Somatostatin was discovered in 1971, by Guillemin and his colleagues during their search for the hypothalamic growth hormone-releasing factor. A peptide was found in ovine hypothalamus which inhibited the release of growth hormone from cultured anterior pituitary cells. 1,2 Determination 3 of its amino acid sequence indicated that it was a tetradecapeptide with a molecular weight of 1639 (Figure lJ. An identical peptide was later isolated from porcine hypothalamus by Schally and his coworkers. 4 The peptide was named somatostatin in the belief that it was a hypothalamic releasing factor whose sole function was to inhibit the secretion of growth hormone. It soon became evident, however, that a peptide with identical immunologic characteristics and biologic activity was present in the D cells of pancreatic islets, in D-like cells of the gastrointestinal tract, in parafollicular cells of the thyroid gland, and in extrahypo­ thalamic neurons of both the central and peripheral nervous system in various species, including man. Moreover, studies employing synthetic somatostatin5 demonstrated that the peptide possessed a wide spectrum of biologic activities in addition to its inhibition of growth hormone. 56 S 0 MAT 0 S TAT I N 6 1 2 3 4 5 7 Ala-Gly-Cys-Lys-Asn-Phe-Phe I I S Trp 8 ~ L~S 9 I I Cys-Ser-Thr-Phe-Thr 14 13 12 11 10 FIG. 1: Structure of somatostatin 57 II. GENERAL DISTRIBUTION AND ACTIONS Somatostatin is widely distributed within both the central and peripheral nervous systems and in various other tissues (Table 1).