The phasic contractions of mucosal and denuded detrusor strips in juvenile vs. adult pigs

Bahareh Vahabi1,2, Marcus Drake2. 1University of the West of England, Applied Sciences, BS16 1QY, UK, 2Bristol Urological Institute, Biomed. BS10 5NB, UK

Introduction & Objectives: Phasic contractions (PCs) have been shown to be increased in the overactive bladder and animal models of detrusor overactivity including young animals (1). PCs are perceived to be myogenic in nature and are modulated by activation of various types of receptors (muscarinic, purinergic, and adrenergic) (1). Recently it has become apparent that the mucosa is an active component of the bladder and also plays an important role in mediating the PCs (2). The aim was to study the basal and cholinergic-induced PCs in bladder strips from juvenile vs. adult pigs and the role of mucosa.

Methods: Longitudinal strips of denuded detrusor or mucosa (composed of the urothelium, lamina propria and a thin layer of smooth muscle (muscularis mucosa)), isolated from juvenile (≈6-weeks old) and adult (≈6-months old) female pig bladders, were mounted in perspex microbaths, superfused with Krebs’ solution and maintained at 37ºC. Isometric tension was measured, via UF1 force transducers connected to a Powerlab using Chart software. Basal PCs were recorded after 60 min of equilibration. Denuded detrusor strips were then superfused constantly for 30min with 0.1µM carbachol (CCh) solution to induce PCs. The amplitude and frequency of basal and CCh- induced PCs were recorded and compared using Student’s unpaired t-test.

Results: Denuded detrusor strips from both juvenile and adult pig bladders did not develop basal PCs. Conversely the mucosal strips from both groups developed PCs. In juvenile pigs the amplitude of basal PCs in mucosal strips (n=21) was significantly (p<0.05) greater than in adult pigs (n=22) (juv. 0.043±0.009 vs. adult 0.020±0.004 g/mg tissue). In contrast the frequency of PCs in juvenile mucosal strips was significantly (p<0.05) lower than adults (juv. 24.38±1.21 vs. adult 29.46±2.00 events in 5min). Stimulating the denuded strips with 0.1µM CCh resulted in development of PCs in both juvenile (n=22) and adult pig (n=24) bladder tissues. However, there was no significant difference in the amplitude and frequency of CCh stimulated PCs between juvenile and adult pig bladder denuded detrusor strips.

Conclusions: Basal PCs were detected in mucosal but not denuded detrusor strips taken from both juvenile and adult pigs. The amplitude of basal PCs in mucosal strips from juvenile pig bladders was significantly greater than that of adult pigs. However, there was no significant difference in amplitude or the frequency of cholinergic stimulated PCs in denuded detrusor strips taken from both groups. Recent studies have demonstrated a role of muscularis mucosa in generation and regulation of PCs in the guinea pig urinary bladder (2). This may also apply to the pig urinary bladder, hence the detection of basal PCs in mucosal but not the denuded strips. Alteration in the properties of muscularis mucosa as a result of ageing may explain the differences seen in the amplitude of PCs in juvenile vs. adult pigs.

1) Ng et al (2006) Am J Physiol Regul Integr Comp Physiol. 291:R1049-R1059

2) Heppner et al (2011) Am J Physiol Regul Integr Comp Physiol. 301:R362-R351