INSULIN-LIKE-GROWTH-FACTOR I (IGF-I) SERUM LEVEL MODIFICATIONS DURINGTRANSDERMAL ESTRADIOL TREATMENT IN POSTMENOPAUSAL WOMEN - A POSSIBLE BIMODAL EFFECT DEPENDING ON BASAL IGF-I VALUES

The objective of this study was to determine the influence of transder mal estradiol administration on insulin-like growth factor I (IGF-I) s erum level in a series larger than those published to date. Thirty-nin e postmenopausal women with vasomotor symptoms were studied; blood sam ples (after overnight fast) were obtained just before and at the 6th m onth of treatment with transdermal estradiol 0.05 mg/day, and serum le vels of ICF-I, growth hormone and sex hormone binding globulin (SHBG) were evaluated. Sixteen of the 39 women did not show variations of IGF -I values (group A), while 11 showed an increase (group B) and 12 show ed a decrease (group C) by at least 20% with transdermal estradiol tre atment. IGF-I basal levels were higher in group C as compared to group A (p < 0.05) and to group B (p < 0.01), intermediate in group A, and lower in group B. Group C showed a significant lt increase of SHBG val ues with transdermal estradiol treatment. Transdermal estradiol seems to induce a bimodal effect an IGF-I serum levels, depending on IGF-I b asal values. This could be caused by a different responsivity to estro gen action on the liver (the major site of circulating ICF-I productio n) and also, possibly, by a different degree in insulin sensitivity ch anges caused by estrogen.