Carcinoid syndrome leads to facial flushing due to the synthesis of which compound?

Carcinoid syndrome is primarily associated with neuroendocrine tumors that often secrete a variety of bioactive substances, one of the most significant being serotonin. These tumors often originate in the gastrointestinal tract, and in advanced cases where the tumor secretes large amounts of serotonin and other byproducts into the systemic circulation, several characteristic symptoms arise, including facial flushing.

Serotonin is synthesized from the amino acid tryptophan. Once released into the bloodstream, high levels of serotonin can lead to various effects, including vasodilation, which is responsible for the flushing observed in patients with carcinoid syndrome. The flushing generally occurs in episodes and may be triggered by factors such as stress or certain foods, further reflecting the role of serotonin in mediating vascular responses.

While other compounds mentioned in the choices are important in various physiological pathways, they are not the primary mediators responsible for the facial flushing seen in carcinoid syndrome. For example, dopamine from tyrosine plays a role in neurotransmission and is not directly linked to the flushing mechanism; histamine from histidine is involved in immune responses and allergic reactions but does not correlate with the syndrome described; and melatonin from serotonin is a product influenced by serotonin levels but does not play a