LH bioactivity increases more than immunoreactivity during puberty.

We have measured bioactive LH in the plasma of 60 normal boys and 45 normal girls throughout puberty because the rise in immunoreactive LH has seemed too small to account for the profound changes in sexual maturation during adolescence. Bioactive LH was determined using an in vitro bioassay (rat interstitial cell testosterone production); I-LH was measured by radioimmunoassay using the same LH standard, LER 907. Bioactive LH was measurable in all 270 plasma samples; I-LH in 218. In both boys and girls, B-LH rose more than I-LH when compared to chronological age, bone age, and pubertal stage. In boys, B-LH increased 8.2-fold (P < 0.001) from prepuberty to late puberty, whereas I-LH rose 3.0-fold (P < 0.001). Similarly, in girls B-LH increased 23.1-fold (P < 0.001) while I-LH increased 4.9-fold (P < 0.001). Between pubertal stages there was less overlap of individual values of B-LH, in comparison to those of I-LH. We conclude that B-LH increases more than I-LH during normal puberty and is a more discriminating measure of maturation. One implication of these findings is that a qualitative change in gonadotropin secretion may occur during puberty.