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Is there a nitrergic modulation of the rat external anal sphincter?
MedLine Citation:
PMID:  22872659     Owner:  NLM     Status:  Publisher    
Nitric oxide (NO) is known to relax the internal anal sphincter (IAS), but its effect on the external anal sphincter (EAS) is unknown. The aim of this study was to investigate if there is a nitrergic nerve plexus that modulates the EAS, similar to that found in oesophageal striated muscle. An in vitro ring preparation of rat anal canal was used to evaluate the effects of the nitric oxide synthase (NOS) inhibitor N(ω)-Nitro-L-Arginine (L-NNA) and the NO donor sodium nitroprusside (SNP) on the EAS under conditions of neuromuscular blockade and the effect of the NO donor SNP on nerve-evoked contractions. Immunohistological experiments were conducted to determine if the neuronal isoform of NO synthase (nNOS) is present in the EAS. During direct muscle stimulation neither L-NNA (p = 0.32) nor SNP (p = 0.19) significantly changed the EF50, which is the frequency at which 50% of maximal contraction is reached, compared to a time dependent control. Nerve evoked contractions were also not altered by addition of SNP to the tissue bath. Immunohistohistological experiments clearly showed co-localisation of nNOS positive nerve fibres at motor endplates of the oesophagus but not in the EAS. The IAS was richly innervated by nitrergic fibres, but these did not extend into the EAS. In conclusion, there are no nitrergic motor fibres innervating the EAS and neurotransmission at the motor endplates is not affected by NO. And NO does not affect muscle force directly under conditions of neuromuscular blockade. Therefore, there is no evidence, that the EAS contraction is directly modulated by NO or by pudendal nitrergic fibres or diffusion from neighbouring nitrergic plexuses of the anal canal.
Judith Evers; Maria Buffini; Simon Craven; Ronan O'Connell; James F X Jones
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Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-8-7
Journal Detail:
Title:  Experimental physiology     Volume:  -     ISSN:  1469-445X     ISO Abbreviation:  Exp. Physiol.     Publication Date:  2012 Aug 
Date Detail:
Created Date:  2012-8-8     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  9002940     Medline TA:  Exp Physiol     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
1 University College Dublin;
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