Abstract
Remodeling of vaginal extracellular matrix and smooth muscle likely plays a critical role in reducing the risk of maternal injury during vaginal delivery by altering the mechanical properties to increase distension and reduce stress. Long-Evans rats were divided into five groups to examine the passive mechanical and active contractile properties throughout pregnancy and postpartum: virgin (n = 17), mid-pregnant (Day 14–16, n = 12), late-pregnant (Day 20–22, n = 14), immediate postpartum (0–2 h after delivery, n = 14), and 4 week postpartum (n = 15). Longitudinal sections of vaginal tissue were loaded to failure uniaxially for passive mechanical or active contractile properties were examined. For passive mechanics, the tangent modulus decreased 45% by mid-pregnancy and immediately postpartum (p < 0.001). The ultimate strain continuously increased up to 43% higher than virgin animals (p = 0.007) in the immediate postpartum group. For active mechanics, the maximal contractile force was 36–56% lower through immediate postpartum animals, and was significantly more sensitive to K+ throughout pregnancy and postpartum (p = 0.003). The changes observed in the passive and active properties of the rat vagina are consistent with what would be expected from a tissue that is remodeling to maximize its ability to distend at the time of vaginal delivery to facilitate passage of the fetus with minimal injury.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Abramowitch, S. D., S. L.-Y. Woo, T. D. Clineff, and R. E. Debski. An evaluation of the quasi-linear viscoelastic properties of the healing medial collateral ligament in a goat model. Ann. Biomed. Eng. 32(3):329–335, 2004.
Abramowitch, S. D., A. Feola, Z. Jallah, and P. A. Moalli. Tissue mechanics, animal models, and pelvic organ prolapse: a review. Eur. J. Obstet. Gynecol. Reprod. Biol. 144(Suppl 1):S146–S158, 2009.
Alperin, M., A. Feola, R. Duerr, P. Moalli, and S. Abramowitch. Pregnancy- and delivery-induced biomechanical changes in rat vagina persist postpartum. Int. Urogynecol. J. Pelvic Floor Dysfunct. 21(9):1169–1174, 2010.
Damaser, M. S., C. Whitbeck, P. Chichester, and R. M. Levin. Effect of vaginal distension on blood flow and hypoxia of urogenital organs of the female rat. J. Appl. Physiol. 98(5):1884–1890, 2005.
Daucher, J. A., K. A. Clark, D. B. Stolz, L. A. Meyn, and P. A. Moalli. Adaptations of the rat vagina in pregnancy to accommodate delivery. Obstet. Gynecol. 109(1):128–135, 2007.
Davidge, S. T., R. E. Gandley, and M. K. McLaughlin. Altered active but not passive properties of mesenteric resistance arteries from the vitamin E-deprived rat. J. Pharm. 123(2):275–280, 1998.
DeLancey, J. O. Anatomic aspects of vaginal eversion after hysterectomy. Am. J. Obstet. Gynecol. 166(6 Pt 1):1717–1724, 1992; discussion 1724-8.
DeLancey, J. O. The hidden epidemic of pelvic floor dysfunction: achievable goals for improved prevention and treatment. Am. J. Obstet. Gynecol. 192(5):1488–1495, 2005.
Drutz, H. P., and M. Alarab. Pelvic organ prolapse: demographics and future growth prospects. Int. Urogynecol. J Pelvic Floor Dysfunct. 17(Suppl 1):S6–S9, 2006.
Giraldi, A., P. Alm, V. Werkstrom, L. Myllymaki, G. Wagner, and K. E. Andersson. Morphological and functional characterization of a rat vaginal smooth muscle sphincter. Int. J. Impot. Res. 14(4):271–282, 2002.
Gregorevic, P., D. R. Plant, N. Stupka, and G. S. Lynch. Changes in contractile activation characteristics of rat fast and slow skeletal muscle fibres during regeneration. J. Physiol. 558(2):549–560, 2004.
Kim, N. N., K. Min, M. A. Pessina, R. Munarriz, I. Goldstein, and A. M. Traish. Effects of ovariectomy and steroid hormones on vaginal smooth muscle contractility. Int. J. Impot. Res. 16(1):43–50, 2004.
Lowder, J. L., K. M. Debes, D. K. Moon, N. Howden, S. D. Abramowitch, and P. A. Moalli. Biomechanical adaptations of the rat vagina and supportive tissues in pregnancy to accommodate delivery. Obstet. Gynecol. 109(1):136–143, 2007.
Mant, J., R. Painter, and M. Vessey. Epidemiology of genital prolapse: observations from the Oxford Family Planning Association Study. Br. J. Obstet. Gynaecol. 104(5):579–585, 1997.
Moalli, P. A., N. S. Howden, J. L. Lowder, J. Navarro, K. M. Debes, S. D. Abramowitch, and S. L.-Y. Woo. A rat model to study the structural properties of the vagina and its supportive tissues. Am. J. Obstet. Gynecol. 192(1):80–88, 2005.
Olsen, A. L., V. J. Smith, J. O. Bergstrom, J. C. Colling, and A. L. Clark. Epidemiology of surgically managed pelvic organ prolapse and urinary incontinence. Obstet. Gynecol. 89(4):501–506, 1997.
Pan, H. Q., J. M. Kerns, D. L. Lin, D. Sypert, J. Steward, C. R. V. Hoover, P. Zaszczurynski, R. S. Butler, and M. S. Damaser. Dual simulated childbirth injury delays anatomic recovery. Am. J. Physiol. Renal Physiol. 296(2):F277–F283, 2009.
Rubod, C., M. Boukerrou, M. Brieu, P. Dubois, and M. Cosson. Biomechanical properties of vaginal tissue. Part 1: new experimental protocol. J. Urol. 178(1):320–325, 2007; discussion 325.
Scheffler, S. U., T. D. Clineff, C. D. Papageorgiou, R. E. Debski, C. B. Ma, and S. L.-Y. Woo. Structure and function of the healing medial collateral ligament in a goat model. Ann. Biomed. Eng. 29(2):173–180, 2001.
Subak, L. L., L. E. Waetjen, S. Va Den Eeden, D. H. Vittinghoff, and J. S. Brown. Cost of pelvic organ prolapse surgery in the United States. Obstet. Gynecol. 98(4):646–651, 2001.
Wen, Y., Y. Y. Zhao, S. Li, M. L. Polan, and B. H. Chen. Differences in mRNA and protein expression of small proteoglycans in vaginal wall tissue from women with and without stress urinary incontinence. Hum. Reprod. 22(6):1718–1724, 2007.
Woo, S. L.-Y., C. A. Orlando, J. F. Camp, and W. H. Akeson. Effects of postmortem storage by freezing on ligament tensile behavior. J. Biomech. 19(5):399–404, 1986.
Woo, S. L.-Y., M. I. Danto, K. J. Ohland, T. Q. Lee, and P. O. Newton. The use of a laser micrometer system to determine the cross-sectional shape and area of ligaments: a comparative study with two existing methods. J. Biomech. Eng. 112(4):426–431, 1990.
Yanagishita, M. Proteoglycans and hyaluronan in female reproductive organs. EXS 70:179–190, 1994.
Acknowledgment
This research received financial support from the NIH R01HD-045590 and K12HD-043441.
Author information
Authors and Affiliations
Corresponding author
Additional information
Associate Editor Michael R. Torry oversaw the review of this article.
Rights and permissions
About this article
Cite this article
Feola, A., Moalli, P., Alperin, M. et al. Impact of Pregnancy and Vaginal Delivery on the Passive and Active Mechanics of the Rat Vagina. Ann Biomed Eng 39, 549–558 (2011). https://doi.org/10.1007/s10439-010-0153-9
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s10439-010-0153-9