A. Arukwe et A. Goksoyr, CHANGES IN 3 HEPATIC CYTOCHROME-P450 SUBFAMILIES DURING A REPRODUCTIVE-CYCLE IN TURBOT (SCOPHTHALMUS-MAXIMUS L), The Journal of experimental zoology, 277(4), 1997, pp. 313-325
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.