Histamine is an organic nitrogenous compound involved in local immune responses, as well as regulating physiological function in the gut and acting as a neurotransmitter for the brain, spinal cord, and uterus

1. Histamine

2. Introduction
Histamine Means: Tissue amine
Chemical formula: C5H9N3

3. 3
Structure of Histamine - C5H9N3
H
H
H H
H
H
H
H H

4. 4
Histamine
• Meaning "tissue amine" (histos — tissue) — abundantly present in animal
tissues — also in plants like "stinging nettle"
• Mediator of hypersensitivity and tissue potential tissue injury —
Physiological role
• The primary site the mast cell granules (or basophils) — skin, intestinal and
gastric mucosa, lungs, liver and placenta
• Other sites
central nervous system: neurotransmitter
the fundus of the stomach: major acid secretagogues, epidermis, gastric mucosa and
growing regions
also blood, body secretions, venoms & pathological fluids

5. 5
Histamine – Synthesis
Synthesized locally from amino acid histidine
Histidine Histamine
L-histidine decarboxylase

6. 6
Histamine – Storage and Release
• Metabolized by P450 system, 2 pathways:
Methylation to N-me histamine (N-me transferase), & to N-me imidazole
acetic acid (MAO) - eliminated in urine
Oxidative deamination to imidazole acetic acid (DAO), and to imidazole
acetic acid riboside - eliminated in urine
• In mast cells— held by acidic protein and heparin (-ve charged) — histamine
is +ve charged
• Ineffective orally — liver destroys all absorbed from intestine

7. 7
Histamine – Pharmacologicalactions
• Blood vessels: Dilatation of small vessels — arterioles, capillaries and venules
• SC administration — flushing, heat, increased HR and CO — little fall in
• Rapid IV injection: Fall in BP early (H1) and persistent (H2) — only H1
effect with low dose
• Dilatation of cranial vessels
• H1 component vasodilatation — mediated indirectly by EDRF But H2
component - mediation is directly on smooth muscle Of blood vessels
• Larger arteries and veins — constriction mediated by H1 receptor
• Increased capillary permeability — exudation of plasma

8. 8
Mechanism of Action of Histamine
Histamine
H1 Receptors
Ca2+
Smooth muscle contraction
Increased capillary
permeability Vasodilation
Sensory nerve endings pain
& itching
H1 Receptors
cAMP
Gastric acid secretion Blood
vessels: vasodilation
Increased capillary
permeability
H1 Receptors
cAMP
histamine release
Secretion
Vasodilation

9. 9
Adverse effects of histamine release
• Itching, Urticaria
• Flushing
• Hypotension
• Tachycardia
• Bronchospasm
• Angioedema
• Wakefullness
• Increased acidity (Gastric acid secretion)

10. ThankYou!
10
Mudassir Husain
Email: mudassirprnc@gmail.com
Website: www.yoututor.in