Effect of thyroxine treatment on carnitine levels in mice

The effect in mice of 8 subcutaneous injections of 20 microgram of L-thyroxine at 12 hr-intervals on the carnitine concentration in the heart and skeletal muscle tissue was studied. In skeletal muscle tissue, the thyroxine treatment resulted in a depressed carnitine concentration. The mean values were 1.59 +/- 0.034 (S.E.M.) and 2.03 +/- 0.045 mumol/g noncollagen protein and 1.11 +/- 0.035 and 1.45 +/- 0.037 mumol/g dry weight for the thyroxine treated and the control animals, respectively. Thyroxine produced myocardial hypertrophy. The thyroxine treated animals had lower cardiac values when dry weight was used as reference base 4.17 +/- 0.10 mumol/g dry weight than the control group, 4.69 +/- 0.18 mumol/g dry weight. No statistically significant difference was found between the two groups when the cardiac carnitine concentration was expressed per g noncollagen protein or as carnitine in the entire hearts. Thus, thyroxine has been showed to influence the metabolism of carnitine in mice.