Ex vivo assessment of mouse cervical remodeling through pregnancy via 23Na MRS

Abstract

Preterm birth occurs in 12.5% of births in the United States and can lead to risk of infant death or to lifelong serious health complications. A greater understanding by which the two main processes, uterine contraction and cervical remodeling are regulated is required to reduce rates of preterm birth. The cervix must undergo extensive remodeling through pregnancy in preparation for parturition, the process of labor and delivery of young. One key aspect of this dynamic process is a change in the composition and abundance of glycosaminoglycans (GAGs) and proteoglycans within the extracellular matrix, which influences the loss of tensile strength or stiffness of the cervix during labor. 23Na NMR spectroscopy has previously been validated as a method to quantify GAGs in tissues. In the current study, the Na+ concentration was measured at several time points through pregnancy in mouse cervices using 23Na NMR spectroscopy. The Na+ concentration increased progressively during pregnancy and peaked one day before birth followed by a rapid decline after birth. The same trend was seen in GAGs as measured by a biochemical assay using independent cervix samples over the course of pregnancy. We suggest that monitoring the Na+ concentration via 23Na NMR spectroscopy can serve as an informative physiological marker in evaluating the stages of cervical remodeling ex vivo and warrants further investigation to determine its utility as a diagnostic tool for the identification of women at risk for impending preterm birth.

Figure 1

Hexuronic acid levels in proestrus nonpregnant (NP), pregnant (d6-18) and cervix collected 2–4, 24, and 48 hours postpartum (pp2–4, 24 and 48 h). Each group represents the mean ± S.E.M. of 5 samples. (*) P < 0.05 when compared to d6. Data was analyzed by One Way ANOVA. Differences among treatment means were determined using Student-Newman-Keuls’ test.

Figure 2

Na⁺ concentration (mmol/g tissue wet weight) as a function of gestation day/hour post partum (hpp). Each group represents the mean ± S.D. of 5 samples. (*) P < 0.05 when compared to d10. Data was analyzed by One-Way ANOVA.

Figure 3

Water content in tissue wet weight as a function of gestation day (10–18) /hours post partum(24hpp and 48hpp). Each group represents the mean ± S.D. of 5 samples. (*) P < 0.05 when compared to gestation day 10. Data was analyzed by One-Way ANOVA.

Figure 4

Calculated fixed charge density using Na+ concentration and water content. (−)FCD is plotted as a function of gestation day/hours post partum. Error analysis is applied in the calculation.