Signs of damage in pelvic floor muscles at the end of pregnancy in rabbits

Shift from Pro- to Anti-Inflammatory Phase in Pelvic Floor Muscles at Postpartum Matches Histological Signs of Regeneration in Multiparous Rabbits

Background and Objectives: Pelvic floor muscles (PFM) play a core role in defecation and micturition. Weakening of PFM underlies urogynecological disorders such as pelvic organ prolapse and stress urinary incontinence. Vaginal delivery damages PFM. Muscle trauma implies an inflammatory response mediated by myeloid cells, essential for subsequent recovery. Molecular signaling characterizing the pro-inflammatory phase shifts M1 macrophages to M2 macrophages, which modulate muscle repair. The present study aimed to evaluate histological characteristics and the presence of M1 and M2 macrophages in bulbospongiosus (Bsm) and pubococcygeus muscles (Pcm). Materials and Methods: Muscles from young nulliparous (N) and multiparous rabbits on postpartum days three (M3) and twenty (M20) were excised and histologically processed to measure the myofiber cross-sectional area (CSA) and count the centralized myonuclei in hematoxylin-eosinstained sections. Using immunohistochemistry, M1 and M2 macrophages were estimated in muscle sections. Kruskal-Wallis or one-way ANOVA testing, followed by post hoc tests, were conducted to identify significant differences (p < 0.05). Results: The myofiber CSA of both the Bsm and Pcm of the M3 group were more extensive than those of the N and M20 groups. Centralized myonuclei estimated in sections from both muscles of M20 rabbits were higher than those of N rabbits. Such histological outcomes matched significant increases in HLA-DR immunostaining in M3 rabbits with the CD206 immunostaining in muscle sections from M20 rabbits. Conclusions: A shift from the pro- to anti-inflammatory phase in the bulbospongiosus and pubococcygeus muscles of multiparous rabbits matches with centralized myonuclei, suggesting the ongoing regeneration of muscles.

Multiparity Reduces Urethral and Vaginal Pressures Following the Bulboglandularis Muscle Stimulation in Rabbits

Unlike male mammals showing a well-delimited external urethral sphincter, female mammals have urogenital sphincters shaped by muscles like the urethrovaginal sphincter. Childbirth-related injuries affect morphometry and function of urogenital sphincters in women, which frequently underlies pelvic floor disorders, including stress urinary incontinence and pelvic organ prolapse. The bulboglandularis muscle (Bgm) seems to shape a urogenital sphincter in rabbits. We determined herein the effect of multiparity on urethral and vaginal pressures generated by the Bgm stimulation in age-matched nulliparous and multiparous chinchilla-breed rabbits to stimulate the Bgm with trains of ascending frequencies (from 1 to 100 Hz; 4 s duration each). Subsequently, the Bgm was excised, measured in width, and weighed. Significant differences (P ≤ 0.05) were determined with Mann-Whitney U or Student t-tests or repeated measures two-way ANOVA followed by Tukey tests. Spearman's partial coefficients were calculated to investigate the correlation between the highest pressure (urethral or vaginal) and the Bgm width. Multiparity reduced the weight and the width in the Bgm origin and medial regions. Urethral and vaginal pressures increased in response to the electrical stimulation of Bgm with frequencies from 20 to 100 Hz. Multiparas showed significant reductions in both types of pressures. We detected a strong correlation (conditioned by multiparity) between the medial Bgm width and the highest vaginal pressure. Our present findings demonstrate that multiparity impairs the function of Bgm, resulting in diminished urethral and vaginal pressures. Furthermore, the significant narrowness of the Bgm was correlated with the vaginal pressure recorded.

Ultrasound monitoring of pregnancy in mini-lop rabbits

Ultrasound plays a considerable role in human and animal reproduction in terms of early detection of pregnancy, prediction of parturition time, and diagnosis of fetal abnormalities. The present study aimed to evaluate the ultrasound implementation for monitoring of gestation in mini-lop rabbits. Fifteen heads of pubertal does were selected and kept in normal conditions of feeding and temperature. Animals were mated with three bucks from the same breed. The pregnancy monitoring was begun from five days post-mating (dpm) to kindling using a 12.5 MHz ultrasonic transducer. The examinations were performed at fixed dpm for all does (5, 7, 12, 16, 20, and 26). Furthermore, randomly selected does (2-3 does per day; one doe was fixed) were subjected to daily ultrasound examination to estimate the relationship between the ultrasound biometrics with the gestational age (GA) and days to parturition. The pregnancy rate was 80%, and the mean number of live kits at birth was 4.2 in the present study. Based on the ultrasound records, the gestation length can be divided into three tertiles of pregnancy (TOP) in rabbits. The first TOP (0-10 dpm) was monitored by detecting and measuring the gestational sac diameter from 6 to 10 dpm. The 2nd TOP (11-12 dpm) was characterized by detection and measurement of Crown Rump Length and Fetal Heart Rate. From 15 to 20 dpm, bi-parietal diameter and head circumference were positively correlated with the GA (p-value < 0.05). Abdominal circumference and femur length were detectable and measurable during the 3rd TOP (21 dpm-kindling). Pregnancy was detected as early as six dpm with acceptable markers in mini-lop rabbits. Highly significant negative correlations were detected between days to parturition and the sonographic biometrics. Three abnormal fetuses were successfully detected and described, too.

The Expression of Hormone Receptors as a Gateway toward Understanding Endocrine Actions in Female Pelvic Floor Muscles

OBJECTIVE

To provide an overview of the hormone actions and receptors expressed in the female pelvic floor muscles, relevant for understanding the pelvic floor disorders.

METHODS

We performed a literature review focused on the expression of hormone receptors mainly in the pelvic floor muscles of women and female rats and rabbits.

RESULTS

The impairment of the pelvic floor muscles can lead to the onset of pelvic floor dysfunctions, including stress urinary incontinence in women. Hormone milieu is associated with the structure and function alterations of pelvic floor muscles, a notion supported by the fact that these muscles express different hormone receptors. Nuclear receptors, such as steroid receptors, are up till now the most investigated. The present review accounts for the limited studies conducted to elucidate the expression of hormone receptors in pelvic floor muscles in females.

CONCLUSION

Hormone receptor expression is the cornerstone in some hormone-based therapies, which require further detailed studies on the distribution of receptors in particular pelvic floor muscles, as well as their association with muscle effectors, involved in the alterations relevant for understanding pelvic floor disorders.