Molecular Biology of Somatostatin Receptors*

SOMATOSTATIN [somatotropin release-inhibiting factor (SRIF)] is a 14-amino acid polypeptide that is widely distributed throughout the central nervous system and peripheral tissues (Ref. 1; reviewed in Refs. 2–4). It potently inhibits basal and stimulated secretion from a wide variety of endocrine and exocrine cells and functions as a neurotransmitter/neuromodulator in the central nervous system with effects on locomotor activity and cognitive functions (1–12). Somatostatin also has antiproliferative effects and may be an important hormonal regulator of cell proliferation and differentiation (Refs. 13–15 and reviewed in Ref. 16). The first evidence for somatostatin-like activity came from studies of Krulich et al. (17), reported in 1968, who while looking for GHRF described a factor in hypothalamic extracts that inhibited GH secretion from anterior pituitaries in culture. Based on the identification of this inhibitory activity, Krulich et al. (17) proposed that the secretion of GH was regulated by stimulatory (GHRF) and inhibitory (somatostatin) factors. Hellman and Lernmark (18) independently found a similar activity in extracts of pigeon pancreatic islets that inhibited insulin secretion in vitro. Although seemingly unrelated, we now know that both groups had identified somatostatin, the sequence of which was reported by Brazeau et al. (1) in 1972.