The insulin-like growth factor-I system and hormone replacement therapy.

Objective: To determine the effects of hormone replacement therapy on plasma concentrations of free and total insulin-like growth factor (IGF)-I, IGF binding protein (BP)-1, and IGFBP-3.
Design: Clinical study.
Setting: Gynecologic clinic at a university hospital.
Patient(s): Seventy-one postmenopausal women.
Intervention(s): Six cycles of four different hormonal replacement therapy regimens: oral conjugated estrogens, transdermal estradiol, oral conjugated estrogens and norethisterone, and transdermal estradiol and norethisterone acetate.
Main Outcome Measure(s): Blood samples were collected before and after treatment for measurement of free and total IGF-I, IGFBP-1, and IGFBP-3.
Result(s): Conjugated estrogen replacement therapy is associated with a decrease in plasma concentration of total IGF-I and increase in concentrations of free IGF-I and IGFBP-1. Transdermal estrogens have no effect on total and free IGF-I and IGFBP-1 concentrations. Oral norethisterone plus conjugated estrogens increased free IGF-I and IGFBP-1 concentrations but did not change IGF-I concentrations. Transdermal conjugated estrogens plus norethisterone acetate increased free IGF-I concentrations but not total IGF-I or IGFBP-1 concentrations. The plasma concentration of IGFBP-3 did not change in any group.
Conclusion(s): Alterations in total IGF-I concentration can occur depending on the route of hormone replacement therapy administration. Free IGF-I concentrations were elevated in all study groups except that treated with transdermal estrogens.