In vivo evidence for a vitamin B-6 requirement in carnitine synthesis

The purpose of this study was to determine whether there is a requirement for vitamin B-6 (B6) in carnitine synthesis. Rats were fed a B6-deficient (-B6) (0.04 mg pyridoxine [PN]/kg) diet (ad libitum or meal-fed) or a control (+B6) (5.7 mg PN/kg) diet (ad libitum or pair-fed). These diets were fed for 6 wk, then some of the rats were repleted with the +B6 diet for 2 wk. Total acid-soluble carnitine (TCN) and free carnitine (FCN) levels were compared in the plasma, liver, skeletal muscle, heart muscle and urine and rats fed +B6 or -B6 diets. In -B6 rats vs. +B6 rats, TCN levels were significantly lower (P less than 0.05) in the plasma, skeletal muscle, heart muscle and urine, but not in the liver. However, if rats were fasted for 3 d, liver TCN concentration of -B6 rats was significantly lower than that of +B6 rats. After B6-deficient rats were repleted with the +B6 diet, the TCN level in the plasma, liver, skeletal muscle, heart muscle and urine returned to the levels of control rats. Thus, the decrease in TCN and FCN levels with a B6-deficient diet and the increase of these levels after B6 repletion provides evidence for the B6 requirement in the biosynthesis of carnitine.