Differences in the Ratio of Bioactive to Immunoreactive Serum Luteinizing Hormone during Vasomotor Flushes and Hormonal Therapy in Postmenopausal Women

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Abstract
With the recognition of differences between serum bioactive (bio) and immunoreactive (i) LH concentrations in various clinical situations, we measured changes in the bio:i LH ratio in postmenopausal (PM) women in response to iv GnRH, during the vasomotor flush, and in response to both estrogen and progestin treatment. Bio LH was measured using the mouse interstitial cell assay and LER 907 as standard, with conversion to milliinternational units per ml (Second International Reference Preparation of human menopausal gonadotropin). In 22 PM women, aged 42–56 yr, serum bio LH [455 ± 73 (±SE) mIU/ml] and the bio:i LH ratio (8.3 ± 0.7) were significantly higher than in premenopausal women (25.5 ± 5 mIU/ml and 1.5 ± 0.2, respectively; P < 0.002). In response to 150 µg iv GnRH, there was a greater rise in levels of iLH and bioLH in PM women than in premenopausal women, but there were no changes in the bio:i LH ratio after GnRH. During nine flushing episodes in three women, documented by digital temperature and iLH pulses, there was a significant increase in the bio:i LH ratio (P < 0.001). After treatment of seven PM women for 2 months with 0.625 mg conjugated estrogens and seven other PM women with 150 mg im depomedroxyprogesterone acetate, vasomotor symptoms decreased significantly. Serum iLH did not change after treatment, but bio:i LH ratios decreased significantly, and 7 of 14 women had levels in the premenopausal range. These data suggest that bioLH and the bio:i LH ratio correlate better than iLH with symptomatology in PM women.