Concentration of oestrone and oestradiol in follicular fluid and ovarian venous blood of women.

The concentrations of oestrone and oestradiol as measured by a double isotope derivative method in fluid from Graafian follicles at different phases of the menstrual cycle were compared to the corresponding concentrations in ovarian and peripheral venous plasma collected simultaneously. In follicular fluid the concentration of oestradiol was much greater than that of oestrone. The concentrations of oestrogens were similar in fluid collected from small follicles at all phases of the cycle. The concentration of oestradiol in large follicles (greater than 1 cm diameter) was much higher in the mid-late follicular phase of the cycle (mean = 5390 plus or minus 1330 nmol/l) than in large or small follicles at other phases of the cycle. In the mid-late follicular phase of the cycle large follicles were invariably associated with high concentrations of oestradiol in venous plasma draining the corresponding ovary (mean 49 plus or minus 12 nmol/l). The mean ratio of oestradiol/oestrone in fluid from large follicles in which the concentration of oestradiol was greater than 1400 nmol/l (18.0 plus or minus 1.0, n = 10) was significantly higher than the ratio in corresponding samples of ovarian venous plasma (10.7 plus or minus 1.4, n = 11). These findings suggest that when the concentration of oestradiol in a Graafian follicle exceeds 3500 nmol/l it is likely to be functionally active.