Glomerular clearance and tubular reabsorption of IgG1 and IgG4 in microalbuminuric patients with non-insulin-dependent diabetes mellitus (NIDDM).

The alteration in glomerular clearance (GC) and tubular reabsorption (TR) of IgG subclass (IgG1 and IgG4, same molecular weight, but differing charge) was investigated in 14 microalbuminuric patients with non-insulin-dependent diabetes mellitus (NIDDM) by inhibiting TR of proteins by L-arginine infusion; 16 healthy volunteers served as controls. In healthy volunteers, GC was in the following order: IgG1 > IgG4 > or = albumin. In microalbuminuric patients, as compared with control, GC of albumin was increased significantly; the GC of IgG4 was twice that of control, while GC of IgG1 decreased reciprocally. The TR in controls was in the following order; albumin > IgG1 > IgG4. In microalbuminuric patients, TR of albumin was significantly reduced, TR of IgG1 was moderately reduced and that of IgG4 remained at same level as controls. These observations suggest that the enhancement of GC of albumin in NIDDM was produced by an impaired glomerular anionic charge barrier, while the mechanism for the reduction in TR of albumin was attributable to other undefined mechanisms.