Scott C. Chappel

Inhibin: Differences in Bioactivity within Human Follicular Fluid in the Follicular and Luteal Stages of the Menstrual Cycle

Summary The presence of a nonsteroidal substance (inhibin) within human follicular fluid (HFF) with the ability to suppress pituitary follicle-stimulating hormone (FSH) but not luteinizing hormone (LH) secretion was determined by two methods. The first method consisted of infusion of HFF directly into the anterior pituitary gland of ovariectomized rhesus monkeys. The second employed a pituitary cell culture system. Release of LH and FSH was stimulated in HFF-treated cells by the addition of luteinizing hormone-releasing hormone (LHRH) to the tissue culture medium. In both methods, to determine the presence of inhibin, we used the criterion of a decreased release of FSH into the medium or serum that was not accompanied by an concomitant decrement in LH concentrations. Both methods detected the presence of inhibin within HFF from women during the follicular but not the luteal phase of the menstrual cycle. This finding suggests that this substance may play a role in the regulation of FSH secretion at a specific stage of the reproductive cycle in women.

Pituitary follicle-stimulating hormone heterogeneity: assessment of biologic activities of each follicle-stimulating hormone form**Supported by NIH grant R01-14742.

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.