Gonadotropin and free alpha-subunit secretion in patients during GnRH-agonist treatment

In female patients gonadotropin and free alpha-subunit serum levels during GnRH-agonist (GnRH-a) treatment were investigated. Using two different immunoassays (RIA, IRMA) as well as LH in-vitro bioassay evidence was found for pituitary secretion of incomplete LH molecular forms which are detected false positive in RIA measurements but neither in IRMA nor in bioassay. In the GnRH-a induced desensitization state suppression of LH serum levels was more profound as compared to FSH. In contrast to gonadotropins free alpha-subunit serum levels were shown to increase in a biphasic course leading to ninefold higher levels persisting during GnRH-a treatment. A further increase was achieved by exogenous GnRH but not by estradiol. In conclusion these in-vivo data give evidence for a gradually different suppression of gonadotropic secretion by the use of GnRH-a. The mechanisms of inhibition are discussed to be directed to steps in the processing of beta-subunit synthesis but not of alpha-subunit.