The effect of heating (37-41°C) on spontaneous and agonist-evoked contractions in rabbit mucosa-intact and denuded preparations

The bladder may be exposed to mild heating from either external devices that deliver microwave therapies for cancer or during fever (1). The aims of this study were to determine if: 1) heating from 37°C to 41°C for 15 minutes decreased spontaneous activity of mucosa-intact bladder; 2) heating had a direct effect on detrusor muscle contractility or activation of motor nerves. All procedures accorded with current UK legislation. Two male and ten female rabbits (4.5±0.6kg) were sacrificed. The urinary bladder was placed in gassed (95% O2/5% CO2) and chilled (4°C) Tyrode’s solution and the ventral wall opened longitudinally. Strips of rabbit mucosa-intact and denuded preparations (approximate length 10 x diameter 2 mm) were mounted in a horizontal superfusion trough and tied to an isometric tension transducer connected to bridge amplifier. A thermocouple (0.2 mm diameter) was inserted into the sub-urothelial layer, and the preparation stretched to 20 mN resting tension. For mucosa-intact strips a heating device was positioned <5 mm above the mucosa, perpendicular to the preparation and calibrated prior to the experiment. Denuded mucosa preparations were exposed to electrical field stimulation (EFS: 0.1 ms pulses, 8 Hz) or 0.1 µM carbachol whilst the Tyrode’s solution was heated from 37°C to 41°C and back down to 37°C. Spontaneous contraction amplitude and frequency were measured during 15 minute heat exposures. Data are medians [25, 75% quartiles], data sets were compared by ANOVA, with Bonferroni post-hoc tests, the null hypothesis was rejected at p