Tannic acid inhibition of amino acid and sugar absorption by mouse and vole intestine: Tests following acute and subchronic exposure

The acute effects of tannin (tannic acid; TA) on nutrient absorption were studied by measuring sugar and amino acid uptake across the brash border (luminal membrane) of intact intestine in the presence and absence of TA. Incubation of tissue for 4–9 min in TA solution (1 mg/ml) caused a reduction in passive influx ofl-glucose in voles and mice and a reduction in carrier-mediated influx ofd-glucose and total influx ofl-proline in mice, but not voles. In subchronic experiments, mice and voles were fed for 7–14 days a diet with 4% TA, but there was no significant effect on intestinal brush border uptake ofl-glucose,d-glucose, orl-proline (or three other amino acids tested in voles). In a synthesis of our study with others in the literature, three inferences are made from the patterns of effects across solutes, time scales of exposure, and species. First, the transport inhibitory effects following acute exposure are probably mediated by two processes: increased resistance to passive flux across an effective unstirred layer juxtaposed to the brush border membrane, perhaps due to tannin-mucin binding, and reduced Na⁺-coupled nutrient uptake across the intestinal brush border. Second, there is a species sensitivity difference in TA's effect on the second process. Third, the negative effects observed at the acute time scale in vitro do not necessarily occur in animals eating TA subchronically because little TA reaches the luminal membrane, or if it does its effects are quickly reversed when the tissue is removed and washed with solution free of TA.