Comparison of in-vitro bioactivity and immunoreactivity of serum LH in normal cyclic and hypogonadal women treated with low doses of LH-RH.

The in-vitro test of rat interstitial cell testosterone secretion and a radioimmunoassay (RIA) were used to explore the nature of the LH released in women in response to LH-RH. The ratio of in-vitro bioactivity to immunoreactivity (B:I) calculated for serum samples collected from hypogonadal women using the standard LER-907 for comparison was 13.25 +/- 0.56. This mean ratio was significantly elevated (P less than 0.02) above that found for normal cyclic women, 9.48 +/- 0.49. After one i.v. injection of 10 micrograms LH-RH, 5 hypogonadal and 6 luteal-phase women showed an initial significant drop in the B:I ratio (P less than 0.05 and P less than 0.02 respectively) followed by a steady significant rise (P less than 0.03; P less than 0.01 respectively). This drop in the B:I ratio as immunoreactive LH rose and the rise in the B:I ratio as immunoreactive LH fell may be the result of the release of two or more kinds of LH, one or more with a slower in-vivo clearance rate and an increased B:I ratio.