Developmental changes in mucosal iron binding proteins in the guinea pig. Expression of transferrin, H and L ferritin and binding of iron to a low molecular weight protein.

Neonatal animals show an increased intestinal iron absorption despite being iron replete. We have used the developing guinea pig to determine whether alterations in the expression of iron binding proteins in duodenal enterocytes can account for the difference in iron absorption between neonatal and adult guinea pigs. No mRNA for transferrin was detected in the enterocytes. H ferritin mRNA remained constant from birth into adulthood whilst there was a small increase (< 2-fold) in L ferritin mRNA. Western blotting showed a clear increase in immunoreactive ferritin, levels reaching those of the adult 19 days after birth. We have also demonstrated that in the neonate, 80% of newly absorbed iron in the enterocyte is associated with a low molecular weight fraction (LMW-IBF), whereas in the adult, ferritin and LMW-IBF bind iron to the same extent. We conclude that changes in expression of ferritin during ontogeny are accompanied by a change in distribution of iron binding between ferritin and LMW-IBF implicating these proteins in the regulation of iron absorption.