Somatostatin [SST, GHIH (growth hormone-inhibiting hormone) or SRIF (somatotropin release-inhibiting factor)] is a cyclic peptide existing in two isoforms and is produced in the pancreas islet, GI tract and the central nervous system. Tetradecapeptide Somatostatin-14 (SRIF-14, the originally identified somatostatin) and the 28-amino acid Somatostatin-28 (SRIF-28) have similar biological activities but differ in their potency. Somatostatins inhibit the release of growth hormone in contrast to Growth Hormone Factor (GRF), which stimulates the release of growth hormone. Somatostains also inhibit the release of prolactin and thyrotropin, peptide hormones from the pituitary gland and glucagon and insulin from the pancreas. It also controls the secretion of gut hormones and functions as a neurotransmitter.