AJP - Regulatory, Integrative and Comparative Physiology, Vol 242, Issue 3 181-R184, Copyright © 1982 by American Physiological Society
Rhythmic contractions of the teat sphincter in bovines: an expulsion mechanism
A. M. Lefcourt
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.
