Further evidence that big,big prolactin is preferentially secreted in women with hyperprolactinemia and normal ovarian function.

The heterogeneity of human serum prolactin (PRL) in 12 women with hyperprolactinemia and different derangements of the hypothalamic-pituitary-ovarian axis was studied. The patients were subdivided into three groups: four women with hyperprolactinemia and normal ovarian function (group I), four women with hyperprolactinemia associated with sporadic endometrial bleedings and a positive progestin test (group II), and four women with amenorrhea and a negative progestin test (group III). Gel filtration chromatography of serum samples from patients in group I revealed in three of them that most (80%) of their immunoreactive PRL eluted as big,big PRL (Mr greater than 100,000); whereas the rest of the patients, including those from groups II and III, exhibited a distribution pattern similar to that obtained in normal menstruating women. All PRL species had similar affinities for the antibody, as disclosed by the slopes generated in dose-response curves. These results indicate that ovarian function in hyperprolactinemia might be dependent upon PRL heterogeneity and suggest that big,big PRL may have, under in vivo conditions, a low degree of biologic activity.