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Animal models for pelvic organ prolapse: systematic review
Marina Gabriela M C Mori da Cunha1,2, Katerina Mackova1,2,3, Lucie Hajkova Hympanova3
1Centre for Surgical Technologies, Group Biomedical Sciences, KU Leuven, Leuven, Belgium.
This review examines how various animal models have been used to study the causes of pelvic organ prolapse. Researchers analyzed 51 studies to understand how factors like pregnancy, childbirth, aging, and menopause affect pelvic floor health. While some models show specific structural changes, no single animal model perfectly replicates the human condition. The findings highlight the need for more standardized research methods to better understand this complex disorder.
Area of Science:
- Pelvic organ prolapse research within reproductive medicine
- Comparative physiology and animal models
Background:
The biological mechanisms driving pelvic organ prolapse remain poorly defined due to limited human clinical data. That uncertainty drove researchers to rely on diverse animal subjects to investigate potential risk factors. Prior research has shown that pregnancy and childbirth are major contributors to pelvic floor dysfunction. However, the lack of standardized experimental protocols has hindered the translation of findings from animals to humans. No prior work had resolved how different species respond to hormonal shifts associated with menopause. This gap motivated a comprehensive evaluation of existing literature to determine the validity of current models. Investigators needed to synthesize scattered evidence to guide future experimental designs. Establishing a clear baseline for these models is necessary to improve our understanding of this condition.
Purpose Of The Study:
The aim of this study was to summarize existing knowledge regarding the pathogenesis of pelvic organ prolapse as generated through animal models. Researchers sought to identify which species are currently utilized to investigate known risk factors. The team focused on variables such as pregnancy, labor, delivery, parity, aging, and menopause. This investigation was motivated by the need to understand how these factors contribute to pelvic floor damage. No prior work had successfully synthesized the scattered data across different species to evaluate model validity. That uncertainty drove the authors to conduct a comprehensive narrative review of the available literature. They intended to determine if these models accurately reflect human disease progression. This effort provides a foundation for future researchers to select appropriate subjects for studying pelvic floor health.
Main Methods:
The review approach involved a systematic search of MEDLINE, Embase, Cochrane, and Web of Science databases. Investigators screened 7426 potential records to identify relevant studies focusing on pelvic floor dysfunction. Fifty-one articles met the inclusion criteria for this synthesis. The team evaluated how various risk factors, including parity and menopause, were tested in different species. They assessed the structural and physiological outcomes reported in each selected publication. The design focused on extracting data related to pregnancy, labor, and aging. Researchers categorized findings by species to compare responses to these specific challenges. This narrative strategy allowed for the integration of diverse experimental results despite significant variations in study design.
Main Results:
Key findings from the literature indicate that pregnancy exerts a consistent, measurable effect on pelvic floor tissues across multiple species. In rat models, simulated vaginal delivery induces persistent damage to the vaginal muscular layer and microvasculature. Sheep demonstrate altered vaginal compliance after their first delivery, although the effects of subsequent births remain inconsistent. Squirrel monkeys are the only species identified that can develop spontaneous prolapse, particularly after levator ani denervation. Because animals do not undergo natural menopause, ovariectomy is utilized to simulate this state. The timing of this procedure and the interval until measurement significantly influence the observed outcomes. Several species show increased collagen content following long-term induced menopause. Rodents exhibit minimal age-related changes beyond variations in elastin, while no usable data exists for other species.
Conclusions:
The authors suggest that pregnancy consistently impacts pelvic floor structures across various species. Simulated vaginal delivery in rats causes lasting damage to muscular layers and blood vessels without triggering full prolapse. Evidence from sheep indicates that initial delivery alters vaginal compliance, though subsequent births yield mixed results. Squirrel monkeys represent a unique model capable of developing spontaneous prolapse, especially following levator ani muscle denervation. Researchers note that induced menopause via ovariectomy serves as a proxy for human aging in these studies. Long-term collagen content changes appear linked to menopause in several species, whereas rodents primarily exhibit elastin variations. The synthesis indicates that current models provide partial insights rather than a complete replication of human disease. Future efforts should prioritize methodological uniformity to enhance the reliability of these comparative investigations.
Frequently Asked Questions
The researchers propose that levator ani muscle denervation facilitates prolapse in squirrel monkeys that have undergone vaginal delivery. This specific surgical intervention, combined with the stress of birth, allows these primates to develop spontaneous prolapse, unlike other species studied in the literature.
Ovariectomy is the primary tool used to simulate menopause in animal subjects. Because these species do not experience natural reproductive senescence, investigators surgically remove the ovaries to study the hormonal impacts on pelvic floor tissues and collagen levels.
Methodological uniformity was absent across the 51 analyzed studies. This lack of consistency prevented the researchers from performing a meta-analysis, forcing them to present the data as a narrative review instead of a statistical synthesis of the findings.
Pregnancy serves as a consistent variable across species, showing measurable effects on pelvic floor health. In contrast, the impact of additional deliveries in sheep remains inconsistent, demonstrating that the number of births does not always correlate with predictable structural changes.
In rodents, researchers observed no significant effects of aging beyond changes in elastin. Conversely, other species showed measurable increases in collagen content following induced menopause, highlighting a distinct difference in how different animal models respond to the aging process.
The authors state that current animal models do not perfectly replicate human pelvic organ prolapse. They emphasize that while these subjects provide insights into specific risk factors, they should be interpreted as partial representations of the complex human condition.
