Quantitative aspects of zinc absorption by isolated, vascularly perfused rat intestine

Quantitative measurements of zinc absorption were made using the isolated, vascularly perfused rat intestine as a model. The perfused intestine retains the ability to discriminate between absorption processes for calciu, copper, iron and zinc. Measurements of zinc absorption by the perfused intestine, using atomic absorption spectrophotometry, indicated the presence of a zinc pool within intestinal mucosal cells. The zinc concentration in the lumen of the perfused intestine was directly related to the amount of zinc that appeared in the vascular perfusate. Intestines obtained from zinc-deficient animals exhibited an ability to process greater quantities of zinc which resulted in enhanced absorption. The maximal rate of zinc absorption was 229 nmoles per hour with intestines from rats fed adequate amounts of zinc and 627 nmoles per hour when a zinc-deficient diet was fed. Administration of zinc to rats before isolation and perfusion of the intestine resulted in greater intracellular retention of zinc taken up from the lumen and correspondingly lesser amounts (75 nmoles per hour) transferred to the vascular supply. These data provide quantitative evidence that the perfused intestine retains its ability to exercise homeostatic control over the zinc absorption process and that the intestinal cell is a major site of regulation.