Transfer across mucosal epithelium, tissue content and metabolic fate of 125I-(ipodate-sodium) on isolated everted segments of rat small intestine.

1. Transfer and tissue content of 125I-radioactivity was measured after administration of 125I-(ipodate-sodium) to everted rat jejunal segments. 2. After having administered 10(-5) M 125I-(ipodate-sodium) on both sides of the everted sacs the S/M ratio of the concentration of 125I-radioactivity was 1.5 in jejunal segments and 2.3 in ileal segments. The tissue content was nearly equal for both segments. According to the apparent partition coefficient for ipodate-sodium at pH 7, the 125I-radioactivity is accumulated in the tissue about 10-fold. 3. Lowering of the temperature of the incubation medium from 37 degrees C to 15 degrees C prevents the building up of a concentration gradient between the serosal and the mucosal side on either jejunal and ileal segments whereas the tissue content of 125I-radioactivity was nearly unchanged. 4. With increasing concentrations (1.6--10(-6)--9.6-10(-4) M) of 125I-(ipodate-sodium) administered on the mucosal side the transfer and the tissue content of 125I-radioactivity were decreased. This appears to be a toxic effect since in jejunal segments also the S/M ratio for the concentration of glucose decreases. 5. The analysis of the 125I-radioactivity in the serosal fluid of jejunal segments showed that the bulk of the 125I-radioactivity was present in the aqueous phase and only 33% as the unchanged ipodate-sodium in the organic phase. 10% of the 125I-radioactivity must be attributed to inorganic iodine. The concentration of 125I-(ipodate-sodium) administered in the mucosal fluid only was 3.2-10(-6) M. At lower temperature (7 degrees C) the bulk of the 125I-radioactivity in the serosal fluid was found in the organic phase, i.e. as unchanged ipodate-sodium. 6. After the incubation of the aqueous phase with beta-glucuronidase or NaOH about 97% of the 125I-radioactivity could be extracted into the organic phase. This means that the bulk of the 125I-radioactivity in the aqueous phase is present as a conjugate, e.g. ester glucuronide of the unchanged ipodate. 7. Apparently, the process of the conjugation of ipodate-sodium in the mucosal cells is involved in the transfer of the 125I-radioactivity across the mucosal epithelium.