The effect of thyroid hormones and temperature on protein and nucleic acid contents of liver and muscle of Sarotherodon mossambica

Individual diurnal plasma profiles of thyroid hormones in rainbow trout (Oncorhynchus mykiss) in relation to cortisol, growth hormone, and growth rate

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.

The effects of thyroid hormones and starvation on hepatic mitochondrial nucleic acids of rainbow trout (Oncorhynchus mykiss)

Twenty four hours after an intraperitoneal injection of thyroxine (T4; 4.4, 44 ng/g body wt) or triiodothyronine (T3; 3.3, 33 ng/g body wt), DNA and RNA were significantly reduced in isolated liver mitochondria of rainbow trout. Total liver DNA was increased with the higher doses in both T4- and T3-injected specimens while total RNA was significantly reduced with the same doses. Total circulating plasma T4 was reduced with the injections of T3 or starvation, and plasma T3 was increased severalfold with the T3 injections. Plasma T4 also increased fivefold after a higher dose of T4 injection while starvation significantly reduced the concentration, when measured by radioimmunoassay.

Oxidative metabolism in a teleost, Anabas testudineus Bloch: effect of thyroid hormones on hepatic enzyme activities

In vivo administration of L-thyroxine (L-T4) in Anabas testudineus, while significantly stimulated the activities of cytochrome c oxidase and alpha-glycerophosphate dehydrogenase (alpha-GPDH), inhibited glucose-6-phosphate dehydrogenase (G-6-PDH), cytosolic and mitochondrial malate dehydrogenase (cyt. MDH; mit. MDH), and Mg2+ DNP-dependent adenosine triphosphatase (Mg2+ ATPase) activities. The activities of lactate dehydrogenase (LDH), succinate dehydrogenase (SDH), and catalase remained unaltered after L-T4 treatment. Administration of protein synthesis inhibitors such as actinomycin D, while significantly inhibited cytochrome oxidase, alpha-GPDH, catalase, SDH, and Mg2+ ATPase activities, did not change LDH, cyt. MDH, and mit. MDH activities. Chloramphenicol injection significantly stimulated cytochrome oxidase, alpha-GPDH, and G-6-PDH activities. Simultaneous injections of actinomycin D or chloramphenicol with 3,5,3'-triiodo-L-thyronine (L-T3) or L-T4 prevented the effects of thyroid hormones on enzyme activities, when compared to the respective controls.

Branchial Na+ -K+ -ATPase activity in freshwater or saltwater acclimated tilapia, Oreochromis (Sarotherodon) mossambicus: effects of cortisol and thyroxine

The ability of cortisol to stimulate branchial Na+ -K+ -ATPase activity in tilapia was further augmented by thyroxine. The effects of hormonal treatments were greater in the saltwater acclimated fish than in the freshwater acclimated ones.