Kinetic analysis of zinc uptake and serosal transfer by vascularly perfused rat intestine.

Transport kinetics were examined for uptake of 65Zn from the lumen and for transport of mucosal 65Zn subsequent to uptake in the isolated, vascularly perfused intestines of rats fed either a zinc-deficient or zinc-adequate diet. Zinc depletion influenced the intestinal transport of zinc by stimulating a saturable uptake mechanism, reducing secretion of mucosal 65Zn into the lumen, and increasing the rate of 65Zn turnover in a rapidly absorbed mucosal zinc compartment. Uptake of 65Zn involved both saturable and nonsaturable processes. The saturable process was stimulated by zinc depletion with the apparent maximal transport rate for the saturable mechanism increasing from 60 to 180 nmol Zn X g-1 X 30 min-1. Most of the 65Zn taken up was not involved in the short-term secretion or absorption, and mucosal 65Zn retention was independent of dietary zinc status. Absorption of mucosal 65Zn was nonsaturable, involved a rapid exchanging zinc compartment, and was stimulated by zinc depletion. The half-life for 65Zn in this mucosal zinc compartment was approximately 24 min in the zinc-adequate group and 13 min in the zinc-depleted group.