Histamine receptor expressed in: Stomach, heart & CNS

Histamine receptor expressed in: CNS & PNS

Histamine receptor expressed in: Bone marrow & hematopoietic cells

HR that causes Bronchocomstriction, Vasodilation, Food intake & Sleep-wake regulation.

Histamine receptor that modulates Gastric acid secretions

Histamine receptor that mediates Neurotransmitter release.

Histamine receptor that mediates immune response.

In B cells, blocks humoral immunity.

In B cells, blocks cellular immunity.

In Th1 cells, enhances IFN-y and Th1 cell proliferation.

In Th1 cells, inhibits IFN-y and Th1 cell proliferation.

In Th2 cells, supresses IL-4, IL-13 & Th2 proliferation

In Treg cells, supress TGF-B.

In dendritic cells, increases AP-capacity and Th1 priming

In dendritic cells, induces IL-10 production, suppress AP and aids in development of IL-10.

H1R mediates:

H2R mediates:

Indicated: Nasal congestion & Allergic conjunctivitis (eye drops)

MAO: Binds to H1R -> inverse agonist -> Temporary relief

Indicated in: Sneezing, runny nose, itchy, watery eyes, insomnia, pruritis, urticaria, insect bites, allergic rashes & nausea.

Anaphylaxis

Motion sickness

Parkinsonism

MOA: Binds to H1R -> inverse agonist -> (-) Histamine activation

Cross BBB -> (-) HR in CNS -> drowsiness & (-) cough center

Antimuscarinic -> competitive antagonist of M2R -> Anti-parkinson

Na channel blocker -> Anesthetic properties

Cross the placenta & detected in milk breast.

Antihistamine effects: drowsiness and confusion

Anticholinergic side effects: dry mouth, dilated pupils, blurred vision, reduced bowel sounds, and urinary retention

Indicated in: Allergic rhinitis

Has less sedative and CNS adverse effects

MOA: Binds to H1R (highly selective) -> inverse agonist -> Histamine inactivation

(-) of transmembrane flux of Ca and cAMP