Different urinary albumin responses to submaximal exercise by normoalbuminuric diabetic children and controls

It is not clear if exercise could be useful to identify diabetic patients at risk for the development of nephropathy. We evaluated the responses of blood pressure (BP) and urinary albumin (Alb) and retinol-binding protein (RBP) excretion to standardized sub-maximal exercise in 17 normoalbuminuric normotensive children with IDDM and 17 matched normal subjects. RBP was used as an index of tubular function. Standardization of exercise load was based on heart rate (HR) which was maintained at 70% of the maximum calculated to age. A step exercise test lasted for 35 min; baseline BP and HR were taken at midtime and during cooling down. Pre- and postexercise urines were obtained for Alb, RBP and creatinine determinations. Both groups showed a significantly increased systolic BP at the midpoint but the percent variations were not different. HR responses did not differ and demonstrated the exercise effectiveness. Great variability in Alb excretion was observed within the normal range for both groups. The baseline Alb/creatine ration was not significantly different between normal and diabetic subjects, but became different following exercise (6.6 +/- 4.1 vs 17.7 +/- 18.7 mg/g. P < 0.05). While this ratio decreased in the control group (14.8 +/- 11.1 to 6.6 +/- mg/g, P < 0.02), it increased (9.0 +/- 7.1 to 17.7 +/- 18.7 mg/g, P = 0.05) in diabetic patients. Percent variations in the two groups occurred in opposite directions and were significantly different. RBP/creatinine followed the same pattern within each group; normals showed a tendency to a decrease (0.058 +/- 0.064 to 0.030 +/- 0.039 microgram/g, P = 0.05) and diabetic patients to an increase (0.116 +/- 0.125 to 0.247 +/- 0.247 microgram/g, P = 0.06). We conclude that there was a variable proteinuric response to exercise among diabetic subjects with normal renal function as evaluated by albumin excretion. A subset of IDDM patients responded abnormally to the exercise stress, increasing albumin excretion to levels compatible with microalbuminuria. Whether this heterogeneity reflects individual risk for diabetic renal disease require further investigation.