Comparison of Nb2 lymphoma cell bioassay with immunoassay for human prolactin: the role of estrogen.

The Nb2 lymphoma cell bioassay (BA-PRL) is a sensitive measure of serum prolactin under physiologic conditions. Since estrogens prime the lactotroph, prolactin heterogeneity and hence bioassayable prolactin may be influenced. A study was performed to observe the effect on BA-PRL of changing estradiol (E2) concentrations. In 13 normal subjects clomiphene citrate was administered to stimulate ovarian activity and blood samples were obtained before and after stimulation. Estradiol, BA-PRL and immunoassayable prolactin (RIA-PRL) were measured. While there was a substantial increase in E2 post-stimulation (p less than 0.001), there was no significant change in BA-PRL, RIA-PRL or BA/RIA-PRL ratios. Despite the lack of change in the mean BA/RIA-PRL ratio over a wide range of E2 concentrations that include and exceed those normally seen in spontaneous menstrual cycles, it is difficult to drawn conclusions regarding an association between E2 and BA/RIA-PRL ratios as there was no discernible change in the concentration of prolactin (possibly due to the antiestrogenic effect of clomiphene citrate).