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ALTERATION OF SURFACE MEMBRANE GLYCOPROTEIN SYNTHESIS IN THE SMALL INTESTINE OF RATS WITH NUTRITIONAL IRON DEFICIENCY (NID)

We studied the activity and kinetic parameters of brush border membrane (BBM) enzymes in villus cells and the concentration of the secretory component (SC) of p-IgA in subcellular fractions of crypt cells in 35 day old rats with NID and in controls. In rats with NID, the specific and the total activities of sucrase, maltase, lactase, aminopeptidase and diamine oxidase were decreased from -17 to -66% (p<0.05) compared to the controls. The lower activity of sucrase in the BBM of rats with NID (2.26 times) was associated with much slower enzyme synthesis rate (2.19 times) than in controls. Km of sucrase determined in villus cells was identical in rats with NID and controls but the Vmax was reduced proportionally to the enzymatic activity (1.21 and 1.24 times lower than control values). Electron microscopy of epithelial villus cells from rats with NID revealed a rarefaction of transport vesicles without structural changes of BBM or of the cellular organelles. In villus and crypt cells of rats with NID, SC was reduced to a level about one-half (p<0.05) that of the controls. When SC was measured in subcellular fractions of crypt cells, SC content in each fraction was 2 to 3 times lower in rats with NID than in controls. In conclusion, the decrease in disaccharidases and in SC in the small intestine of NID rats is due to an alteration of the synthesis with reduced transport of these glycoproteins to the BBM.