Dose Response and Functional Consequences of Choline Induced Changes in Carnitine Homeostasis in Guinea Pigs

This study further characterized a newly discovered interaction of two nutrients, choline and carnitine. Increased dietary choline had previously been demonstrated to cause a conservation of carnitine in humans and guinea pigs, and an increased muscle carnitine concentration guinea pigs. The first part of this study compared the effect of varied doses of choline on urinary excretion of carnitine, tissue and whole body carnitine concentrations, and body composition. It was demonstrated that a choline dose of 2 g/kg diet results in a near maximal effect on urinary conservation of carnitine, which is mediated by an increase in the fractional tubular reabsorption of carnitine. There was also a dose dependent decrease in the ratio of fat/protein of carcasses of choline supplemented animals. The second part of the study evaluated functional consequences of the choline-carnitine interaction. Indirect calorimetry was used to evaluate energy substrate utilization in choline supplemented (3 g/kg diet) and nonsupplemented guinea pigs. There was no effect of choline supplementation on fatty acid oxidation in the guinea pigs when fed, unfed, or during treadmill exercise. The mechanism of how choline supplementation affects body fat composition in guinea pigs remains unknown, but appears to be independent of effects on capacity for fatty acid oxidation.