In vivo myometrial activity during early pregnancy and pseudopregnancy in the rats

Linda H. Crane*, Len Martin

*Corresponding author for this work

Research output: Contribution to journalArticleResearchpeer-review

21 Citations (Scopus)


Video-laparoscopic studies in early pregnant and pseudopregnant rats showed large changes in frequency, direction of propagation and nature of myométrial contractions. Day 2 patterns of activity were essentially the same as in unmated animals at the equivalent stage of the cycle. From Days 3 to 5 there was a large increase in longitudinal and circular contractions propagating towards the oviduct, circular contractions making the greatest contribution. This circular activity may be important in retaining and spacing embryos. Circular contractions propagating towards the cervix showed smaller increases and there was a transient diminution in the frequency of longitudinal contractions in this direction on Day 5. In pregnant rats, the frequency of discrete contractions declined on Days 6-7. However, circular tone appeared to be increased and uteri showed dramatic twisting and curling, apparently due to resistance to the shortening imposed by longitudinal contractions. None of the major changes in activity appeared to be caused by embryos, because they were seen in pseudopregnant rats and, after embryo implantation, in both horns of unilaterally pregnant rats. The earliest divergence from the activity patterns of unmated rats occurred when progesterone levels first increased significantly above those of the undisturbed oestrous cycle, suggesting that progesterone has a major influence on myométrial activity. The complexity of the changes in activity raises questions about other regulatory factors, particularly in regard to coordination between the circular and longitudinal muscle layers. Anomalous results from pregnant, unilaterally pregnant, and pseudopregnant animals on Day 7 suggested that embryos exert systemic effects on myométrial activity.

Original languageEnglish
Pages (from-to)233-244
Number of pages12
JournalReproduction, Fertility and Development
Issue number3
Publication statusPublished - 1 Jan 1991
Externally publishedYes


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