Diurnal variation in glomerular charge selectivity, urinary albumin excretion and blood pressure in insulin-dependent diabetic patients

Abstract

The urinary albumin excretion rate (AER) in a subgroup of patients with insulin-dependent diabetes mellitus (IDDM) steadily increases. In these patients a concomitant reduction of the glomerular charge selectivity index (SI) has been demonstrated. The aim of the present study was to evaluate whether diurnal variation in AER could be related to a diurnal variation in SI and/or a diurnal blood pressure variation. Thirty-three patients with IDDM, 27 with normal albumin excretion (AER < 20 micrograms/min; group D(o)) and six with incipient nephropathy (AER from 20 to 200 micrograms/min; group DA), were studied. AER and SI (renal clearance ratio of total-IgG/IgG4) were measured in three different urine collecting periods: period A (8:00 a.m. to 12:00 a.m.), period B (12:00 a.m. to bedtime) and period C (bedtime to 8:00 a.m.). A significant increase in SI was seen during the nighttime: period A, 1.6 (0.2 to 3.8; mean, range); period B, 1.7 (0.3 to 3.0); and period C, 2.0 (0.2 to 4.0); P = 0.01. Corresponding to this observation, an overall significant decrease in AER was found: period A, 10 (3 to 137) micrograms/min (median, range); period B, 8 (3 to 84) micrograms/min; and period C, 5 (0 to 78) micrograms/min; P < 0.001. In all three sampling periods a negative correlation was found between AER and SI. When group D(o) was analyzed alone, the results were similar. Diurnal variation in blood pressure was significantly positively correlated with AER in group DA, but was not correlated to variation in AER in D(o). We suggest that in normoalbuminuric IDDM patients diurnal variation in AER is related to diurnal variation in SI.