Nocturnal secretory dynamics of inhibin B and testosterone in pre- and peripubertal boys

To investigate the secretory dynamics of testosterone and inhibin B, we collected samples every 20 min from 2000 h to 0800 h in 20 boys. Boys in group 1 (n = 5) were aged less than 8 yr, group 2 (n = 5) were aged more than 8 yr but 1.5 yr or more before pubertal onset, group 3 (n = 5) were studied 1.0 yr or less before pubertal onset, and group 4 (n = 5) were in early puberty. Testosterone increased after midnight in peripubertal boys, coinciding with the onset of LH pulsatility, and showed a pulsatile pattern in 6 of 10 of these boys. Cross-correlation analysis indicated significant temporal coupling between LH and testosterone. Inhibin B was higher in groups 3 and 4, compared with groups 1 and 2 (P < 0.01) and showed a downward trend overnight with no evidence of pulsatility and no evidence of short-term interactions with LH, FSH, or testosterone. Inhibin B and LH nocturnal means were both inversely correlated with time before pubertal onset (r(s) > -0.85, P < 0.01). Only LH nocturnal mean and amplitude, respectively, contributed independently to prediction of testosterone and inhibin B nocturnal means, explaining 71 and 65% of their variability. We conclude that both testosterone and inhibin B are related to nocturnal LH release in peripubertal boys but over different time scales.