Background: This study was designed to determine the effect of lactation and weaning on the catabolism of branched-chain amino acids (BCAA).
Methods: Rates of transamination and oxidation of leucine and branched chain alpha-ketoacid dehydrogenase (BCKD) activity were measured in homogenates of mammary gland, skeletal muscle and liver on day 12 of lactation and 24 h after separation of dams from the litter (weaning).
Results: Lactating dams consumed 250% more protein than control rats, extra protein is required for protein synthesis by the mammary gland, the extent to which the excess of amino acids consumed during lactation is utilized or oxidized by different tissues is not known. The rate of transamination of [1-14C] leucine by mammary tissue of lactating dams was sixfold higher than in virgin rats. The rate of transamination remained elevated fourfold in postweaning dams. Rates of transamination were three times higher in mammary tissue than in muscle of lactating dams. Rate of oxidation [1-14C] leucine by lactating mammary tissue was tenfold higher than in control tissue.
Conclusions: The capacity of mammary tissue for transamination and oxidation of leucine increased greatly during lactation, suggesting that the mammary gland may play an important role in the catabolism of BCAA during lactation.