Somatostatin: A hormone widely distributed throughout the body, especially in the hypothalamus and pancreas, that acts as an important regulator of endocrine and nervous system function by inhibiting the secretion of several other hormones such as growth hormone, insulin, and gastrin. It exerts its biologic actions by binding to specific high-affinity receptors on the cell surface. The gene encoding somatostatin is termed SST and is on chromosome 3 in region 3q28.