CHARACTERIZATION OF THE BINDING OF [H-3] (+/-)-L-364,718 - A NEW POTENT, NONPEPTIDE CHOLECYSTOKININ ANTAGONIST RADIOLIGAND SELECTIVE FOR PERIPHERAL RECEPTORS

  • 1 September 1986
    • journal article
    • research article
    • Vol. 30  (3) , 212-217
Abstract
[3H]-(.+-.)-L-364,718 a new, potent selective nonpeptide peripheral cholecystokinin (CCK) antagonist bound saturably and reversibly to rat pancreatic membranes. The radioligand recognized a single class of binding sites with a high affinity (Kd = 0.23 nM). The binidng of [3H]-(.+-.)-L-364,718 was stereospecific in that the more biologically active (.sbd.)-enantiomer demonstrated greater potency than the (+)-enantiomer. The rank order of potency of various CCK agonists and antagonists in displacing [3H]-(.+-.)-L-364,718 correlated with their ability to displace [125I]CCK-8 and their known pharmacological activities in peripheral tissues. However, the absolute potencies of agonists were greater in displacing [125I)CCK-8 than [3H]-(.+-.)-L-364,718. As described for other physiologically relevant receptor systems, the potency for displacement of [3H]-(.+-.)-L-364,718 binding by CCK agonists, but not antagonists, was reduced by guanosine 5''-(.beta.,.gamma.-imido)triphosphate and NaCl and enhanced by MgCl2. [3H]-(.+-.)-L-364,718 also demonstrated specific binding to bovine gall bladder tissue but not guinea pig brain or gastric glands, consistent with its selectivity as a peripheral CCK antagonist. [3H]-(.+-.)-L-364,718 binding to pancreatic membranes was not affected by various pharmacological agents known to interact with other common peptide and nonpeptide receptor systems. These data indicate that [3H]-(.+-.)-L-364,718 represents a new potent nonpeptide antagonist radioligand for the study of peripheral CCK receptors which may allow differentiation of agonist and antagonist interactions.