somatostatin

Somatostatin is the body's broad “stop” hormone. Its name comes from its first-discovered job — stopping the release of growth hormone (“somatotropin”) — but it turns out to inhibit a remarkably wide range of secretions throughout the body.

From the hypothalamus, somatostatin reaches the anterior pituitary through the portal system and brakes the release of growth hormone, balancing the stimulating effect of GHRH. It also dampens TSH release, so it influences both the growth and thyroid axes from above.

Beyond the brain, somatostatin is made by delta cells in the pancreatic islets and by cells in the gut. There it acts locally to slow the secretion of insulin, glucagon, and many digestive hormones, and to reduce gut motility and nutrient absorption — effectively turning down digestion and hormone output across the board.

Its powerful inhibitory reach is exploited in medicine. Long-acting somatostatin analogs such as octreotide are used to shrink the hormone output of certain pituitary and gut tumors, including in acromegaly and some neuroendocrine tumors.