Is the effect of somatostatin on muscarinic receptors selective to M1 type

Abstract The effect of somatostatin on muscarinic receptors (mAchR) was investigated through saturation experiments of [ 3 H]oxotremorine-M-acetate and oxotremorine/[ 3 H]N-methyl-scopolamine competition experiments. Somatostatin converted oxotremorine high affinity binding sites to low affinity sites in the hippocampus and cerebral cortex whose mAchR were dominantly of M1 type. Somatostatin did not alter agonist binding in the medulla-pons where M2 receptors were abundant. Therefore, the effect of somatostatin on mAchR seems to be selective to high affinity binding sites of M1 receptors.