Metallothionein in rat lung during postnatal development

Zn and Cu concentration, content, and distribution in lung were quantitated in neonatal and adult Lewis rats. Total lung Cu and Zn content rose dramatically during postnatal development, paralleling increases in lung and body weight. Cu concentration was 2-fold higher in adult lung than in neonatal lung whereas Zn concentration was unaffected by developmental age. A Cu-containing protein with an approximate molecular weight of 10,000 Da was identified immunologically as metallothionein (MT). At term, native MT concentration in the lung was 4-fold higher than in adult lungs. By day 4 postpartum, MT concentration was reduced by half and reached a level characteristic of the adult by 7 days postpartum. MT was localized in nuclear and cytoplasmic compartments of positive lung cells by immunofluorescent techniques; initially, nuclear MT staining was more intense than cytoplasmic staining.