Plasma and urine free L-carnitine in human diabetes mellitus.

L-carnitine is essential for the transport of long-chain fatty acids into mitochondria and their oxidation. Recently, a relationship between plasma free fatty acids (FFA) and L-carnitine metabolism has been observed. Plasma free L-carnitine (FC), FFA, triglycerides, cholesterol, blood glucose concentration and daily excretion of FC were determined in 20 diabetic patients as well as in 18 control subjects. Both in male diabetics and in male controls, plasma FC was significantly higher than in females. Mean plasma FC was found to be significantly reduced in diabetics (21 +/- 2 vs 35 +/- 2 mumol/1 in non-diabetic subjects; p less than 0.005). Daily urinary excretion of FC was clearly lower in diabetic patients than in controls (172 +/- 34 vs 403 +/- 38 mumol/24 h; p less than 0.001). The reduced plasma FC in diabetes mellitus may be due to redistribution between circulating free and esterified carnitine and to increased utilization of FC for synthesis of acylcarnitine in tissues.