Vasomotor refers to actions upon ablood vessel which alter its diameter.[1][2] More specifically, it can refer tovasodilator action andvasoconstrictor action.
Sympathetic nerve fibers travel around thetunica media of the artery, secreteneurotransmitters such asnorepinephrine into theextracellular fluid surrounding the smooth muscle (tunica media) from the terminal knob of the axon. The smooth muscle cell membranes have α and β-adrenergic receptors for these neurotransmitters. Activation ofα-adrenergic receptors promotes vasoconstriction, while the activation of β-adrenergic receptors mediates the relaxation of muscle cells, resulting invasodilation. Normally, α-adrenergic receptors predominate in smooth muscle of resistance vessels.[3]
Endothelin, andangiotensin are the vasoconstrictors of smooth muscles whilenitric oxide andprostacyclin are vasodilators of the smooth muscles.[3]
Some vasoactive chemicals such as vasodilatoracetylcholine are known for causing reduced/increased blood flow in the tumours by vasomotor changes. Inadequate blood supply to the tumour cells can cause the cells to be radio-resistant and resulted in reduced accessibility tochemotherapeutic agents.[4]
Injuries to nerves of the lower trunk of thebrachial plexus (Klumpke's paralysis) and compression ofmedian nerve at theflexor retinaculum of the hand (Carpal Tunnel Syndrome) can cause vasomotor changes at the areas innervated by the nerves. This area of the skin will become warmer because of vasodilation (loss of vasoconstriction).[5]
Depression of thevasomotor center of the brain can cause the loss ofvasomotor tone of blood vessels, resulting in massive dilatation of veins. This will result in a condition called asneurogenic shock.[6]