Characterization of specific somatostatin binding sites in guinea pig lung

Somatostatin binding sites have been demonstrated in the cytosolic fraction of guinea-pig lung. Binding of 125I-Tyr11-somatostatin was dependent on time and temperature, saturable, reversible and highly specific. Under equilibrium condition, i.e. 60 min at 25 degrees C, native somatostatin inhibited tracer binding in a dose-dependent manner. Two types of somatostatin binding sites were defined by Scatchard analysis: a small population with a high affinity (Kd = 23.4 nM) and a large population with a low affinity (Kd = 253.5 nM) for somatostatin. The biphasic nature of the dissociation process confirmed the heterogeneity of somatostatin binding sites. Apart from somatostatin, no peptide (1 microM) tested influenced the binding of 125I-Tyr11-somatostatin. The present data represent the first analysis of somatostatin binding sites in lung.