THE EFFECT OF DIGITONIN AND ALTERED THYROID STATUS ON PALMITIC ACID OXIDATION BY ISOLATED RAT-LIVER MITOCHONDRIA

The effect of altered thyroid status and food-deprivation on palmitic acid oxidation in isolated rat liver mitochondria was studied in the a bsence and presence of digitonin. Mitochondria prepared from triiodoth yronine-treated (hyperthyroid) and food-deprived rats metabolized palm itic acid at the same rate as the untreated controls (euthyroid). Mito chondria prepared from thyroidectomized (hypothyroid) rats metabolized palmitic acid at a rate lower than was that seen with mitochondria fr om euthyroid controls in either the fed or fasted state. Fasting had n o effect on palmitic acid oxidation by mitochondria prepared from euth yroid rats but diminished the rates seen in both hyper- and hypothyroi d states. Digitonin (0.04 mg/ mg mitochondrial protein) increased the sensitivity of the rate of fatty acid oxidation to inhibition by alpha -bromopalmitic acid. The addition of digitonin to the incubation mixtu re resulted in two-fold increases in the rate of palmitic acid oxidati on in all states. This study shows that the limitations imposed by hyp othyroidism on fatty acid oxidation in intact liver are preserved in i solated mitochondria.