The assessment of rat ureteral pressure generation in vitro: regional heterogeneity and influence of distending pressure

Contraction of ureteral smooth muscle drives the urine bolus to the urinary bladder for storage prior to micturition. This study describes a novel approach to the measurement of ureteral pressure generation in vitro and the influence of distending pressure on acetylcholine-stimulated ureteral lumenal pressure generation. Isolated segments of ureters obtained from Wistar rats were pressurised in a blind-ended sac arrangement and contractile responses were recorded as phasic oscillations in ureteral luminal pressure. Distal segments generated greater luminal pressures than proximal segments (p<0.001) in response to acetylcholine. Increasing baseline distending pressures in the range 2-10 mmHg in proximal segments was associated with greater frequency of contraction (p<0.001) and decreased magnitude of contraction (p<0.001) when expressed as % maximum response. Nifedipine (10(-5) M) or removal of extracellular Ca2+ abolished the contractions. Isometric contractile responses of ureteral ring preparations were not significantly influenced by pretensions equivalent to distending pressures in the range 2-10 mmHg. This is the first study to fully establish the influence of baseline ureteral distending pressure upon ureteral luminal pressure generation in vitro and demonstrates regional heterogeneity of ureteral contractile responses. It is suggested that this experimental approach may be a useful methodology for the investigation of ureteral function during urinary outflow obstruction.