Cold-induced increase in brown fat thyroxine 5'-monodeiodinase is attenuated in Zucker obese rat.
In this study we examined the possibility that the reduced brown adipose tissue (BAT) thermogenesis in the Zucker obese rat may result from a limited capacity for enzymic conversion of thyroxine (T4) to triiodothyronine (T3) in BAT. A total of 34 lean and obese rats, approximately 4 mo old were divided into three treatment groups: group 1 (5 lean and 6 obese) was fed Purina rat chow for 21 days, and group 2 (5 lean and 6 obese) was fed a cafeteria diet for 21 days, and group 3 (6 lean and 6 obese) was fed Purina rat chow and maintained in the cold (8 +/- 1 degrees C) for 7 days. The lean and obese rats in all three groups of animals were matched closely for age and respective body weight. Activity of T4 5'-deiodinase was determined as the rate of T3 production from added T4 under controlled in vitro conditions. Serum T4 and T3 were determined by radioimmunoassay. The rate of T4-to-T3 conversion in BAT was similar in the lean and obese rats maintained at room temperature, whether fed rat chow or a cafeteria diet (approximately 40-50 pmol T3/scapular BAT depot per h). However, expressed per scapular BAT depot, lean rats exposed to cold displayed about a fivefold increase in BAT T3 production (P less than 0.0001), whereas only a small increase was observed in the cold-exposed obese rats. Serum T3 levels tended to be reduced in the Zucker obese rats. Our data indicate a reduced capacity for T3 production in Zucker rat BAT exposed to cold.(ABSTRACT TRUNCATED AT 250 WORDS)
D000064:Acclimatization; D002001:Adipose Tissue, Brown / Q000201:enzymology / Q000502:physiology*; D000818:Animals; D001835:Body Weight; D003080:Cold Temperature; D004032:Diet; D002149:Energy Intake; D005260:Female; D006801:Humans; D007453:Iodide Peroxidase / Q000378:metabolism*; D051381:Rats; D011924:Rats, Zucker; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood
D014284:Triiodothyronine; D007453:Iodide Peroxidase; D013974:Thyroxine