histamine

Vascular system, H1 receptor – Effects

Vasodilation (via endothelium), vasoconstriction (coronary), ↑ permeability, edema, ↓ blood pressure, triple response. Mechanism: NO & prostaglandin release.

Vascular system, H2 receptor – Effects

Vasodilation, ↓ blood pressure, triple response. Mechanism: direct smooth muscle relaxation via cAMP.

Heart, H1 receptor – Effects

Slows AV conduction, speeds heart rate, ↑ contraction force. Mechanism: direct cardiac Ca2+ influx.

Heart, H2 receptor – Effects

Speeds heart rate, ↑ contraction force, ↑ AV conduction. Mechanism: cAMP accumulation, Ca2+ influx.

Lung, H1 receptor – Effects

Bronchoconstriction, ↑ mucus viscosity, cough. Mechanism: smooth muscle contraction, vagal sensory nerve stimulation.

Lung, H2 receptor – Effects

Slight bronchodilation, ↑ mucus secretion.

Lung fibroblast migration, H4 receptor – Effects

Enhances fibronectin-induced migration.

Uterus, H1 receptor – Effects

Contraction via smooth muscle effects.

CNS, H1 receptor – Effects

Vasodilation, ↓ histamine & neurotransmitter release, ↓ appetite, ↑ wakefulness. Mechanism: autoreceptor.

CNS, H3 receptor – Effects

Vasodilation, ↓ histamine & presynaptic neurotransmitter release, MAPK activation (memory, survival). Mechanism: autoreceptor & heteroreceptor.

PNS, H1 receptor – Effects

Acts as neurotransmitter. Mechanism: sensory nerve endings (pain, itch).

PNS, H3 receptor – Effects

↓ presynaptic neurotransmitter release. Mechanism: heteroreceptor.

Gastric glands, H2 receptor – Effects

Stimulates gastric acid & pepsin secretion. Mechanism: direct effect on parietal cells.

Exocrine glands, H1 receptor – Effects

↑ intestinal motility, salivary, sweat, pancreatic, lacrimal secretions. Mechanism: signal transduction.

Immune system, H1 receptor – Effects

↑ dendritic antigen presentation & Th1 priming. Mechanism: signal transduction.

Immune system, H2 receptor – Effects

↓ histamine release, ↓ leukocyte activity. Mechanism: signal transduction.

Immune system, H4 receptor – Effects

Priming of immune system, chemotaxis, Th activation, mast cell degranulation, cytokine production. Mechanism: signal transduction.