Development of contractile properties in the fetal porcine urinary bladder

• Published in: Pediatric research Vol. 83; no. 1; pp. 148 - 155
• Main Authors: Jakobsen, Lotte K, Trelborg, Karina F, Simonsen, Ulf, Andersson, Karl-Erik, Olsen, L H
• Format: Journal Article
• Language: English
• Published: New York Nature Publishing Group US 01-01-2018; Nature Publishing Group
• Subjects: 631/136; 631/57/343/1667; 692/4025/1334; Adenosine Triphosphate - analogs & derivatives; Adenosine Triphosphate - physiology; Animals; basic-science-investigation; Bladder; Electromagnetic Fields; Female; Fetuses; In Vitro Techniques; Isometric Contraction - physiology; Male; Medicine; Medicine & Public Health; Muscle Contraction - physiology; Muscle Development; Muscle, Smooth - embryology; Muscle, Smooth - physiology; Neonatal care; Pediatric Surgery; Pediatrics; Potassium Chloride - chemistry; Pregnancy; Pregnancy, Animal; Receptors, Purinergic - physiology; Smooth muscle; Stress, Mechanical; Swine; Urinary Bladder - embryology; Urinary Bladder - physiology
• ISSN: 0031-3998; 1530-0447
• DOI: 10.1038/pr.2017.181

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
S
pontaneous myogenic contractions become irregular and contractile responses to muscarinic receptor stimulation increase during gestation, as the bladder reservoir and voiding functions develop.