Maintained fertility in a patient with hyperprolactinemia due to big, big prolactin.

The heterogeneity of serum PRL in a hyperprolactinemic but fertile woman (Patient A) was studied by gel chromatography. Ninety percent of her PRL eluted with the void volume as "big, big" PRL and only 6% coincided with monomeric "little" PRL. Sera from a woman who had hyperprolactinemia associated with infertility (Patient B) and a normal woman (Patient C) exhibited the usual heterogeneous distribution, where 5% and 19%, respectively, eluted as big, big PRL and 76% and 65%, respectively, eluted as little PRL. Serial dilutions of the serum from Patient A displayed nonparallelism to the lines obtained from similar dilutions of both PRL standard and serum from a normal woman, suggesting possible immunological differences among the three forms of the circulating hormone. This finding, together with reports that suggest big, big PRL has a low receptor affinity, may account for the apparent lack of any biological effect upon Patient A from her sustained hyperprolactinemia.