Age-Dependent Variation of Copper in Tissue and Proteins of Neonatal Rat Small Intestine 1 2

Abstract

Tissue copper levels in the small intestine of neonatal rats increased rapidly following birth, reaching a maximum value of 302.6 ± 22.2 μg/g dry wt on Day 7 and then steadily declined to 6.4 ± 0.5 μg/g dry wt on Day 21. When subjected to gel filtration on Sephadex G-75, high-speed supernatant prepared from the small intestine of rats aged 0 to 21 days eluted as two copper-containing fractions corresponding to molecular weights of 60,000 and 9000 daltons. The copper contents of both fractions varied with age in a manner that correlated significantly with the variations observed in the tissue copper levels. However, orally administered ⁶⁴Cu was found to be associated primarily with the low-molecular-weight fraction in 5-day-old rats. Furthermore, the amount of ⁶⁴Cu in the low-molecular-weight fraction did not appear to turnover during the 42 hr following administration of the dose. These results suggest that a portion of the copper ingested by the neonatal rat is initially sequestered in the small intestine by low (9000 daltons) −molecular-weight cystolic proteins either as a mechanism for detoxifying excess copper or as a pool for the slow release of copper and maintenance of copper homeostasis during a period of rapid growth and development.