Background: Low plasma IgG levels have long been reported as an important complication of the nephrotic syndrome. Few studies in vivo have evaluated IgG synthesis in nephrotic patients and no data are available on the effect of dietary protein restriction on the rate of IgG synthesis.
Methods: We compared the IgG synthesis rates of seven nephrotic patients who assumed, for 4 weeks, either a normal protein diet (NPD) (1.20+/-0.06 g/kg/day) or a low-protein diet (LPD) (0.66+/-0.04 g/kg/day) with those of seven normal subjects (matched for age and body mass index). The post-absorptive fractional synthesis rate (FSR) and absolute synthesis rate (ASR) of IgG were evaluated during the last 120 min of a 5 h 5,5,5-D3-l-leucine infusion.
Results: Compared with controls, in nephrotic patients the plasma IgG levels and pool were significantly reduced (P<0.05), while IgG FSR and ASR were increased by 4- and 2.5-fold, respectively (P<0.05). The LPD regimen did not affect plasma IgG FSR, ASR, circulating concentrations and intravascular pool (P = NS). There was a significant negative correlation between plasma IgG FSR and the IgG intravascular pool in nephrotic patients evaluated during both the NPD (r = -0.828; P<0.05) and LPD (r = -0.861; P<0.05) regimens.
Conclusions: Nephrotic syndrome patients with low plasma IgG levels have increased IgG FSR and ASR which are not affected by reduced dietary protein intake.