Lefcourt A M
Am J Physiol. 1982 Mar;242(3):R181-4. doi: 10.1152/ajpregu.1982.242.3.R181.
Spontaneous and induced rhythmic contractions of the teat sphincter muscle were measured in conscious bovines using a pressure transponding device. Contractions were induced or the frequency of contractions was increased by intravenous injection of phenylephrine. Epinephrine, isoxsuprine, and phentolamine inhibited contractions and prior administration of phentolamine blocked the response to phenylephrine. Contractions in adjacent teats were asyncronous and the frequency of spontaneous contractions (0-20/min) increased with time after milking, presumably due to the effect of the increased muscle tension that resulted from the accumulation of milk within the gland cistern and the teat cistern. Furthermore, the contractions were found to be peristaltic in nature. Squeezing the tip of the teat was found to induce one or more contractions, whereas squeezing the teat elsewhere had no effect. It was hypothesized that peristaltic contractions in response to irritation of the tip of the teat might represent an expulsion mechanism.
使用压力感应装置在清醒的牛身上测量乳头括约肌的自发和诱发节律性收缩。通过静脉注射去氧肾上腺素诱发收缩或增加收缩频率。肾上腺素、异舒普林和酚妥拉明抑制收缩，预先给予酚妥拉明可阻断对去氧肾上腺素的反应。相邻乳头的收缩是异步的，自发收缩频率（0 - 20次/分钟）在挤奶后随时间增加，推测是由于腺泡和乳头池内乳汁积聚导致肌肉张力增加的影响。此外，发现这些收缩本质上是蠕动性的。发现挤压乳头尖端会诱发一次或多次收缩，而在其他部位挤压乳头则没有效果。据推测，对乳头尖端刺激产生的蠕动性收缩可能代表一种排出机制。
