Kinetics of zinc absorption by the rat jejunum: effects of adrenalectomy and dexamethasone.

Effects of dexamethasone and adrenalectomy on the kinetics of jejunal 65Zn uptake and absorption were studied in the anesthetized adult rat. The jejunal lumen was perfused in situ with 5 mM glucose in 150 mM saline containing 65Zn and [14C]polyethylene glycol as volume marker. Over the 30-min perfusion period, the rate of net 65Zn removal from the perfusate was biexponential due to the establishment of a return flux to the lumen. An open two-compartment model satisfactorily describes these observations: (formula; see text) Dexamethasone (2 mg/kg ip 7 h before perfusion) increased k12 by 75% (P less than 0.0002) and decreased k20 by 45% (P less than 0.04). Both effects were independent of adrenalectomy. Mathematical simulations using the compartmental model and experimentally determined kinetic constants predicted that transfer of 65Zn into the body should be enhanced by adrenalectomy and retarded by dexamethasone administered to adrenalectomized rats. Dexamethasone and adrenalectomy thus differentially affect Zn uptake and absorption in this system, suggesting a possible adrenocortical hormone involvement in the regulation of Zn absorption. These changes are apparently not mediated via metallothionein.