Changes in three hepatic cytochrome P450 subfamilies during a reproductive cycle in turbot (Scophthalmus maximus L.)

Sexual differentiation of the hepatic cytochrome P450 system was characterized in 2-year-old farmed turbot (Scophthalmus maximus L.) during their first spawning period (January–September). The fish were kept in tanks supplied with continuously flowing seawater (34.5%, ppt) at a constant temperature of 16°C and natural photoperiod (60°N). Sampling of liver samples (n = 4–6) was performed once every month for 9 months. Pronounced sex differences were recorded in the activities of 7-ethoxyresorufin O-deethylase (EROD), 7-ethoxycoumarin O-deethylase (ECOD), and NADPH-cytochrome P450 reductase during spawning (May–July). EROD activity in female fish decreased gradually towards the onset of ovulation in May–July to rise again in the postspawning period. The decrease correlated with increasing gonadosomatic index and estradiol17β (E2) levels in plasma. Immunochemical detection of CYP1A (58 kDa), CYP2K-like (47 and 52 kDa), and CYP3A-like (58 and 60 kDa) proteins in Western blotting, and ELISA showed higher protein levels in male compared to female fish from April/May-June, and significant differences were observed in June (CYP2K-like also in April and May). Analysis of monthly variations within sexes during the reproductive cycle shows significant monthly changes in all parameters in both female and male fish. Both CYP2K- and CYP3A-like protein levels were significantly elevated in male fish during spawning in June. To study the induction response during spawning, β-naphthoflavone (BNF) 75 mg/kg body weight) was administered intraperitoneally to both sexes in June. BNF caused a significant increase in EROD and ECOD activities and CYP1A protein levels but had no effect on NADPH-cytochrome P450 reductase activity or CYP2K-like/CYP3A-like proteins. This study documents, for the first time in any fish species or lower vertebrate, the sexual differentiation in the liver of three different CYP subfamilies during sexual maturation and spawning. J. Exp. Zool. 277:313–325, 1997. © 1997 Wiley-Liss, Inc.