The etiology of microalbuminuria in early non-insulin-dependent diabetes mellitus.

Glomerular or tubular contribution for microalbuminuria was estimated by assessing albumin excretion rate (AER) in glomerular urine obtained by L-arginine infusion (AI) and glomerular filtration rate (GFR) in 20 non-insulin-dependent diabetes mellitus (NIDDM) patients before and after glycemic control, and in 19 age-matched controls. Glycemic control normalized AER during AI, while it decreased AER before AI, though it was still above normal. Glycemic control increased tubular reabsorption rate of albumin, but it was still less than normal. Tubular reabsorption rate of albumin declined in close relation with duration of diabetes mellitus, while AER in glomerular urine had no correlation with the duration. GFR had no correlation with AER before or during AI. In conclusion, impaired tubular reabsorption of albumin plays a key role for microalbuminuria in NIDDM.