Yamamoto M, Fisher J E, Thiede M A, Caulfield M P, Rosenblatt M, Duong L T
Merck, Sharp, and Dohme Research Laboratories, West Point, Pennsylvania 19486.
Endocrinology. 1992 Feb;130(2):741-7. doi: 10.1210/endo.130.2.1733722.
PTH-related protein (PTHrP) is found in high concentrations in the milk of various mammals. However, little is known about the regulation of PTHrP production or the physiological role(s) of PTHrP in the mammary glands. To address these questions, we examined in lactating rats 1) the longitudinal changes in PTHrP concentrations in milk and PTHrP mRNA levels in the mammary glands throughout lactation, 2) the effects of the nonsuckling interval on milk PTHrP concentration, and 3) the correlation between PTHrP and calcium concentrations in milk. PTHrP concentrations in milk, measured by RIA and in vitro bioassay, increased with the duration of lactation. The maximal concentrations of PTHrP (observed between days 19-21 of lactation in rats milked serially) were 4.8- to 8.0-fold higher than the concentrations on day 7. PTHrP mRNA levels in the mammary glands also increased during the late stages of lactation. The longitudinal changes in calcium concentrations in milk were small and did not parallel the changes in PTHrP. When pups were removed from the mother for 4-24 h, milk PTHrP decreased while calcium increased in a time-dependent manner. As a whole, calcium concentrations in milk did not correlate with PTHrP throughout lactation. These data suggest that the production and secretion of PTHrP into milk are regulated independently of the other major milk proteins by a factor(s) that changes with progression of lactation and in relation to suckling status.
甲状旁腺激素相关蛋白（PTHrP）在各种哺乳动物的乳汁中含量很高。然而，关于PTHrP产生的调节或PTHrP在乳腺中的生理作用知之甚少。为了解决这些问题，我们对泌乳大鼠进行了研究：1）整个泌乳期乳汁中PTHrP浓度和乳腺中PTHrP mRNA水平的纵向变化；2）非哺乳间隔对乳汁PTHrP浓度的影响；3）PTHrP与乳汁中钙浓度之间的相关性。通过放射免疫分析（RIA）和体外生物测定法测量，乳汁中PTHrP浓度随泌乳时间延长而增加。PTHrP的最大浓度（在连续挤奶的大鼠泌乳第19 - 21天之间观察到）比第7天的浓度高4.8至8.0倍。乳腺中PTHrP mRNA水平在泌乳后期也有所增加。乳汁中钙浓度的纵向变化很小，与PTHrP的变化不平行。当幼崽从母鼠身边移开4 - 24小时时，乳汁中PTHrP减少，而钙则呈时间依赖性增加。总体而言，整个泌乳期乳汁中的钙浓度与PTHrP不相关。这些数据表明，PTHrP向乳汁中的产生和分泌受一个随泌乳进程和哺乳状态变化的因素独立调节，与其他主要乳蛋白无关。
