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The effect of handling and blood removal on plasma levels and hepatic deiodination of thyroid hormones in adult male and female rainbow trout, Oncorhynchus mykiss

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Abstract:

We studied the effects of handling and blood removal (0.4% of body mass) on the thyroid system of fasted ~1000-g adult male and female rainbow trout, Oncorhynchus mykiss, over a 3-day period. Relative to undisturbed controls, bleeding lowered the mean hematocrit (HCT) by 19% and on day 1 increased the hepatic inner-ring deiodination of 3,5,3'-triiodothyronine (T3) (T3IRD), but did not alter thyroxine (T4) outer-ring deiodination (T4ORD) or inner-ring deiodination (T4IRD) activity or plasma T4 or T3 levels. Regardless of treatment, hepatic T4ORD activity and HCT were lower in females than in males, and over the 3 days following bleeding, the plasma T3 level increased and the plasma T4 level decreased progressively for both sexes. We conclude that handling and bleeding induce a temporary increase in hepatic T3 conversion to 3,3'-diiodothyronine with no change in T4 conversion to reverse T3. This is consistent with independent control of T3IRD and T4IRD activities. Furthermore, HCT and hepatic T4ORD activity are lower in adult females, and 10 days after transfer of trout to smaller tanks, plasma T4 and T3 levels may still be adjusting.

Nous avons étudié les effets de 3 jours de manipulations et de prélèvements de sang (0,4 % de la masse totale) sur le système thyroïdien de truites arc-en-ciel (Oncorhynchus mykiss) adultes d'environ ~1000 g, mâles et femelles, soumises au jeûne. Par comparaison à des truites témoins non perturbées, la saignée diminue l'hématocrite moyen (HCT) de 19 % et, au jour 1, augmente la désiodation hépatique de l'anneau interne de la 3,5,3'-triiodothyronine (T3) (T3IRD), mais n'affecte pas la désiodation de l'anneau externe de la thyroxine (T4) (T4ORD) ou la T4IRD, ni les concentrations plasmatiques de T4 et de T3. Dans tous les traitements, l'activité de T4ORD hépatique et l'HCT étaient toujours moins élevés chez les femelles que chez les mâles et, durant les 3 jours suivant la saignée, la concentration plasmatique de T3 augmentait et celle de T4 diminuait progressivement chez les deux sexes. Il semble donc que les manipulations et les saignées provoquent une augmentation temporaire de la conversion hépatique de T3 en 3,3'-diiodothyronine, sans qu'il y ait modification de la conversion inverse de T4 en T3. Cela est compatible avec l'existence d'un contrôle indépendant des activités de T3IRD et de T4IRD. De plus, l'HCT et l'activité de T4ORD hépatique sont moins élevés chez les femelles adultes; 10 jours après le transfert des truites dans des aquariums plus petits, les concentrations plasmatiques de T4 et de T3 peuvent n'être pas encore totalement ajustées.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: February 1, 2002

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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