49 INSULIN-LIKE GROWTH FACTOR(IGF)AND CARRIER PROTEIN SERUM LEVELS IN TALL GIRLS ON HIGH-DOSE ESTROGENS

Abstract

To further elucidate the behavior of IGF under highdose estrogens we have determined total IGF (tIGF) by a competitive protein binding assay, IGF-I by RIA and IGF carrier protein levels by a modification of the protein binding assay in 17 excessively tall girls (mean age ± SD:13.9 ± 1.3 yrs, mean bone age ± SD:12.4 ± 0.6 yrs) before and 12 months after initiation of estrogen treatment (ethinylestradiol (EE) 300 μg per day). Before therapy the mean ± SD serum level of tIGF was 427 ± 43.4 μU/ml,of IGF-I 182.9 ±36.4 ng/ml.tIGF decreased to 370.7 ± 72 μU/ml(86% of level before) ,IGF-I to 128.3 ± 19.3 ng/ml(70% of level before).Carrier protein concentrations did not change significantly (430.3 ±58.4 ngeq/ml vs. 415.9 ± 77.5 ngeq/ml,n.s.) There was a significant positive correlation between Δ IGF-I and growth rate(r=0.55,p < 0.05) and a significant negative correlation between Δ IGF-I and growth rate(r=0.66, p < 0.001) on EE.- Our results are in keeping with the assumption that growth inhibition observed with highdose estrogens is at least in part due to a specific effect on IGF production.While the net carrier protein content is unchanged, the possibility has to be tested that IGF metabolism may be increased by a change of the carrier protein composition.

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