Myometrial electrophysiologic activity and gap junctions in the pregnant rabbit

Electromyographic activity of the myometrium, intrauterine pressure, and myometrial gap junctions were examined in rabbits at various stages of pregnancy and during parturition. Electromyographic activity occurred throughout pregnancy and was characterized by electromyographic bursts lasting up to 5 minutes at a frequency of one to four per hour. The gap junction area of plasma membrane showed a significant increase at delivery at a time when electromyographic activity changed to rhythmic bursts of short duration at a frequency of about one per minute. This study shows that the rabbit uterus is active throughout pregnancy; furthermore, the development of large numbers of gap junctions between myometrial cells occurs at a time when uterine activity changes to the expulsive activity required for labor.