The beneficial effects of L-carnitine administration were studied in vivo in isolated perfused working hearts from control and diabetic rats. Control and streptozocin-induced diabetic (STZ-D) rats were treated daily for 6 wk with high-dose L-carnitine (3 g · kg−1 · day−1 i.p.). STZ-D results in loss of body weight and hypoinsulinemia. These effects were not altered by L-carnitine treatment. Myocardial free-carnitine levels were decreased in the untreated diabetic rats. L-Carnitine treatment of the diabetic rats increased myocardial free-carnitine levels, which were comparable with those of control rats. Six weeks after STZ administration, hearts from untreated diabetic animals exhibited depressed left ventricular developed pressure, cardiac contractility, and ventricular relaxation rates compared with control animals. However, this depression was not seen in the L-carnitine-treated diabetic animals. L-Carnitine treatment of diabetic rats significantly reduced plasma glucose and lipid levels but had no effect on control rats. Furthermore, thyroid hormone levels were higher in the L-carnitine-treated diabetic rats than in the untreated diabetic group. The data suggest that high-dose L-carnitine treatment may reduce the severity of diabetes and result in improved cardiac performance.

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