Minipig urethra: a suitable animal model in vitro.

The study demonstrates that the minipig urethra is an appropriate animal model for in vitro experiments and therefore promising for long-term animal tests of artificial urinary sphincter systems in vivo. Freshly explanted porcine and minipig urethras were connected to a fluid reservoir that simulated the bladder pressure. This bladder pressure was adjusted by changing the water level (hydrostatic pressure). Specially designed aluminum sphincters loaded with a fluid-filled container were used to close/open the urethras. Results from minipigs and domestic pigs were compared to data published for human urethras. We measured the leak-point pressures (LPP) by adjusting the bladder pressure at a constant sphincter length and by changing the sphincter length at a constant bladder pressure. Because the urethral tissue shows visco-elastic behavior, LPPs for both opening and closing were measured. By fitting the in vitro data, we evaluated the three characteristic parameters from the empirical urethra compression model, i.e. wall pressure < pW >opening = −(12.9 ± 0.9) cmH2O, < pW >closing = (8.6 ± 1.1) cmH2O, < FR >opening = (0.06 ± 0.02) N, < FR >closing = (0.10 ± 0.02) N, < LR >opening = (3.0 ± 0.3) mm, < LR >closing = (5.1 ± 0.3) mm,and (male) minipig urethras:< pW >opening = −(13.4 ± 0.3) cmH2O, < pW >closing = −(8.6 ± 0.4) cmH2O,< FR >opening = (0.19 ± 0.01) N, < FR >closing = (0.21 ± 0.02) N,< LR >opening = (2.4 ± 0.1) mm, < LR >closing = (3.3 ± 1.0) mm. These {\it in vitro} tests quantified by means of the urethra compression model demonstrate that the minipig (especially the male one) represents a suitable animal model for testing artificial urinary sphincters.