RENAL FUNCTIONAL RESERVE IN IDDM PATIENTS

The aim of this study was to determine whether renal functional reserv e (RER) is altered in insulin-dependent diabetic (IDDM) patients accor ding to the stage of diabetic nephropathy. RFR was examined in 33 IDDM patients in similar glycaemic and metabolic control and compared to 1 2 healthy control subjects, during eight 1 h clearance periods prior t o, during and alter a 3-h stimulation by amino acid infusion (4.5 mg.k g(-1).min(-1)). RFR was calculated as the difference between stimulate d and baseline glomerular filtration rates (GFR). In 14 early normoten sive diabetic patients with normal urinary albumin excretion, mean bas eline GFR (133 +/- 3 ml.min(-1).1.73 m(-2)) was higher whereas RFR (10 +/- 4 ml.min(-1).1.73 m(-2)) was lower (p < 0.05) than in control sub jects (113 +/- 4 and 28 +/- 2 ml.min(-1).1.73 m(-2), respectively), In 10 normotensive patients who had lived with IDDM for 16 years and who had microalbuminuria, baseline GFR and RFR (109 +/- 7 and 24 +/- 6 ml .min(-1).1.73 m(-2), respectively) were similar to those in control su bjects. in 9 patients who had suffered IDDM for 23 years and had devel oped macroalbuminuria and hypertension, baseline GFR (78 +/- 8 ml.min( -1).1.73 m(-2)) was lower than in control subjects (p < 0.05) and RFR (8 +/- 4 ml.min(-1).1.73 m(-2)) was not significant. In addition, rena l vascular resistance decreased significantly during infusion (p < 0.0 5) in microalbuminuric normotensive patients as well as in control sub jects (by 9 +/- 4 and 11 +/- 4 mm Hg.l(-1).min(-1).1.73 m(-2), respect ively) but not in normoalbuminuric normotensive or macroalbuminuric hy pertensive patients. These results indicate that microalbuminuric norm otensive patients retain a normal RFR, whereas RFR is reduced or suppr essed at two opposite stages of the disease: in normoalbuminuric normo tensive patients with a high GFR and in macroalbuminuric hypertensive patients with a decreased GFR. This dissimilar impairment reveals perm anent glomerular hyperfiltration in both early IDDM without nephropath y and IDDM with overt diabetic nephropathy, but not in IDDM with incip ient nephropathy.