ビタミンB_6の腸管吸収機構 : (II)反転腸管(Everted sac)による研究

抄録

The transport of ^3H-pyridoxine (^3H-PIN) across the intestinal wall was studied by the everted sacs of rat small intestine, mainly at an initial ^3H-PIN concentration of 0.3 μM on the mucosal side and zero on the serosal side. When the sacs were incubated at 37℃ for 4h, the serosal concentration of labelled compounds continued to increase throughout the incubation period, but did not reach the mucosal level, whereas in the tissue the labelled compounds were concentratively accumulated. Ten-fold increase of the initial mucosal concentration of ^3H-PIN from 0.3 to 3 μM did not significantly affect the time course of the serosal to mucosal concentration ratio, although the extent of accumulation in the tissue was much lowered. Futheremore, addition of 300 μM 4-deoxypyridoxine to 0.3 μM ^3H-PIN in the initial mucosal solution did not inhibit the transport at all, but rather stimulated it despite the extreme depression of accumulation in the tissue. By lowering the temperature of incubation to 0℃, where a very little uptake by the tissue was observed, the rate of transport across the wall became about 60% of that at 37℃. When 0.3 μM ^3H-PIN was initially present on both sides of the sacs, the serosal concentration decreased considerably during the early period of incubation, and the tissue accumulated the labelled compounds correspondingly more rapidly. These results have suggested that PIN even at a low concentration as 0.3 μM is transported by simple diffusion across the intestinal wall, and the accumulation of the vitamin by the tissue has no positive role in this transport process but rather decreases the B_6 compounds on the serosal side.