Effective Expression of Prolactin Receptor Gene and its Relationship with Milk Production

1.催乳素受体基因在乳汁发生过程中的表达在小鼠乳腺组织中，催乳素受体基因的表达水平在妊娠前5天下降了约60%，并一直维持到妊娠第18天10：00。在接下来的12小时内，催乳素受体基因的表达水平增加了约6倍。在哺乳期第0天维持较高水平。在体内和体外，催乳素受体mRNA的增加是由于皮质酮的增加所致。在去卵巢的中期妊娠小鼠乳腺中也发现类似的变化。结论：1.催乳素受体基因在临产前约12小时表达。乳汁蓄积/脱乳对哺乳小鼠乳腺催乳素受体基因表达的影响断奶后12h小鼠乳腺组织中催乳素受体基因表达开始下降，18h达最低水平，断奶24 h后开始哺乳6h，6h内恢复正常。催乳素受体的数目与催乳素受体mRNA值的变化是平行的，当乳腺积乳量达到最大时，催乳素受体基因的表达就会减慢。哺乳腺中的催乳素受体mRNA增加，幼崽在吸奶时会在其中分泌乳汁。结论：控制催乳素受体基因表达的主要因素是乳汁在乳腺中的积聚程度。

1. Prolactin receptor gene expression at lactogenesisIn the mouse mammary gland, the level of prolactin receptor mRNA decreased about 60% during the first 5 days of pregnancy, and its low levels were maintained until 10 : 00 on day 18 of pregnancy. The level of prolactin receptor mRNA increased about 6 folds during the next 12 h period. The high level was maintained on day zero of lactation. The increase in the prolactin receptor mRNA was caused by the increase in corticosterone in vivo and in vitro. The similar changes were found in the ovariectomized midpregnant mouse mammary gland. It is concluded that the prolactin receptor gene expresses about 12 h before the onset of parturition.2. Effect of accumulation/removal of milk on prolactin receptor gene expressionProlactin receptor mRNA in the lactating mouse mammary gland began to decrease 12 h after removal of pups from their mother and its level was the lowest at 18 h. Mice which had been weaned for 24 h were allowed to nurse foster pups for 6 h. Prolactin receptor mRNA was restored during the 6 h-nursing period. The number of prolactin receptor changed in parallel with the level of prolactin receptor mRNA.Prolactin receptor gene expression slowed when the mammary gland accumulated milk maximum. Prolactin receptor mRNA increased in the mammry gland in which milk was suckled by the pups. It is concluded that the main factor controlling the prolactin receptor gene expression is the degree of milk accumulation in the mammary gland.