Midcycle increase of prolactin seen in normal women is absent in subjects with unexplained infertility

Objective: To compare the bioactive and immunoactive PRL in normal and unexplained infertility subjects. Design: Prospective study. Setting: Department of Obstetrics and Gynecology, Wayne State University and The University of Michigan. Patient(s): Twelve normal, fertile women compared with 12 patients with unexplained infertility. Intervention(s): Serum samples were obtained across the menstrual cycle and for each subject, 5 pools were prepared by combining serum aliquots from the early follicular, late follicular, midcycle, and midluteal and late luteal phases of the cycle. Main Outcome Measure(s): Niobium lymphoma cell bioassay and an immunoradiometric assay were used to quantitate PRL. Result(s): A midcycle increase in PRL was seen in controls by both assays and these levels were greater compared with other cycle stages. Comparison of midcycle PRL between groups showed differences only between bioactive PRL (34.2 ± 8.3 versus 19.2 ± 3.4 ng/mL [conversion factor to SI unit, 1.00]). The ratios between bioactive and immunoactive PRL were comparable. Significant correlation between bioactive and immunoactive PRL was seen for both control (r = 0.616) and unexplained infertility (r = 0.660) groups. Conclusion(s): The midcycle elevations of bioactive and immunoactive PRL seen in normal women were absent in women with unexplained infertility. This alteration in PRL dynamics may be a part of subtle differences in the reproductive hormone profile of women with unexplained infertility compared with their fertile counterparts.