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  • Title: Individual diurnal plasma profiles of thyroid hormones in rainbow trout (Oncorhynchus mykiss) in relation to cortisol, growth hormone, and growth rate.
    Author: Gomez JM, Boujard T, Boeuf G, Solari A, Le Bail PY.
    Journal: Gen Comp Endocrinol; 1997 Jul; 107(1):74-83. PubMed ID: 9208307.
    Abstract:
    In order to characterize the individual diurnal plasma profiles of triiodothyronine (T3) and thyroxine (T4) in rainbow trout (Oncorhynchus mykiss), blood samples from 41 fish were taken every hour during a 24-hr period, through a catheter inserted into the dorsal aorta. The possible influences of day-night alternation, sex, and diet (feed intake, time of meals) on thyroid hormone (TH) profiles were analyzed. The existence of relations between diurnal plasma profiles of T3, T4, T3/T4 ratio, and those of the growth hormone (GH), cortisol (previously described in Gomez et al., J. Exp. Zool. 274, 171-180, 1996), and the growth rate was monitored. Average daily T3 and T4 concentrations were, respectively, 2.6 +/- 0.2 and 5.5 +/- 0.3 ng/ml (n = 41). Our study showed little or no variation in plasma T3 concentrations during one 24-hr period, while those of T4 fluctuated markedly. T4 peaks occurred from a baseline of 4.0 +/- 0.2 ng/ml at a frequency of 2.5 +/- 0.2 peaks/24 hr, with an amplitude of 3.0 +/- 0.4 ng/ml, and a duration of 4.3 +/- 0.4 hr. There was a significant difference between the average circulating T3 level during the day and that at night (2.4 +/- 0.2 vs 2.7 +/- 0.2 ng/ml). No influence of sex or food factors was observed on daily TH concentrations. TH peaks occurred irregularly and asynchronously without apparent influence of day-night alternation, sex, and diet. The growth rate was significantly correlated with the daily T3 concentration (r = 0.77), but not with T4. No significant relationships were found between daily concentrations of T3, T4, GH, and cortisol. The absence of a relationship between TH and GH concentrations suggests that, in salmonids, GH may have no observable short-term action on the conversion of T4 to T3.
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