Changes in cathepsin D activity of maternal tissues during lactation and weaning in rats

Background. A loss of proteins from maternal tissues during lactation has b een demonstrated. Protein loss could be explained by intracellular proteoly sis. Methods. Cathepsin D activity was studied in the liver, muscle and mammary gland of lactating and weaned rat dams. Lactation was studied at maximal mi lk production (L-14) and at the final stage of lactation (L-21). Results. Basal activity (virgin rats) was three times higher in liver and m ammary gland than in muscle. At both stages, L-14 and L-21, cathepsin D act ivity increased in liver (50%) as well as in the gland (164%), but no chang e was observed in muscle, when compared with controls. Twenty-four hours af ter litter separation, enzyme activity in the liver decreased to basal leve ls, while in the mammary gland cathepsin D activity showed a significant de crease but remained higher than control levels. Conclusion. Our results show that liver exhibits adaptive changes in the ca tabolism of proteins in response to the increased demands imposed by lactat ion on the maternal organism, and when the stimuli disappear activity retur ns to basal levels. The high activity in mammary gland indicates fast turno ver of structures and biomolecules as an answer to the high synthetic activ ity in this tissue. Activity remained higher in the weaning rats, as a resu lt of the regression process which the mammary gland is undergoing. (C) 199 9 IMSS. Published by Elsevier Science Inc.