Somatostatin receptors (SSTRs) are activated by somatostatin secreted from nerve and endocrine cells. SSTRs are expressed in a tissue-specific manner and involved in the regulation of secretion of insulin, glucagon and growth hormone as well as cell growth induced by neuronal excitation in both the central and peripheral nervous systems. Aberrant expression of somatostatin receptors is known in a large number of human tumors. The human medullary thyroid carcinoma cell line TT expresses all SSTR subtypes. SSTR4 is highly expressed in human brain, lungs, gastrointestinal tract, pancreas and prostates. It inhibits the release of many hormones and other secretory proteins.