The guinea pig as a model of gradual urethral obstruction.

We developed a new model of partial urethral obstruction using the guinea pig. We placed jeweler's jump rings loosely around the proximal urethra of immature guinea pigs and allowed the obstruction to develop gradually as the animal grew. After four or eight weeks of obstruction, we studied the filling and emptying characteristics of the bladder during continuous repetitive cycling under urethane anesthesia. Following this examination, bladders were removed and weighed. Wet weight was compared to urodynamic findings. We identified four abnormal urodynamic patterns: high pressure voiding, instability, poor compliance and decompensation. All obstructed bladders showed weight gain associated with muscle hypertrophy, but the degree of weight gain was different for each of the various urodynamic categories. High pressure voiding was associated with the least weight gain, whereas instability and decompensation showed the most weight gain. The results are consistent with a thesis that partial urethral outlet obstruction in the guinea pig gives rise to several distinct forms of abnormal voiding characterized by high pressure in the early stages, and progressing to more advanced forms of dysfunction characterized by instability and decompensation in the later stages.