Human Follicular Fluid Contains a Follicle-Stimulating Hormone (FSH) Receptor Binding Inhibitor Which Has FSH Agonist Activity, is Immunologically Similar to FSH, But Can Be Distinguished from FSH*

Abstract

We have previously reported the presence in human follicular fluid (hFF) of a high (greater than 5000) mol wt FSH receptor binding inhibitor (FSH-BI). This hFF FSH-BI was further purified by removal of material insoluble in acidified acetone (pH 4.1) but soluble in diethyl ether (pH 10.5), followed by molecular sieving through Sephacryl S-100. FSH-BI activity eluted from S-100 with an elution volume similar to that of hFSH, but could be distinguished from hFSH on the basis of a differential sensitivity to acid inactivation. Human FSH was inactivated in acetone at pH 4.1 (1 h, 25 C), whereas hFF FSH-BI retained activity under these conditions. Human FF FSH-BI also demonstrated FSH-like agonist activity, defined as the ability to stimulate basal levels of estradiol synthesis in cultured rat Sertoli cells. Human FSH-BI strongly cross-reacted to a commercially available monoclonal antibody used to measure serum hFSH. Indeed, recovery of FSH immunologic activity was significantly greater (134-fold on a mass basis) after partial purification, indicating that antibody recognition sites were apparently masked in unfractionated hFF. In summary, large mol wt hFSH-BI has been partially purified from hFF and found to be similar in size to pituitary hFSH and to have FSH-like agonist activity in vitro. Although distinguishable from pituitary hFSH on the basis of stability to acid, hFSH-BI appears immunologically related to pituitary hFSH so that measurements of hFSH levels in hFF using immunologic techniques should be interpreted with caution.

Low Levels of Follicle-Stimulating Hormone Receptor-Activation Inhibitors in Serum and Follicular Fluid from Normal Controls and Anovulatory Patients with or without Polycystic Ovary Syndrome

“…However, not all FSH-binding inhibitory activity results in inhibition of FSH, because part of these binding inhibitors have FSH agonist activity (22). Results of the present study show that the biological activity of FSH in the context of serum proteins is approximately 50% of the activity in the absence of serum.…”

Purification of high-molecular-weight follicle-stimulating hormone binding inhibitor in porcine follicular fluids

“…The concentrations (µ /\; mean ± sem) of 17 high-molecular-weight FSHBI was performed using the fraction of UK 10 retentate of large amounts of follicular fluids from medium follicles that was not retained on Blue Sepharose CL6B. Figure 3 shows anion-exchange FPLC of the fraction not retained on Blue Sepharese CL6B and FSHBI activity of the eluates.…”

“…Sluss et al. Lee et al (17,18) have reported the presence of high-molecular-weight (M 5 7 000) FSHBI in human follicular fluids. Lee et al (17,18) have reported the presence of high-molecular-weight (M 5 7 000) FSHBI in human follicular fluids.…”

Definition and Measurement of Follicle Stimulating Hormone

“…Analysis of binding kinetics can give results that are different for intact and deglycosylated FSH (212). These assays may also be affected by FSH-like molecules (213) or other inhibitory materials (214). The physiological basis of such molecules remains to be clarified.…”