Changes in contractile properties in hypertrophic rat urinary bladder.
Hypertrophy was induced in female rat urinary bladders by partial obstruction of the urethra. After 6 weeks 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: greater than 0.9 cm.). This shift, responsible for the decreased ability to pressure production of the H bladders at small volumes indicates a dramatic remodelling of the smooth muscle in the hypertrophic bladder wall.
D000818:Animals; D005260:Female; D006984:Hypertrophy; D009119:Muscle Contraction; D009130:Muscle, Smooth / Q000503:physiopathology*; D011312:Pressure; D051381:Rats; D011919:Rats, Inbred Strains; D014524:Urethral Obstruction / Q000209:etiology; D001743:Urinary Bladder / Q000473:pathology / Q000503:physiopathology*