Appearance of gap junctions in the myometrium of women during labor.

Myometrial tissue from 29 women who underwent cesarean section in various stages of labor were examined quantitatively in the electron microscope. Gap injections were presented between smooth muscle cells with low frequency in women with a closed cervix and infrequent contractions of the uterus. There was a statistically significant correlation between increased cervical dilation or increased frequency of uterine contractions and increased area of gap junctions. Tissues from women in premature labor had more gap junctions than tissues from other women who underwent cesarean section either prematurely or at term. We propose that the formation of gap junctions may be stimulated by some physiologic change. The appearance of gap junctions may then terminate pregnancy by resulting in coordinated, synchronized muscle activity and dilatation of the cervix followed by expulsion of the fetus.