title: A comparative study of structure and function of the longitudinal muscle of the anal canal and the internal anal sphincter in pigs.
abstract: OBJECTIVE
  This study aims to compare the physiology of the longitudinal muscle of the anal canal with the internal anal sphincter in pigs.
  
  
  METHODS
  Histology and in vitro studies were performed to compare the effect of neural responses induced by electric stimulation and through nicotinic, purinergic, and serotoninergic receptors.
  
  
  RESULTS
  The longitudinal muscle and the internal anal sphincter are constituted exclusively by smooth muscle. Strips from the internal anal sphincter a) developed myogenic tone; b) responded to electric stimulation with an "on" relaxation antagonized by nitric oxide synthase inhibitors and purinergic P2Y1 antagonists, and with an "off" contraction antagonized by atropine and phentolamine; and c) responded to stimulation of nicotinic receptors with a relaxation antagonized by nitrergic and purinergic P2Y1 antagonists, responded to stimulation of serotoninergic 5-hydroxytryptamine 3 receptors with a contraction, and relaxed to carbachol and purinergic P2X agonists. Strips from the longitudinal muscle a) did not develop tone, b) responded to electric stimulation with an "on" contraction antagonized by atropine, and c) did not respond to stimulation of nicotinic or serotoninergic 5-hydroxytryptamine 3 receptors, and carbachol and purinergic P2X agonists induced a contraction.
  
  
  CONCLUSIONS
  The motility of the internal anal sphincter includes myogenic tone, relaxation mediated by nitric oxide and purinergic P2Y1 receptors, and contraction mediated by cholinergic motor neurons and sympathetic fibers. The motility of the longitudinal muscle is limited to a contraction mediated by cholinergic neurons, suggesting that longitudinal muscle contracts during relaxation of the internal sphincter, shortening the anal canal. Nicotinic, muscarinic, and serotoninergic receptors might be therapeutic targets for anal motor disorders.
authors: Department of Surgery, Hospital de Mataró, Universitat Autònoma de Barcelona, 08304, Mataró, Spain.
authors: Alvaro
authors: A
authors: Opazo
authors: Begoña
authors: B
authors: Lecea
authors: Carme
authors: C
authors: Admella
authors: Maria José
authors: MJ
authors: Fantova
authors: Marcel
authors: M
authors: Jiménez
authors: Joan
authors: J
authors: Martí-Ragué
authors: Pere
authors: P
authors: Clavé
mesh_terms: D000244:Adenosine Diphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D001003:Anal Canal / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D000704:Analysis of Variance; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D004558:Electric Stimulation; D008297:Male; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000294:innervation / Q000502:physiology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D009599:Nitroprusside / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide / Q000494:pharmacology; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000502:physiology; D011985:Receptors, Serotonin / Q000187:drug effects / Q000502:physiology; D013552:Swine; D013873:Thionucleotides / Q000494:pharmacology
chemical_list: D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D011976:Receptors, Muscarinic; D011978:Receptors, Nicotinic; D011985:Receptors, Serotonin; D013873:Thionucleotides; D009599:Nitroprusside; C030812:adenosine 5'-O-(2-thiodiphosphate); D000244:Adenosine Diphosphate; D001285:Atropine; D002217:Carbachol; D019001:Nitric Oxide Synthase; D010646:Phentolamine