Structural and cellular adaptation of duodenal iron uptake in rats maintained on an iron-deficient diet

Iron deficiency induced in rats maintained on a commercial diet with a low iron content has been used to investigate adaptive mechanisms that enhance duodenal iron uptake. These adaptive changes have been divided into those t hat result from changes in villus surface area (structural adaptation) and those that reflect changes in the way individual enterocytes express iron t ransport function (cellular adaptation). Cellular adaptation was assessed b y carrying out microdensitometry of autoradiographs prepared from duodenal tissue previously incubated for 5 min in 200 mu mol/l Fe-59(2+)-ascorbate. Structural adaptation was studied by performing image analysis of microdiss ected and sectioned villi. Cellular adaptation involved increased iron upta ke by enterocytes present in the lower villus. Thus iron deficiency resulte d in a threefold enhanced expression of uptake in the lower 100 mu m villus (3.9+/-2.4 versus 12.6+/-1.5 arbitrary units, P<0.001). Maximal uptake was reached in the upper region of both control and iron-deficient villi, but iron deficiency had no effect on cellular uptake at this part of the villus . Structural adaptation involved the lengthening (+16%, P<0.05) and broaden ing (+14%) of villi in the duodenum of iron-deficient rats. The resultant e xpansion in villus area caused a further increase in uptake that was mostly expressed in the upper villus. Maximal uptake corrected for structure occu rred in the middle third of villi from control and iron-deficient rats. Cel lular plus structural adaptation produced a twofold increase in iron uptake . More than half of this effect was caused by changes in villus structure. [H-3]Thymidine labelling experiments revealed a slightly earlier expression of enterocyte iron uptake in iron deficiency.