Serum levels of insulin-like growth factor I and insulin-like growth factor-binding protein-1 and -3 in women with regular menstrual cycles

Objective: To investigate the cyclic changes of serum insulin-like growth factor I (IGF-I), IGF-binding protein-1 (IGFBP-1) and IGFBP-3 levels during ovulatory menstrual cycle. Design: A prospective study following a preset protocol. Setting: A tertiary-care academic medical center. Participants: Thirty young female adults with regular menstrual cycles were recruited (18 with normal luteal phase and 12 with inadequate luteal function confirmed by serum P levels). Main Outcome Measures: Serum concentrations of IGF-I, IGFBP- 1, and IGFBP-3 from women with regular menstrual cycles were assayed. Circulating E₂ and P levels also were determined to certify the ovulatory cycles. Results: In women with normal luteal function, there was a peak of serum IGFBP-1 levels before ovulation concomitant with the preovulatory E₂ peak. The nadir of serum IGFBP-1 levels was in the midluteal phase. Circulating IGFBP-1 elevated rapidly during late luteal phase and reached a peak on the 1st day of menstruation then declined slightly until a preovulatory IGFBP-1 peak occurred. In women with inadequate luteal function (midluteal serum levels of P < 10 ng/mL [conversion factor to SI unit, 3.180]), the preovulatory increase in serum IGFBP-1 was not significant and the circulating IGFBP-1 levels fluctuated throughout the menstrual cycle except for a unique peak of serum IGFBP-1 on the 1st day of menstruation. By contrast, there were no cyclic changes of serum IGF-I and IGFBP-3 levels in women with regular menstrual cycles, including both normal and inadequate luteal functions. Conclusions: The preovulatory increase in serum IGFBP-1 levels may be of follicular origin and associated with the subsequent luteal function in females with ovulatory cycles. However, the involvement of IGFBP- 1 in the process of follicular maturation and luteogenesis, as well as the regulation of luteal function, needs to be explored further.