Somatostatin is a 14 or 28 amino acid regulatory peptide that inhibits hormone secretion from the pituitary, pancreas, and other endocrine sites. A family of 6 GPCRs, sst1, sst2A, sst2B, sst3, sst4 and sst5, mediate the biological activity of somatostatins. The somatostatin receptors couple to Gi to inhibit cAMP production, and also increase MAP kinase signalling. Several tumors have been shown to overexpress somatostatin receptors, and binding of somatostatin to these tumor cells stimulates or inhibits proliferation, depending on the receptor subtypes expressed. Somatostatin has been implicated in seizure susceptibility in animal models, and activation of sst4 with selective agonists increases seizure activity.