Contrasting renal functional reserve in very long-term Type I diabetic patients with and without nephropathy

Aims. This study was to determine whether renal functional reserve (RFR) is present in patients who have suffered long-lasting Type I (insulin-dependent) diabetes mellitus.¶Methods. Renal functional reserve was elicited by a 3-h amino acid infusion (4.5 mg · kg–1· min–1) in 10 patients with nephropathy (DN +) and 10 patients without nephropathy (DN–) who had lived with diabetes for 24 ± 3 and 27 ± 3 years, respectively and in 15 healthy control subjects. Renal functional reserve was calculated as the difference between amino acid-stimulated and baseline glomerular filtration rates (GFR).¶Results. Baseline glomerular filtration rate in DN– patients (106 ± 8) and control subjects (112 ± 3 ml · min–1· (1.73m2)–1) was significantly higher (p < 0.01) than in DN + patients (79 ± 7 ml · min–1· (1.73m2)–1). Renal functional reserve was absent in DN + patients, whereas it represented 26 ± 4 % of the baseline in DN– patients and 23 ± 2 % in control subjects. Renal vascular resistance decreased statistically significantly during amino acid infusion in DN– patients and control subjects but not in DN + patients.¶Conclusions/hypothesis. These results indicate that very long-term Type I diabetic patients without diabetic nephropathy still have a normal renal functional reserve. In contrast, this reserve is suppressed in similarly long-term macroalbuminuric and hypertensive patients with overt nephropathy in spite of their remarkably maintained glomerular filtration rate. This opposite impairment supports the interpretation that glomerular hyperfiltration is a determining mechanism in human diabetic nephropathy. [Diabetologia (2000) 43: 227–230]