Effect of food restriction on tissue carnitine concentration in rats

The effect of feeding different amounts of a standard laboratory pellet diet on tissue carnitine concentration was studied in four groups of rats. Group I was fed ad libitum, whereas food intake was restricted to 25, 20, and 15g protein/kg body weight/day in group II, III, and IV, respectively. The intake of food, protein, energy and carnitine was constant and adjusted to actual body weight in groups 2-4. Six weeks food restriction had no effect on muscle carnitine. Restricted diet caused lowered concentrations of carnitine in serum (group I, fed ad libitum, total 95.0 +/- 13.8, free 80.2 +/- 2.7; group II total 78.4 +/- 8.4, free 56.9 +/- 4.7; group III total 81.7 +/- 8.8, free 66.0 +/- 8.8; and group IV total 73.8 +/- 8.7, free 59.5 +/- 7.6 micromol/l) and urinary carnitine excretion (group I, total 7.1 +/- 3.3, free 6.3 +/- 3.1; group II, total 2.5 +/- 0.7, free 2.2 +/- 0.7; group III, total 1.9 +/- 0.8, free 1.6 +/- 0.8; and group IV, total 1.3 +/- 0.4 free 1.1 +/- 0.3 micromol/day). In contrast, the liver carnitine tended to increase when dietary intake was reduced (group I total 1.1 +/- 0.1, free 1.0 +/- 0.1; group II total 1.5 +/- 0.2, free 1.4 +/- 0.2; group III total 1.3 +/- 0.1, free 1.1 +/- 0.1; and group IV total 1.5 +/- 0.2, free 1.4 +/- 0.2 micromol/g dry wt). The highest liver carnitine concentrations were observed during the lowest dietary intake when also the serum and urine carnitine were lowest. We conclude that the amount of food intake has a direct impact on carnitine concentrations in the liver, serum, and urine while muscle carnitine concentration remains relatively stable despite wide variations in food intake.