Alperin Marianna, Kaddis Timothy, Pichika Rajeswari, Esparza Mary C, Lieber Richard L
Department of Reproductive Medicine, University of California, San Diego, San Diego, California; Division of Urogynecology and Pelvic Reconstructive Surgery, University of California, San Diego, San Diego, California.
Department of Reproductive Medicine, University of California, San Diego, San Diego, California.
Am J Obstet Gynecol. 2016 Aug;215(2):210.e1-7. doi: 10.1016/j.ajog.2016.02.018. Epub 2016 Feb 12.
Birth trauma to pelvic floor muscles is a major risk factor for pelvic floor disorders. Intramuscular extracellular matrix determines muscle stiffness, supports contractile component, and shields myofibers from mechanical strain.
Our goal was to determine whether pregnancy alters extracellular matrix mechanical and biochemical properties in a rat model, which may provide insights into the pathogenesis of pelvic floor muscle birth injury. To examine whether pregnancy effects were unique to pelvic floor muscles, we also studied a hind limb muscle.
Passive mechanical properties of coccygeus, iliocaudalis, pubocaudalis, and tibialis anterior were compared among 3-month old Sprague-Dawley virgin, late-pregnant, and postpartum rats. Muscle tangent stiffness was calculated as the slope of the stress-sarcomere length curve between 2.5 and 4.0 μm, obtained from a stress-relaxation protocol at a bundle level. Elastin and collagen isoform concentrations were quantified by the use of enzyme-linked immunosorbent assay. Enzymatic and glycosylated collagen crosslinks were determined by high-performance liquid chromatography. Data were compared by the use of repeated-measures, 2-way analysis of variance with Tukey post-hoc testing. Correlations between mechanical and biochemical parameters were assessed by linear regressions. Significance was set to P < .05. Results are reported as mean ± SEM.
Pregnancy significantly increased stiffness in coccygeus (P < .05) and pubocaudalis (P < .0001) relative to virgin controls, with no change in iliocaudalis. Postpartum, pelvic floor muscle stiffness did not differ from virgins (P > .3). A substantial increase in collagen V in coccygeus and pubocaudalis was observed in late-pregnant, compared with virgin, animals, (P < .001). Enzymatic crosslinks decreased in coccygeus (P < .0001) and pubocaudalis (P < .02) in pregnancy, whereas glycosylated crosslinks were significantly elevated in late-pregnant rats in all pelvic floor muscles (P < .05). Correlations between muscle stiffness and biochemical parameters were inconsistent. In contrast to the changes observed in pelvic floor muscles, the tibialis anterior was unaltered by pregnancy.
In contrast to other pelvic tissues, pelvic floor muscle stiffness increased in pregnancy, returning to prepregnancy state postpartum. This adaptation may shield myofibers from excessive mechanical strain during parturition. Biochemical alterations in pelvic floor muscle extracellular matrix due to pregnancy include increase in collagen V and a differential response in enzymatic vs glycosylated collagen crosslinks. The relationships between pelvic floor muscle biochemical and mechanical parameters remain unclear.
盆底肌肉的分娩创伤是盆底功能障碍的主要危险因素。肌内细胞外基质决定肌肉硬度，支持收缩成分，并保护肌纤维免受机械应变。
我们的目标是确定妊娠是否会改变大鼠模型中细胞外基质的力学和生化特性，这可能有助于深入了解盆底肌肉分娩损伤的发病机制。为了研究妊娠效应是否是盆底肌肉所特有的，我们还研究了后肢肌肉。
比较3个月大的斯普拉格-道利未孕、妊娠晚期和产后大鼠的尾骨肌、髂尾肌、耻骨尾肌和胫前肌的被动力学特性。肌肉切线刚度计算为从束水平的应力松弛实验中获得的2.5至4.0μm之间应力-肌节长度曲线的斜率。通过酶联免疫吸附测定法定量弹性蛋白和胶原蛋白异构体浓度。通过高效液相色谱法测定酶促和糖基化胶原蛋白交联。使用重复测量的双向方差分析和Tukey事后检验比较数据。通过线性回归评估力学和生化参数之间的相关性。显著性设定为P <.05。结果以平均值±标准误报告。
与未孕对照组相比，妊娠显著增加了尾骨肌（P <.05）和耻骨尾肌（P <.0001）的硬度，而髂尾肌无变化。产后，盆底肌肉硬度与未孕大鼠无差异（P>.3）。与未孕动物相比，妊娠晚期尾骨肌和耻骨尾肌中的胶原蛋白V显著增加（P <.001）。妊娠期间，尾骨肌（P <.0001）和耻骨尾肌（P <.02）中的酶促交联减少，而所有盆底肌肉中妊娠晚期大鼠的糖基化交联显著升高（P <.05）。肌肉硬度与生化参数之间的相关性不一致。与盆底肌肉中观察到的变化相反，妊娠对胫前肌没有影响。
与其他盆腔组织不同，盆底肌肉硬度在妊娠期间增加，产后恢复到妊娠前状态。这种适应性变化可能在分娩过程中保护肌纤维免受过度的机械应变。妊娠导致的盆底肌肉细胞外基质生化改变包括胶原蛋白V增加以及酶促与糖基化胶原蛋白交联的不同反应。盆底肌肉生化和力学参数之间的关系仍不清楚。
