Prolactin size heterogeneity in human follicular fluid: a preliminary study

Follicular fluid from mature preovulatory follicles was examined for the presence of prolactin (PRL) heterogeneity. Two pools of follicular fluid aspirates were used: one from follicles in which the ova were successfully fertilized in vitro and the other from follicles in which the ova were not successfully fertilized. Follicular fluid aspirates were concentrated by ultrafiltration and subjected to Sephadex G-100 gel chromatography. Fractions were assayed for immunoactive PRL by radioimmunoassay (RIA-PRL) and for bioactive PRL by the Nb2 lymphoma cell bioassay (BA-PRL). The major portion of RIA-PRL activity appeared as a low-molecular-weight component and accounted for 88% of the total PRL activity in the fertilized group and 87% in the unfertilized group. A high-molecular-weight component was also evident (12% and 13% for the two groups, respectively). The high-molecular-weight component in both groups was not active as PRL in the bioassay. These results demonstrate that while two immunoactive, heterogeneous forms of PRL exist in human follicular fluid when measured by RIA, it is only the low-molecular-weight form of PRL that is biologically active as established by Nb2 lymphoma cell bioassay.