Abnormality in urinary protein excretion in Japanese men with impaired glucose tolerance

OBJECTIVE - To examine whether subjects with impaired glucose tolerance (IG T) for more than 2 years have any abnormality in the kidney. RESEARCH DESIGN AND METHODS - We measured urinary excretion rate and cleara nce of various plasma proteins with different molecular radii and different isoelectric points in 22 Japanese men with IGT (IGT group) and 37 age-matc hed healthy control subjects (control group). RESULTS - Clearance of ceruloplasmin (molecular radius similar to 45 Angstr om; isoelectric point 4.4), IgG4 (molecular radius 55 Angstrom; isoelectric point 5.4), and IgG (molecular radius 55 isoelectric point 7.4) was signif icantly higher in the IGT group than in the control group, whereas there we re no significant differences in urinary excretion rate of albumin (molecul ar radius 36 Angstrom; isoelectric points 4.8-5.2) and clearance of alpha(2 )-macroglobulin (molecular radius 88 Angstrom; isoelectric point 5.4) betwe en the two groups. CONCLUSIONS - In the present study, we found that clearance of neutral-char ged IgG, negatively charged IgG4, and ceruloplasmin with molecular radii of similar to 45-55 Angstrom was selectively increased in IGT subjects. This finding does not seem to be explained by impairment of charge and pore-size selectivity in the glomerulus. Therefore, considering the present result t ogether with our recent finding that enhanced glomerular filtration rate (G FR) after acute protein loading in healthy subjects induced a selective inc rease in clearance of IgG, IgG4, and ceruloplasmin, we suggest that increas ed intraglomerular hydraulic pressure, although enhanced GFR was not demons trated, may be at work in these mildly hyperglycemic subjects.