Instant growth inhibition by low dose oestrogens in excessively tall boys

Abstract

Abstract. A major problem in the androgen treatment of escessive height in boys is acceleration of growth velocity especially in the early stages of therapy. Oestrogen treatment in tall girls, in contrast, instantly decelerates growth velocity, probably by its plasma somatomedin lowering effect. As oestrogen administration in male subjects causes a similar somatomedin depression and immediate growth inhibition is also wanted in the treatment of excessive height in boys, the effect of short-term low dose oestrogen therapy (ethinyloestradiol, Ee, Lynoral®, 0.050 mg daily) on growth was studied in 10 constitutionally tall boys. During oestrogen therapy three week ulnar growth rate (TUG-rate) dropped instantly from 0.84 ± 0.42 to 0.33 ± 0.27 mm (P < 0.02) within 6 weeks. Three week body growth rate also changed significantly from 0.48 ± 0.23 to 0.12 ± 0.37 cm during oestrogen loading (P < 0.05). The magnitude of the latter changes, however, allows only evaluation of the whole group, whereas changes in TUG-rates far exceeded the limits of confidence in most individual boys. Growth deceleration during Ee was accompanied by a significant decrease in serum alkaline phosphatase activities (from 299 ± 72 U/l before to 240 ± 79 U/l during Ee, P < 0.01), plasma calcium (from 2.45 ± 0.06 to 2.35 ± 0.05 mmol/l during Ee, P < 0.05) and plasma testosterone levels (from 392 ± 128 ng/100 ml before to 27 ± 7 ng/100 ml during Ee, P < 0.005). Within 2 months after stopping Ee administration plasma testosterone levels were normal again (432 ± 282 ng/100 ml). Testicular size was not affected. Mild reversible gynaecomastia, however, was present in all boys. The results demonstrate an instant growth decelerating effect of low dose oestrogen administration in tall boys reminiscent to the findings in tall girls under the same low dose regimen. Furthermore these data provide a theoretical base for combining androgens and oestrogens in the early stages of treatment of excessive height in boys in order to antagonize the initial growth accelerating effect of androgens alone.