. Clearance (nl/min/cm2) was calculated based on the
accumulated amount of FD4 at 30 min. Both M→S and S→M fluxes increased with increasing temperature
at B, I-30 and I-60. Ischemic gut (I-30 and I-60) had about a three-fold higher (M→S)/(S→M) flux ratio than
that of normal gut (p < 0.001). At 4°C, neither M→S nor S→M flux was different between B and I-30, but both
M→S and S→M fluxes significantly increased at I-60, suggesting an increase in permeation via a passive
mechanism. Increased bidirectional fluxes at 37°C were obtained in the I-30 and I-60 gut sacs when compared
to B. We conclude that FD4 is actively transported across the intestinal mucosa in the S→M direction and
that ischemic injury increases passive diffusion of the probe across the gut wall.

Keywords: Permeability, Gut ischemia, Temperature dependency mechanism