Abstract
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<0.05. During 15 minutes of exposure to 41°C the mucosa-intact preparations exhibited significantly reduced spontaneous contraction amplitude (83 [48,94]%) when compared to control preparations maintained at 37°C (94 [83,119]%). Post-heating, the amplitude of spontaneous contractions returned to control within 30 minutes. During this recovery period there was a reduction in the frequency of contractions in the heated preparations in comparison to the control preparations. Carbachol (0.1 µM) generated a rise in contraction tone of denuded preparations at 37°C and 41°C (n=5). The magnitude of the carbachol-induced contractions was significantly reduced at 41°C (0.7 [0.1, 1.3] mN) compared to control at 37°C (1.1 [0.3, 3.1] mN) and recovered completely on return to 37°C. (1.3 [0.4, 2.9] mN). The EFS contraction amplitude did not significantly alter during and post-heating, indicating there was no evidence of nerve block. Mild local heating suppressed spontaneous activity of mucosa-intact tissue and global heating suppressed carbachol (0.1µM)-induced contraction of denuded tissue. These data suggest that mild heating affects both detrusor contractility and mucosal-dependent mechanisms that generate spontaneous contractile activity. (1) Stelfox HT, Straus SE, Ghali WA, Conly J, Laupland K, Lewin A. (2010) Temporal Artery versus Bladder Thermometry during Adult Medical-Surgical Intensive Care Monitoring: An Observational Study. BMC anaesthesiology, 10:13.