Short term, low dose estradiol accelerates ulnar growth in boys

We previously described a biphasic dose-response curve for ethinyl estradiol on short term growth in patients with Turner′s syndrome. To investigate whether there is a similar phenomenon in boys, we measured the 3-week ulnar growth velocity (TUG) after administration of different doses of estradiol to five prepubertal or early pubertal boys. Basal TUG was determined initially. Subsequently, the boys received a 4- day iv infusion of estradiol at each of three doses (4, 20, and 90 Mg/day) given double blind in a randomized sequence. TUG was determined before and after each infusion and was allowed to return to baseline before giving the second and third infusions. Mean TUG increased from 0.45 ± 0.11 (μSEM) to 1.38 ± 0.51 mm/3 weeks after the 4 μg/day infusion (P < 0.05), from 0.49 ± 0.11 to 1.0 ± 0.4 mm/3 weeks after the 20 Mg/day infusion (P = NS), and from 0.46 ± 0.1 to 0.84 ± 0.12 mm/3 weeks after the 90 Mg/day infusion (P = NS). The mean serum estradiol level was 10 ± 2.3 pg/ml during the 4 Mg/day infusion, 16 ± 2.3 pg/ml during the 20 Mg/day infusion, and 96 ± 12 pg/ml during the 90 Mg/day infusion. Mean serum somatomedin-C levels were significantly higher only after the 20 and 90 Mg/day estradiol infusions. We conclude that low dose estrogen can stimulate ulnar growth in boys and may play a role in the male pubertal growth spurt.