Mechanisms for altered carnitine content in hypertrophied rat hearts

Carnitine levels are reduced in hypertrophied hearts of rats subjected to aortic constriction (banding) and elevated in hypertrophied hearts of spontaneously hypertensive rats (SHR). In an attempt to determine the mechanisms for these alterations, L-[14C]carnitine transport was examined in isolated perfused hearts. Total carnitine uptake was significantly reduced by approximately 20% in hypertrophied hearts of banded rats at all perfusate carnitine concentrations employed. The reduction in total uptake was due to a 40% reduction in carrier-mediated carnitine uptake with no difference in uptake by diffusion. In contrast, carnitine uptake was not altered in isolated hypertrophied hearts of SHR. However, serum carnitine levels were elevated in SHR, which could result in increased myocardial carnitine uptake in vivo. The data suggest that altered carnitine content in hypertrophied hearts of aortic-banded rats is due to an alteration in the carrier-mediated carnitine transport system in the myocardium. However, altered carnitine content in hypertrophied hearts of SHR is not due to a change in the carnitine transport system per se but may rather be due to a change in serum carnitine levels.