EFFECT OF PARTIAL URETHRAL OBSTRUCTION ON FORCE DEVELOPMENT OF THE GUINEA-PIG BLADDER

We created gradual partial urethral obstruction in 20 guinea pigs usin g silver jeweler's jump rings. After 4 or 8 weeks obstruction all anim als underwent cystometry and were assigned to one of five urodynamic c ategories: normal, high pressure voiding, unstable, low compliance, or decompensated. After sacrifice, the contractile responses of bladder strips to electrical field stimulation of intramural nerves, direct el ectrical muscle stimulation, 0.1 mM carbachol, and high K+ solution we re sampled by computer for phase plot analysis. Following 8 weeks obst ruction, the value of the phase plot parameter Fiso, indicative of the number of contractile muscle units, was reduced to 60% of the control response to nerve stimulation (P < 0.05) and to 77% of the control re sponse to carbachol stimulation (P < 0.05). Parameter C, the slope of the phase plot (indicative of unit recruitment during force developmen t), was unchanged for all forms of stimulation. Although in the latter case not statistically significant, obstruction affected responses to nerve and muscle stimulation similarly suggesting that muscle change may possibly be a common denominator of dysfunction. In view of the re duction in Fiso and the increase in bladder weight, instability may re present a more advanced form of dysfunction due to obstruction than hi gh pressure voiding, (C) 1993 Wiley-Liss, Inc.