Relationships between insulin-like growth hormone factor-I and estradiol in reproductive aging

Objective: To evaluate gonadotropins, estrogen, and insulin-like growth hormone factor (IGF)-I and its binding proteins throughout the normal menstrual cycle and during aging within the reproductive life span. Design: Daily blood samples were obtained from 17 normally cycling women. Setting: Center for Fertility and Reproductive Medicine, Newark, New Jersey. Participants: Ten women aged 19 to 34 years old and seven women aged 42 to 47 years old. Main Outcome Measures: Luteinizing hormone (LH), FSH, E(2), and P were assayed in daily blood samples. Early follicular, late follicular, midluteal phase, and samples taken at ovulation were also assayed for IGF-I and IGFBP-I and IGFBP-III. Results: Follicle-stimulating hormone (FSH) increased significantly with reproductive aging. IGF-I and its binding proteins did not fluctuate through the menstrual cycle. IGF-I and its binding proteins did not change over the 28-year time span studied, in the face of significantly increased circulating estradiol associated with reproductive aging. Conclusion: Rising E(2) may be a subtle harbinger of the perimenopause. IGF-I and its binding proteins did not decrease with cycle stage or with aging during the reproductive years, perhaps because of increased estradiol stimulation of the somatotrophic axis. (C) 1997 by American Society for Reproductive Medicine.