SIGNALLING PATHWAY OF HISTAMINE RECEPTORS
Histamine bind to a different type of histamine G-coupled protein
receptors and exerts its action. The four histamine receptors which are
identified by researchers are H1, H2, H3 and H4 (Figure 5) ,
where the first two receptors i.e. H1 and H2 are important targets for
clinically effective drugs. In some human tumours, these histamine
receptors are recognized by genomic-based methods for example colorectal
cancer, melanoma, and breast cancer, vaginal, cervical and ovarian
cancer. The H1 receptors are on smooth muscles, endothelial cells, as
well as brain and, are also found in peripheral nerve endings and
mediate vascular permeability at the site of inflammation. H1 receptor
activation causes anaphylactic reactions such as bronchoconstriction,
hypotension, flushing and tachycardia . When histamine bind to the H1
receptor in the brain elevates other things like wakefulness and
appetite suppression. In the peripheral nerve, histamine mediates
stimulation which leads to pain and itching sensations. The H2 receptors
are mainly located in gastric parietal cells and cause gastric
secretions. In histaminergic neurons, H3 receptors are mostly found
which regulate 5-HT3, dopamine, Norepinephrine, Acetylcholine and
histamine. Its mRNA is situated in the peak of the spinal cord, bone
marrow and peripheral hematopoietic cells play a vital role in the
variation of myoblast and promyeloblast along with chemotaxis .