OBJECTIVE: We investigated the mechanisms of desensitization induced by gonadotropin-releasing hormone agonist in the pituitary. STUDY DESIGN: Effects of gonadotropin-releasing hormone agonist on the pituitary were studied in vitro and in vivo in the rat. In the clinical study serum luteinizing hormone was measured by radioimmunoassay with a polyclonal luteinizing hormone antibody (luteinizing hormone-radioimmunoassay) and by immunoradiometric assay with monoclonal luteinizing hormone antibodies (luteinizing hormone-immunoradiometric assay) during gonadotropin-releasing hormone agonist treatment. RESULTS: In the in vitro study bead-attached pituitary cells that were desensitized with a continuous infusion of 10(-7)mol/L gonadotropin-releasing hormone responded to 50 mmol/L K+. In the in vivo study gonadotropin-releasing hormone binding sites and rat luteinizing hormone beta-messenger ribonucleic acid in the pituitary decreased during gonadotropin-releasing hormone agonist treatment, but serum levels of rat luteinizing hormone did not decrease. In addition, a disparity between luteinizing hormone-radioimmunoassay and luteinizing hormone-immunoradiometric assay was demonstrated during gonadotropin-releasing hormone agonist treatment. CONCLUSION: Pituitary desensitization in response to gonadotropin-releasing hormone agonist may not be wholly receptor mediated and a nonreceptor process may be involved.
OBJECTIVE: We investigated the mechanisms of desensitization induced by gonadotropin-releasing hormone agonist in the pituitary. STUDY DESIGN: Effects of gonadotropin-releasing hormone agonist on the pituitary were studied in vitro and in vivo in the rat. In the clinical study serum luteinizing hormone was measured by radioimmunoassay with a polyclonal luteinizing hormone antibody (luteinizing hormone-radioimmunoassay) and by immunoradiometric assay with monoclonal luteinizing hormone antibodies (luteinizing hormone-immunoradiometric assay) during gonadotropin-releasing hormone agonist treatment. RESULTS: In the in vitro study bead-attached pituitary cells that were desensitized with a continuous infusion of 10(-7)mol/L gonadotropin-releasing hormone responded to 50 mmol/L K+. In the in vivo study gonadotropin-releasing hormone binding sites and rat luteinizing hormone beta-messenger ribonucleic acid in the pituitary decreased during gonadotropin-releasing hormone agonist treatment, but serum levels of rat luteinizing hormone did not decrease. In addition, a disparity between luteinizing hormone-radioimmunoassay and luteinizing hormone-immunoradiometric assay was demonstrated during gonadotropin-releasing hormone agonist treatment. CONCLUSION: Pituitary desensitization in response to gonadotropin-releasing hormone agonist may not be wholly receptor mediated and a nonreceptor process may be involved.
Authors: B Predieri; S Luisi; E Casarosa; E Farinelli; F Antoniazzi; M Wasniewska; S Bernasconi; F Petraglia; L Iughetti Journal: J Endocrinol Invest Date: 2010-06-04 Impact factor: 4.256