Increased pulsatility, process irregularity, and nocturnal trough concentrations of growth hormone in amenorrheic compared to eumenorrheic athletes

Amenorrheic athletes exhibit a spectrum of neuroendocrine disturbances, inc luding alterations in the GH-insulin-like growth factor I (IGF-I) axis. Whe ther these changes are due to exercise or amenorrhea is incompletely charac terized. The present study investigates spontaneous (overnight) and exercis e-stimulated GH secretion and associated IGF-binding proteins (IGFBPs) in a menorrheic (AA; n = 5), and eumenorrheic athletes (n = 5) matched for age, percent body fat (dual energy x-ray absorptiometry), training history, and maximal oxygen consumption. Each volunteer participated in two hospital adm issions consisting of a 50-min submaximal exercise bout (70% maximal oxygen consumption) and an 8-h nocturnal sampling period. Deconvolution analysis of serum GH concentration time series revealed increases in the half-life o f GH (60%) and the number of secretory bursts (85%) as well as a decrease i n their half-duration (50%) and the mass of GH secreted per pulse (300%) in the AA cohort. Time occupancy at elevated trough GH concentrations was sig nificantly increased, and GH pulsatility (approximate entropy) was more irr egular in the AA group. During exercise, AA exhibited a reversal of the nor mal relationship between IGF-I and GH, and a 4- to Ei-fold blunting of stim ulated peak and integrated GH secretion. Fasting levels of plasma TGF-I, IG FBP-3, and IGFBP-1 appeared to be unaffected by menstrual status. In ensemb le, this phenotype of GH release in amenorrheic athletes suggests disrupted neuroregulation of episodic GH secretion, possibly reflecting decreased so matostinergic inhibition basally, and reduced GHRH output in response to ex ercise compared with eumenorrheic athletes. Accordingly, we postulate that the amenorrheic state, beyond the exercise experience per se, alters the ne uroendocrine control of GH output in amenorrheic athletes.