Biochemical and pharmacological characterization of somatostatin receptors in rat brain.

We have characterized specific receptors for tetradecapeptide somatostatin (SS-14) of rat brain using 125I-labeled Tyr11-SS-14([125I-Tyr11]SS-14) as radioligand. [125I-Tyr11]SS-14 binding was sensitive to time, pH, temperature and ionic strength of the buffer, and was optimal in 50mM HEPES/KOH buffer, pH 7.5, at 25 degrees C for 60 minutes. Scatchard analysis indicated that the rat forebrain membranes had a single binding site with an apparent dissociation constant (Kd) of 0.522 +/- 0.044 nM and maximum binding capacity (Bmax) was 233 +/- 37 fmol/mg protein (mean +/- SEM). Ca2+, Mg2+, Mn2+ and Co2+ had a significant effect on the specific binding, which indicates that these metal ions might affect somatostatin receptor activity in the brain. Among CNS acting drugs, Ca2+ antagonists, antischizophrenic drugs, antidepressants and anticholinergic drugs had relative effects on [125I-Tyr11]SS-14 bindings to rat cerebral cortex membranes.