INVIVO MYOMETRIAL ACTIVITY IN THE RAT DURING THE ESTROUS-CYCLE - STUDIES WITH A NOVEL TECHNIQUE OF VIDEO LAPAROSCOPY

Previous techniques of recording myometrial activity in vivo gave limited information about the nature of contractions, and disrupted normal reproductive events. To overcome these drawbacks we developed a new in vivo method of video laparoscopy (VL). This involves positioning a laparoscope in the abdomen of anaesthetized rats to view the caudal ends of both uterine horns. Myometrial activity is recorded by video camera onto video tape. Myometrial contractions are classified according to the muscle layers involved, the interaction between layers and the direction of propagation. Experiments with intrauterine balloons and electromyography (EMG) in conscious and ketamine/xylazine anaesthetized rats showed that this anaesthetic does not have major effects on myometrial activity. To validate the VL method, recordings were obtained throughout the oestrous cycle and compared with results obtained with EMG in conscious rats. The frequency and pattern of activity were similar with both techniques although more information was obtained from VL. Frequency of contractions was highest in oestrus and dioestrus and lowest in pro-oestrus, when contractions occurred in groups separated by quiescent intervals. At all stages, longitudinal contractions propagating towards the cervix predominated. Circular muscle activity was only seen at oestrus and dioestrus; that at oestrus consisted of weak peristalses, that at dioestrus was more complex. A major advantage of VL is that is does not interfere with the course of the oestrous cycle, pseudopregnancy or early pregnancy.