Myometrial tissues from guinea pigs, sheep, and human subjects at various stages of gestation and postpartum were quantitatively examined in the electron microscope for the presence of gap junctions between muscle cells. Gap junctions were found in tissues from guinea pigs and sheep which were being delivered or ready to be delivered and in tissues taken immediately post partum. Gap junctions were also present in 19 tissues obtained from 69 women undergoing elective or emergency cesarean section for a variety of reasons. The frequency of their occurrence varies in relation to the presence or absence of labor and other conditions. We propose that gap junctions are required for effective muscle contractions leading to termination of pregnancy in all animals, including human beings. The absence of gap junctions throughout gestation may be necessary for maintenance of pregnancy and the premature appearance of the cell contacts may lead to premature labor.
PIP: The authors hypothesize that gap junctions, or cell-to-cell contacts, are present exclusively only at term and during labor. The absence of gap junctions between contractile cells during pregnancy could prevent coordinated contractions and thus maintain pregnancy. This study examines myometrial tissues from guinea pigs, sheep and human subjects at various stages of gestation and postpartum. The electron microscope was used to examine tissues without reference to any history of the donor women. Gap junctions were found in the myometria of guinea pigs and sheep when the animals were ready to be delivered (fall in progesterone in sheep), being delivered, or immediately thereafter and never at other times. The gap junctions were also found in 17 of 39 tissues from women in labor and in 2 of 30 women thought not to be in labor (eg, no detectable uterine contraction and closed cervix). The frequency of occurence of gap junction varies relative to the presence or absence of labor and other conditions. The presence of jap junctions prior to or during labor has important physiologic implications for maintenance and termination of pregnancy. Further studies should be done to clarify the role of gap junctions in human labor and to assess excitants and inhibitors of uterine contractions relative to the occurrence of gap junctions.