The effect of vitamin B-6 deficiency on carnitine metabolism during fasting in rats

Graduation date: 1987The purpose of this study was, first, to investigate whether there\ud is a vitamin B-6 requirement for carnitine synthesis and, second, to investigate\ud the effect of fasting on vitamin B-6 metabolism. An experimental\ud group of 72 rats (6 per group) were fed either a vitamin B-6 deficient\ud diet (-B6) (ad libitum, meal-fed) or a control diet (+B6) (ad libitum,\ud pair-fed). These diets were fed for 6 weeks and then the rats were repleted\ud with the control diet for 2 weeks. The animals were fasted for 3\ud days before and after repletion. Total acid soluble carnitine (TCN) and\ud free carnitine (FCN) levels were compared in the plasma, liver, skeletal\ud muscle, heart muscle and in the urine of rats fed +B6 diet and -B6 diets.\ud The concentrations of pyridoxal 5'-phosphate (PLP) in the plasma, liver,\ud skeletal muscle, and heart muscle and urinary 4-pyridoxic acid (4-PA) excretion\ud were compared in rats fed the +B6 or -B6 diet. Similar comparisons\ud were made in fasted and non-fasted rats. Also, plasma glucose, liver\ud glycogen, and free fatty acid concentrations were compared.\ud In rats fed the -B6 vs +B6 diet, the TCN concentration was significantly\ud (P < 0.05) lower in the plasma, skeletal muscle, heart muscle and\ud urine. With fasting, the liver TCN concentration of -B6 rats was also\ud significantly lower than that of +B6 rats. After the -B6 rats were repleted\ud with the +B6 diet, the TCN concentrations in the plasma, liver,\ud skeletal muscle, heart muscle, and urine returned to those of the control\ud rats. Thus, the decrease in TCN and FCN concentrations, and the increase\ud of these concentrations after repletion provides evidence for a\ud vitamin B-6 requirement in the biosynthesis of carnitine.\ud Fasting resulted in increased concentrations of PLP in the plasma,\ud liver, and heart muscle of rats fed a -B6 diet. The urinary 4-PA excretion\ud of -B6 rats also increased with fasting. These changes are consistent\ud with a redistribution of vitamin B-6 (as PLP) when there is a caloric\ud deficit. Thus, with fasting, PLP is supplied by an endogenous source,\ud possibly skeletal muscle glycogen phosphorylase. In -B6 vs +B6 rats, liver\ud glycogen concentration was higher and plasma FFA concentration was lower