Objective: To investigate the cyclic changes of serum insulin-like growth factor (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 nad 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.