Mucus and iron absorption regulation in rats fed various levels of dietary iron

We tested two hypotheses: (1) that iron binding by secreted mucus enhances iron absorption (Quarterman, Digestion 37: 1, 1987) and (2) that iron binding by secreted mucus prevents excess iron absorption. Rats were fed diets containing 6, 200 or 500 mg Fe/kg diet (Fe-0, Fe-200 and Fe-500 rats, respectively) for 3 wk. Iron absorption was measured in fasted rats using 59FeCl3 in a 10-min in situ duodenal ligated-segment procedure. After draining the segment contents, the mucus layer was separated from the under-lying mucosal surface using Quarterman's agar cast technique. In comparison with that in Fe-200 rats, iron absorption in Fe-0 rats was markedly increased, but the 59Fe and the total mucus in the mucus layer were decreased. The 59Fe absorption and total mucus and total iron in the mucus layer were similar in Fe-500 rats and Fe-200 rats, but the 59Fe in the mucus layer was marginally lower in Fe-500 rats. There was no evidence that mucus enhanced iron absorption; it appeared to trap or bind iron proportionally to the amount of secreted mucus, suggesting protection against excess absorption. Mucus secretion and possibly synthesis were decreased in the Fe-0 rats.