What maintains the high intra-follicular estradiol concentration in pre-ovulatory follicles?

We were able to identify perlecan as the most likely candidate for the major estrogen-binding protein in the follicular fluid.

We used dialysis membrane with a pore size of <3 KD to characterize the estrogen-binding capacity of the follicular fluid. We performed PCR, western blot, and ELISA on luteinized granulosa cells to determine if sex hormone-binding globulin (SHBG) is produced by granulosa cells, and finally we used affinity columns and mass spectrometry to identify the estrogen-binding protein in the follicular fluid.

The purpose of the study was to establish the mechanism by which the estrogen concentration difference between the follicular fluid and the serum is maintained.

We found that a significant estrogen concentration difference is maintained in a cell-free system and is lost with proteolysis of the follicular fluid proteins. Luteinized granulosa cells are likely not a source of SHBG, as we were not able to detect expression of SHBG in these cells. Perlecan was the most highly enriched follicular fluid protein in the affinity columns. Conclusions: We were able to identify perlecan as the most likely candidate for the major estrogen-binding protein in the follicular fluid.