Abstract
Background
In early fetal life, the bladder is merely a conduit allowing urine to pass through freely into the amniotic cavity. As the striated external urethral sphincter evolves, the bladder acquires its reservoir and voiding functions. We characterized the myogenic and neurogenic contractions of the normal fetal porcine bladder from midterm until close to full-term gestation.
Methods
Contractile responses were measured in vitro using bladder strips from fetuses at 60 (N=23) and 100 days (N=21) of gestation. Spontaneous activity, and the responses to potassium chloride (KCl) solution, electrical field stimulation (EFS), and receptor activation were recorded. The smooth muscle content was evaluated histologically.
Results
Histological studies revealed that the fractional content of smooth muscle doubled between the two time points, and passive tension was adjusted to take that into account. Spontaneous activity was regular at 60 days, changing toward an irregular pattern at 100 days. Contractile force elicited by KCl and carbachol increased significantly with gestational age, while contractions to the purinergic agonist, α–β-methylene adenosine 5′-triphosphate did not. The responses to EFS were almost completely blocked by atropine.
Conclusion
Spontaneous myogenic contractions become irregular and contractile responses to muscarinic receptor stimulation increase during gestation, as the bladder reservoir and voiding functions develop.
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Acknowledgements
We highly appreciate the technical assistance from the laboratory technician Kristina Lystlund Lauridsen in the processing of histological examinations, and the assistance from Simon Gabriel Comerma Steffensen and Yutao Lu during the in vitro studies. Performing and interpreting the FFT would not have been possible without the kind help from the engineer, Martin Nors Skov, and a professor in physics, Michael Pedersen.
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This study was supported by a grant from the Lundbeck Foundation.
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Jakobsen, L., Trelborg, K., Simonsen, U. et al. Development of contractile properties in the fetal porcine urinary bladder. Pediatr Res 83, 148–155 (2018). https://doi.org/10.1038/pr.2017.181
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DOI: https://doi.org/10.1038/pr.2017.181
