Evidence for two somatostatin-14 receptor types in rat brain cortex.

The binding characteristics of a stable somatostatin analogue, SMS 201-995, have been evaluated in a somatostatin receptor binding assay using [125I-Tyr11]somatostatin, and cortical, pituitary or pancreatic membranes. High affinity binding sites for somatostatin-14 and for SMS 201-995 were identified in rat cortex (Kd = 0.60 nM) as well as in pituitary (Kd = 0.74 nM) and pancreatic beta-cells (Kd = 0.18 nM). In the cortex, in contrary to the two other tissues, SMS 201-995 only labels a part (approximately 75%) of the receptors recognized by somatostatin-14. This suggests the presence in the cortex of more than one population of somatostatin receptors. In conclusion, SMS 201-995 appears as a valuable tool for differentiating the two somatostatin receptor types.