Development of Copper Intestinal Absorption in the Rat

We investigated changes in the kinetic characteristics of copper absorption at three stages of rat development: suckling, weanling, and adolescence, as well as the inducibility of metallothionein (MT) in small intestine and kidney. Using an in vivo, single-pass intestinal perfusion procedure, we found that the rates of copper absorption in suckling and weanling rats were concentration-dependent and there was no difference between these two groups of rats. However, in adolescent rats, there was a saturable component, with an apparent K_t of 10-13 μM, and a nonsaturable component with a diffusion coefficient of 3.2 s⁻¹ (3.2 × 10 cm²/s). Intestinal copper retention was also concentration-dependent; the suckling rats showed much greater tissue levels of this element than the weanlings or the adolescents. MT intestinal content after stimulation with ip zinc chloride was significantly higher in the adolescent rats than that in the weanlings and sucklings, indicating that physiological mechanisms other than MT induction may play a role in copper retention early in life. The increase in MT levels in adolescence may be related to the onset of copper absorption saturability in the mature small intestine.