Vasomotor refers to actions upon a blood vessel which alter its diameter.
Sympathetic nerve fibers travel around the tunica media of the artery, secrete neurotransmitters such as norepinephrine into the extracellular 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.
Normally, α-adrenergic receptors predominate in smooth muscle of resistance vessels.
[3] Some vasoactive chemicals such as vasodilator acetylcholine are known for causing reduced/increased blood flow in the tumours by vasomotor changes.