Fox L K, Hancock D D, McDonald J S, Gaskins C T
Department of Veterinary Clinical Medicine and Surgery, Washington State University, Pullman 99163.
J Dairy Sci. 1988 Nov;71(11):2915-22. doi: 10.3168/jds.S0022-0302(88)79889-6.
Experiment 1 was conducted to determine NAGase activity in skim, fat, and cell pellet fractions of foremilk and stripping milk from infection-free quarters. Changes in milk NAGase activity during a 12 h in vitro incubation were also determined. Eight cows, two quarters per cow, were used. One quarter of each cow received an intramammary infusion of oyster glycogen. N-Acetyl-beta-D-glucosaminidase activity was highest in stripping milk and in milk from infused quarters. The percentages of NAGase activity in skim, fat, and cell pellet fractions were 62.6, 22.4, and 12.6. The NAGase activity of milk incubated in vitro did not significantly change over time. Experiment 2 was conducted to determine if neutrophils lost NAGase activity during extravasation into milk. Leukocytosis was induced in infection-free quarters of five cows. The NAGase activities of peripheral neutrophils and milk neutrophils were not significantly different. Results from both studies suggest that the major source of milk NAGase is the mammary epithelial cell and that milk somatic cells contribute less than 15% of the total milk NAGase activity.
进行实验1以测定来自未感染乳腺的初乳和挤奶的脱脂、脂肪和细胞沉淀部分中的N-乙酰-β-D-氨基葡萄糖苷酶（NAGase）活性。还测定了体外孵育12小时期间牛奶中NAGase活性的变化。使用了8头奶牛，每头奶牛两个乳腺。每头奶牛的一个乳腺接受了乳腺内牡蛎糖原灌注。NAGase活性在挤奶和灌注乳腺的牛奶中最高。脱脂、脂肪和细胞沉淀部分中NAGase活性的百分比分别为62.6%、22.4%和12.6%。体外孵育的牛奶中NAGase活性随时间没有显著变化。进行实验2以确定中性粒细胞在渗入牛奶过程中是否丧失NAGase活性。在5头奶牛未感染的乳腺中诱导白细胞增多。外周血中性粒细胞和牛奶中性粒细胞的NAGase活性没有显著差异。两项研究的结果均表明，牛奶中NAGase的主要来源是乳腺上皮细胞，并且牛奶中的体细胞对牛奶中NAGase总活性的贡献小于15%。
