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Mechanisms involved in the pituitary desensitization induced by gonadotropin-releasing hormone agonists
T Uemura1, T Yanagisawa, K Shirasu
1Department of Obstetrics and Gynecology, School of Medicine, Yokohama City University, Kanagawa Pref., Japan.
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.