Plasma insulin-like growth factor-I and its binding proteins 1 and 3 during continuous nonoral and oral combined hormone replacement therapy.

OBJECTIVE

We determined the effects of continuous combined nonoral and oral estrogen-progestin therapy on plasma levels of insulin-like growth factor-I (IGF-I) and its binding proteins 1 (IGFBP-1) and 3 (IGFBP-3).

DESIGN

Forty women complaining of climacteric symptoms were randomized to receive either transdermal estradiol patches (50 microg daily) in combination with an intrauterine system releasing 20 microg of levonorgestrel daily or an established regimen of an oral dose of 2 mg of estradiol and 1 mg of norethisterone acetate daily for 1 year. Fifteen women in the nonoral therapy group and 17 in the oral therapy group completed the 1-year prospective study.

RESULTS

Plasma levels of IGF-I decreased significantly in the oral therapy group, but no changes were observed in the plasma levels of its binding proteins. Transdermal estrogen in combination with intrauterine levonorgestrel did not induce any change in plasma IGF-I, whereas the plasma levels of IGFBP-3 decreased. IGFBP-1 concentrations increased, which may be related to the induction of this protein into the endometrium by the intrauterine levonorgestrel delivery.

CONCLUSIONS

Both the nonoral and oral continuous combined estrogen-progestin therapies used in this study produced only minor changes in the circulating concentrations of IGF-I and its binding proteins.