Chapter I Somatostatin receptors

Publisher Summary Somatostatin (somatotropin release-inhibiting factor, SRIF) was initially characterized as a 14-amino acid hypothalamic neurohormonal peptide involved in the inhibitory control of growth hormone (GH) secretion from anterior pituitary somatotrophs. Somatostatin binding sites were first identified in a clonal pituitary cell line (GH4C1) by radioligand binding studies using a monoiodinated somatostatin analog (tyrosine-substituted in position eleven). Brain binding sites were subsequently identified and shown to be sensitive to guanine nucleotides and divalent cations that indicated that they were coupled to trimeric G proteins. Numerous physiological and pharmacological studies have pointed to the existence of a multiplicity of brain somatostatin receptor subtypes. Somatostatin binding sites were first classified into two subclasses, based on the differential binding of somatostatin analogs such as octreotide. The octreotide-sensitive and insensitive sites were also differentiated by their ionic requirements to millimolar magnesium and 120 millimolar sodium, respectively. This chapter tabulates the affinities and maximal binding capacities of the most commonly used radioactive ligands for SRIF1 and SRIF2 binding sites. The chapter focuses on more recent data concerning the selective distribution of individual sst receptor subtypes as gathered using autoradiography, in situ hybridization, and immunohistochemistry.