Intrinsic activity and effects of guanyl-5'-yl imidodiphosphate, Gpp(NH)p and sodium ion on the affinity of dynorphin 1-13, nalorphine and nalorphine-7,8-oxide to kappa-opioid receptor.

Nalorphine and nalorphine-7,8-oxide (nalorphine epoxide) behaved as partial agonists on the kappa-receptor in the electrically stimulated mouse vas deferens. The effects of a GTP-analogue, GppNHp and Na+ on the inhibition of [3H]ethylketocyclazocine binding by dynorphin 1-13, nalorphine, its epoxide and naloxone (antagonist) were studied with a synaptosomal fraction of guinea pig brain (except a cerebellum) and compared with the intrinsic activity of the test drugs, which was estimated in the electrically stimulated mouse vas deferens. The effects of GppNHp and Na+ on the affinity of the drugs to the kappa-receptor correlated with their intrinsic activities.