Binding of steroids by proteins in follicular fluid of the human ovary.

Steroid-protein interactions were studied in the antral fluid of preovulatory follicles of the human ovary. Two high affinity binding systems are described. These steroid-binding proteins do not differ from those identified in the plasma of women (transcortin and sex binding protein), as indicated by similar specificity, binding affinity, and electrophoretic pattern. Their concentrations in the fluid are either similar to or lower than those in plasma. Since the steroid concentrations in antral fluid are approximately 20- to 100-fold higher than the binding capacities of the specific steroid binders, the buffer role that many authors attribute to the proteins which bind steroids is unlikely in antral fluid.