Review Question - QID 109602

Octreotide, a somatostatin analogue, is used to treat various neuroendocrine tumors such as Zollinger-Ellison syndrome (as seen in this patient) and carcinoid tumors. When somatostatin is produced by the hypothalamus, it functions to inhibit the production and release of growth hormone and thyroid stimulating hormone.

Somatostatin is produced by multiple tissues and has variable inhibitory effects depending on the tissue upon which it is acting. When it is produced in the gastrointestinal tract, somatostatin functions to decrease gastric secretion and gallbladder contraction. When it is produced in the endocrine pancreas, somatostatin functions to decrease insulin and glucagon release. When it is produced in the hypothalamus, it inhibits the production and release of growth hormone and thyroid stimulating hormone.

Incorrect Answers:
Answer 2: Cholecystokinin (CCK) is a GI hormone that is produced in the duodenum in response to fatty acids and amino acids. CCK increases pancreatic secretion, gallbladder contraction, and gastric emptying. Somatostatin from the gastrointestinal tract, not the hypothalamus, inhibits CCK release by inhibiting the secretion of CCK-releasing peptide.

Answer 3: Prolactin is released from the anterior pituitary and functions to stimulate milk production and inhibits ovulation or spermatogenesis. Its release is inhibited by dopamine from the hypothalamus.

Answer 4: Gastrin is secreted by G cells in the stomach antrum and increases gastric H+ secretion and gastric motility. Somatostatin from the gastrointestinal tract, not the hypothalamus, will decrease gastrin secretion.

Answer 5: Thyrotropin-releasing hormone is produced by the hypothalamus and functions to increase thyroid stimulating hormone and prolactin production. It partly counteracts somatostatin by promoting prolactin release.

Bullet Summary:
Somatostatin from the hypothalamus inhibits the production and release of growth hormone and thyroid stimulating hormone.