EFFECTS OF PROPIONYL-L-CARNITINE AND INSULIN ON THE ELECTRORETINOGRAM, NERVE-CONDUCTION AND NERVE BLOOD-FLOW IN RATS WITH STREPTOZOTOCIN-INDUCED DIABETES

The effect of an analogue of L-carnitine, propionyl-L-carnitine, on th e electroretinogram, motor nerve conduction velocity and nerve blood f low was determined in rats with streptozotocin-induced diabetes, and w as compared with the effects of insulin alone or combined therapy. Ora l administration of propionyl-L-carnitine (3 g/kg daily for 4 weeks) s ignificantly increased caudal nerve motor conduction velocity and scia tic nerve blood flow in diabetic rats. There were no differences in th e effects of insulin (8-10 U daily for 4 weeks), propionyl-L-carnitine and combined therapy. Although propionyl-L-carnitine significantly sh ortened the peak latency of the electroretinogram b-wave in diabetic r ats, its effect was far weaker than that of insulin or combined therap y, with combined therapy producing the greatest improvement. These eff ects of propionyl-L-carnitine were accompanied by a decrease of serum lipid levels, an increase of the sciatic nerve carnitine content, and no changes of the tissue (nerve and retinal) sorbitol and myo-inositol concentrations. In contrast, insulin significantly reduced the tissue sorbitol content and markedly increased myo-inositol. These findings suggest that propionyl-L-carnitine may improve diabetic neuropathy and retinopathy without influencing the polyol pathway, and that this ben eficial effect may be mediated through the amelioration of microcircul ation and tissue carnitine content, thus probably increasing fatty aci d oxidation.