Table 1 Histamine and Its Activities
From: The Role of Antihistamines in the Treatment of Vasomotor Rhinitis
Receptor | H1 |
|---|---|
Signal conduction through | Gq/11 and others |
Location of receptors | Multiple sites throughout the body including: Smooth muscle bronchi and gastrointestinal tract, cardiac tissue, blood vessels, sensory nerves, endothelium, central nervous system |
Chromosome location | 3p25, 3p14-21 |
Signal conduction induces | Increased cyclic GMP, increased intracellular cytosolic calcium, activation of phospholipase C, activation of guanyl cyclase, nitric oxide production |
Antagonists (reverse agonists) | Over 40 exist. Examples of "second generation" include cetirizine, desloratadine, fexofenadine, loratadine, azelastine, olopatadine Examples of "first generation" antihistamines are chlorpheniramine, diphenhydramine, pyribenzamine, and others |
Activities | Increases vascular permeability producing a fall in blood pressure, flush, headache, and reflex tachycardia; itch; smooth muscle contraction in bronchi and gastrointestinal tract; stimulation of vagal nerve receptors producing reflex smooth muscle contraction in airways; cough via stimulation of sensory nerves in airways; eosinophil chemotaxis; decreased AV node conduction time; enhancement of release of histamine and arachidonic acid derivatives; nitric oxide formation |
Nasal symptoms produced | Sneezing, itching, rhinorrhea, and perhaps some degree of nasal congestion via increased vascular permeability with leakage of fluid into the tissues and vasodilatation? |