Effect of triiodothyronine on phospholipid metabolism in skeletal muscles of the rat

The aim of the present study was to examine the effect of treatment with tr iiodothyronine (T-3) on certain aspects of phospholipid metabolism in skele tal muscles. Rats were injected with triiodothyronine (T-3) daily (10 mu g x 100 g(-1) b.w., s.c.) for six days. Saline - treated rats served as contr ols. 24 h after the last dose of T-3, 14C palmitic acid suspended in the se rum of a donor rat, was administered intravenously. Thirty min later, sampl es of the soleus; white and red section of the gastrocnemius and blood from the abdominal aorta were taken. The muscle phospholipids were extracted an d separated into different fractions by means of thin layer chromatography. The following fractions were obtained: shingomeylin, phosphatidylcholine p hosphatidylethanolamine, phosphatidylinositol, phosphatidylserine and cardi olipin. The phospholipids were quantified and their radioactivity was measu red. The plasma free fatty acid concentration and radioactivity was also de termined. Treatment with T-3 reduced the content of phosphatidylinositol an d phosphatidylserine in each muscle type, whereas the concentration of othe r phospholipids remained stable. T-3 increased markedly incorporation of th e blood-borne fatty acids into each phospholipid fraction in the muscles. I t is concluded that an excess of T-3 influences the metabolism of phospholi pids in skeletal muscles.