We studied 24-h ambulatory systolic and diastolic blood pressure (SBP, DBP), 16-h daytime and 8-h nighttime urinary excretion of albumin (UAE) and retinol-binding protein (URBP) in 20 type 1 diabetic patients (group 1) with normoalbuminuria (UAE < 20 micrograms/min) and 20 type 1 diabetic patients (group 2) with microalbuminuria and low proteinuria (UAE 20-500 micrograms/min). The groups were comparable in age, diabetes duration and actual glycaemic control. Daytime and nighttime SBP and DBP were higher in group 2 compared to group 1 (p < 0.01). Nighttime decrease in SBP and DBP correlated with nighttime decrease in UAE in group 2 (p < 0.05, p < 0.001). There was no correlation between BP and actual glycemic control in either group. Daytime UAE was found in group 2 by 20% higher than nighttime UAE. We found higher daytime and nighttime URBP in group 2 compared to group 1 (p < 0.05). We conclude, that microalbuminuric and low-proteinuric patients had elevated BP and nighttime decrease in BP correlated with nighttime decrease in UAE but not with actual glycemic control. Increased URBP in these patients suggests impaired proximal renal tubular function in early stages of diabetic nephropathy.

Keywords: Adult; Albuminuria; Blood Pressure; Blood Pressure Monitoring, Ambulatory; Circadian Rhythm; Diabetes Mellitus, Type 1 /physiopathology/; Diabetic Nephropathies /diagnosis/; Female; Humans; Male; Retinol-Binding Proteins /urine/