ESPE Abstracts

Introduction: Male puberty is initiated by endocrine signaling in the hypothalamic-pituitary axis whereby follicle-stimulating hormone (FSH) and luteinizing hormone (LH) enable testicular maturation and synthesis of testosterone. Recent publications have eluded to overnutrition and obesity as relevant factors that may accelerate the timing of puberty. Attainment of testicular volume (TV) 4 ml measured by Prader orchidometer remains the definition of male puberty onset. We recently established ultrasound references for testicular growth as an objective alternative to orchidometry.

Objectives: (i) Model endocrine profiles with reference to ultrasound-determined testicular growth throughout puberty and (ii) determine associations between hormones and standard deviation (SD) scores for body mass index (BMI), weight, waist circumference (WC) and subscapularis skinfold (SSF).

Methods: Testicular ultrasound, bioimpedance, biometric assessments and blood collection was conducted in a cross-sectional cohort of 417 healthy Norwegian boys, age 6-16 years. Circulating levels of testosterone were quantified by liquid chromatography tandem-mass spectrometry (LC-MS/MS). Sex hormone-binding globulin (SHBG), FSH and LH were analyzed using IMMULITE 2000 xpi.

Results: Hormone levels plotted against testicular growth aligned well with TV 4 ml marking the start of testosterone production. TV 4 ml also corresponded to the peak LH/testosterone ratio, a marker of Leydig cell function. Dimension reduction of all serum hormone levels into an endocrine profile principle component was able to predict puberty transition at TV ≥ 4 ml (receiver operating characteristic AUC = 0.88, P<0.001). For pubertal boys with TV ≥ 4 ml, individual hormones exhibited no correlation with SD scores for testicular growth. For pubertal boys we observed significant inverse Spearman correlations between serum levels of SHBG and SD scores for BMI (r = -0.31, P<0.001), WC (r = -0.24, P<0.01), weight (r = -0.29, P<0.01) and SSF (r = -0.24, P<0.01). For BMI and weight SD scores, significant positive correlations persisted with respect to calculated free testosterone index. Circulating total testosterone correlated inversely with body fat percentage (r = -0.32, P<0.001) and positively with body muscle percentage (r = 0.33, P<0.001).

Conclusion: Ultrasound-determined TV and endocrine status are markers of male puberty onset and progression. Our endocrine model with respect to TV supports the current definition of male puberty onset at TV 4 ml. Our data show significant correlations between free testosterone and SD scores for BMI and weight, suggesting that overweight and obesity may accelerate pubertal development.