Localization and expression of BCAT during pregnancy and lactation in the rat mammary gland

During lactation, branched-chain aminotransferase (BCAT) gene expression in creases in the mammary gland. To determine the cell type and whether this i nduction is present only during lactation, female rats were randomly assign ed to one of three experimental groups: pregnancy, lactation, or postweanin g. Mammary gland BCAT activity during the first days of pregnancy was simil ar to that of virgin rats, increasing significantly from day 16 to the last day of pregnancy. Maximal BCAT activity occurred on day 12 of lactation. D uring postweaning, BCAT activity decreased rapidly to values close to those observed in virgin rats. Analyses by Western and Northern blot revealed th at changes in enzyme activity were accompanied by parallel changes in the a mount of enzyme and its mRNA. Immunohistochemical studies of the mammary gl and showed a progressive increase in mitochondrial BCAT (mBCAT)-specific st aining of the epithelial acinar cells during lactation, reaching high level s by day 12. Immunoreactivity decreased rapidly after weaning. There was a significant correlation between total BCAT activity and milk production. Th ese results indicate that the pattern of mBCAT gene expression follows lact ogenesis stages I and II and is restricted to the milk-producing epithelial acinar cells. Furthermore, BCAT activity is associated with milk productio n in the mammary gland during lactation.