title: Competition of various LH--RH analogs and fragments with 135I-LH--RH for specific binding sites on isolated pituitary plasma membranes.
abstract: The displacement by various LH--RH analogs and fragments of 125I-LH--RH specifically bound to plasma membranes isolated from rat anterior pituitaries was investigated. The addition of increasing amounts of unlabelled LH--RH resulted in an increasing displacement of bound 125I-LH--RH. When some fragments of LH--RH or of an analog with little biological activities were incubated, a much weaker affinity for LH--RH binding sites could be observed. No correlation between biological effectiveness and binding affinity was, however, found when several highly active LH--RH analogs were tested. The potent analogs competed much less efficiently for specific binding sites on isolated plasma membranes than LH--RH. Binding experiments with iodine-labelled (D-Ser(But)6-LH--RH(1--9)-nonapeptide-ethylamide indicated that the small binding affinity of the superactive analog may be due to a lower association rate while the dissociation rate is comparable to that of LH--RH. Contrary to LH--RH, no binding equilibrium was reached during 2 h of incubation of the analog with plasma membranes. The physiological role of LH--RH binding sites on isolated pituitary plasma membranes remains to be elucidated.
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000378:metabolism*; D007700:Kinetics; D010903:Pituitary Gland, Anterior / Q000378:metabolism*; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism*
chemical_list: D011956:Receptors, Cell Surface; D007987:Gonadotropin-Releasing Hormone