Effect of fasting on thyroid hormone levels, and TRα and TRβ mRNA accumulation in late-stage embryo and juvenile rainbow trout, Oncorhynchus mykiss

The accumulation of mRNA encoding for hepatic and intestinal T-3-receptor (TR) and body and liver masses were measured in fed and 3-week fasted juvenile and swim up stage rainbow trout embryos. Plasma and total body thyroid hormone (TH) levels were measured for juvenile and swim up stages, respectively. Fasted juveniles exhibited a lower hepatosomatic index (HSI), liver mass and plasma T-4 and T-3 concentrations than fed animals, but there were no changes in body mass or the accumulation of mRNA encoding for either of the TR alpha or TR beta isoforms in liver or intestine. TR beta mRNA accumulation was greater than TR alpha mRNA accumulation in both tissues. Fasted embryos had lower whole body TH levels and body, liver and intestinal tract masses, in addition to a lower intestinosomatic index. However, there was no change in HSI. Fasting did not affect whole body or hepatic TR alpha and TR beta mRNA accumulation, although intestinal tract TR alpha and TR beta mRNA accumulation was lower in the fasted embryos. The HSI and body mass changes in fasted juvenile and embryo stages, respectively, indicated that both developmental stages were impacted by fasting. Both stages also showed evidence of decreased TH production. The lower TR gene expression in the intestinal tract of fasted embryos may suggest a role for THs in the transitional stage of intestinal development during this period of development. (c) 2005 Elsevier Inc. All rights reserved.