Capuco A V, Wood D L, Baldwin R, Mcleod K, Paape M J
Gene Evaluation and Mapping Laboratory, USDA-ARS, Beltsville, MD 20705, USA.
J Dairy Sci. 2001 Oct;84(10):2177-87. doi: 10.3168/jds.S0022-0302(01)74664-4.
This investigation evaluated mammary cell loss and replacement during lactation and the impact of administration of bST on these processes. During lactation, a gradual decrease in number of mammary epithelial cells within the mammary glands occurs and largely accounts for the decline in milk production with advancing lactation. This decrease is not appreciably impacted by the loss of viable epithelial cells in milk. Rather, the net decline in cell number (approximately 50% during the entire lactation) results from continual death by apoptosis. Accompanying the decline in mammary cell number by apoptosis is a degree of cell renewal. Approximately 0.3% of mammary cells in lactating, nonpregnant cows were labeled by a 24-h in vivo treatment with the thymidine analog, bromodeoxyuridine. During the entire lactation, the number of new cells amounts to approximately 50% of the number of cells initially present. By the end of lactation, most cells present in the mammary gland were formed after calving. Increasing cell replacement or decreasing apoptosis during lactation may provide a means to increase persistency of lactation. Indeed, administration of bST to Holstein cows during midlactation increased the proportion of mammary epithelial cells expressing the nuclear proliferation antigen, Ki-67, from 0.5 to 1.6%. Bovine somatotropin appears to increase the rate of cell renewal in the lactating mammary gland. Knowledge of molecular regulation of apoptosis and cell proliferation should provide a means to modulate cell turnover in the mammary gland. A change in the ratio of epithelial proliferation to cell death during lactation will affect the persistency of lactation.
本研究评估了泌乳期间乳腺细胞的损失与更替，以及注射牛生长激素（bST）对这些过程的影响。在泌乳期间，乳腺内的乳腺上皮细胞数量逐渐减少，这在很大程度上导致了随着泌乳期推进产奶量的下降。这种减少并未因乳汁中存活上皮细胞的损失而受到明显影响。相反，细胞数量的净减少（在整个泌乳期约为50%）是由细胞凋亡导致的持续死亡引起。伴随细胞凋亡导致的乳腺细胞数量下降的是一定程度的细胞更新。用胸苷类似物溴脱氧尿苷进行24小时体内处理后，约0.3%的泌乳期未孕奶牛的乳腺细胞被标记。在整个泌乳期，新细胞的数量约为最初存在细胞数量的50%。到泌乳期末，乳腺中存在的大多数细胞是在产犊后形成的。在泌乳期间增加细胞更替或减少细胞凋亡可能提供一种提高泌乳持续性的方法。事实上，在泌乳中期给荷斯坦奶牛注射bST，使表达核增殖抗原Ki-67的乳腺上皮细胞比例从0.5%增加到了1.6%。牛生长激素似乎能提高泌乳期乳腺的细胞更新率。了解细胞凋亡和细胞增殖的分子调控机制应该能提供一种调节乳腺细胞更新的方法。泌乳期间上皮细胞增殖与细胞死亡比例的变化将影响泌乳的持续性。
