AJP - Gastrointestinal and Liver Physiology, Vol 270, Issue 3 498-G505, Copyright © 1996 by American Physiological Society

ARTICLES

Rat intestinal and hepatic ferritin subunit expression during development and after dietary iron feeding

K. Y. Yeh, X. Alvarez-Hernandez, J. Glass and M. Yeh
Department of Medicine, Louisiana State University Medical Center, Shreveport, 71130-3932, USA.

Ferritin consists of 24 heavy (H) and light (L) subunits in varying proportions in different tissues and plays a significant role in iron metabolism. We studied rat ferritin subunit expression in the duodenum and liver during early life, when a cycle of iron depletion and repletion occurs. In both tissues, ferritin contents decreased to low levels from day 3 to day 12. The ferritin on day 3 had an H/L mRNA ration of 0.9 and an H/L subunit ratio of 0.6. The decrease of tissue ferritin levels, but not mRNA, on day 12 suggests translational repression consistent with iron depletion. In the duodenum, a twofold increase in both H and mRNA and subunit protein occurred on day 18. The subsequent increase of H mRNA was accompanied by a 50% decrease in L mRNA, resulting in the increase of H/L mRNA and subunit ratios to 7.9 and 9, respectively, by day 32. In contrast, liver H/L mRNA and subunit ratios were similar throughout development. The possibility that dietary iron regulates duodenal ferritin subunit expression was investigated. When day 12 rats were fed 6 ml of a milk formula containing 56 microgram/ml iron for 18 h, dietary iron increased the duodenal levels of L mRNA but not H mRNA. In contrast, hepatic H and L mRNA levels did not change. Dietary iron promoted greater increases in ferritin protein than mRNA in both tissues. Thus a shift from L-rich to H-rich ferritin isoforms occurs in the duodenum but not in the liver during neonatal development. This change is regulated at the pretranslational level and is independent of dietary iron.

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