title: Regulation of opioid antagonist and mu, kappa or delta agonist binding by guanine nucleotide and sodium.
abstract: Effects of 5'-guanylylimidodiphosphate (Gpp(NH)p) and sodium on the inhibition by various opioids of [3H]-naloxone binding to guinea-pig brain membrane preparations were studied. The ratio of the concentration required to produce a 50% inhibition of [3H]-naloxone binding in the presence of both Gpp(NH)p and sodium to that in the absence of both Gpp(NH)p and sodium (IC50 ratio) was less than 1 for antagonists, from 3 to 10 for mixed agonist-antagonists, from 16 to 85 for either kappa, delta, or peptide mu agonists, and more than 200 for morphine-like nonpeptide mu agonists. Exceptionally, the IC50 ratio of N,N-diallyl-[D-Ala2,D-Leu5]-enkephalin, an opioid which had been shown not to have an agonist activity in guinea-pig ileum but to have a naloxone-reversible agonist activity in mouse vas deferens, was less than 1. The significance of the different IC50 ratio among opioids employed in the present study was discussed.
mesh_terms: D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D001921:Brain / Q000378:metabolism; D006150:Guanine Nucleotides / Q000502:physiology*; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D008566:Membranes / Q000378:metabolism; D009270:Naloxone / Q000378:metabolism; D011957:Receptors, Opioid / Q000378:metabolism*; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D012964:Sodium / Q000502:physiology*
chemical_list: D006150:Guanine Nucleotides; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D017473:Receptors, Opioid, kappa; D017450:Receptors, Opioid, mu; D006165:Guanylyl Imidodiphosphate; D009270:Naloxone; D012964:Sodium