Growth hormone (GH) is strongly related to body composition, physical activity and pubertal progression. Adolescent girls decrease physical activity during puberty while their weight increases. Since leptin is a good index of energy balance in active young women, we hypothesized that leptin is related to GH secretion in this population while taking into account fitness, fatness and age at menarche.

METHODS. We measured body composition and maximal oxygen consumption (VO₂max) in 37 post-pubertal adolescent girls ages 16 to 21 yr. GH was sampled every 10 min and leptin hourly for 24-hours. We first analyzed 6-hour time-blocks by repeated measures for GH and leptin, with BMI, percent body fat and VO₂max as co-variates for the entire group and a lean subgroup. The deconvolution method was used to characterize GH pulsatility from individual time points.

RESULTS. GH varied through the day (P < 0.0001) with the highest concentrations overnight. BMI, percent body fat, VO₂max were related to GH concentrations in the entire group while leptin predicted GH in the entire group as well as the lean subgroup of girls. Higher leptin was related to lower GH concentrations (P = 0.011) regardless of time. A log leptin level increase by 1 U decreased GH by 27%. Pulsatility characteristics showed a one-year increase of age at menarche increasing total GH input by 20% (P = 0.0035) independently from BMI.

CONCLUSION. In post-pubertal adolescent girls, leptin is related to GH concentration across the lean to overweight BMI spectrum. Growth hormone pulsatile secretion was greater in girls with later age at menarche.