Twenty-four hour growth hormone and leptin secretion in active postpubertal adolescent girls: Impact of fitness, fatness, and age at menarche

Abstract

Context: GH is strongly related to body composition, physical activity, and pubertal progression. Adolescent girls decrease physical activity during puberty, whereas their weight increases. Because 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 postpubertal adolescent girls aged 16-21 yr. GH was sampled every 10 min and leptin hourly for 24 h. We first analyzed 6-h time blocks by repeated measures for GH and leptin, with body mass index (BMI), percent body fat, and VO2max as covariates 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, and VO2max were related to GH concentrations in the entire group, whereas 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 unit decreased GH by 27%. Pulsatility characteristics showed a 1-yr increase of age at menarche increasing total GH input by 20% (P = 0.0035) independently from BMI. Conclusion: In postpubertal adolescent girls, leptin is related to GH concentration across the lean to overweight BMI spectrum. GH pulsatile secretion was greater in girls with later age at menarche. Copyright © 2006 by The Endocrine Society.