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  • 1995-1999  (2)
  • 1
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Exposure of sea bass Dicentrarchus labrax oocytes to 25, 50, 100, and 300 IU ml−1 of human chorionic gonadotropin (hCG) resulted in a dose-dependent increase (ED50=60 IU ml−1) in the maximal maturation and volume response rate over a 120-h incubation period. Oocytes responded in a similar dose-dependent manner to graded doses of homologous sea bass pituitary extract (ED50=3·3#10−2 PE ml−1). The response latency of sea bass oocytes to endogenous and exogenous gonadotropins was similar (t1/2≃45 and 48 h, respectively). Both 17α,20β-dihydroxy-4-pregnen-3-one (17,20βP) and 17α,20β,21-trihydroxy-4-pregnen-3-one (20βS) stimulated maturation in a dose- and time-dependent manner with t1/2 values less than those of hCG (15 h and 7·5 h at 100 ng ml−1, respectively); 17α,20α-dehydroxy-4-pregnen-3-one (17,20αP) was ineffective. 17,20βP was more potent at all doses tested. The stimulatory actions of gonadotropin and maturation-inducing steroid (MIS) involved both transcription and translation since maturation was significantly inhibited in the presence of actinomycin D and cycloheximide. Moreover, pituitary extract and hCG stimulated release of higher levels of 17,20βP in a dose- and time-dependent manner in follicle incubations as compared to 20βS suggesting that this steroid may in fact be the MIS in this species.
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  • 2
    ISSN: 1573-5168
    Keywords: Fructose 1,6 biphosphatase ; sea bass ; diet composition ; reproductive cycle ; spawning ; liver ; ovaries ; testes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The fructose 1,6 biphosphatase (FBPase) activity was measured in the liver and gonads of broodstock sea bass that were fed three experimental diets over the reproductive cycle. Enzyme activity was measured at the pre-spawning (November), spawning (February) and post-spawning (May) periods. Additionally, some biometric indices were calculated at these three times. The different diets, one with standard composition (51% protein, 13% lipid, 10% digestible carbohydrates), one with a high-carbohydrate content (32% protein, 13% lipid, 32% digestible carbohydrates) and one deficient in ω3 essential fatty acids (51% protein, 13% lipid, 10% digestible carbohydrates), had similar affects on growth and gonad development, as deduced from the similar weight, condition factor, hepatosomatic index, gonadosomatic index and liposomatic index over the reproductive cycle. FBPase activity was detected at all times in the liver of both sexes, and in the ovaries but not in the testes. In general, females showed greater liver activity than males, especially at spawning time. During post-spawning, FBPase activity fell in tissues of both sexes. Enzyme activity was also affected, mostly in the liver, by the different types of feed; hepatic activity in fish fed the high-carbohydrate diet fell during the spawning and post-spawning periods, though at a different level for each sex. The diet deficient in ω3 EFA presented the lowest FBPase activity, compared with the other diets, in females during the spawning period; there was very little change in males or females over the reproductive cycle. The results showed that the highest gluconeogenic activity in sea bass broodstock occurred at the spawning time and the females had larger glucose requirements than males over the reproductive cycle, as demonstrated by the absence of FBPase activity in testes. This work also confirmed the adaptative capacity of this enzyme to different nutritional and physiological conditions.
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