[1][2] Histamine is a neurotransmitter involved in various physiological processes.
There are four main types of histamine receptors: H1, H2, H3, and H4.
H1 receptors are linked to allergic responses, H2 to gastric acid regulation, H3 to neurotransmitter release modulation, and H4 to immune system function.
There are four known histamine receptors: There are several splice variants of H3 present in various species.
H1 causes an increase in PIP2 hydrolysis, H2 stimulates gastric acid secretion, and H3 mediates feedback inhibition of histamine.