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  • 1
    Electronic Resource
    Electronic Resource
    Influence of the combination of time of feeding and ration level on the diurnal hormone rhythms in rainbow trout (1995)
    Springer
    Fish physiology and biochemistry 14 (1995), S. 25-36 
    Details
    ISSN: 1573-5168
    Keywords: circadian rhythms ; feeding time ; ration level ; growth hormone ; cortisol ; thyroid hormones ; glucose ; rainbow trout
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The study examined the combined effects of time of feeding (post-dawn, midday-pre-dusk) and ration level (1.5%, 2.0%, 2.5%) on the diurnal rhythms of plasma growth hormone (GH), L-thyroxine (T4), triiodo-L-thyronine (T3), cortisol and glucose concentrations in rainbow trout (Oncorhynchus mykiss) maintained under constant ambient water temperature and natural photoperiod. Plasma GH and glucose concentrations exhibited marked diurnal rhythms, with significant postprandial peaks that were phase-shifted with time of feeding. The ration level did not appear to alter these feeding time-entrained rhythms, but the amplitude of the changes (peaks) were more pronounced in trout fed the higher ration levels. Plasma cortisol concentrations showed distinct diurnal rhythms, with peaks during the photophase and the scotophase in all the treatment groups. The time of feeding did not appear to influence these rhythms, and there was no evidence of a postprandial increase in any group. Plasma GH, cortisol and glucose concentrations were significantly higher in groups fed the 2.5% ration compared with animals fed either 1.5 or 2.0% rations. The diurnal rhythms of plasma T4 concentrations were not affected by the time of feeding or ration level; the peak values generally occurred during the photophase in all the treatment groups. Plasma T3 concentrations did not show any significant diurnal patterns, nor were they influenced by ration levels or time of feeding.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00004288
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  • 2
    Electronic Resource
    Electronic Resource
    Role of thyroid hormones in tilapia larvae (Oreochromis mossambicus): II. Changes in the hormones and 5′-monodeiodinase activity during development (1992)
    Springer
    Fish physiology and biochemistry 9 (1992), S. 487-496 
    Details
    ISSN: 1573-5168
    Keywords: Tilapia ; eggs and larvae ; thyroid hormones ; 5′-monodeiodinase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Thyroid hormone profiles and 5′-monodeiodinase activity were determined in tilapia at different stages of early development. The results showed that both T4 and T3 were present in significant amounts in fertilized eggs. There was a steady decrease in both T4 and T3 levels during embryonic development. The levels continued to decline after hatching until around 7 days later when most of the yolk had been absorbed. The T4 level started to rise then, suggesting that the larval thyroid had begun to produce T4 at this time, which coincided with the period of faster growth of the larvae. The T3 level remained fairly constant until around 20 days after which it rose significantly. In vitro determination of 5′-monodeiodinase activity (5′-D activity) in the whole-body homogenates of larvae showed that the enzymatic conversion of T4 to T3 was not detectable in eggs and 3-day-old larvae but detected in 5-day-old and older larvae. There was a gradual increase in the Vmax as development proceeded indicating increasing 5′-D activity during larval development. The Km values did not differ significantly in the different stages of development. These results are discussed in relation to the growth and development of the larvae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02274229
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  • 3
    Electronic Resource
    Electronic Resource
    Hepatic 5′-monodeiodinase activity in teleosts in vitro: A survey of thirty-three species (1990)
    Springer
    Fish physiology and biochemistry 8 (1990), S. 1-10 
    Details
    ISSN: 1573-5168
    Keywords: teleost fish ; hepatic 5′-monodeiodinase ; thyroid hormones ; triiodothyronine ; monodeiodination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The in vitro hepatic 5′-monodeiodination of thyroxine (T4) to triiodothyronine (T3) in Oreochromis mossambicus, Channa striata, Clarias batrachus, Cyprinus carpio and Oxyeleotris marmorata was found to be time, pH and temperature dependent, and related to the amount of substrate (T4) and homogenate introduced into the reaction vessel, in a manner which was consistent with Menton-Michaelis kinetics, and thus indicative of an enzyme-regulated process. Dithiothreitol introduced into the reaction vessel stimulated T3 production in a dose-related manner. Hepatic 5′-monodeiodinase activity was also detected in a further 28 species of teleosts suggesting that the peripheral monodeiodination of T4, which is well-documented in salmonids, is also widespread amongst other teleost fishes. All species examined exhibited evidence of enzymatic deiodination, but there were marked differences in Km and Vmax values between the species. There was no apparent phylogenetic or environmental relationships to explain the widely divergent Km and/or Vmax values, nor was there a correlation between Km and Vmax when the species were considered together.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00004426
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  • 4
    Electronic Resource
    Electronic Resource
    Does the time of feeding affect the diurnal rhythms of plasma hormone and glucose concentration and hepatic glycogen content of rainbow trout? (1994)
    Springer
    Fish physiology and biochemistry 13 (1994), S. 133-140 
    Details
    ISSN: 1573-5168
    Keywords: diurnal rhythms ; feeding strategy ; growth hormone ; cortisol ; thyroid hormones ; T4 ; T3 ; teleost fish
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The diurnal rhythms of plasma glucose, cortisol, growth hormone (GH) and thyroid hormone (T4, T3) concentrations and hepatic glycogen content were measured in rainbow trout that had been entrained to a specific time of daily feeding (post-dawn, midday, pre-dusk); the purpose of the study was to investigate the significance of feeding time on hormones and metabolite patterns. Plasma GH, cortisol and T4 concentrations all showed evidence of a diurnal rhythm in some treatment groups. There was a significant interaction between the time of feeding and plasma GH and cortisol concentration rhythms; for GH, this appeared to be related to the phase-shifting of the post-prandial increases in plasma GH concentrations, and for cortisol, the rhythms were only evident in fish fed in the post-dawn period [diurnal rhythms were not evident in treatment groups fed in at midday or pre-dusk]. Peak plasma T4 concentrations were evident during the photophase in all three treatment groups; however, the time of feeding had a negligible effect on the timing of those peaks. There were no apparent diurnal rhythms of plasma T3 and glucose concentrations, hepatic glycogen content or hepatosomatic index in any of the three treatment groups.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00004338
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