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 micrograms/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 (+/- SEM) to 1.38 +/- 0.51 mm/3 weeks after the 4 micrograms/day infusion (P less than 0.05), from 0.49 +/- 0.11 to 1.0 +/- 0.4 mm/3 weeks after the 20 micrograms/day infusion (P = NS), and from 0.46 +/- 0.1 to 0.84 +/- 0.12 mm/3 weeks after the 90 micrograms/day infusion (P = NS). The mean serum estradiol level was 10 +/- 2.3 pg/ml during the 4 micrograms/day infusion, 16 +/- 2.3 pg/ml during the 20 micrograms/day infusion, and 96 +/- 12 pg/ml during the 90 micrograms/day infusion. Mean serum somatomedin-C levels were significantly higher only after the 20 and 90 micrograms/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.