Effects of butyltin compounds on follicular steroidogenesis in the bullfrog(Rana catesbeiana)

The effects of butyltin compounds on follicular steroidogenesis in amphibians were examined using ovarian follicles of Rana catesbeiana. Isolated follicles were cultured for 18 h in the presence and absence of frog pituitary homogenate (FPH) or various steroid precursors, and the steroid levels in the follicles or culture media were measured by radioimmunoassay (RIA). Among the butyltin compounds, tributyltin (TBT) strongly inhibited the FPH-induced synthesis of pregnenolone (P5), progesterone (P4) and testosterone (T). It also inhibited the conversion of P5–P4 and T to estradiol-17β(E2) and it partially suppressed the conversion of androstenedione (AD) to T, but not P4 to 17α-hydroxyprogesterone (17α-OHP4). A high concentration of dibutyltin (DBT) also inhibited steroidogenesis by the follicles while monobutyltin (MBT) and tetrabutylin (TeBT) had no effect. These results suggest that the initial step of steroidogenesis (P5 synthesis) and enzymes such as 3β-HSD, 17β-HSD and aromatase are inhibited by TBT or DBT. However, 17α-hydroxylase was not suppressed by TBT or the other butyltin compounds.