Table 2.

Vasoactive substances, mechanism of action, and clinical symptoms in carcinoid syndrome.

Name	Mechanism of action	Associated with
Serotonin (5-HT) [21, 35]	Vasoconstriction or vasodilatation Increased gut motility Increased secretion of water, sodium, chloride, and potassium	Diarrhoea, flushing, palpitations
Tachykinins (substance K, substance P, neuropeptide K, neurokinin A) [36–38]	Cutaneous vasodilatation, tachycardia, hypotension, and increased small intestine motility	Diarrhoea, flushing, palpitations
Histamine [5, 39]	Vasodilatation	Flushing, wheezing, palpitations
Kallikrein [40]	Release/stimulation of bradykinin resulting in hypotension	Flushing, palpitations
Prostaglandin [41]	Increased intestinal motility and fluid secretion Vasodilatation	Diarrhoea, flushing, palpitations
Catecholamines (norepinephrine) [42, 43]	Initiate cascade resulting in serotonin release	Flushing, palpitations
Motilin [44]	Initiation of interdigestive migrating motor complex (IMMC)	Diarrhoea