RESUMO
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.
Assuntos
Pulmão/metabolismo , Receptores de Neurotransmissores/metabolismo , Somatostatina/metabolismo , Animais , Citosol/metabolismo , Cobaias , Concentração de Íons de Hidrogênio , Radioisótopos do Iodo , Masculino , Receptores de SomatostatinaRESUMO
In guinea pigs sensitized with 1 microgram ovalbumin together with 100 mg Al(OH)3, somatostatin levels were selectively increased up to two and 3 times in tissue extracts from trachea and bronchi, respectively, but not in lung as compared to controls. The increase of somatostatin levels observed in trachea and bronchi after sensitization was associated with a decrease in the binding capacity of both high- and low-affinity binding sites (without changes in the affinity values) in the corresponding cytosolic fractions. These results suggests that an increase in airways somatostatin content may be involved in the pathogenesis of anaphylactic bronchoconstriction.
