To study spontaneous pulsatile LHRH/LH secretion around the onset of puberty, nocturnal plasma LH was measured by means of a highly sensitive immunoradiometric assay in 30 boys (aged 5.6–16.8 yr) investigated for potential problems with growth and/or development. Blood was withdrawn at 10- to 20-min intervals from 2000–0800 h. Pulse analysis was accomplished by a computerized peak detection algorithm. Pituitary and gonadal responsiveness was assessed by a standard exogenous LHRH challenge and testosterone. Subsequent clinical progress was monitored for a mean duration of 2.08 ± 0.16 yr and used as the basis for classifying patients retrospectively into three groups: 1) prepubertal (n = 14), 2) peripubertal (n = 11), and 3) pubertal (n = 5). LH pulses were undetectable in 9 and present in 5 prepubertal subjects, the youngest of whom was aged 7.3 yr. In peripubertal and pubertal individuals, 2–7 LH pulses/12 h were detectable. LH pulses were detectable before sleep by midpuberty (Tanner stage 3). There was a highly significant (P < 0.0001) increase in LH/LHRH pulse frequency from 0.93 ± 0.38 to 4.55 ± 0.43/12 h (mean ± SEM) between the prepubertal and peripubertal groups and a further increase to 6.20 ± 0.37/12 h in the pubertal group. LH pulse amplitude remained under 1.0 U/L in both the prepubertal and peripubertal groups and only increased significantly to 2.02 ± 0.17 U/L in pubertal boys. Response to LHRH increased significantly between the prepubertal (2.47 ± 0.49 U/L) and peripubertal (6.53 ± 2.02 U/L) patients. T increased significantly at each stage, with the greatest rise between the peripubertal and pubertal stages.

Our results show that 1) LH pulses are detectable in some younger prepubertal subjects, albeit infrequently; 2) nocturnal LH/LHRH pulses increase in frequency for 1–2 yr before the clinical onset of puberty, while pituitary response to LHRH increases concurrently; and 3) the greatest changes in LH pulse amplitude and testosterone occurred after the clinical onset of puberty. We conclude that modulation of pituitary LH secretion resulting from an increase in the frequency of LHRH secretion is an important characteristic of the transition between juvenile and peripubertal stages in man.