INRA, UMR1080, Production du lait, Rennes, France.
J Dairy Sci. 2012 Jan;95(1):177-87. doi: 10.3168/jds.2011-4461.
To assess the regulation of mammary cell activity, survival, and proliferation by prolactin (PRL), 5 Holstein cows in early lactation received daily i.m. injections of 1mg of quinagolide, a suppressor of PRL release, for 9 wk, whereas 4 control cows received the vehicle (water) only. During the last week of treatment, one udder half was milked once a day (1×) and the other twice a day (2×). Mammary biopsies were harvested 1 wk before and 4 and 8 wk after the start of quinagolide treatment. The quinagolide injections reduced milk yield and resulted in lower levels of κ-casein and α-lactalbumin mRNA in the mammary biopsies at wk 4 compared with the control cows. In the mammary tissue of the quinagolide-treated cows at wk 8 of treatment, cell proliferation (as determined by proliferating cell nuclear antigen labeling) was lower and apoptosis (as determined by the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay) was higher than in the mammary tissue of the control cows. During differential milking, mammary epithelial cells (MEC) were extracted from the milk by centrifugation and purified by immunocytochemical binding to allow variations in the levels of mammary transcripts to be observed. After 9 wk of treatment, levels of α-lactalbumin and κ-casein mRNA were lower in the MEC isolated from milk of the quinagolide-treated cows. This effect was associated with lower PRL receptor mRNA levels and a tendency toward lower viability in the milk-isolated MEC from the 2×-milked glands. The decrease from 2× milking to 1× milking also downregulated α-lactalbumin and κ-casein transcripts in the milk-isolated MEC. Viability was higher for the MEC collected from the 1×-milked udder halves compared with the 2×-milked halves. In conclusion, the reduction in milk yield after chronic administration of the PRL-release inhibitor quinagolide is associated with a reduction in mammary cell activity, survival, and proliferation in lactating dairy cows. Reduced milking frequency was also associated with a decrease in MEC activity.
为了评估催乳素（PRL）对乳腺细胞活性、存活和增殖的调节作用，5 头处于泌乳早期的荷斯坦奶牛每天接受 1mg 喹那高利德（一种 PRL 释放抑制剂）的肌内注射，共 9 周，而 4 头对照奶牛仅接受载体（水）。在治疗的最后一周，每只乳房每天挤奶一次（1×），另一只每天挤奶两次（2×）。在喹那高利德治疗开始前 1 周、治疗后 4 周和 8 周采集乳腺活检。喹那高利德注射减少了产奶量，并导致与对照组奶牛相比，在第 4 周的乳腺活检中κ-酪蛋白和α-乳白蛋白 mRNA 的水平降低。在治疗 8 周时，喹那高利德处理的奶牛的乳腺组织中，细胞增殖（通过增殖细胞核抗原标记确定）降低，凋亡（通过末端脱氧核苷酸转移酶介导的 dUTP 缺口末端标记测定确定）升高，高于对照组奶牛的乳腺组织。在差异挤奶过程中，通过离心从牛奶中提取乳腺上皮细胞（MEC），并通过免疫细胞化学结合进行纯化，以观察乳腺转录物水平的变化。治疗 9 周后，从喹那高利德处理奶牛的牛奶中分离的 MEC 中α-乳白蛋白和κ-酪蛋白 mRNA 的水平降低。这种效应与催乳素受体 mRNA 水平降低和 2×挤奶的乳腺分离 MEC 的活力降低有关。从 2×挤奶到 1×挤奶的减少也下调了牛奶分离的 MEC 中的α-乳白蛋白和κ-酪蛋白转录物。与 2×挤奶的乳房相比，从 1×挤奶的乳房收集的 MEC 的活力更高。总之，在慢性给予 PRL 释放抑制剂喹那高利德后，产奶量减少与泌乳奶牛乳腺细胞活性、存活和增殖减少有关。减少挤奶频率也与 MEC 活性降低有关。
