Histamine, meaning ‘tissue amine’ (histos—tissue) is almost ubiquitously present in animal tissues and in certain plants, e.g. stinging nettle. Its pharmacology was studied in detail by Dale in the beginning of the 20th century when close parallelism was noted between its actions and the manifestations of certain allergic reactions. It was implicated as a mediator of hypersensitivity phenomena and tissue injury reactions. It is now known to play important physiological roles.

1. DR. Chavan P.R.
Pharm D

2.  Autos—self, akos—healing substance or
remedy.
 Generally act locally at the site of synthesis and
release.
 Local hormones.
 Produced by specific cells, and are transported
through circulation to act on distant target
tissues.

3.  Amine autacoids
- Histamine, 5-Hydroxytryptamine (Serotonin)
 Lipid derived autacoids
- Prostaglandins, Leukotrienes, Platelet activating factor
 Peptide autacoids
- Plasma kinins (Bradykinin, Kallidin), Angiotensin
 Others
- cytokines (interleukins, TNFα, GM-CSF, etc.) and
several peptides like gastrin, somatostatin, vasoactive
intestinal peptide and many others

4.  Tissue amine
 A mediator of hypersensitivity phenomena and
tissue injury reactions
 Storage - mast cell
 Histamine rich tissue- skin, gastric and intestinal
mucosa, lungs, liver and placenta
 Nonmast cell histamine - brain, epidermis, gastric
mucosa, growing regions, blood, most body
secretions, venoms and pathological fluids.
 Turnover of mast cell histamine is slow, while that
of nonmast cell histamine is fast..

10. 1. Blood vessels
- Dilatation of smaller blood vessels, including
arterioles, capillaries and venules.
- Red spot: due to intense capillary dilatation.
- Wheal: due to exudation of fluid from
capillaries and venules.
- Flare: i.E. Redness in the surrounding area due
to arteriolar dilatation mediated by axon reflex
- Dilatation of cranial vessels causes pulsatile
headache.

11. 2. Heart
- rate as well as force of contraction is increased
- H1 mediated negative dromotropic (slowing of
A-V conduction) effect
3. Visceral smooth muscle
- Histamine causes bronchoconstriction
- Large doses cause abdominal cramps and colic
by increasing intestinal contractions.
- Guineapig uterus is contracted while that or rat
is relaxed

12. 4. Glands
- increase in gastric secretion
5. Sensory nerve endings
- Itching occurs when histamine is injected i.v. or
intracutaneously.
- Higher concentrations injected more deeply
cause pain.
- These are reflections of the capacity of
histamine to stimulate nerve endings.

13. 6. Autonomic ganglia and adrenal medulla
- These are stimulated and release of Adr occurs,
which can cause a secondary rise in BP.
7. CNS
- Histamine does not penetrate bloodbrain barrier—
no central effects are seen on i.v. injection.
- However, intracerebroventricular administration
produces rise in BP, cardiac stimulation,
behavioural arousal, hypothermia, vomiting and
ADH release.
- These effects are mediated through both H1 and
H2 receptors.

14. 1. Gastric secretion
2. Allergic phenomena
3. As transmitter
4. Inflammation
5. Tissue growth and repair
6. Headache

15.  Histamine has no therapeutic use.
 In the past it has been used to test acid
secreting capacity of stomach, bronchial
hyperreactivity in asthmatics, and for diagnosis
of pheochromocytoma, but these
pharmacological tests are risky and obsolete
now.

16.  Orally active
 H1 selective histamine analogue
 Used to control vertigo in patients of Meniéré’s
disease: possibly acts by causing vasodilatation
in the internal ear.
 Contraindicated in asthmatics and ulcer
patients.
 Vertin 8 mg tab., 1/2 to 1 tab. Qid.

17.  A variety of stimuli
1. Tissue damage: trauma, stings and venoms,
proteolytic enzymes, phospholipase A.
2. Antigen: antibody reaction involving IgE
antibodies.
3. Polymers: like dextran, polyvinyl pyrrolidone
(PVP).
4. Some basic drugs: tubocurarine, morphine,
atropine, pentamidine, polymyxin B, vancomycin
and even some antihistaminics directly release
histamine without an immunological reaction.
5. Surface acting agents: like Tween 80, compound
48/80 etc.