[125I][D-Tyr25,Nle28,31]CCK-(25-33): a convenient new aminopeptidase resistant cholecystokinin analogue for radioligand binding and autoradiography.

The 125I-labeled sulfated cholecystokinin (CCK) analogue, [D-Tyr25,Nle28,31]CCK-(25-33), bound saturably to membranes from rat cerebral cortex and to brain tissue sections. Competition studies suggested binding to sites of the CCKB subtypes. The high affinity for brain membranes (Kd = 0.14 nM) and high specific binding to brain sections (80-90% specific binding), as well as its high specific radioactivity, makes it a suitable ligand for autoradiographic studies of cholecystokinin receptors.