THE GNRH CHALLENGE TEST - A QUANTITATIVE MEASURE OF PITUITARY DESENSITIZATION DURING GNRH AGONIST ADMINISTRATION

OBJECTIVE The use of GnRH agonists for desensitization of the pituitar y is widespread in gynaecological practice. For indications such as co ntraception and treatment of uterine leiomyomata partial desensitizati on may suffice. With respect to partial desensitization of the pituita ry we have addressed three basic questions: (1) Is the degree of pitui tary desensitization dependent on the dose of agonist used? (2) What i s the optimal way to measure the degree of pituitary desensitization? (3) Is it possible to create a standard to express the degree of pitui tary desensitization? DESIGN AND PATIENTS Twenty-four women were rando mized into 4 groups of 6 women. To achieve pituitary desensitization, the groups received 0.1, 0.25, 0.5 and 1.0 mu g/min GnRH respectively, for 6 weeks. MEASUREMENTS Pituitary desensitization was measured by g onadotrophin levels and responses to a 100-mu g bolus of GnRH and an o estradiol benzoate challenge-test. RESULTS The level of LH and the res ponses of LH and FSH to the GnRH challenge showed significant dose-dep endent suppression. Multiple regression indicated the LH response to t he GnRH challenge was the best way to measure pituitary desensitizatio n. From the LH responses to the GnRH-challenge a 'standard curve' was established for the assessment of the degree of pituitary desensitizat ion. CONCLUSION The LH response to the GnRH challenge test is the best available measure of pituitary desensitization during GnRH agonist tr eatment.