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

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Abstract
The presence of a nonsteroidal substance (inhibin) within human follicular fluid (HFF) with the ability to suppress pituitary follicle-stimulating hormone (follitropin FSH) but not luteinizing hormone (lutropin LH) secretion was determined by 2 methods. The 1st method consisted of infusion of HFF directly into the anterior pituitary gland of ovariectomized rhesus monkeys. The 2nd employed a hamster pituitary cell culture system. LH and FSH release was stimulated in HFF-treated cells by the addition of luteinizing hormone-releasing hormone (luliberin) to the tissue culture medium. In both methods, to determine the presence of inhibin, the criterion of a decreased FSH release into the medium or serum that was not accompanied by concomitant decrement in LH concentrations was used. Both methods detected the presence of inhibin within HFF from women during the follicular but not the luteal phase of the menstrual cycle. This substance may play a role in the regulation of FSH secretion at a specific stage of the reproductive cycle in women.