Effects of Thyroxine, Epinephrine and Cold Exposure on Lipolysis in Genetically Obese (ob/ob) Mice

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Abstract
Treatment of ob/ob mice with T4 [thyroxine] 24 h prior to cold exposure did not alter plasma concentrations of glucose, insulin and FFA [free fatty acids] during cold exposure, although ob/ob mice remained hyperglycemic and hyperinsulinemic when compared to nonobese mice. FFA content of and FFA release from isolated adipocytes were significantly elevated in T4-treated obese mice after cold stress as compared to untreated obese mice. T4 treatment also produced a marked increase in epinephrine-stimulated FFA release from fat cells of obese mice in vitro. Apparently, correction of the hypothyroid status of ob/ob mice with pharmacological doses of T4 improved the in vitro lipolytic response of fat cells, but did not alter the circulating concentrations of important energy sources for thermogenesis in vivo.