Measurement of the Rate of Myofibrillar Protein Degradation Using the Arteriovenous Difference in Plasma 3-Methylhistidine Concentration of Rats

There are several methods for measuring the rate of myofibrillar protein degradation using 3-methylhistidine (3-MeHis) levels in urine, plasma and isolated muscle. However. these methods lack the accuracy of rate measurements. Therefore, it is necessary to develop a new method for determining the rate of myofibrillar protein degradation. We characterized an arteriovenous difference method using 3-MeHis plasma concentration. Rats were fasted overnight and subsequently administered leucine (135 mg/100 g BW) or fed a 20% casein diet. The rate of myofibrillar protein degradation was calculated by multiplying the femoral artery blood flow rate by the arteriovenous difference in 3-MeHis concentrations (vein-artery). The blood was collected from the femoral vein and abdominal aorta. The release of 3-MeHis from hindlimb muscle was significantly Suppressed (p < 0.05) in rats fed leucine or the 20% casein diet. indicating that myofibrillar protein degradation was suppressed. These results suggest that the evaluation of the rate of myofibrillar protein degradation using the arteriovenous difference method reflects nutritional conditions in a more physiological manner.