Uterine and abdominal contractions were studied in cows near and during calving by means of microballoons imbedded in the uterine mucosa, connected to external strain gauges and recorded electronically. Uterine "activity" is defined as a function of intensity and time. "Abdominal units" are defined as a function of intensity. A transition period was found in which irregular, brief, non-coordinated contractions of the prepartum period were transformed into regular, long, coordinated, propagated contractions of parturition. Uterine contractions did 90% of the work of parturition and were directly, but not linearly, proportional to fetal "resistance." Abdominal efforts were intense, brief, and not related to fetal size. Uterine peristalsis is proposed as initiated by the circular muscle contractions and composed of sequential contractions of adjacent circular muscle ring segments synchronized by propagation of the action impulse through the longitudinal muscles. Evidence was found of a local progesterone effect.
- Copyright © 1963 by American Physiological Society