Stimulation of carnitine acylcarnitine translocase activity in heart mitochondria from hyperthyroid rats

The effect of hyperthyroidism on fatty acid oxidation and on carnitine-acylcarnitine translocase activity in rat heart mitochondria has been studied. The rates of palmitoylcarnitine supported respiration as well as the carnitine-palmitoylcarnitine exchange reaction were both stimulated (approx. 36%) in heart mitochondria from hyperthyroid rats. Kinetic analysis of the carnitine-carnitine exchange reaction showed that thyroid hormone affects the Vmax of this process, while having no effect on the Km values. The level of cardiolipin was significantly higher (approx. 40%) in heart mitoplasts from hyperthyroid rats than from the control rats. It can be concluded that thyroid hormones produce a stimulation of heart mitochondrial carnitine translocase activity and that the basis of this effect is likely an increase in the cardiolipin content.