title: Thyroxine stimulates phosphatidylglycerolphosphate synthase activity in rat heart mitochondria.
abstract: The effect of administration of exogenous thyroxine on mitochondrial phosphatidylglycerol content and biosynthesis was investigated in rat heart ventricles. Rats were treated for 5 consecutive days with thyroxine (250 mg/kg body weight) and on the sixth day after an overnight fast the mass of ventricular mitochondrial phosphatidylglycerol and cardiolipin content were determined. Saline-treated animals served as controls. Thyroxine treatment did not affect body weight but increased heart weight 30% compared with controls. In addition, the ratio of heart weight/body weight (x 1000) was increased from 0.69 in controls to 0.89 in thyroxine-treated rats consistent with this model. Thyroxine-treatment resulted in a 34% increase (P < 0.05) in phosphatidylglycerol and a 23% increase (P < 0.05) in cardiolipin content in ventricular mitochondrial fractions compared with controls. The mechanism for the increase in ventricular mitochondrial phosphatidylglycerol was investigated. Phosphatidic acid:cytidine-5'-triphosphate-1,2-diacylglycerol cytidylyltransferase and phosphatidylglycerolphosphate phosphatase activities were unaltered in the ventricular mitochondria of thyroxine-treated rats. In contrast, phosphatidylglycerolphosphate synthase activity was increased 3.5-fold (P < 0.05) in these mitochondrial fractions compared with controls. As a control for the effectiveness of thyroxine on mitochondria, cardiolipin synthase activity was determined. A 2.8-fold increase (P < 0.05) in cardiolipin synthase activity was observed in ventricular mitochondrial fractions of thyroxine-treated rats compared with controls. We postulate that thyroxine-treatment of rats produces an increase in the pool size of ventricular mitochondrial phosphatidylglycerol and that the mechanism is an increase in phosphatidylglycerolphosphate synthase activity.
authors.affiliation: Department of Internal Medicine, University of Manitoba, Winnipeg, Canada.
authors.forename: S G
authors.initials: SG
authors.lastname: Cao
authors.forename: P
authors.initials: P
authors.lastname: Cheng
authors.forename: A
authors.initials: A
authors.lastname: Angel
authors.forename: G M
authors.initials: GM
authors.lastname: Hatch
mesh_terms: D000818:Animals; D001835:Body Weight; D002308:Cardiolipins / Q000096:biosynthesis*; D008297:Male; D008565:Membrane Proteins; D008929:Mitochondria, Heart / Q000187:drug effects* / Q000201:enzymology; D009929:Organ Size; D010715:Phosphatidylglycerols / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D013974:Thyroxine / Q000494:pharmacology*; D017855:Transferases (Other Substituted Phosphate Groups) / Q000378:metabolism*
chemical_list: D002308:Cardiolipins; D008565:Membrane Proteins; D010715:Phosphatidylglycerols; D017855:Transferases (Other Substituted Phosphate Groups); C100091:cardiolipin synthetase; D013974:Thyroxine