Nitric Oxide In GIT acts Primarily By (AIPG 2010,2011)
|A||Smooth Muscle relaxant|
I. NO is a very important inhibitory neurotransmitter in the GIT, released from non-adrenergic non-cholinergic neurons.
II. NO acts as an intra- and extracellular signalling molecule in vascular and smooth muscle GIT cells and it is an important mediator in numerous physiological and pathophysiological conditions.
III. NO is synthesized from L-arginine by the action of NO synthase (NOS) that is present in nitrergic neurons of GIT. NO could be also synthesized in other cell types such as smooth muscle cells.NO is synthesized from L-arginine by the action of NO synthase (NOS) that is present in nitrergic neurons of GIT.The most widely reported action of NO in the gut is relaxation of smooth muscle through activation of the soluble guanylate cyclase and the accumulation of the cyclic guanosine 3', 5'-monophosphate (cGMP).
IV. The most widely reported action of NO in the gut is relaxation of smooth muscle through activation of soluble guanylate cyclase and the accumulation of cyclic guanosine 3 ', 5'-monophosphate (cGMP). In GIT smooth muscle cells, NO and NO donors evoke different responses including contractile effects, relaxations followed by contractions or contractions followed by relaxations, which depends on the type of NO donor, tissue and species.
V. Deficiency of nitrergic innervations has been shown in gastrointestinal Tissues of patients with various diseases such as are Achalasia and Hirschsprung's disease.
VI. Peristalsis is an excellent example of the integrated activity of the enteric nervous system. It appears that local stretch releases serotonin, which activates sensory neurons that activate the myenteric plexus.
VII. Cholinergic neurons passing in a retrograde direction in this plexus activate neurons that release substance P and acetylcholine, causing smooth muscle contraction.
VIII. At the same time, cholinergic neurons passing in an anterograde direction activate neurons that secrete NO, vasoactive intestinal polypeptide (VIP), and adenosine triphosphate (ATP), producing the relaxation ahead of the stimulus