Pituitary follicle-stimulating hormone heterogeneity: assessment of biologic activities of each follicle-stimulating hormone form.

The multiple species of follicle-stimulating hormone (FSH) present within pituitary tissue were separated by the technique of polyacrylamide gel isoelectric focusing. The ability of each FSH species to stimulate the secretion of plasminogen activator from cultured granulosa cells was tested (FSH in vitro bioassay). A wide range of biologic/radioimmunologic FSH activity was observed when FSH species were compared. As the isoelectric point of the FSH molecule declined, so did the biologic activity. A second series of studies was performed to determine which forms of FSH were secreted by pituitary tissue in vitro. All of the forms of FSH present in pituitary tissue were secreted into culture medium. However, the relative proportions of FSH forms in the pituitary and medium were not always similar. Exposure of pituitary tissue to luteinizing hormone-releasing hormone elicited an increase in the relative proportion of the more biologically active forms of FSH that were secreted. These studies suggest that the hormonal milieu surrounding the pituitary affects not only the quantity but also the potency of the FSH signal emitted. Thus, the basis for observed differences between biologic and immunologic FSH activities observed during some endocrine states may be the result of preferential secretion of certain FSH species.