Ovarian follicular fluid contains immunoreactive estriol: lack of correlation with estradiol concentrations

Estradiol and estrone concentrations in ovarian follicular fluid change acc ording to the ovulatory cycle, but no studies on the possible presence and/ or changes of estriol are available. The aim of the present study was to ev aluate whether estriol is measurable in follicular fluid and how its concen tration changes according to the volume of ovarian follicles and to the mat urational stage of oocytes. A group of women (n = 39) undergoing a program of induction of ovulation wa s included in this study and divided into three groups according to the cau ses of infertility: those with unexplained infertility (n = 11); those with endocrine disturbances (n = 5); and normal ovulatory women (n = 23) (contr ols). The follicles recruited (n = 116) on the basis of morphology and the appearance of the oocyte cumulus-corona complex were divided into: mature ( n = 22); intermediate (n = 75); immature (n = 11); and atretic (n = 8). Ova rian follicles were also divided according to the diameter of each: < 1.5 c m (n = 38); 1.6-2.4 cm (n = 66); and > 2.5 cm (n = 12). Ovarian follicular fluids were aspirated under ultrasound guidance and a blood specimen was co llected from each subject. Estriol and estradiol concentrations were evalua ted by radioimmunoassay in serum and follicular fluid following an ether ex traction. Estriol was found in high concentration in each sample of follicular fluid, significantly higher than in the respective serum sample (p < 0.01). Altho ugh the estradiol concentration was significantly lower in follicles contai ning immature and atretic oocytes than in intermediate or mature follicles (p < 0.01), the estriol concentration did not depend upon the maturational stage. In addition, the follicular fluid estriol concentration did not diff er according to the causes of infertility. Follicular fluid and serum estra diol concentrations showed significant correlation (p < 0.01), whereas no s ignificant correlation was observed between serum and follicular estriol co ncentrations. The present data show that follicular fluid contains a high concentration o f estriol and that its changes are independent of the ovulatory cycle and e stradiol concentrations, supporting an independent origin and suggesting a different function of estriol.