Regulation of cartilage glycosaminoglycan synthesis in the rainbow trout, Oncorhynchus mykiss, by 3,3',5-tri-iodo-L-thyronine and IGF-I

Area of Science:

• Comparative Endocrinology
• Aquaculture Research
• Skeletal Biology

Background:

• Thyroid hormones (T3) and insulin-like growth factors (IGFs) are crucial for vertebrate growth and development.
• Understanding their roles in fish cartilage is vital for aquaculture and comparative physiology.

Purpose of the Study:

• To investigate the individual and combined effects of T3 and recombinant human IGF-I (rhIGF-I) on cartilage growth in rainbow trout (Oncorhynchus mykiss).
• To assess the impact on chondrocyte proliferation and sulfated glycosaminoglycan (sGAG) synthesis.

Main Methods:

• Isolated branchial cartilage from rainbow trout was used for in vitro and in vivo experiments.
• Uptake of 3H-methyl thymidine and 35S-sulfate measured chondrocyte proliferation and sGAG synthesis, respectively.
• Fish were injected with varying doses of T3, and cartilage was exposed to T3 and rhIGF-I in vitro.

Main Results:

• In vivo T3 administration increased both thymidine and sulfate uptake at 6 days post-injection in a dose-dependent manner.
• In vitro, T3 and rhIGF-I significantly stimulated sulfate uptake in a dose-dependent manner, with rhIGF-I showing a greater maximal effect.
• T3 primarily affected sGAG synthesis, while thymidine uptake was less consistently influenced.
• Combined T3 and rhIGF-I treatments resulted in additive increases in sulfate uptake.

Conclusions:

• Both T3 and IGF-I are significant modulators of sulfated glycosaminoglycan synthesis in rainbow trout cartilage.
• These hormones play distinct but complementary roles in regulating cartilage matrix production.
• The findings contribute to understanding the endocrinology of fish skeletal development.