LEUCINE CATABOLISM IN MAMMARY TISSUE, LIVER AND SKELETAL-MUSCLE OF DAM RAT DURING LACTATION AND WEANING

Background: This study was designed to determine the effect of lactati on and weaning on the catabolism of branched-chain amino acids (BCAA). Methods: Rates of transamination and oxidation of leucine and branche d chain alpha-ketoacid dehydrogenase (BCKD) activity were measured in homogenates of mammary gland, skeletal muscle and liver on day 12 of l actation and 24 h after separation of darns 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 lactati on is utilized or oxidized by different tissues is not known. The rate of transamination of [1-C-14] leucine by mammary tissue of lactating dams was sixfold higher than in virgin rats. The rate of transaminatio n remained elevated fourfold in postweaning dams. Rates of transaminat ion were three times higher in mammary tissue than in muscle of lactat ing dams. Rate of oxidation [1-C-14] leucine by lactating mammary tiss ue was tenfold higher than in control tissue. Conclusions: The capacit y of mammary tissue for transamination and oxidation of leucine increa sed greatly during lactation, suggesting that the mammary gland may pl ay an important role in the catabolism of BCAA during lactation.