Sensitive in vitro bioassay for the measurement of serum follicle-stimulating hormone.

A sensitive in vitro bioassay for measuring serum follicle-stimulating hormone (FSH) levels has been developed based on the stimulation of estrogen production by cultured rat granulosa cells. In the presence of androstenedione, FSH stimulated estrogen production in a dose-dependent manner. Cell sensitivity to FSH was further enhanced by the addition of diethylstilbestrol, a phosphodiesterase inhibitor, insulin, and human chorionic gonadotropin. Although the inclusion of 4% gonadotropin-free serum from hypophysectomized rats inhibited granulosa cell responsiveness, pretreatment of serum with polyethylene glycol (12%) substantially eliminated the serum interfering effect without loss of FSH activity. In normal male and female rats, serum bioactive FSH levels were low, while castration increased these levels 2.6-and 5.7-fold, respectively. These increases were suppressed by treatment with testosterone propionate or estradiol benzoate. This in vitro assay allows the measurement of circulating bioactive FSH and provides a convenient tool to advance studies on the role of FSH in the neuroendocrine control of gonadal maturation and reproductive cycles.