Polycyclic aromatic hydrocarbons inhibit in vitro ovarian steroidogenesis in the flounder (Platichthys flesus L.)

The in vitro effect of polycyclic aromatic hydrocarbons (PAHs) on ovarian s teroidogenesis of the flounder (Platichthys flesus L.) was determined. Full y vitellogenic ovary tissue was in vitro incubated in the presence of phena nthrene, benzo[a]pyrene or chrysene, using 17 alpha-hydroxyprogesterone or androstenedione as precursors. Androstenedione (A), testosterone (T) and 17 beta-estradiol (E-2) synthesised in the presence of PAHs were assayed by r adioimmunoassay and results compared with control incubations. In order to establish the effect of PAHs on the steroidogenic enzyme systems cytochrome P450 17,20-lyase (P450-17,201), 17 beta-hydroxysteroid dehydrogenase (17 b eta- HSD) and cytochrome P450 aromatase (P450-arom), results were also comp ared with the action of ketoconazole (KCZ) and aminoglutethimide (AMG), whi ch are, respectively, inhibitors of cytochrome P450 steroidogenic enzymes a nd of P450-arom. KCZ inhibited secretion of A and E-2 in 65% and T in 40%, as a consequence of inhibited P450-17.201 and P450-arom. AMG inhibited P450 -arom, which resulted in decreased E-2 synthesis to approximately 50% of co ntrol incubations. All the three PAHs inhibited A secretion by approximatel y 50% and E-2 from 10 to 40%. Because steroid conjugation was also inhibite d by phenanthrene, it could be concluded that PAH action was mediated by an inhibitory effect over P450-17,201, 17 beta-HSD and P450-arom. Except for 17 beta-HSD, PAHs resembled KCZ, and P450-17,201 was the most sensitive to their inhibitory effect. In conclusion, PAHs strongly blocked the activity of P450-17,201, a rate-limiting enzyme for conversion of C21 to C19 steroid s, and showed, therefore, the potential to disrupt the reproductive cycle o f fish living in polluted environments, due to impairment of steroid biosyn thesis. (C) 2000 Elsevier Science B.V. All rights reserved.