Murine Live Bladder Tissue Model to Study the Microvasculature Properties and Function In Situ

Regulation of microvascular blood flow in the bladder has historically been associated with regulation by pre-capillary arterioles and more recently to post-capillary venules. Although pericytes are known to regulate capillary vessel diameter in various capillary beds (e.g. brain, retina, heart and kidney), their role in regulating bladder capillary diameter remains controversial.

We have developed a mouse full-thickness live bladder tissue model in which the microvasculature of the mucosa can be visualised in situ, enabling the regulation of suburothelial capillary diameter to be investigated. Bladder tissue viability was first investigated by fluorescence imaging of tissue labelled with Hoechst and propidium iodide to determine the live to dead cell ratio. Data indicated that tissue was viable in situ for up to 5 hours (>60%; P>0.05; n = 3 per time point). Real time DIC images of live tissue sections were collected for all experiments in which live tissue was exposed to vasoactive agents to investigate the pericyte-mediated regulation of capillary diameter. Images were analysed off line and vessel diameter was measured at both pericyte and non-pericyte sites along a capillary for each experiment. Angiotensin II (100 nM) and endothelin I (1 nM) evoked a pericyte-mediated vasoconstriction of suburothelial capillaries at pericyte sites (13.3 ± 5.8%, 22.0 ± 9.7%) that was significantly greater (p<0.05, n = 6 per drug) than that measured at non-pericyte sites (3.2 ± 2.7%, 6.0 ± 3.4%). Prostaglandin E2 (30 μM) evoked a pericyte-mediated dilation of capillaries (12.1 ± 2.6%) that was significantly greater than that measured at non-pericyte sites (2.3 ± 2.3%, p = 0.03, n = 3).

In this study we therefore demonstrate that suburothelial capillary pericytes act to regulate capillary diameter in response to agents previously reported to regulate capillary beds of other organs. This indicates that in addition to smooth muscle-mediated regulation of upstream vessels in the bladder, spatial regulation of capillary diameter downstream of these vessels also occurs in the bladder.