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Histamine in Short

Article Review   by:eulita     Original Author: Dr. Barsha
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Many  illustrious  personalities  (physiologist  /pharmacologists/  clinicians)  have  worked  on  histamine; some prominent names being Dale, Laidlaw, Best and Lewis.  
 
 Chemistry, biosynthesis and source –
 
        i.    Histamine is amine of the aminoacid histidine.
       ii.   Histamine is synthesized by enzymatic decarboxylation of histidine, the enzyme being histidine    decaboxylase. 
       iii.  In  our  body  histamine can  be  obtained from  many  tissues but most notably from the mast cells of the tissues and the blood basophils.
      iv.  Other  important  sources  are  gastro  intestinal  mucosa  and  CNS.
       v.  Certain bee venom and stings of certain insects are rich in histamine.
 
In  the  mast  cells, histamine  is complexed with heparin and the heparin histamine complex is dissociated to cause release of pharmacologically active histamine. In allergic states following the contact of the antigen with a mast cell, the mast cell is degranulated (= mast cell granules are lysed) histamine is released from the mast cell.
 
Actions.    
      The actions  of  histamine can be divided into two  major  categories : 
                     (A)  On smooth  muscles (B)  On exocrine  glands of stomach.
 
                                  (A) Actions on smooth muscles
                                            1. It causes relaxation of the arterioles and probably also of the smooth muscles of precapillary sphincter, leading to engorgement of the capillaries.
 
                                             2. Histamine causes contraction of bronchial (specially in  susceptible  persons)  and  intestinal  smooth  muscles  leading  to  bronchospasm  and  diarrhea. 
                                           Mast cells occur plentifully in mucous membrane of tracheobronchial tree. An injection  of  histamine  therefore can produce a sharp fall of blood pressure and  violent attack of asthma;  there may  be urticaria. Fall of BP  is due  to acute dilatation of  the arterioles (the‘resistance   vessels’).
                                           Urticaria is due to transudate of fluid from the capillary to the tissue which in turn is due to  capillary engorgement. Ultimately, speaking, histamine injection in  susceptible persons  can  produce, anaphylactic shock, characterized by severe fall of  BP  and  asthma. In  short, histamine stimulates the  parietal  cells of  the  stomach  and  thus  increases  the  secretion of  HCl.   

    1.  In addition, histamine also  is  related  to  the  pain  and  itching  sensation. 
 
    2.  Some  rapidly  growing  tissues  produce histamine in large amounts.  Thus, embryos, regenerating liver and rapidly healing wounds produce histamine.  It is possible, that for the smooth functioning ofthe rapidly  growing tissues, histamine is necessary.  

    3.  Some  neurons of  the brain are histaminergic,  ie, their neurotransmitters  is  histamine.  Such histaminergic  neurons  play  a role  in  thermoregulation  by  hypothalamus. 
 
Published: November 07, 2008   
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