Smooth muscle contractions in the urinary bladder: Alterations between juvenile and adult detrusor and the influences of G protein-coupled receptor stimulation

Introduction: The prevalence of bladder contractile disorders increases with older age, and the mechanisms within the urinary bladder tissue that are altered remain unknown. There is the potential for dysfunction to be due to receptor changes within the different layers of the urinary bladder (Phelps et al., 2023). Of particular interest is the detrusor smooth muscle which provides the main contractile force during voiding, and as such, variations in this muscle could present in cases of overactive or underactive bladder (Moro et al., 2021).

Aim: This study will identify if there are alterations to G protein-coupled receptor (GPCR) activation pathways for urinary bladder detrusor contractions between juvenile and adult tissues.

Methods: Porcine urinary bladders from Large White-Landrace-Duroc cross-bred pigs were used as the tissue in this study. Juvenile samples were taken from prepubescent pigs (6 months old, 80kg live weight) and adult samples from sow pigs (2-3 years old, 200kg live weight). Strips of detrusor smooth muscle were dissected and mounted in functional organ baths containing Krebs-Henseleit bicarbonate solution at 37°C and gassed with carbogen (95% O2, 5% CO2). Tissue contractions (grams) were recorded before and after the addition of a single dose of GPCR agonist in the absence and presence of selective inhibitors of extracellular Ca2+ influx, intracellular Ca2+ release, or Rho kinase. An unpaired Student’s two-tailed t-test was used to compare responses between juvenile and adult detrusor smooth muscle. Ethical approval was not required for this study as tissues were sourced from the local abattoir after slaughter for the routine commercial provision of food.

Results: Urinary bladder detrusor smooth muscle from both juvenile and adult animals contracted in response to a single dose application of muscarinic receptor agonist carbachol (1µM), histamine (100µM), 5-HT (100µM), neurokinin-A (300nM), prostaglandin-E2 (PGE2, 10µM), and angiotensin-II (ATII, 100nM). Younger tissue was more sensitive to stimulation with histamine, whereas adult tissue was more sensitive to stimulation by 5-HT, PGE2, and ATII. Inhibition of extracellular Ca2+ entry into the tissue or blocking the Rho kinase pathway impacted all contractions, with no difference between juvenile and adult detrusor. Impairment of intracellular Ca2+ release inhibited contractile responses to PGE2 in the adult detrusor, but not in the juvenile detrusor.

Conclusions: The age-related variations in responses to agonist stimulation may provide insights into potential systems that could contribute to dysfunction in urinary bladder contraction.