Journal of Clinical Endocrinology & Metabolism, Vol 58, 755-757, Copyright © 1984 by Endocrine Society

ARTICLES

Stimulation of LH fragments with reduced bioactivity following GnRH agonist administration in women

DR Meldrum, Z Tsao, SE Monroe, GD Braunstein, J Sladek, JK Lu, W Vale, J Rivier, HL Judd and RJ Chang

In eumenorrheic women with endometriosis and in oligo-amenorrheic women with polycystic ovarian disease (PCO), chronic administration of a long- acting GnRH agonist (GnRH-a) reduced the circulating concentrations of estrogens and androgens to levels similar to those of castrated women. The concommittant elevation of LH in both groups suggested that the measured immunoreactive LH had reduced bioactivity. In seven women with endometriosis, bioactive LH (BA LH) measured as the in-vitro secretion of testosterone by dispersed Leydig cells, was significantly (p less than 0.001) reduced from 10.8 +/- 1.2 (SEM) to 4.4 +/- 0.2 mIU/ml at the end of 28 days of GnRH-a therapy. In five women with PCO, BA LH decreased from 44.2 +/- 15.5 to 5.7 +/- 0.6 mIU/ml (p = 0.06). These changes of BA LH appeared to be responsible for the suppression of ovarian androgen secretion during GnRH-a treatment and in turn may have contributed to the profound decreases of estrogen production by reducing the amount of precursor androgen available for aromatization. Free alpha subunit levels increased simultaneously with the decrease of BA LH at the end of therapy, suggesting a post-receptor effect of GnRH- a. Beta subunit levels became undetectable. Cross-reaction of alpha subunit in the RIA for LH was sufficient to only partially account for the LH levels measured. On sephadex G-100 chromatography the excess immunoreactive material was detected at and immediately following the alpha subunit tracer. Further studies will be necessary to elucidate the chemical nature of the immunoreactive LH secreted during GnRH-a therapy.

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