des-AA-1,2,5[D-Trp8, IAmp9]somatostatin-14 allows the identification of native rat somatostatin sst1 receptor subtype

Somatostatin exerts multiple activities by interacting with at least five different receptor subtypes (sst[1-5]). The affinity of des-AA(1,2,5)-[D-Trp8, IAmp9]somatostatin-14 (CH-275) was studied by competition experiments using the non-selective radioligand [125I][Leu8, D-Trp22, Tyr25]somatostatin-28 in areas of the rat brain and pituitary known to express identified receptor subtypes. In the cerebellar nuclei and cerebral cortex, which possess the somatostatin sst1 receptor subtype, CH-275 exhibited a moderate affinity (IC50: 10-50 nM). Conversely, in the hippocampus, immature cerebellum and pituitary which contain different subsets of receptors mRNAs (sst[2-5]), the IC50 values were > 1 microM. These data indicate that CH-275 is an appropriate ligand for the identification of native rat somatostatin sst1 receptor subtype.