18. Histamine and 5-HT

Question 1

Describe the similarities between Histamine and 5-HT

Answer 1

-Both biogenic amines

-Small Molecules which act as hormones and autacoids

-important as neurotransmitters, local hormones in vasculature and in smooth muscle

-both dietary sources do not effect body.s pool

Question 2

Describe an Allergy and which receptor it’s related to

Answer 2

-A sensitivity to a specific substance (allergen), that is contacted through the skin inhaled into the lungs or injected. Related to H1 receptor

Question 3

Describe a Peptic ulcer And which receptor it’s related to

Answer 3

a break in the lining of the stomach, first part of the small intestine, or occasionally the lower Oesophagus can be caused by overactive histamines. Related to H2 receptors.

Question 4

Describe Histamine syntheses

Answer 4

-Made from a Histidine with the enzyme Histidine Decarboxylase.

Question 5

Describe what happens to Dietary Histamine

Answer 5

Quickly degraded cannot be added to pool within the body.

Question 6

Describe the storage of histamine

Answer 6

-Stored in Mast cells, these are predominantly found in the lungs, skin, gut and stomach.

-The mast cells store histamine within granules which are exocytosed when stimulated, this is done with IgE dependent receptors, can also be activated by bacterial products, complement peptides, some drugs or trauma to the tissues.

Question 7

Name all the Histamine Receptors

Answer 7

4 receptors
H1
H2
H3
H4

Question 8

Describe H1 receptors

Answer 8

Location, Found throughout the body specifically in smooth muscles, on vascular endothelial cells, in the heart and the CNS

Type of receptor, G-protein coupled, linked to Gq which activates Phospholipase C.

Effect, Mediates an increase in vascular permeability and vasodilation at sites on inflammation induced by histamine. Can cause smooth muscle contraction of bronchi.

Conditions from overactivation, Allergies, nausea and sleep disorders.

Question 9

Describe H2 receptors

Answer 9

Location, mainly in gastric parietal cells.

Type of receptor, G-Protein coupled, linked to intercellular Gs

Effect, mainly Increases the release of gastric acid, also regulates cardiac output and rate and modulate actions of immune cells

Conditions from overactivation, Peptic ulcers.

Question 10

Describe H3 receptors

Answer 10

Location, Mostly in CNS.

Type of receptor, G-protein coupled, linked to intercellular Gi

Effect, may function to release histamine within the CNS.

Conditions from overaction, Unknown.

Question 11

Describe H4 receptors

Answer 11

Location, within components of the immune system like the spleen, thymus and leukocytes

Type of receptor, Unknown likely G-protein coupled

Effect, Unknown.

Effect from overactivation, unknown

Question 12

Describe Histamines effect on the skin

Answer 12

-When bit by an insect or injected by histamine the wheal and flare reaction will occur where the capillaries will dilate causing swelling and redness, activation of the peripheral nerves will cause a pain or itch.

Question 13

Name 2 H1 receptor antagonists what there used to treat and there side effects

Answer 13

-mepyramine and a newer drug cetirizine used to treat allergies, has sedative actions, local aesthetic actions and motion sickness.

Question 14

Name a H2 receptor antagonist what there used to treat and there side effects

Answer 14

-Cimetidine used to treat gastric ulcers and reflux oesophagitis, can cause potentiation of other drugs like anticoagulants and antidepressants.