Hormonal regulation of inhibin B secretion by immature rat Sertoli cells in vitro: Possible use as a bioassay for estrogen detection

The influences of follicle-stimulating hormone (FSH), gonadal steroids, and culture time were studied in relation to inhibin B production by Sertoli c ells of immature rats cultured in vitro. Sertoli cell-enriched cultures wer e established from 18-day-old rats and were maintained in medium supplement ed with insulin, transferrin, and epidermal growth factor at 34 degrees C. A recently developed ELISA for the measurement of inhibin B was used to ass ess the effects of recombinant human FSH (rh FSH), testosterone (T), and es tradiol (E-2) on inhibin B production and accumulation in the culture media of Sertoli cell-enriched cultures and to optimize the cell culture system to serve as a bioassay for the detection and quantification of estrogens an d estrogenlike substances. Prolonging the incubation time (24, 48, or 72 ho urs) of Sertoli cells with control medium without rh FSH, T, or E-2 resulte d in a time-dependent increase of inhibin B production. Incubation with rh FSH (1, 2.5, 5, or 10 U/L) caused a dose- and time-dependent increase of in hibin B production by Sertoli cells (but not by cultured Leydig cells), rea ching a plateau at 5 U/L rh FSH. Addition of T in concentrations of 2.88, 5 , or 50 ng/ml to medium without rh FSH and E-2 significantly lowered the da ily production rate of inhibin B (P < 0.05). In contrast, addition of E-2 ( 0.01 and 0.1 ng/ml) caused a dose-responsive increase in inhibin B producti on after 24 and 48 hours. The relative increment of inhibin B production in duced by E-2 was maximal after 24 hours in the presence of 2.5 U/L rh FSH ( acting synergistically) and in the absence of T. When these conditions are implemented, the Sertoli cell culture system may serve as a bioassay for es trogenic substances, and it may reflect the possibly harmful effect they ma y have on spermatogenesis.