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

1. 泌乳素受体基因在泌乳期的表达在小鼠乳腺中，泌乳素受体mRNA水平在妊娠前5天下降约60%，其低水平一直维持到妊娠第18天10:00。泌乳素受体mRNA水平在12 h内升高约6倍。在泌乳第0天维持高水平。催乳素受体mRNA的升高是由体内和体外皮质酮升高引起的。在去卵巢的孕中期小鼠乳腺中也发现了类似的变化。由此可见，催乳素受体基因在分娩前约12 h表达。泌乳对泌乳素受体基因表达的影响泌乳小鼠乳腺泌乳素受体mRNA在离乳12 h后开始下降，在18 h时达到最低水平。断奶24 h的小鼠喂奶6 h，泌乳素受体mRNA在喂奶6 h期间恢复。泌乳素受体数量与泌乳素受体mRNA水平平行变化。泌乳素受体基因表达在乳腺积聚乳汁最多时减慢。泌乳素受体mRNA在幼鼠吸吮乳汁的乳腺中升高。综上所述，控制泌乳素受体基因表达的主要因素是乳腺内泌乳的蓄积程度。

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.