Table 4.

H3 Receptor Antagonists

Receptor	H3
Signal conduction through	Gi/o
Location of receptors	Mainly expressed on presynaptic nerves in the peripheral sympathetic adrenergic system and histaminergic nerves in the central nervous system. Receptors can be found in airways and gastrointestinal tract
Chromosome location	20q13.33
Signal conduction induces	Decreased cyclic AMP, induction MAP kinase
Antagonists (reverse agonists)	None available clinically: Thioperamide, alobenpropit, and others Very little data regarding effect of H1 antagonists on the H3 receptor are available (13)
Activities	Opposes bronchoconstriction and gastric acid; suppression of norepinephrine release at presynaptic nerve endings
Nasal symptoms produced	Can produce nasal decongestion by blocking effect of histamine on adrenergic postsynaptic receptors