Persistently low immunoreactive and normally bioactive plasma LH during male puberty

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 less than .05) as was that of peak bioactivity (1.89 +/- 1.2 vs. 0.83 +/- 0.35, P less than .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.