title: Individual diurnal plasma profiles of thyroid hormones in rainbow trout (Oncorhynchus mykiss) in relation to cortisol, growth hormone, and growth rate.
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.
authors.affiliation: Laboratoire de Physiologie des Poissons, INRA, Rennes, France.
authors.forename: J M
authors.initials: JM
authors.lastname: Gomez
authors.forename: T
authors.initials: T
authors.lastname: Boujard
authors.forename: G
authors.initials: G
authors.lastname: Boeuf
authors.forename: A
authors.initials: A
authors.lastname: Solari
authors.forename: P Y
authors.initials: PY
authors.lastname: Le Bail
mesh_terms: D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology*; D005260:Female; D013006:Growth Hormone / Q000097:blood*; D006854:Hydrocortisone / Q000097:blood*; D008297:Male; D017686:Oncorhynchus mykiss / Q000097:blood / Q000254:growth & development*; D011863:Radioimmunoassay; D012044:Regression Analysis; D013963:Thyroid Hormones / Q000097:blood*; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
chemical_list: D013963:Thyroid Hormones; D014284:Triiodothyronine; D013006:Growth Hormone; D013974:Thyroxine; D006854:Hydrocortisone