[I-125-TYR(1)]BIPHALIN BINDING TO OPIOID RECEPTORS OF RAT-BRAIN AND NG108-15 CELL-MEMBRANES

Mono iodinated analogues of biphalin [(Tyr-D-Ala-Gly-Phe-NH-)(2)], bot h nonradioactive [I-Tyr(1)]biphalin and radioactive [I-125-Tyr(1)]biph alin have been synthesized. The radioligand binding profiles of these compounds for two types of tissues, rat brain membranes, and NG108-15 cell membranes were identical to the parent biphalin. This is addition al evidence for the hypothesis that biphalin behaves like a monomeric ligand and that only one intact tyrosine is necessary for high biologi cal activity. The second tyrosine could be used for successful radioio dination which may greatly simplify biochemical and pharmacological st udies of biphalin. The results of receptor binding studies show that t he binding of both biphalin and [I-Tyr(1)]biphalin to the delta and mu opioid receptors are not independent. [I-125-Tyr(1)]Biphalin binds to delta receptors as shown in NG108-15 cell membranes. Nevertheless, [I -125]biphalin binding to delta receptors in rat brain membranes was ha rdly evident and mu receptor binding predominated or at least was much more readily detectable in this preparation. (C) 1998 Elsevier Scienc e Inc.