Clonidine-displacing substance is present in peripheral tissues of the rat.

Clonidine-displacing substance (CDS) is biologically active in the brain, as well as the gastric fundus, platelets and vas deferens. We sought to determine whether CDS is contained within peripheral tissues in the rat. Using competitive radioimmunoassay with a clonidine-specific antiserum and 3H-p-aminoclonidine rat adrenal gland and gastric fundus were shown to contain significantly greater amounts of CDS-like radioimmunoactivity than the brain; intermediate-to-low activity was present in the heart, small intestine, serum, kidney and liver. Lung and skeletal muscle exhibited near-background levels. CDS may not be unique to the brain, but also may be synthesized and stored in peripheral organs.