Persistently Low Immunoreactive and Normally Bioactive Plasma LH During Male Puberty

Summary

Low basal and LRH-stimulated (50 mcg/m² i.v.) levels of plasma immunoreactive (IR) LH were repeatedly found in 8 boys aged 13 to 16 years who had been referred because of delayed onset of puberty (basal IR-LH 0.19 ± 0.1 and peak 0.48 ± 0.2 vs. 0.24 ± 0.09 and 1.71 ± 0.9 mIU/ml in matched normal controls, respectively). Upon termination of puberty (no more than 3.5 years after referral) IR-LH levels were still low in all 8. Using a rat Leydig cell bioassay system with LER-907 (NPA) as standard, LH bioactivity in these patients was compared with that in 8 matched controls (basal LH was 0.32 ± 0.33 and 0.11 ± 0.07, and peak levels 0.8 ± 0.47 and 1.22 ± 0.44 mIU/ml respectively). The ratio of basal LH bioactivity to IR-LH was higher in the patients (1.24 ± 0.95) than in controls (0.47 ± 0.26, P < .05) as was that of peak bioactivity (1.89 ± 1.2 vs. 0.83 ± 0.35, P < .05). In the three patients tested during sleep IR-LH levels showed no significant change. Basal plasma testosterone levels were appropriate for pubertal stage (400 ± 80 ng/dl) and in the four patients tested following prolonged LRH stimulation (500 mcg i.v. over 3 hours) increased to 530 ± 60 ng/dl. It is concluded that in some boys there may be consistently low plasma levels of IR-LH in association with normal LH bioactivity.

Key-Words

Gonadotropins - Immunoreactive LH - Bioactive LH - Puberty