Guanine nucleotides differentiate agonist and antagonist interactions with opiate receptors

Opiate receptor binding is regulated by guanine nucleotides differentially for agonists and antagonists. Guanosine-5′-triphosphate (GTP), its stable analogue guanyl-5′-yl-imidodiphosphate (Gpp(NH)p) and GDP inhibit binding of the 3H-agonists dihydromorphine, etorphine and enkephalins but not the 3H-antagonists naloxone or diprenorphine. GMP, ATP, ADP and AMP fail to alter either agonist or antagonist binding. Effects are more pronounced in the presence than in the absence of sodium.