Somatostatin receptor agonists and antagonists

Somatostatin is a cyclic peptide that is widely distributed in the CNS, the periphery and in a variety of tumours. Two biologically active forms, somatotropin release-inhibiting factor (SRIF)-14 and SRIF-28, exert their effects through activation of five G-protein-coupled receptor subtypes (sst(1) - sst(5)). These peptides act as neurotransmitters or hormones and inhibit the secretion of other peptides, such as insulin, growth hormone and glucagon. Metabolically stable peptide and structurally diverse non-peptide analogues have been developed as subtype-selective agonists and antagonists. The availability of these novel SRIF analogues will greatly facilitate our understanding of the function and role of specific SRIF receptors. SRIF analogues offer therapeutic potential in the regulation of hormone secretion, diseases of the CNS and periphery and in the treatment and diagnosis of various tumours. This review will focus on an overview of SRIF, new developments related to SRIF role and function and the discovery of novel peptide and non-peptide agonists and antagonists.