VASOACTIVE AMINES

Definition

A substance containing amino groups that acts on blood vessels to alter their permeability.

Two vasoactive amines – Histamine and serotonin.

Stored as preformed molecules in mast cells and other cells.

First mediators released in acute inflammation.

HISTAMINE

Produced mainly by mast cells.

Also by circulating basophils and platelets.

SYNTHESIS

Decarboxylation of histidine by the enzyme histidine decarboxylase.

Histamine released from mast cell granules in response to :

1. Physical injury such as trauma or heat.

2. Immune reactions involving binding of IgE antibodies to Fcreceptors on mast cells.

3. C3a and c5a fragments of complements called anaphylatoxins.

4. Leukocyte derived histamine releasing proteins.

5. Neuropeptides (substance P)

6. Cytokines( IL1,IL8)

Actions of Histamine

Vasodilation.

Increase vascular permeability by inducing venular endothelial contraction and formation of interendothelial gaps.

Serotonin

5-hydroxy tryptamine.

Biochemically derived from tryptophan

Found in platelet granules.

Also found in neurons and enterochromaffincells.

Released in response to platelet aggregation

Serotonin from enterochromafincells blood taken up by platelets and stored released during aggregation

Actions of serotonin

Vasoconstriction during clotting.

Neurotransmitter

Regulates intestinal motility.

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