Biology Reference
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of the muscle protein myosin heavy chain (Coughlin et al., 2001). In T3-
treated juvenile coho salmon, mean values of hematocrit were signifi cantly
decreased and the prolonged contraction (tetani) and twitch rates of
contraction, relaxation and maximum force were signifi cantly increased
(Katzman and Cech, 2001).
T4 treatment stimulated lipid mobilization in parr, by decreasing total
lipids and increasing lipolytic enzyme activity in the liver and dark muscle,
as well as in mesenteric fat by decreasing total tissue mass and increasing
lipase activity (Sheridan, 1986).
Few reports suggested that T3 enhances lipid
metabolism including synthesis, mobilization and degradation (Farbridge
and Leatherland, 1988). A study in trout demonstrated that T3 could induce
the liver (Na+K+)-ATPase activity (Pirini et al., 2002). Using dispersed
salmon hepatocytes, Bhattacharya et al (1985) showed a stimulation of
protein metabolism
in vitro
by T3.
6.3.1.2.3 Eye
Pioneer works demonstrated that administration of T4 favored proportions
of porphyropsin in rods of rainbow trout (Munz and Swanson, 1965; Cristy,
1974; Allen, 1977). Similarly, Beatty (1969, 1972) showed in the kokanee
salmon (
O. nerka
), a species of salmon, which does not normally exhibit
any signifi cant porphyropsin at any time of its life cycle that treatment
with thyroid hormones or TSH induced the rhodopsin to porphyropsin
conversion. Moreover, when PTU (goitrogen; Sullivan et al., 1987) or
methimazole (deiodinase inhibitor; Alexander et al., 1998) has been
administered to smoltifying coho salmon, there was impairment to the
retinae pigmentary changes. A recent study by quantitative real-time
PCR showed that TH-treated parr of rainbow trout had downregulated
ultraviolet-sensitive (SWS1) opsin expression in all quadrants of retina and
upregulated short wavelength-sensitive (SWS2) and middle wavelength-
sensitive (RH2) opsin expressions in the temporal quadrants (Veldhoen
et al., 2006). Proteomic analysis of opsins and thyroid hormone-induced
retinal development using rainbow trout as a model of cone apoptosis and
cone regeneration also demonstrated these changes in opsins (Allison et al.,
2006b). In coho salmon, Temple and collaborators (2008a, b) showed that at
least two RH2 opsin
subtypes were expressed in MWS cones and that they
were differentially expressed among alevin, parr and TH-treated alevin
groups. They also demonstrated that, concerning the spectral absorbance
of rods, TH-treated alevins were long wavelength shifted, consistent with
an increase in A2 (Temple et al., 2008a). Exogenous TH induced an increase
in spectral absorbance of all photoreceptors, consistent with an increase in
vitamin A2 (Temple et al., 2008b), which is agreement with the seasonal
