Abstract
BackgroundAt term, cervical ripening in coordination with uterine contractions becomes a prerequisite for a normal vaginal delivery. Currently, cervical ripening is considered to occur independently from uterine contractions. Many evidences suggest that cervical ripening resembles an inflammatory process. Comparatively little attention has been paid to the increased flexibility of the pelvic symphysis that occurs in many species to enable safe delivery. The aim of this study was to investigate whether the guinea-pig interpubic joint relaxation process observed during late pregnancy and parturition resembles an inflammatory process.MethodsSamples of pubic symphysis were taken from pregnant guinea-pigs sacrificed along gestation, parturition and postpartum. Serial sections of paraffin-embedded tissues were used to measure the interpubic distance on digitalized images, stained with Giemsa to quantify leukocyte infiltration and to describe the vascular area changes, or studied by the picrosirius-polarization method to evaluate collagen remodeling. P4 and E2 serum levels were measured by a sequential immunometric assay.ResultsData showed that the pubic relaxation is associated with an increase in collagen remodeling. In addition, a positive correlation between E2 serum levels and the increase in the interpubic distance was found. On the other hand, a leukocyte infiltration in the interpubic tissue around parturition was described, with the presence of almost all inflammatory cells types. At the same time, histological images show an increase in vascular area (angiogenesis). Eosinophils reached their highest level immediately before parturition; whereas for the neutrophilic and mononuclear infiltration higher values were recorded one day after parturition. Correlation analysis showed that eosinophils and mononuclear cells were positively correlated with E2 levels, but only eosinophilic infiltration was associated with collagen remodeling. Additionally, we observed typical histological images of dissolution of the connective tissue matrix around eosinophils.ConclusionThe present study shows that a timely regulated influx of infiltrating leukocytes is associated with an extensive collagen remodeling process that allows the pubic separation for a normal delivery in guinea-pig. Thus, the findings in this study support the hypothesis that the guinea-pig pubic symphyseal relaxation at parturition resembles an inflammatory process.
Highlights
At term, cervical ripening in coordination with uterine contractions becomes a prerequisite for a normal vaginal delivery
Based on the aforementioned evidences, we suggest that an inflammatory response could be involved in the guinea-pig interpubic joint relaxation process during late pregnancy and parturition
Changes in the length of interpubic ligament are associated with both E2 serum levels and collagen remodeling During pregnancy, the length of the ligament increased from 0.86 mm in nonpregnant controls to ~18–20 mm on the day of parturition
Summary
Cervical ripening in coordination with uterine contractions becomes a prerequisite for a normal vaginal delivery. Little attention has been paid to the increased flexibility of the pelvic symphysis that occurs in many species to enable safe delivery. Little attention has been paid to the modifications of the pelvic girdle that occurs in many species to enable safe delivery In most mammals, these modifications involve sexual dimorphism of the bony pelvis that causes the female to have a sufficiently large birth canal as well as increased flexibility of the sacroiliac and/or pelvic symphysis during late pregnancy. In adult female guinea-pigs, the interpubic joint is a nonsynovial joint of the cartilaginous type that is movable and connected to the pubic bones by fibrous (symphysis) cartilage [4] This fibrocartilage consists largely of compact collagen fibers embedded in an amorphous matrix that contains proteoglycans [5,6]. Relaxation of this articulation occur during the end of pregnancy showing proliferation of the connective tissue cells, increases in the vascularity, weight, and length of the interpubic ligament [7,8,9]
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