Changes in Contractile Properties in Hypertrophic Rat Urinary Bladder

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Abstract
Hypertrophy was induced in female rat urinary bladders by partial obstruction of the urethra. After 6 wk the bladder weight had increased almost 7-fold compared to the matched controls. At this stage the animals were anesthetized and the pelvic nerves stimulated bilaterally at different bladder volumes. Isovolumetric pressures were measured by means of a catheter inserted via the urethra. For control (C) bladders maximum active pressure (104 .+-. 11 cm H2O, n = 5) was attained with 0.10 ml content. For volumes above this a rapid progressive decrease in active pressure was noted. For hypertrophic (H) bladders maximum active pressure (92 .+-. 14 cm H2O, n = 6) was reached at 0.50 ml. Further filling decreased active pressure only slightly. By use of the law of Laplace the volume-active pressure relations were transformed to radius-force curves. The maximum active stress was similar for C and H bladders. The radius-force relation for H bladders was shifted to the right compared to the C curve (optimum radius for active force: C: 0.4 cm, H: > 0.9 cm.). This shift, responsible for the decreased ability to pressure production of the H bladders at small volumes indicates a dramatic remodeling of the smooth muscle in the hypertrophic bladder wall.