Remodeling of mammary tissue and lactation persistency

这项研究计划的长期目标是提高我们对控制乳腺退化所涉及的生物过程的了解，并开发经济上可行且消费者可以接受的技术或实践，以改善奶牛的哺乳持久性，并使奶牛能够更长时间地哺乳。延长哺乳时间会减少奶牛在哺乳早期的生命比例，从而减少与此阶段相关的疾病、代谢紊乱和繁殖失败的发生。尽管对持续哺乳的生物控制知之甚少，但已显示出影响持续哺乳的因素，如挤奶频率、排乳完好率、产次、光周期、营养摄入量和妊娠。最近在我的实验室进行的工作表明，与人们所认为的相反，催乳素(PRL)在乳用反刍动物中是催乳素(PRL)。如果PRL的基础水平与产奶量水平没有明显的相关性，挤奶诱导的PRL释放与产奶量水平相关，PRL的抗凋亡作用已在啮齿类动物的乳腺中得到报道，因此，我们在PRL分泌受到抑制的奶牛的腺体中发现了更多的细胞凋亡。因此，PRL，特别是挤奶诱导的PRL，可能通过限制细胞丢失和维持细胞分化而成为持续哺乳的重要因素。然而，我们也发现PRL的生乳作用是在乳腺水平上进行调节的，其机制尚不清楚。我的假设是：-挤奶诱导的激素释放对维持乳腺上皮细胞的分化、分泌活动和生存非常重要。-几个因素通过调节挤奶时激素的释放量和/或乳腺对它们的反应来影响产奶量和哺乳持久性。我的短期目标是：1-确定控制挤奶诱导的PRL2释放的因素的大小--确定局部因素影响哺乳持久性的机制。3-确定系统性因素影响哺乳持续性的机制(S)

The long range objectives of this research program are to improve our knowledge of the biological process involved in the control of mammary gland involution and to develop economically viable and consumer acceptable technologies or practices that would improve lactation persistency and enable longer lactation in dairy cows. Extended lactation would reduce the proportion of cow's lifetime spent in early lactation and, thus, the occurrence of disease, metabolic disorder and reproduction failure associated with this period.Although little is known about the biological control of persistency, factors such as milking frequency, completeness of milk removal, parity, photoperiod, nutrient intake and gestation have been shown to affect it. Recent work carried out in my laboratory, have demonstrated that the hormone prolactin (PRL), contrary to what was believed, is galactopoietic in dairy ruminants. If basal level of PRL was not clearly associated with level of milk production, the milking-induced PRL release was correlated to level of milk production Anti-apoptotic effects of PRL have been reported in the mammary gland of rodents and, accordingly, we found more apoptosis in the glands of cows where PRL secretion was inhibited. Therefore, it is possible that PRL, especially the milking-induced PRL, is an important factor for lactation persistency by limiting the loss of cells and maintaining cell differentiation. However, we also found that the galactopoietic action of PRL is modulated at the level of the mammary gland by a mechanism that remains to be elucidated. My hypotheses are:-The milking-induced release of hormone is important to maintain the differentiation, the secretory activity and the survival of the mammary epithelial cells.- Several factors affect milk production and lactation persistency by modulating the amount of hormones release at milking and/or mammary gland responsiveness to them.My short range objectives are:1- To determine the factors controling the magnitude of milking-induced release of PRL2- To determine the mechanisms by which local factors affect lactation persistency.3- To determine the mechanism(s) by which systemic factors affect lactation persistency