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 patie nts at risk for the development of nephropathy. We evaluated the respo nses of blood pressure (BP) and urinary albumin (Alb) and retinol-bind ing protein (RBP) excretion to standardized sub-maximal exercise in 17 normoalbuminuric normotensive children with IDDM and 17 matched norma l subjects. RBP was used as an index of tubular function. Standardizat ion 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 coolin g down. Pre- and postexercise urines were obtained for Alb, RBP and cr eatinine determinations. Both groups showed a significantly increased systolic BP at the midpoint but the percent variations were not differ ent. HR responses did not differ and demonstrated the exercise effecti veness, Great variability in Alb excretion was observed within the nor mal range for both groups. The baseline Alb/creatinine ratio was not s ignificantly different between normal and diabetic subjects, but becam e 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 t o 6.6 +/- 4.1 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 differen t. 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 m u g/g, P = 0.05) and diabetic patients to an increase (0.116 +/- 0.125 to 0.247 +/- 0.247 mu g/g, P = 0.06). We conclude that there was a va riable proteinuric response to exercise among diabetic subjects with n ormal renal function as evaluated by albumin excretion. A subset of ID DM patients responded abnormally to the exercise stress, increasing al bumin excretion to levels compatible with microalbuminuria. Whether th is heterogeneity reflects individual risk for diabetic renal disease r equires further investigation.