Investig Clin Urol.  2016 Jul;57(4):249-259. 10.4111/icu.2016.57.4.249.

Progressive changes in detrusor function and micturition patterns with chroinc bladder ischemia

• Zhao Z
• Azad R
• Yang JH
• Siroky MB
• Azadzoi KM

• KMID: 2426502
• DOI: http://doi.org/10.4111/icu.2016.57.4.249

Abstract

PURPOSE
Lower urinary tract symptoms (LUTS) are bothersome constellation of voiding symptoms in men and women as they age. Multiple factors and comorbidities are attributed to this problem but underlying mechanisms of nonobstructive nonneurogenic detrusor overactivity, detrusor underactivity and LUTS remain largely unknown. Our goal was to characterize detrusor function and voiding patterns in relation to muscarinic receptors expression, nerve fiber density, and neural ultrastructure in chronic bladder ischemia.
MATERIALS AND METHODS
Iliac artery atherosclerosis and bladder ischemia were produced in male Sprague-Dawley rats. At 8 and 16 weeks after ischemia, micturition patterns and cystometrograms were recorded in conscious rats then bladder blood flow and nonvoiding spontaneous contractions were measured under general anesthesia. Bladder tissues were processed for Western blotting, immunostaining, and transmission electron microscopy.
RESULTS
Bladder responses to ischemic insult depended on the duration of ischemia. Micturition patterns and cystometric changes at 8-week ischemia suggested detrusor overactivity, while voiding behavior and cystometrograms at 16-week ischemia implied abnormal detrusor function resembling underactivity. Upregulation of muscarinic M2 receptor was found after 8- and 16 weeks of ischemia. Downregulation of M3 and upregulation of M1 were detected at 16-week ischemia. Neural structural damage and marked neurodegeneration were found after 8 and 16 weeks of ischemia, respectively.
CONCLUSIONS
Prolonged ischemia may be a mediating variable in progression of overactive bladder to dysfunctional patterns similar to detrusor underactivity. The mechanism appears to involve differential expression of M1, M2, and M3 receptors, neural structural injury, and progressive loss of nerve fibers.

Keyword

Contraction; Ischemia; Urinary bladder; Urination

MeSH Terms

Animals
Axons/ultrastructure
Chronic Disease
Disease Progression
Ischemia/metabolism/pathology/*physiopathology
Male
Microscopy, Electron
Muscle Contraction/physiology
Nerve Fibers/pathology
Rats, Sprague-Dawley
Receptors, Muscarinic/metabolism
Regional Blood Flow/physiology
Urinary Bladder/*blood supply/innervation/metabolism/physiopathology
Urinary Bladder, Overactive/metabolism/pathology/*physiopathology
Urination/*physiology

Figure

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  Fig. 1 Cystometrograms with intravesical infusion of saline at 150 µL per minute in conscious rats. Voiding bladder contractions, micturition frequency and voided volumes are shown at 8- and 16-week bladder ischemia versus sham controls. Changes in intravesical pressure and micturition patterns consistent with bladder overactivity and changes resembling detrusor underactivity were evident in the 8- and 16-week ischemic bladders, respectively.

• 

  Fig. 2 Cystometrograms in anesthetized rats with constant intravesical volume of 0.8 mL without saline infusion. After 8-week ischemia, increased fluctuations in intravesical pressure similar to detrusor overactivity were present. After 16-week ischemia, the bladder tended to contract frequently but produced little changes in intravesical pressure, suggesting frequent contractile activities of reduced strength.

• 

  Fig. 3 Western blotting of muscarinic receptors in 8-week ischemic bladders versus sham. A significant increase in muscarinic M2 receptor expression was found after 8-week bladder ischemia compared with sham control. Both M1 and M3 expression showed a tendency to increase after 8 weeks ischemia but did not reach significance.

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  Fig. 4 Western blotting of muscarinic receptors in 16-week ischemic bladders versus sham. After 16-week bladder ischemia, in addition to M2 upregulation, a significant increase in M1 expression and significant decrease in M3 expression were found compared with corresponding sham controls.

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  Fig. 5 Transmission electron microscopy of nerve bundles after 8- (C) and 16-week (D) bladder ischemia are shown versus corresponding sham controls (A and B, respectively). Disrupted axonal ultrastructures after 8-week bladder ischemia and swollen degenerating axons with considerable connective tissue proliferation around the nerve bundles are shown after 16-week bladder ischemia (×9,300).

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  Fig. 6 Immunoreactive nerve fibers in the ischemic (C and D) and sham control (A and B) bladder tissues are shown at ×400 magnifications. Progressive decrease in neural density was evident with increasing duration of ischemia. The number of immunopositive nerves decreased after 8-week bladder ischemia but did not reach significance. After 16-week bladder ischemia, immunoreactive nerve fibers density significantly decreased versus sham control. Arrows point to immunopositive nerve fibers. SE, standard error.

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