The H1 histamine receptor is the primary mediator of the acute “allergic” response to Histamine. It’s a G-protein coupled receptor (Gq/11) found on smooth muscle, vascular endothelium, sensory neurons, airways, and the brain.
Activation Effects
- Vasodilation (flushing)
- Increased vascular permeability (hives, angioedema)
- Bronchoconstriction
- Nerve stimulation (itch, pain)
- Mucus secretion
- In the brain: wakefulness, arousal (see Sleep and Histamine)
Blocked By
H1 Antihistamines — cetirizine, loratadine, fexofenadine (second-generation); diphenhydramine, hydroxyzine (first-generation, cross BBB).