title: Photoaffinity labeling of gonadotropin releasing hormone receptors in control and desensitized pituitary cells.
abstract: Gonadotropin releasing hormone (GnRH), preincubated with cultured rat pituitary cells, induced down regulation of GnRH receptors in a time- and dose-dependent manner. The specific binding was inhibited by 50% after 30 min and maximal inhibition (70%) was obtained after 75 min preincubation with 1 microM GnRH. Preincubation of the cells for 2 h with 10 nM GnRH inhibited the specific binding by 20%, reaching a plateau of 70% inhibition with 0.1 microM GnRH. Concomitantly, exposure of the cells to GnRH caused a time- and dose-dependent desensitization of LH release. The responsiveness of the desensitized cells was not parallel to the binding capacity and was inhibited to a greater extent (93%). Photoactivation of GnRH receptors with iodinated [azidobenzoyl-D-Lys6]GnRH in control and desensitized cells resulted in the identification of a single specific band with the same apparent molecular weight of 60K daltons. These results indicate that structural alterations of GnRH receptors are not associated with GnRH-induced desensitization. Therefore, desensitization may involve conformational changes in the receptor or more likely a post-receptor mechanism.
mesh_terms: D000345:Affinity Labels / Q000494:pharmacology*; D000818:Animals; D001386:Azides / Q000494:pharmacology*; D002478:Cells, Cultured; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology*; D007700:Kinetics; D007986:Luteinizing Hormone / Q000378:metabolism; D010777:Photochemistry; D010903:Pituitary Gland, Anterior / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism*; D011966:Receptors, LHRH
chemical_list: D000345:Affinity Labels; D001386:Azides; D011956:Receptors, Cell Surface; D011966:Receptors, LHRH; D007987:Gonadotropin-Releasing Hormone; C031737:LHRH, N-epsilon-azidobenzoyl-Lys(6)-; D007986:Luteinizing Hormone