The effect of long-term fasting on the branched chain acylcarnitines and branched chain carnitine acyltransferases.

The effect of fasting for 8 days on the levels of carnitine acyltransferases in heart, liver, liver mitochondria, skeletal muscle, skeletal muscle mitochondria, kidney, and testes in young adult male rats was determined. The specific activities of acetyl-, octanyl-, isobutyryl-, and isovaleryl-carnitine acyltransferase in mitochondria isolated from the livers of fasted animals were significantly higher than the levels of the transferases isolated from livers of fed animals. Similar results were obtained with the 500 x g supernatant fluids from liver. In contrast, the specific activities of carnitine acyltransferases of 500 x g supernatant fractions isolated from heart, skeletal muscle, kidney, and testes were the same for fed as fasted animals. The total carnitine content of liver, muscle, heart, and kidney was less in animals fasted for 8 days than in fed animals, but the amount/g of organ was higher in the animals fasted for 8 days. The amount of specific short-chain acylcarnitines in liver, muscle, and heart was determined for both fed and fasted animals. The amount of isobutyrylcarnitine and isovalerylcarnitine increased significantly in muscle from fasted animals. These data are consistent with the previous suggestion that carnitine may have a role in the metabolism of the branched-chain amino acids.