CHANGES IN 3 HEPATIC CYTOCHROME-P450 SUBFAMILIES DURING A REPRODUCTIVE-CYCLE IN TURBOT (SCOPHTHALMUS-MAXIMUS L)

Sexual differentiation of the hepatic cytochrome P450 system was chara cterized in 2-year-old farmed turbot (Scophthalmus maximum L.) during their first spawning period (January-September). The fish were kept in tanks supplied with continuously flowing seawater (34.5 parts per tho usand, ppt) at a constant temperature of 16 degrees C and natural phot operiod (60 degrees N). Sampling of liver samples (n = 4-6) was perfor med once every month for 9 months. Pronounced sex differences were rec orded in the activities of 7-ethoxyresorufin O-deethylase (EROD), 7-et hoxycoumarin O-deethylase (ECOD), and NADPH-cytochrome P450 reductase during spawning (May-July). EROD activity in female fish decreased gra dually towards the onset of ovulation in May-July to rise again in the postspawning period. The decrease correlated with increasing gonadoso matic index and estradiol-17 beta (E(2)) levels in plasma. Immunochemi cal 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 h igher protein levels in male compared to female fish from April/May-Ju ne, 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 param eters in both female and male fish. Both CYP2K- and CYP3A-like protein levels were significantly elevated in male fish during spawning in Ju ne. To study the induction response during spawning, beta-naphthoflavo ne (BNF) 75 mg/kg body weight) was administered intraperitoneally to b oth sexes in June. BNF caused a significant increase in EROD and ECOD activities and CYP1A protein levels but had no effect on NADPH-cytochr ome P450 reductase activity or CYP2K-like/CYP3A-like proteins. This st udy documents, for the first time in any fish species or lower vertebr ate, the sexual differentiation in the liver of three different CYP su bfamilies during sexual maturation and spawning. (C) 1997 Wiley-Liss, Inc.