Somatostatin receptors on cortical neurones and adenohypophysis: comparison between specific binding and adenylate cyclase inhibition.

Primary cultures of mouse embryonic neurones from the cerebral cortex and rat pituitary membranes were used to identify and characterize further the somatostatin receptors coupled to an adenylate cyclase and to compare these receptors with specific binding sites for a non-reducible somatostatin analog. 125I-CGP 23996 on both tissues. 125I-CGP 23996 bound specifically to a single population of sites on cortical neurones and pituitary membranes, with a high affinity (Kd = 2.76 and 1.95 nM respectively). The rank order of potency of somatostatin-(1-14) and some analogs (somatostatin-28, [D-Trp8,D-Cys14]somatostatin-(1-14), native CGP) to displace 125I-CGP 23996 from its binding sites was similar on both tissues. Furthermore this rank order was also found identical for the inhibition of adenylate cyclase activity on cortical neuronal and pituitary membranes. Finally a good correlation was found between the order of potencies of somatostatin analogs evaluated from binding experiments and adenylate cyclase assays, suggesting the presence of the same receptor observed under two different affinity states. According to the classification of somatostatin receptors by Tran and his colleagues (1985) these results support the hypothesis that SSA is the somatostatin receptor coupled with an adenylate cyclase.