H. Henry Lai, Nelson Salas, Christopher P. Smith, Timothy B. Boone, George T. Somogyi

Scott Department of Urology, Baylor College of Medicine, Houston, TX.

Objective: To investigate the plasticity of non-adrenergic, non-cholinergic (NANC) contractions of the normal rat bladder and spinal cord injured (SCI) bladder in the presence of the cholinergic receptor agonist, carbachol.

Methods: Bladder strips were harvested from normal female Sprague-Dawley rats and from age-matched SCI rats 4 weeks after L6 spinal cord transection. The strips were stimulated electrically (20 Hz) to estimate baseline isometric contractions. In one group, 10 mM carbachol was added prior to 500 nM 4-DAMP (a selective muscarinic receptor antagonist). In the other group, no carbachol was added prior to 500nM 4-DAMP. The residual NANC contractions that remained after 4-DAMP administration (expressed as %, residual divided by baseline) were compared in the presence and absence of carbachol pre-treatment.

Results: In normal rat bladder, carbachol decreased the NANC contractions from 74.6±5.0% (no pre-treatment) to 32.0±3.2% (pre-treatment), p<0.0001. In SCI rat bladder, carbachol decreased the NANC contractions even more, from 78.5±21.9% (no pre-treatment) to 13.1±5.6% (pre-treatment), p=0.04. The muscarinic antagonist 4-DAMP became more effective after the bladder was treated with carbachol. This carbachol-induced plasticity was more pronounced in SCI bladder versus normal bladder (13.1±5.6% versus 32.0±3.2%, p=0.006). This observation suggested that cholinergic stimulation (carbachol) inhibited purinergic contractions (the main component of NANC). This plasticity may be mediated through interaction between cholinergic and purinergic receptors.

Conclusion: The NANC contractions of normal and SCI rat bladder is not constant, but is plastic and can be modulated by cholinergic agonist (carbachol).

UroToday.com Coverage of SUFU 2007

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