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Relationships between insulin-like growth hormone factor-I and estradiol in reproductive aging
1Department of Obstetrics and Gynecology, University of Medicine and Dentistry of New Jersey, Newark, USA.
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, E2, 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 E2 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.