Nitric oxide deficiency in the internal anal sphincter of patients with chronic anal fissure.

Anal fissure is a common condition affecting young to middle-aged adults. It causes severe pain on defecation and rectal bleeding. The aetiology remains uncertain. Spasm of the internal anal sphincter is a constant feature. Nitric oxide (NO) is the major inhibitory neurotransmitter of the internal anal sphincter (IAS). In other spasmodic conditions of the GI tract a lack of normal nitric oxide synthase (NOS) activity has been reported. The aim of this preliminary study was to compare the presence of NOS in the internal sphincters of patients with and without chronic anal fissure. Internal anal sphincter biopsies were taken under general anaesthesia from patients having lateral internal sphincterotomy for chronic anal fissure and from sphincter of patients having abdominoperineal resections as controls. Sections of IAS were stained to show the presence of NADPH diaphorase (and hence presence of NOS). Internal anal sphincter was taken from 6 patients with chronic anal fissure and 6 controls. IAS taken from patients with chronic anal fissure showed little NOS presence compared with controls. It may be that there is an abnormal failure of relaxation of internal sphincter in those patients who develop chronic anal fissure caused by an intrinsic lack of neural NOS in the internal anal sphincter.