Somatostatin is a peptide widely distributed in both the central nervous system (CNS) and peripheral tissues. It is found as two bioactive peptides of 14 and 28 amino acids, the latter being an N-terminal-extended form (Reichlin 1983a).
The name somatostatin comes from its initial discovery as an inhibitor of growth hormone (GH) release from anterior pituitary cells (Brazeau et al. 1973). Since then, numerous other physiological activities of somatostatin have been discovered associated with differing peptide and receptor localization (Reichlin 1983a,b). Besides GH, somatostatin is also able to inhibit secretion of prolactin (PRL) and thyroid-stimulating hormone (TSH) (Reichlin 1983a). In the CNS, the highest somatostatin concentrations have been detected in the hypothalamus in the tuberoinfundibular neurons where, acting as a neurohormone, the peptide regulates the hypothalamic-hypophyseal axis (Schettini 1991). Somatostatin-containing neurons are also present in many other areas of the brain, such as the cerebral cortex,