Figure 1.

Binding affinity and potency of J-2156 at the five somatostatin receptor types. Panels in the figure show (A) binding curves of the endogenous somatostatin receptor ligand- somatostatin 14; no selectivity was observed, (B) binding curves of J-2156; more than ~300-fold selectivity for the SST4 receptor was observed relative to that for the other somatostatin receptor types, (C) binding curves of octreotide; low affinity was seen at SST4 receptor. Competition binding assays were run using ¹²⁵I radiolabelled somatostatin 14 (0.05 nM) in the presence of 0.5 μg protein. (D,E) present the concentration response curves showing that SST14 and J-2156 inhibited forskolin (30 μM and 10 μM for rat and human SST4 receptor, respectively)-stimulated cAMP production in H4 cells expressing the rat and the human SST4 receptor types. Similarly, (F) shows that octreotide, the negative control, was unable to inhibit cAMP production in both human and rat SST4 receptor. H-SST1-5, human somatostatin receptor types 1-5; R-SST4, rat somatostatin receptor type 4.