Spontaneous contractility of isolated muscle layers of the pig oviductal isthmus

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Abstract
A new dissection technique for the mechanical separation of the smooth muscle layers of the pig oviductal isthmus is described. The spontaneous contractility of the isolated muscle layers was recorded using transducers designed to reflect the proper force development of the tubal muscle tissue specimens under in vitro conditions. A series of well defined stages of the entire estrous cycle was surveyed, and the isolated tubal muscle contractility was compared with that of the intact isthmus according to previous work. The circular and longitudinal layers are both active during the estrous cycle, showing definite patterns in each stage explored. The circular layer revealed a changing pattern similar to but of lower activity than the intact isthmus, especially during the heat, postovulation and luteal phases. The periods are considered to be relevant because during heat the spermatozoa might be actively transported through the isthmus by the concerted contractions and relaxations of the circular muscles. The same would happen during the luteal phase, especially during the time the ova are descending into the uterus. As important would be the postovulation time, during which the sustained contraction of the circular layer could lock the isthmic lumen, thus preventing improper timing of ova descent. The longitudinal layer follows the intensity of the contraction patterns of the circular layers, being especially active during the periovulatory period.