Mu and delta opiate receptors in rat brain are affected by GTP but not by MIF-1.
The possible competition of MIF-1 (Pro-Leu-Gly-NH2) with 3H-naloxone or 3H-D-Ala-D-Leu-enkephalin (DADLE) for mu and delta opiate receptors in the rat striatum was examined under conditions of varying temperatures and concentrations of sodium and GTP. MIF-1, in concentrations ranging from 10(-14) to 10(-3) M, failed to compete with either 3H-DADLE or 3H-naloxone for delta or mu receptors, GTP (2 microM) facilitated binding (17.7 +/- 1.9%) at all concentrations of MIF-1 in the 1H-DADLE assay; unexpectedly, GTP facilitated binding in the 3H-naloxone assay (11.5 +/- 1.3%) under conditions used to potentiate antagonist binding (addition of NaCl and incubation at 4 degrees C). GTP showed optimal facilitation at a concentration of about 2 microM in both the 3H-DADLE and 3H-naloxone "antagonist" conditions. At higher doses of GTP, 3H-naloxone binding remained high, but 3H-DADLE binding decreased to near or below control values. MIF-1 did not affect these GTP responses, indicating further the lack of effect of this peptide on opiate binding.
D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D016308:Enkephalin, Leucine-2-Alanine; D004745:Enkephalins / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000494:pharmacology*; D009075:MSH Release-Inhibiting Hormone / Q000378:metabolism*; D008297:Male; D009270:Naloxone / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011957:Receptors, Opioid / Q000378:metabolism*; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; D012964:Sodium / Q000494:pharmacology; D013696:Temperature
D004745:Enkephalins; D011957:Receptors, Opioid; D017465:Receptors, Opioid, delta; D017450:Receptors, Opioid, mu; D009270:Naloxone; D016308:Enkephalin, Leucine-2-Alanine; D006160:Guanosine Triphosphate; D009075:MSH Release-Inhibiting Hormone; D012964:Sodium