Human follicular fluid: prolactin is biologically active and ovum fertilization correlates with estradiol concentration

The bioactivity of prolactin (PRL) in follicular fluid (FF) obtained from mature preovulatory follicles was measured by the Nb2 lymphoma-cell bioassay and compared with the immunoreactivity as measured by radioimmunoassay (RIA-PRL). There was a good correlation between the two assay systems (P less than 0.01), and when RIA-PRL was more than 25 ng/ml, both assay systems yielded comparable values, with a mean bioassay/RIA ratio of 1.06 +/- 0.03; however, when RIA-PRL was 25 ng/ml or less, a discrepancy between the two assay systems was evident, with a bioassay/RIA ratio of 1.55 +/- 0.15. The estradiol (E2) concentration of FF obtained from follicles that contained oocytes which were subsequently fertilized was greater than that in follicles containing oocytes which were not fertilized: 588 +/- 62 vs 376 +/- 37 ng/ml (P less than 0.01), respectively. No differences were found in bioassay-PRL, RIA-PRL, progesterone (P), and FF volumes between fertilized and unfertilized groups of follicles. FF from mature preovulatory follicles contained greater concentrations of RIA-PRL compared to immature follicles (34.6 +/- 3.1 vs 8.5 +/- 1.6 ng/ml; P less than 0.001).