Effects of cold acclimation and fasting on thyroxine 5'-deiodinase in brown adipose tissue of ob/ob mice.
Gradual acclimation to mild cold for 6 weeks increases the total activity of thyroxine 5'-deiodinase in brown adipose tissue (BAT) of genetically obese (ob/ob) mice to a level greater than that in similarly acclimated lean mice. This increase is largely due to the growth of the BAT in the ob/ob mouse, because specific activity of the enzyme is only slightly increased. In similarly cold-acclimated lean mice, the specific activity of thyroxine 5'-deiodinase was not altered. BAT mitochondrial GDP binding increased to the same high level in the gradually cold-acclimated ob/ob mouse as in cold-acclimated lean mice. We conclude that the growth and maintenance of BAT in the cold-acclimated ob/ob mouse, as in the cold-acclimated lean mouse, does not require greatly increased activity of thyroxine 5'-deiodinase. Fasting for 48 hr did not alter thyroxine 5'-deiodinase activity of BAT in either lean or ob/ob mice. The fasting-induced increase in activity seen by others in lean mice is probably due to thermoregulatory stimulation of BAT occasioned by the low environmental temperature at which the fasting occurred.
Kates
A L
AL
Department of Biochemistry, University of Ottawa, Ontario, Canada.
Himms-Hagen
J
J
D000064:Acclimatization; D002001:Adipose Tissue, Brown / Q000201:enzymology* / Q000502:physiology; D000818:Animals; D003080:Cold Temperature; D005215:Fasting / Q000502:physiology*; D005260:Female; D007453:Iodide Peroxidase / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008820:Mice, Obese; D011506:Proteins / Q000378:metabolism; D013045:Species Specificity; D013997:Time Factors
D011506:Proteins; D007453:Iodide Peroxidase