Age and sex related variations in biologically active and immunoreactive serum luteinizing hormone

Relatively recent data from the literature show some discrepancies between bioactive LH (Bio-LH) and radioimmunoreactive LH (Ria-LH) in different endocrinological conditions. In 202 subjects of both sexes we have studied biologically active and immunoreactive LH and their ratio (B/l ratio) pattern through life. The results show that in male puberty the in vitro bioassay method gives a more discriminating measurement of serum LH than the radioimmunoassay. The ratio between bioactive and immunoreactive LH is well correlated with the increase of serum testosterone levels from male prepuberty to adulthood. On the contrary, there is no difference of B/l ratio between prepubertal girls and fertile women, in spite of the different gonadotropin levels. Finally LH bioactivity increases less markedly in elderly men than in postmenopausal women. These data suggest that, among several factors which may influence not only the quantity but also the quality of LH secreted, gonadotropin secretion rate and sex steroid milieu play an important role and may partly explain the B/l ratio changes in the situations investigated.