Alperin Marianna, Lawley Danielle M, Esparza Mary C, Lieber Richard L
Division of Urogynecology and Pelvic Reconstructive Surgery, University of California, San Diego, School of Medicine, San Diego, CA.
Department of Reproductive Medicine, University of California, San Diego, School of Medicine, San Diego, CA.
Am J Obstet Gynecol. 2015 Aug;213(2):191.e1-7. doi: 10.1016/j.ajog.2015.05.012. Epub 2015 May 13.
Maternal birth trauma to the pelvic floor muscles (PFMs) is a major risk factor for pelvic floor disorders. Modeling and imaging studies suggest that demands placed on PFMs during childbirth exceed their physiologic limits; however many parous women do not sustain PFM injury. Here we determine whether pregnancy induces adaptations in PFM architecture, the strongest predictor of muscle function, and/or intramuscular extracellular matrix (ECM), responsible for load bearing. To establish if parallel changes occur in muscles outside of the PFM, we also examined a hind limb muscle.
Coccygeus, iliocaudalis, pubocaudalis, and tibialis anterior of 3-month-old Sprague-Dawley virgin, mid-pregnant, and late-pregnant; 6-month-old virgin; and 4- and 12-week postpartum rats (N = 10/group) were fixed in situ and harvested. Major architectural parameters determining muscle's excursion and force-generating capacity were quantified, namely, normalized fiber length (Lfn), physiologic cross-sectional area, and sarcomere length. Hydroxyproline content was used as a surrogate for intramuscular ECM quantity. Analyses were performed by 2-way analysis of variance with Tukey post hoc testing at a significance level of .05.
Pregnancy induced a significant increase in Lfn in all PFMs by the end of gestation relative to virgin controls. Fibers were elongated by 37% in coccygeus (P < .0001), and by 21% in iliocaudalis and pubocaudalis (P < .0001). Importantly, no Lfn change was observed in the tibialis anterior. Physiologic cross-sectional area and sarcomere length were not affected by pregnancy. By 12 weeks' postpartum, Lfn of all PFMs returned to the prepregnancy values. Relative to virgin controls, ECM increased by 140% in coccygeus, 52% in iliocaudalis, and 75% in pubocaudalis in late-pregnant group, but remained unchanged across time in the tibialis anterior. Postpartum, ECM collagen content returned to prepregnancy levels in iliocaudalis and pubocaudalis, but continued to be significantly elevated in coccygeus (P < .0001).
This study demonstrates that pregnancy induces unique adaptations in the structure of the PFMs, which adjust their architectural design by adding sarcomeres in series to increase fiber length as well as mounting a substantial synthesis of collagen in intramuscular ECM.
产妇盆底肌肉（PFM）的分娩创伤是盆底功能障碍的主要危险因素。建模和影像学研究表明，分娩时对PFM的需求超出了其生理极限；然而，许多经产妇并未发生PFM损伤。在此，我们确定妊娠是否会引起PFM结构（肌肉功能的最强预测指标）和/或负责承重的肌内细胞外基质（ECM）的适应性变化。为了确定PFM以外的肌肉是否也会发生类似变化，我们还检查了后肢肌肉。
将3个月大的未孕、孕中期和孕晚期的斯普拉格-道利大鼠；6个月大的未孕大鼠；以及产后4周和12周的大鼠（每组N = 10）的尾骨肌、髂尾肌、耻骨尾肌和胫骨前肌原位固定并取材。对决定肌肉收缩幅度和力量产生能力的主要结构参数进行量化，即标准化纤维长度（Lfn）、生理横截面积和肌节长度。羟脯氨酸含量用作肌内ECM数量的替代指标。采用双向方差分析，并进行Tukey事后检验，显著性水平为0.05。
与未孕对照组相比，妊娠末期所有PFM的Lfn均显著增加。尾骨肌纤维伸长37%（P < 0.0001），髂尾肌和耻骨尾肌纤维伸长21%（P < 0.0001）。重要的是，胫骨前肌未观察到Lfn变化。生理横截面积和肌节长度不受妊娠影响。产后12周时，所有PFM的Lfn均恢复到妊娠前水平。与未孕对照组相比，孕晚期组尾骨肌的ECM增加了140%，髂尾肌增加了52%，耻骨尾肌增加了75%，但胫骨前肌随时间无变化。产后，髂尾肌和耻骨尾肌的ECM胶原蛋白含量恢复到妊娠前水平，但尾骨肌仍显著升高（P < 0.0001）。
本研究表明，妊娠会引起PFM结构的独特适应性变化，通过串联添加肌节来增加纤维长度，以及在肌内ECM中大量合成胶原蛋白，从而调整其结构设计。
