Somatostatin Alterations and Brain Diseases

Soon after its discovery as a hypothalamic growth hormone inhibiting factor, somatostatin-14 (S-14, SRIF) was localized by radioimmunoassay (1, 2) and immunocytochemistry (3–5) in extra-hypothalamic structures. Present in neurons, S-14 is synthesized as part of a prohormone and transported to nerve terminals from which it is released in response to depolarizing stimuli. The peptide is then degraded in situ by enzymes after binding to its specific receptors (6, 7). In the pituitary, S-14 seems to act by inhibiting adenylate cyclase (8–10); but in the brain, its mechanism of action is still poorly understood.