Interaction between transport of zinc and other solutes in human intestine

To investigate the kinetics of zinc absorption, a jejunal segment from healthy human volunteers was intubated with a triple-lumen tube, and isotonic NaCl solutions containing 0, 0.1, 0.3, and 0.9 mM ZnCl2 were infused. There was secretion of zinc when zinc was not added to the test solution but absorption when zinc was added. Over the range of zinc concentrations infused, there were linear increases in the rate of zinc absorption. There was net absorption of sodium and water during the infusion of isotonic saline solution but no net absorption when zinc (0.9 mM) was added to this solution. This impairment was not prevented by adding glucose to the test solution, but the rate of zinc absorption was significantly enhanced in the presence of glucose. The rate of glucose absorption was not affected by adding zinc to a glucose-saline solution. Zinc absorption was significantly stimulated by the addition of glycylleucine to the test solution, whereas the corresponding mixture of glycine and leucine had no effect. The data allow the following conclusions: a) zinc absorption is selectively stimulated by organic solutes and b) zinc inhibits net absorption of sodium and water in the jejunum.