Regional differences in three-dimensional fiber organization, smooth muscle cell phenotype, and contractility in the pregnant mouse cervix.

The orientation and function of smooth muscle in the cervix may contribute to the important biomechanical properties that change during pregnancy. Thus, this study examined the three-dimensional structure, smooth muscle phenotype, and mechanical and contractile functions of the upper and lower cervix of nongravid (not pregnant) and gravid (pregnant) mice. In gravid cervix, we uncovered region-specific changes in the structure and organization of fiber tracts. We also detected a greater proportion of contractile smooth muscle cells (SMCs), but an equal proportion of synthetic SMCs, in the upper versus lower cervix. Furthermore, we revealed that the lower cervix had infrequent spontaneous contractions, distension had a minimal effect on contractility, and the upper cervix had forceful contractions in response to labor-inducing agents (oxytocin and prostaglandin E). These findings identify regional differences in cervix contractility related to contractile SMC content and fiber organization, which could be targeted with diagnostic technologies and for therapeutic intervention.