The fractional synthesis rates of plasma proteins as determined using deuterated water are sensitive to dietary intake of lysine in rats

Traditionally, the effect of dietary lysine upon health is determined through the concentrations of plasma proteins, but sometimes they are not responsive to lysine intake. We hypothesized that the fractional synthesis rates (FSRs) of plasma proteins may be more sensitive to dietary intake of lysine than protein concentrations in plasma. Seventy-two male Sprague–Dawley rats were divided randomly into three groups based on their diets provided for 18 weeks: low lysine (LG), normal lysine (NG) and high lysine (HG). Rats underwent labeling with deuterated water, a more reliable tracer than amino-acid tracers. The FSRs of albumin and immunoglobulin (Ig) G in plasma increased with increasing dietary intake of lysine. However, the albumin concentration in plasma in rats in the LG did not decrease significantly compared with that in the NG, and a similar result was shown for the IgG concentration between the NG and HG. These results suggested that the FSRs of albumin and IgG in plasma were more sensitive to dietary intake of lysine than their concentrations, and could be useful as sensitive indicators of the effect of dietary lysine upon health.