Differences in morphology and contractility of the bulbospongiosus and pubococcygeus muscles in nulliparous and multiparous rabbits

Abstract

In women, birth trauma can result in altered anatomy of supporting structures of the pelvic floor and in the development of urinary incontinence. The goal of this study was to investigate the association between parturition and the morphology and function of perineal and pelvic muscles in the female rabbit. In ten nulliparous and ten multiparous same-age females, we investigated morphological, histological (n = 5 females/group), and contractile characteristics (n = 5 females/group) of the perineal bulbospongiosus (Bsm) and the pelvic pubococcygeus (Pcm) muscles. Bsm and Pcm muscles of multiparous females were significantly lighter, they had a smaller cross-sectional fiber area, and developed significantly lower twitch and tetanic tension force in response to electrical stimulation than muscles of nulliparous females. In female rabbits, multiparity is associated with potentially pathological changes in the morphological and functional characteristics of these perineal and pelvic muscles, possibly as a result of stretching during parturition.

Fiber type composition of pubococcygeus and bulbospongiosus striated muscles is modified by multiparity in the rabbit

“…We found a significant reduction in the percentage of fast type fibers in the Pc muscle accompanied with an increase in the percentage of intermediate fibers. This is supported by the observations reported by Fajardo and collaborators (2008), which found a significative reduction in the contractile force developed by the Pc muscle during a single twitch or tetanus . The proper contractile function of the Pc muscle and activation during the micturition process could require a relative proportion of a particular type of muscle fibers with predominance of oxidative metabolism, which changes after multiparity.…”

“…Our results may indicate that the percentages of fast, intermediate, and slow fibers in Bs and Pc muscles of multiparous rabbits are different than those determined in nulliparous female rabbits. Such a finding matches with alterations in morphometry, single twitch contractile force, and the pattern of muscle activation during micturition in female rabbits …”

“…Previous studies in this model have reported that multiparity alters the reflex activity of the Pc and Bs muscles during the induced micturition . Besides plausible neurological alterations, it is clear that multiparity affects the morphometry of these muscles and reduces their contractile force . Some of such effects are indeed coincident with biochemical and molecular markers indicating the occurrence of ongoing particular damage‐repair processes in the Pc and Bs muscles in multiparous rabbits .…”

Components of the neural circuitry of the vaginocavernosus reflex in rabbits

“…In contrast, large motoneurons innervating the Bcm could be responsible for the short duration response of the muscle. Moreover, in agreement with the finding that this muscle has only a small proportion of small-diameter motoneurons, it has been reported that the Bcm in female rabbits has only 9% of type I fibers (Fajardo et al, 2008).…”

The Role of Pelvic and Perineal Muscles in Reproductive and Excretory Functions

“…In the female rabbit, the morphology of pelvic and perineal muscles is different (Fajardo et al, 2008). The Pcm is heavier and longer than the Bsm.…”