Hormonal regulation of iodothyronine 5'-deiodinase in rat brown adipose tissue

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Abstract
Norepinephrine, isoproterenol, insulin, and glucagon increase the type II (low Km) iodothyronine 5''-deiodinase (5''-D) in the brown adipose tissue (BAT) of intact rats. Cycloheximide or actinomycin D blocks the increase after norepinephrine, suggesting new mRNA synthesis is required for this effect. The 3-to 10-fold increase in BAT 5''-D after insulin administration was also blocked by cycloheximide. The effects of all stimulators are blunted by fasting or streptozotocin-induced diabetes. While all these hormones have the potential for stimulating BAT 5''-D, the dose-response relationships suggest that norepinephrine and insulin are the most potent. These and our earlier studies showing additional effects of thyroid and growth hormones on BAT 5''-D point to the complex regulation of this enzyme, suggesting that the triiodothyronine produced from its action has an important role in the thermogenic response of this tissue.