Hernández-Montes H, Escudero I, Villalpando S
Unidad de Investigación Médica en Nutrición, Hospital de Pediatría, Centro Médico Nacional Siglo XXI, México, D.F.
Arch Med Res. 1999 Jan-Feb;30(1):10-3. doi: 10.1016/s0188-0128(98)00010-4.
A loss of proteins from maternal tissues during lactation has been demonstrated. Protein loss could be explained by intracellular proteolysis.
Cathepsin D activity was studied in the liver, muscle and mammary gland of lactating and weaned rat dams. Lactation was studied at maximal milk production (L-14) and at the final stage of lactation (L-21).
Basal activity (virgin rats) was three times higher in liver and mammary gland than in muscle. At both stages, L-14 and L-21, cathepsin D activity increased in liver (50%) as well as in the gland (164%), but no change was observed in muscle, when compared with controls. Twenty-four hours after litter separation, enzyme activity in the liver decreased to basal levels, while in the mammary gland cathepsin D activity showed a significant decrease but remained higher than control levels.
Our results show that liver exhibits adaptive changes in the catabolism of proteins in response to the increased demands imposed by lactation on the maternal organism, and when the stimuli disappear activity returns to basal levels. The high activity in mammary gland indicates fast turnover of structures and biomolecules as an answer to the high synthetic activity in this tissue. Activity remained higher in the weaning rats, as a result of the regression process which the mammary gland is undergoing.
已证实哺乳期母体组织中蛋白质会流失。蛋白质流失可通过细胞内蛋白水解来解释。
研究了哺乳期和断奶后大鼠母鼠肝脏、肌肉和乳腺中的组织蛋白酶D活性。在乳汁产量最高时（L-14）和哺乳期末期（L-21）研究泌乳情况。
基础活性（未生育大鼠）在肝脏和乳腺中比在肌肉中高3倍。在L-14和L-21这两个阶段，与对照组相比，肝脏中的组织蛋白酶D活性增加了50%，乳腺中的增加了164%，但肌肉中未观察到变化。幼崽分离24小时后，肝脏中的酶活性降至基础水平，而乳腺中的组织蛋白酶D活性显著下降，但仍高于对照水平。
我们的结果表明，肝脏对泌乳给母体机体带来的增加需求做出反应，在蛋白质分解代谢方面表现出适应性变化，当刺激消失时，活性恢复到基础水平。乳腺中的高活性表明结构和生物分子的快速周转，以应对该组织中的高合成活性。由于乳腺正在经历退化过程，断奶大鼠中的活性仍然较高。
