Antihistamine: Mechanism of action and classes
Antihistamines are antagonist or inverse agonist of histamine receptors(HRs) which can help manage the symptoms associated with allergies. This research report aims to explore the mechanism of action and the classes of antihistamines. The report also attempts to answer the hypothesis that increased antihistamine levels will affect the immune function and the allergic response.
Antihistamines counteract the action of histamines by binding to HRs through their antagonistic or reverse agonistic properties. HRs belong to the G-protein-couple receptor family. They are heptahelical transmembrane molecules. They exist in equilibrium as an active and inactive. Histamine shifts the equilibrium to the active state whilst antihistamine shifts the equilibrium in the inactive state. There are four subtypes of HRs ranging from HR1 to HR4. HR1 are coupled to Gq/G11 protein and are located on the membrane of CNS neurons, smooth muscle cells, CVS, neutrophils, eosinophils, monocytes, macrophages, DC, T and B cells, endothelial cells and epithelial cells. HR2 are coupled to Gs protein and are located in primary gastric parietal cells, smooth muscle and CVS. HR3 and H4R are coupled to Gi/o protein and are distributed around the body. HR1 are the major …show more content…
This results in the activation of the Gq/11 which stimulates the inositol phospholipid signalling pathways, resulting in the production of IP3 and DAG. This causes the downstream increase of intracellular calcium and activation phospholipase D and A2. The overall physiological effect is vasoconstriction, bronchoconstriction, increase vascular permeability and the increases release of prostacyclin, platelet-activating factor and NO. This can manifest as an allergic reaction. Therefore, when H1- antihistamines binds to H1R it opposes the effect of histamine preventing or decreases the severity of an allergic
Antihistamines are antagonist or inverse agonist of histamine receptors(HRs) which can help manage the symptoms associated with allergies. This research report aims to explore the mechanism of action and the classes of antihistamines. The report also attempts to answer the hypothesis that increased antihistamine levels will affect the immune function and the allergic response.
Antihistamines counteract the action of histamines by binding to HRs through their antagonistic or reverse agonistic properties. HRs belong to the G-protein-couple receptor family. They are heptahelical transmembrane molecules. They exist in equilibrium as an active and inactive. Histamine shifts the equilibrium to the active state whilst antihistamine shifts the equilibrium in the inactive state. There are four subtypes of HRs ranging from HR1 to HR4. HR1 are coupled to Gq/G11 protein and are located on the membrane of CNS neurons, smooth muscle cells, CVS, neutrophils, eosinophils, monocytes, macrophages, DC, T and B cells, endothelial cells and epithelial cells. HR2 are coupled to Gs protein and are located in primary gastric parietal cells, smooth muscle and CVS. HR3 and H4R are coupled to Gi/o protein and are distributed around the body. HR1 are the major …show more content…
This results in the activation of the Gq/11 which stimulates the inositol phospholipid signalling pathways, resulting in the production of IP3 and DAG. This causes the downstream increase of intracellular calcium and activation phospholipase D and A2. The overall physiological effect is vasoconstriction, bronchoconstriction, increase vascular permeability and the increases release of prostacyclin, platelet-activating factor and NO. This can manifest as an allergic reaction. Therefore, when H1- antihistamines binds to H1R it opposes the effect of histamine preventing or decreases the severity of an allergic