Autocoids is an important topic in pharmacology studied in medical courses. Autocoids are biological factors act like local hormones.

1. BY -:
NITESH KUMAR
B.PHARM 4TH YEAR
JAIPUR COLLEGE OF PHARMACY.
JAIPUR, RAJASTHAN

2. AUTOCOIDS
 A number of substances naturally occurring in the
body are called as local hormones. They differ in
their chemical structure but posses potent biological
actions. These are called as tissue factor or
autocoids.
 Autocoids mean self remedy. These are called as
autocoids because of their self regulatory action.
 Unlike hormones these are produced in tissue and
not by the endocrine glands. They play important
role in allergic reactions.
 E.g. Histamine, 5-Hydroxytryptamine (Serotonin),
Prostaglandin, Bradykinin, Angiotensin &

3. HISTAMINE
 It is synthesized from the amino acid histidine in the
presence of histidine decarboxylase enzyme. It is a
potent biogenic amine.
 It is found in the fixed tissues, in mast cells or in
circulating basophiles. In the cells it is present in the
inactive form.
 It is also synthesized by microflora in the
gastrointestinal tract, however most of the histamine
is destroyed during passage through the liver.
 Histamine is released from mast cells or basophiles
by the substances which damages the store cells i.e.
antigens & certain drugs.
 Histamine is also present in various plants and
animal tissues, venom of bees & wasps.

4. PHYSIOLOGICAL ROLE OF HISTAMINE
Physiological role of histamine is not precisely known
but it is involved to play following roles as-
1. Histamine may play a part in gastric acid secretion
with the hormone gastrin.
2. It also plays part as transmitter in CNS.
3. It also plays a part in tissue growth & repair.
4. It also plays a part in antigen-antibody reaction.
HISTAMINE IN ALLERGIC REACTION
 Liberation of histamine is probably the cause of a
number of toxic effects in man.
 Any process involving mechanical, thermal or
radiant damage will cause its release.
 Many allergic states due to antigen-antibody
reactions also release histamine in the body from
mast cells. Most prominent effects of histamine are
urticaria, bronchoconstriction & hypotension.

5. HISTAMINE RECEPTORS
Histamine produces the various effects by acting on some
receptors which are called as histamine receptors. These
are of two types as follows
1. H1 Receptors 2. H2 Receptors

6. PHARMACOLOGICAL ACTIONS
The effect produced by histamine release depends
upon amount of histamine & site of administration.

7. 1. Blood vessels
It causes constriction of blood vessels. It produces
following effects-
 Dilation of pulmonary vessels
 Stretching of nerve endings around cranial vessels.
It increases cerebrospinal fluid pressure producing
throbbing headache.
 Dilation of venules & capillaries producing decrease
in total peripheral resistance and blood pressure.
 In large doses Increase capillary permeability,
decreasing blood volume and produce flushing
(redness of skin) in neck & face region.
2. Blood pressure
 In moderate doses hypotensive effect is for short
duration. But in large doses it produces prolonged
hypotension

8. 3. Triple response
On intradermal injection it shows three responses as
follows:
a) Flush - Dilation of capillaries at site of injection &
area becomes red. It is called as flush.
b) Bright flare - Flush formation is followed by
formation of bright flare beyond flush. It is an irregular
shaped reaction producing urticaria.
c) Edema - After 10 min. development of localized
edema due to increased permeability of the
capillaries to fluids. It is also called as wheel
formation .
This effect is called as triple response.
4. Heart
 It increases heart rate and contractility of heart.
 In high doses it produces ventricular arrhythmia.

9. 5. Smooth Muscles
 It stimulates smooth muscles of various organs
directly. Bronchial & uterine smooth muscles are
highly sensitive. It shows bronchospasm.
 Histamine induced bronchospasm can be easily
relieved by administration of adrenaline,
Isoprenaline, aminophylline etc. but not by atropine
& other antihistaminic drugs.
6. Exocrine glands
 In smaller doses it stimulates gastric acid secretion.
 In larger doses stimulates secretion of pepsin along
with acid.
 Hence it serves as useful tool for studying stomach’s
secretary capacity & to diagnose achlorhydria &
pernicious anemia

10.  ADVERSE EFFECTS
Hypotension,
Headache,
Diarrhea,
Flushing and Dyspnoea.
 CLINICAL USES
Histamine has minor use in clinical medicine for
the diagnosis of hypo or acholrhydria.

11. ANTI-HISTAMINIC DRUGS / ANTI-HISTAMINES
These are the competitive blockers of histamine
receptors and prevent most of the histamine effects in
our body. CLASSIFICATION
1. H1- Antihistamines
a) Potent H1- Antihistamines with sedative effect. E.g.
Diphenhydramine
b) Potent H1- Antihistamines with less sedative effect
E.g.
Chlorpheniramine
c) Less Potent H1- Antihistamines with less sedative
effect.
E.g. Mepyramine
d) Non sedating H1- Antihistamines E.g. Terfenadine,
Cetrizine
2. H2- Antihistamines-- E.g. Cimetidine, Ranitidine,

12. PHARMACOLOGICAL ACTIONS
1. Anti-histamine effects - These drugs effectively
antagonizes the action of injected histamine on
smooth muscles.
2. Other effects
a) CNS - These normally are sedative in action but in
higher doses it causes excitement.
b) Local Anesthetic - Many antihistamines having quiet
potent local anesthetic action together with quinidine.
c) Cardio-depressant action - Some antihistamines
have
cardio depressant action & hence useful in some
arrhythmia.
d) Autonomic effects - In higher doses these
antagonize
acetyl choline and produces atropine like actions like

13. e) Miscellaneous
Some antihistamine may cause histamine release.
Some
may have anti-5HT action also. Hypersensitivity
reaction
can occur due to topical use of all H1- antihistamines.
SIDE EFFECTS-
 Drowsiness is main side effect (driving is not safe).
 Potentiates the action of other CNS depressants like
tranquilizers, MAO inhibitors etc. thus serious side
effects
can be produced if combined therapy is used.
 Anti-cholinergic effects like dry mouth, blurring of
vision

14. PHARMACOKINETICS
These are readily absorbed by oral route.
Peak effect is seen in 1 hr & duration is 4 hrs.
Metabolized in liver & excreted through urine.
THERAPEUTIC USES
1. To prevent allergic reactions or their symptoms like
allergic
rhinitis (inflammation of nasal mucosal membrane),
Hay
fever, urticaria.
2. Prevention & treatment of motion sickness
(promethazine). But its use in nausea & vomiting in
pregnancy is contraindicated.
3. These are also used for the management of cardiac
arrhythmia & Parkinsonism

15. PROSTAGLANDINS
 These are a family of naturally occurring unsaturated
fatty acid.
 They were first found in seminal fluids. As semen is
present in prostate gland they were named
prostaglandins.
 These are widely distributed in the body including brain
and exert effects on many organs and tissues.
 Prostaglandins are released in response to
inflammation, pain, trauma, bacterial attack & allergic
reactions.
 Prostaglandins are divided into six groups as A, B, C,
D, E & F.

16. •In addition to prostaglandins, recent research has
revealed the existence of other biologically active
lipids biosynthesized from the same precursors as
prostaglandins through interrelated enzymatic
pathways.
These include thromboxanes, prostacyclins, hydro
peroxy eicosa tetraenoic acids (HPETE), hydroxyl
ecosa tetraenoic acids (HETE) & leukotrines

17. SEROTONIN / 5-HYDROXY TRYPTAMINE
 It is another important autocoids widely distributed
in body.
 Its major amount is found in intestinal chromaffin
cells. Also present in platelets and certain neurons
of brain. Pharmacological actions-
 It acts powerfully on smooth muscles of vessels
and gastro-intestinal tract.
 Effect on blood vessels produces triphasic
response as First transient fall in blood pressure
followed by brief rise in blood pressure and then
prolonged hypotension.
 It plays important role in blood coagulation.

18.  It also plays an important role in pathophysiology of
psychosis.
Pharmacokinetic
 It is oxidatively deaminated by Mono Amine Oxidase
enzyme and excreted through urine.
 Degradation of 5- HT may be blocked by MAO
inhibitors which causes elevation of 5-HT level in
brain.
 Some fruits like banana, cheese contain 5-HT. Hence
patients on MAO inhibitors therapy should not eat
such food.
5-HT Antagonists
 E.g. Lysergic acid Diethylamine (LSD) &
Cryptoheptadine.