Specific, Time-Dependent Actions of Low-Dose Ethinyl Estradiol Administration on the Episodic Release of Growth Hormone, Follicle-Stimulating Hormone, and Luteinizing Hormone in Prepubertal Girls with Turner's Syndrome *

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Abstract
To investigate the actions of acute and chronic low doses of ethinyl estradiol (EE) on the pulsatile characteristics of GH and gonadotropin release we studied seven girls with Turner's syndrome [mean age, 7.5 ± 0.75 (±SE) yr] on 3 separate study days. At baseline (study I), blood was drawn every 20 min from 2000–0800 h for GH, LH, and FSH determinations. One month after study I the patients were started on 100 ng/kg EE, orally, daily, and an identical study was repeated 1 week (study II) and 5 weeks (study III) from the initiation of low dose EE therapy. A pulse detection algorithm, Cluster, was used to objectively analyze pulsatility profiles. There were consistent and significant increases in all seven patients after 5 weeks of low dose EE therapy in mean GH concentrations (study I, 7.0 ± 1.1 μg/L; study III, 13.4 ± 1.7; P = 0.008), mean area under the GH pulse (study I, 602 ± 52 μg/L·min; study III, 1350 ± 261; P = 0.026), and mean GH pulse amplitude (study I, 14.0 ± 2.2 μg/L; study III, 32.8 ± 6.0; P = 0.018); with no detectable changes in GH pulse frequency (study I, 5.3 ± 0.6 pulses/12 h; study III, 5.3 ± 0.4). These findings were not accompanied by any significant changes in plasma somatomedin-C or serum estradiol concentrations or urinary cytological maturation indexes. Conversely, the amount of radioimmunoassayable FSH activity was suppressed after low dose EE therapy, with a decrease in mean FSH concentrations (study I, 23.5 ± 6.6 IU/L; study III, 5.9 / 1.2; P = 0.035) and mean pulse amplitude (study I, 28.6 ± 8.6 IU/L; study III, 8.2 ± 1.8; P = 0.O38), with no detectable changes in FSH pulse frequency (study I, 7.6 ± 0.6 pulses/12 h; study III, 7.3 / 0.6). Similar qualitative changes in LH pulsatility were observed after low dose estradiol administration. In conclusion, our results demonstrate that low dose EE therapy results in a significant augmentation of pulsatile GH activity, with reciprocal decreases in gonadotropin concentrations in girls with Turner's syndrome. Such observations indicate an exquisite sensitivity of gonadotrope and somatotrope function to low dose estrogen action in this prepubertal hypogonadal model.