Exercise as a provocative test in early renal disease in type 1 (insulin-dependent) diabetes: albuminuric, systemic and renal haemodynamic responses

Exercise-induced albuminuria vs circadian variations in blood pressure in type 1 diabetes

AIM

To investigated the relationship between exercise-induced ambulatory blood pressure measurement (ABPM) abnormalities in type 1 diabetes mellitus (T1DM) adolescents.

METHODS

We conducted a case-control at the National Obesity Center of the Yaoundé Central Hospital, Cameroon. We compared 24 h ABPM and urinary albumin-to-creatinine ratio (ACR) at rest and after a standardized treadmill exercise between 20 Cameroonian T1DM patients and 20 matched controls. T1DM adolescents were aged 12-18 years, with diabetes for at least one year, without proteinuria, with normal office blood pressure (BP) and renal function according to the general reference population. Non-diabetic controls were adolescents of general population matched for sex, age and BMI.

RESULTS

Mean duration of diabetes was 4.2 ± 2.8 years. The mean 24 h systolic blood pressure (SBP) and diastolic blood pressure (DBP) were respectively 116 ± 9 mmHg in the diabetic group vs 111 ± 8 mmHg in the non-diabetic (P = 0.06), and 69 ± 7 mm Hg vs 66 ± 5 mm Hg (P = 0.19). There was no difference in the diurnal pattern of BP in diabetes patients and non-diabetic controls (SBP: 118 ± 10 mmHg vs 114 ± 10 mmHg, P = 0.11; DBP: 71 ± 7 mmHg vs 68 ± 6 mmHg, P = 0.22). Nighttime BP was higher in the diabetic group with respect to SBP (112 ± 11 mmHg vs 106 ± 7 mmHg, P = 0.06) and to the mean arterial pressure (MAP) (89 ± 9 mmHg vs 81 ± 6 mmHg, P = 0.06). ACR at rest was similar in both groups (5.5 mg/g vs 5.5 mg/g, P = 0.74), but significantly higher in diabetes patients after exercise (10.5 mg/g vs 5.5 mg/g, P = 0.03). SBP was higher in patients having exercise-induced albuminuria (116 ± 10 mmHg vs 108 ± 10 mmHg, P = 0.09).

CONCLUSION

Exercise-induced albuminuria could be useful for early diagnosis of kidney damage in adolescents with T1DM.

Effect of exercise intensity on albuminuria in adolescents with Type 1 diabetes mellitus

AIMS

Exercise may be useful to detect patients with diabetes prone to develop persistent microalbuminuria. We studied the relationship between exercise intensity, measured as maximal oxygen consumption (VO(2)max), and microalbuminuria in patients with Type 1 diabetes mellitus patients.

METHODS

We studied 10 patients, age range 10-18 years, with Type 1 diabetes who were normotensive and normoalbuminuric, with less than 10 years since diagnosis. Patients had normal renal function, without infections or clinical evidence of complications. Metabolic control was intensively adjusted in all patients. They underwent three consecutive physical exercise tests, reaching 100, 80 and 60% of the maximal cardiac frequency response.

RESULTS

Eight patients had adequate to regular metabolic control. All patients had lower than predicted VO(2)max values. At 60%, only three patients showed microalbuminuria in excess of 20 μg/min, two of them had inadequate metabolic control. Post-exercise microalbuminuria exceeded normal values in nine, seven and three patients when submitted to 100, 80 and 60% of exercise intensity, respectively.

CONCLUSIONS

Microalbuminuria increased with exercise intensity. Sex, body composition and VO(2)max were the main factors associated with microalbuminuria. The prognostic significance of albuminuria induced by intense exercise in these subjects with Type 1 diabetes is not yet known.

[Impact of physical activity on metabolic control and the development of chronic complications in patients with type 1 diabetes mellitus]

Together with a balanced diet, regular physical activity is one of the pillars of diabetes mellitus (DM) management. Physical activity theoretically provides the same advantages in people with DM as in the general population and also has some beneficial effects in controlling metabolic factors, such as improving blood glucose levels and insulin sensitivity. In this article, we analyze the main clinical studies published to date that evaluate the impact of physical activity on metabolic control or the development of chronic complications in patients with type 1 diabetes mellitus. In conclusion, most of the evaluated studies show that regular physical activity favorably affects metabolic control in DM (or at least does not have adverse effects). However, there is insufficient information about the impact of physical activity on the development and progression of chronic complications.

Acute effects of different intensities of exercise in normoalbuminuric/normotensive patients with type 1 diabetes

OBJECTIVE

The purpose of this study was to investigate the effect of exercise occurrence and intensity on albumin excretion in normotensive, normoalbuminuric patients with type 1 diabetes.

RESEARCH DESIGN AND METHODS

Eighteen patients (aged 29 +/- 2 years, duration of diabetes 14 +/- 2 years, blood pressure 120 +/- 2/74 +/- 1 mmHg, HbA(1c) 7.0 +/- 0.2% [mean +/- SE]) without microalbuminuria, hypertension, or anti-angiotensin II therapy participated in two exercise studies in a clinical research center. Exercise intensities were defined as moderate (50% heart rate reserve [HRR]) and intense (75% HRR) and were performed in random order. Subjects collected urine for albumin determination on the days before and after exercise. On the day of exercise, subjects exercised for 30 min on a treadmill at the assigned intensity. Timed urine collections were obtained over the day. Blood pressures were measured using an ambulatory blood pressure monitor.

RESULTS

Moderate exercise demonstrated no changes in albumin excretion. Intense exercise demonstrated a significant increase in albumin excretion during the first 4 h compared with the rest of the day (P = 0.03) but returned to normal thereafter. Albumin excretion did not exceed normal levels throughout the study. There was no difference in albumin excretion surrounding days of intense exercise. Ambulatory blood pressures demonstrated nocturnal dipping after moderate and intense exercise (P < 0.001).

CONCLUSIONS

We have demonstrated that normotensive, normoalbuminuric patients without anti-angiotensin II therapy do not have elevated albumin excretion following exercise intensities experienced by most patients with type 1 diabetes.

ACE inhibitor intervention in Type 1 diabetes with low grade microalbuminuria

Several clinical trials have consistently shown that antihypertensive treatment, particularly with angiotensin-converting enzyme inhibitors (ACE-I) reduces albuminuria in Type 1 diabetic patients. More recently, data on the beneficial effects of ACE-I on the preservation of glomerular filtration rate and renal ultrastructure have emerged. However, in general, these trials have recruited a wide spectrum of diabetics, including some patients with severe albuminuria. Thus, the question of the ideal stage at which to instigate what is likely to be lifelong therapy in young people still remains unanswered. Exercise is known to significantly increase both blood pressure (BP) and urinary albumin excretion (UAE), both of which are important determinants of progression of nephropathy in diabetes. Thus, it is possible that exercise may have an adverse effect on diabetic renal disease. The effects of ACE-I on exercise-BP and exercise-UAE in microalbuminuric Type 1 diabetic patients has not been examined in long-term placebo-controlled studies. In the second part of this two-part review, we examine the effects of the ACE-I, lisinopril, 20 mg o.d. for two years, in comparison with placebo, on UAE, 24-hour ambulatory BP, exercise-BP, exercise-UAE and renal haemodynamics in 22 patients with Type 1 diabetes and low-grade microalbuminuria. We further discuss the effects of ACE-I on nephropathy and other complications of diabetes.

Lisinopril reduces albuminuria during exercise in low grade microalbuminuric type 1 diabetic patients: a double blind randomized study

BACKGROUND

Antihypertensive treatment is presently recommended in most type 1 diabetic patients with microalbuminuria. The long-term effect of angiotensin converting enzymes (ACE) inhibitor (ACE-i) treatment on exercise urinary albumin excretion (E-UAE) and exercise blood pressure (E-BP) in type 1 diabetic patients with low grade microalbuminuria is not well documented. In addition, the possible predictive effect of baseline E-UAE on the progression of overnight UAE remains to be clarified.

DESIGN AND METHODS

In a randomized placebo controlled double blind study the effects of 2 years treatment with either lisinopril (20 mg o.d.) or placebo was evaluated in 21 normotensive type 1 diabetic patients with overnight UAE between 20 and 70 microg min-1. Determinations of E-UAE and E-BP were performed after exercise on an ergometercycle with a load of 70% of estimated maximal VO2 for 20 min. Patients in the placebo and lisinopril groups were similar with regard to age (35.8 +/- 11.3 vs. 29.3 +/- 8.6 years), duration of diabetes (19.4 +/- 8.2 vs. 16.8 +/- 5.3 years), and HbA1c (9.0 +/- 1.0 vs. 9.4 +/- 1.7%).

RESULTS

At baseline, E-UAE was similar in the two groups (placebo: 150.1 x or divide 3.7, lisinopril: 96.8 x or divide 1.8 microg min-1 (geometric mean x or divide tolerance factor)). After 2 years treatment E-UAE had increased in the placebo group, whereas E-UAE was reduced in the lisinopril treated patients (placebo: 213.6 x or divide 6.9, lisinopril: 48.3 x or divide 3.1 microg min-1, P = 0.04). The relative increase in E-UAE (E-UAE/Pre-exercise UAE) was similar at baseline in both groups (3.7 x or divide 2.3 vs. 2.8 x or divide 2.0) but significantly higher in the placebo group after 2 years (4.4 x or divide 2.4 compared with 1.6 x or divide 1.7 in the lisinopril group, P < 0.01) These changes over two years in relative increase in E-UAE were significantly different (P = 0.03). Exercise blood pressure was similar in both groups at baseline and over 2 years increased in the placebo group (from 166.5 +/- 15.1-179.9 +/- 35.6 mmHg), in contrast to the lisinopril group where E-BP was slightly reduced (from 168.5 +/- 20.6-165.1 +/- 16.6 mmHg) but the difference in blood pressure over the 2 years did not reach statistical significance. Exercise urinary albumin excretion and E-BP were closely associated (correlation for year 2: r = 0.734, P < 0.001), and also changes over the 2 years in E-UAE and E-BP were positively correlated (r = 0.53, P = 0.01). At year 2, overnight UAE, pre-exercise UAE (pre-E-UAE), E-UAE and E-BP were all closely linked (r-values between 0.6 and 0.9, P-values < 0.01). In the prediction of changes in overnight UAE over 2 years, neither baseline E-UAE nor baseline E-BP conveyed explanatory information in comparison with baseline overnight UAE and HbA1c.

CONCLUSIONS

In type 1 diabetic patients with low-grade microalbuminuria, 2 years of ACE-i treatment with lisinopril significantly reduced E-UAE. Strong correlations were found between E-UAE and E-BP and also changes over 2 years in these parameters were significantly associated.

Metabolic characteristics and urine albumin excretion rate in relation to pubertal maturation in Type 1 diabetes

BACKGROUND

The objective of this study was to assess the impact of pubertal maturation on urinary albumin excretion rate (AER) and persistent microalbuminuria, and to identify possible factors affecting urinary AER in adolescents with Type 1 diabetes.

METHODS

One hundred patients aged 9.1-19.0 years with a duration of diabetes of >2 years out of 138 eligible adolescents with Type 1 diabetes from an outpatient diabetes clinic participated in the study, together with 100 healthy controls. A timed overnight urine sample was collected in the hospital, where all the adolescents stayed for 22-24 h, and microalbuminuria was confirmed with at least one consecutive positive sample (AER 20-200 microg/min).

RESULTS

The prevalence of persistent microalbuminuria was 6%. All the patients affected were girls: one prepubertal (T I), one in late puberty (T IV) and three postpubertal (T V). These patients had significantly higher HbA(1c) levels than did the normoalbuminuric girls with Type 1 diabetes. Neither duration of diabetes nor age differed significantly between the two groups. AER increased more conspicuously with pubertal maturation in the boys with Type 1 diabetes than in the control boys, while the girls with diabetes had significantly higher body mass index (BMI) and serum total and LDL cholesterol than did the control girls. HbA(1c) was independently associated with AER in a multiple regression model. Diastolic blood pressure (BP) was elevated in both girls and boys with Type 1 diabetes as compared with healthy adolescents, while no difference was observed between the patients with microalbuminuria and normoalbuminuria.

CONCLUSIONS

Persistent microalbuminuria was mainly observed in late puberty and after puberty among adolescents with Type 1 diabetes. Female sex and poor metabolic control predispose such adolescents to this condition during pubertal maturation.

Do obesity and non-insulin dependent diabetes mellitus aggravate exercise-induced microproteinuria?

We evaluated the role of obesity in proteinuria by treadmill exercising of simple obese subjects and non-obese subjects with non-insulin dependent diabetes mellitus in whom the albumin excretion rate at rest was within normal range. Non-obese healthy volunteers were studied as the controls. The fractional renal clearances of four endogenous proteins, albumin, IgG, IgG4, and beta2-microglobulin were measured before, during, and after treadmill exercise in 17 simple obese and 15 non-obese diabetic subjects, and in 21 normal subjects. Exercise increased the fractional albumin clearance in all groups. In diabetic subjects, the fractional IgG4 clearance also increased: fractional beta2-microglobulin clearance increased in normal controls and in diabetics. In obese subjects, the fractional clearances of albumin, IgG, and IgG4 were similar to those in normal controls, but fractional beta2-microglobulin clearance was significantly lower. These results suggest that enhanced microalbuminuria in obese subjects is probably of glomerular origin. In normal subjects and diabetics, exercise-induced microproteinuria is probably of both glomerular and tubular origin. Defect in the charge-selective barrier of the glomerular capillary wall has been implicated in diabetics. Thus some additional factors relevant to obesity must be taken into account in the consideration of the mechanism of microalbuminuria in diabetics with obesity.

Nephropathy of type II diabetes: evidence for hereditary factors?

Family studies point to an important genetic element in the genesis of diabetic nephropathy, but it is not known whether renal abnormalities are present prior to the onset of diabetes. To address this issue we examined all consecutive patients suffering from type II diabetes with a duration of more than 10 years who attended a diabetes outpatient clinic. Ninety-four patients had nephropathy, 307 did not. All offspring who were phenotypically normal (no hypertension, normal oral glucose tolerance, non-smoking) and agreed to participate were examined, 26 from nephropathic and 30 from non-nephropathic diabetic parents. They were compared with 30 offspring matched for age, gender and BMI from non-diabetic parents as controls. We measured urinary albumin excretion under baseline conditions and at several time points after ingestion of 300 g cooked beef and submaximal treadmill exercise, respectively. In addition, casual blood pressure, ambulatory blood pressure, urinary albumin and urinary alpha-1-microglobulin were measured. Primary renal disease was excluded by clinical examination. Under baseline conditions, median urinary albumin excretion rate (AER; microgram/min) was significantly (P < 0.005) higher in offspring of nephropathic type II diabetic patients (7.8; range 1.04 to 19.5) than in the offspring of non-nephropathic type II diabetic patients (4.8; 0.36 to 17.5) and controls (4.4; 0.16 to 18.4). Submaximal treadmill exercise caused a greater proportional increase of AER in offspring of nephropathic type II diabetics (median 16-fold) than in offspring of non-nephropathic diabetic patients (6.3-fold) or controls (4.8-fold). In offspring of nephropathic diabetic patients casual and particularly ambulatory systolic blood pressures were significantly higher, but AER was not correlated with blood pressure. In summary, higher values, albeit within the normal range, for baseline and postexercise albuminuria were noted in phenotypically normal offspring of parents with type II diabetes and nephropathy. The observation suggests that changes in transglomerular albumin traffic are demonstrable prior to the onset of diabetes and diabetic nephropathy in subjects with a potential genetic predisposition to these conditions.

Postexercise albuminuria in children with different duration of type-1 diabetes mellitus

About 30% of diabetic patients develop progressive renal failure. We studied albumin, IgG, and transferrin excretion during exercise in diabetic children without signs of nephropathy to investigate proteinuria under these conditions: 39 patients with insulin-dependent diabetes mellitus and 21 healthy children undertook a bicycle exercise test. Albuminuria measured by nephelometry was calculated as the albumin excretion rate (AER) and albumin-to-creatinine ratio before and after exercise. The diabetic group was divided into three subgroups according to disease duration (DI < 5 years, DII 5-10 years, DIII > 10 years). No significant difference in metabolic control (hemoglobin A1c was detected between the diabetic groups (median hemoglobin A1c: DI 7.2%, DII 7.6%, DIII 8.6%). There was no increase in AER in the healthy children after exercise. Before exercise the diabetic groups had an AER similar to controls. No significant increase in albuminuria after exercise was seen in group DI. Both groups with a disease duration of more than 5 years had a significant increase in albuminuria [median before/after: DII 7.8/16.7 (P < 0.05), DIII 0/57.9 (P < 0.05) micrograms/min per 1.73 m2). Of these patients, 43% also had a measurable urinary excretion of IgG and transferrin, indicating structural glomerular damage. There was no correlation of albuminuria and parameters of metabolic control or renal function. We conclude that in diabetic children an exercise test unveils albuminuria in certain patients, while their AER may be normal at rest.

Exercise versus overnight albumin excretion rates in subjects with type 1 diabetes

Diabetic nephropathy is the leading cause of new cases of renal failure in the US and Europe. An elevated albumin excretion rate (AER) on an overnight urine sample is considered an early predictor of end-stage renal failure. An elevated AER on a post-exercise urine sample has previously been considered to be an even earlier marker of renal damage. In a longitudinal prospective study, 373 subjects with insulin-dependent (type 1) diabetes mellitus had a total of 714 renal evaluations, each of which included one exercise and two overnight urine collections for AER determinations. All subjects were at least 13 years old and had diabetes for at least 4 years. There was a strong correlation between exercise and overnight AERs (r = 0.74, P < 0.001). For the 60 subjects with an initial borderline increase of either overnight or exercise AER, the overnight AER values (7.6-20 micrograms/min) progressed first for 52% of subjects whereas the exercise AERs (41-114 micrograms/min) progressed first for 43% of subjects (5% had simultaneous elevations of both). For the 22 subjects in which an abnormal overnight (> 20 micrograms/min) or exercise (> 114 micrograms/min) value was detected first, 17 (77%) had an elevated exercise AER first, whereas only 4 (18%) had an elevated overnight AER first. This study shows that an increase of either the exercise or the overnight AER can occur first, dependent upon the level of abnormality being considered. The two tests correlate closely with one another.(ABSTRACT TRUNCATED AT 250 WORDS)

Post-exercise albuminuria does not predict microalbuminuria in type 1 diabetic patients

To investigate whether post-exercise urinary albumin excretion in Type 1 diabetic children and adolescents may prospectively predict the development of microalbuminuria, we have assessed post-exercise urinary albumin excretion before and after 6.2 +/- 1.7 years of follow-up in 66 diabetic children and adolescents. Post-exercise urinary albumin excretion rose significantly above the pre-exercise values in diabetic patients by 2.7 (-3.8 to 84.2) micrograms min-1 (p < 0.001) and in a group of 9 healthy individuals by 3.9 (-0.7 to 13.7) micrograms min-1 (p < 0.02) without significant differences between groups. Post-exercise albuminuria was greater in postpubertal than prepubertal 9.8 vs 4.3 micrograms min-1 (p < 0.03) and pubertal 9.8 vs 6.0 micrograms min-1 (p < 0.02) patients; post-exercise changes in urinary albumin excretion were also positively related to glycated haemoglobin (r = 0.293; p < 0.05). Eight out of 66 patients developed microalbuminuria at follow-up. Urinary albumin excretion at follow-up was comparable between patients with normal and abnormal post-exercise urinary albumin excretion; moreover post-exercise urinary albumin excretion was within the normal range in 5 out of 8 patients with microalbuminuria at follow-up. In conclusion post-exercise albuminuria does not seem to be a useful predictor of the onset of microalbuminuria in Type 1 diabetic children and adolescents.

Persistent microalbuminuria in adolescents with type I (insulin-dependent) diabetes mellitus is associated to early rather than late puberty. Results of a prospective longitudinal study

Microalbuminuria is generally accepted to be highly predictive of overt diabetic nephropathy which is the leading cause of end-stage renal failure and, consequently, of death in patients with type 1 (insulin-dependent) diabetes mellitus (IDDM). Its early identification and therapy are exceedingly important. We studied prospectively the occurrence of microalbuminuria (MA) in relation to puberty and its pubertal stages in 164 children and adolescent patients (83 girls and 81 boys) with IDDM. Analysing 100 healthy subjects, normal values for albumin excretion (range: 0-10.1 micrograms/min/1.73 m2) according to sex and the different pubertal stages were defined. No significant difference between the groups were noted and, therefore, 20 micrograms/min per 1.73 m2 (3 SD above the mean) was generally defined as cutoff for MA. Of the patients with IDDM studied, 20% (20 females and 12 males) developed persistent MA (22.1-448.2 micrograms/min/1.73 m2) during the study period of 8 years. The first manifestation of persistent MA was in 69% (13 females and 9 males) during stages of early and midpuberty; and in 28% (6 females and 3 males) at a late pubertal stage or at the end of puberty. The only child who developed MA before the onset of puberty (range: 23.5-157.4 micrograms/min/1.73 m2) was found to have dystopic kidney. Therefore, all patients with IDDM should be screened for MA regardless of diabetes duration, sex and level of diabetes control beginning at the very first stage of puberty and neither earlier nor after puberty as suggested by the American Diabetes Association.

Anaerobic threshold can provoke microalbuminuria in non-insulin-dependent diabetics

We examined two groups of non-insulin-dependent diabetic men (group A, 13 patients without microalbuminuria; group B, 9 patients with intermittent microalbuminuria) to ascertain whether the anaerobic threshold (AT) can provoke microalbuminuria, comparing them with 12 healthy subjects matched for age and sex (group C). All subjects exercised on a bicycle ergometer until the AT was reached. In intermittent microalbuminuria, the albumin:creatinine ratio (ACR) was over 0.25 mg/mmol.Cr 1-3-fold in 5 measurements. The ACR after exercise was increased to over 0.25 mg/mmol.Cr in 4/9 cases in group B (P < 0.05), in 2/13 cases in group A, but not at all in group C. We also studied the mechanism of exercise-induced microalbuminuria. In group B, ACR before exercise correlated positively with the baseline plasma glucose. Furthermore, positive correlation was found between ACR after exercise and HbA1c in group B. The AT did not affect the urinary beta 2-microglobulin in any groups. The plasma atrial natriuretic factor (ANF) after exercise was elevated most prominently in group B (P < 0.05). Positive correlation was found between increments of ACR and increments of plasma ANF after exercise in group B. We conclude that the AT can provoke microalbuminuria in some non-insulin-dependent diabetics. The plasma ANF and metabolic control may play an important role in the pathophysiology of exercise-induced microalbuminuria.

Intensity-related exercise albuminuria in insulin dependent diabetic patients

Normoalbuminuric insulin-dependent diabetic (IDDM) patients may present higher rates of urinary albumin excretion after submaximal exercise at a standard intensity. To evaluate whether the urinary albumin excretion of IDDM patients is increased after maximal and submaximal exercise when exercise intensities are adjusted according to individual lactate thresholds, 16 normoalbuminuric IDDM patients (mean time from diagnosis 8 years) and 13 normal controls exercised for 20 min at intensities corresponding to 90% of the first and second lactate thresholds and to maximal tolerance on different days. Urinary albumin excretion, blood lactate concentration, heart rate and blood pressure were measured. Metabolic and cardiovascular responses to submaximal and maximal exercise were similar for patients and controls. After exercise at 90% of the first lactate threshold neither patients or controls demonstrated significant changes in urinary albumin excretion. After exercise at 90% of the second lactate threshold both patients and controls demonstrated a similar increase in urinary albumin excretion. After maximal exercise both patients and controls demonstrated marked and similar elevation in the urinary albumin excretion. There was a significant correlation (r = 0.74, P < 0.001) between blood lactate levels at the end of exercise and the decimal logarithm of post-exercise urinary albumin excretion of the diabetic patients. Thus, when exercise intensities are adjusted for lactate thresholds, normoalbuminuric IDDM patients present normal intensity-related urinary albumin excretion during exercise. These data suggest that previously observed differences in exercise induced albuminuria in IDDM patients might be related to inappropriate standardization of submaximal exercise intensities.

Size- and charge selectivity of glomerular filtration in Type 1 (insulin-dependent) diabetic patients with and without albuminuria

Albuminuria is the first clinical event in the development of diabetic nephropathy. We assessed glomerular charge- and size selectivity in 51 patients with Type 1 (insulin-dependent) diabetes mellitus of juvenile onset and 11 healthy individuals. Patients were allocated to five groups. The urinary albumin excretion rate was normal in group D1; 30-100 mg/24 h in group D2; 101-300 mg/24 h in group D3 and greater than 300 mg/24 h in groups D4 and D5. Group D5 had elevated serum creatinine (above 110 mumol/l). Glomerular filtration rate and renal plasma flow were determined by constant infusion techniques and tubular protein reabsorption by excretion of beta 2-microglobulin. Charge selectivity was estimated from the IgG/IgG4 selectivity index. Size selectivity was measured by dextran clearance. Dextran was measured by refractive index detection after fractionation (2 A fractions in the range 26-64 A) by size exclusion chromatography. IgG/IgG4 selectivity index was significantly decreased in patients with albuminuria (p < 0.001). The drop in IgG/IgG4 selectivity index was found in patients with minimal albuminuria (D2) and was not accompanied by any changes in tubular function or glomerular haemodynamics. Size selectivity was significantly altered only in patients with the most advanced nephropathy (D5) as reflected by an increase in the clearance of 62 A dextran (p < 0.04). We conclude that loss of glomerular charge selectivity precedes or accompanies the formation of new glomerular macromolecular pathways in the development of diabetic nephropathy.

Abnormal plasma noradrenaline response and exercise induced albuminuria in type 1 (insulin-dependent) diabetes mellitus

Submaximal exercise provokes an abnormal elevation in albuminuria in type 1 (insulin-dependent) diabetes mellitus. Plasma catecholamines might be involved in this phenomenon by a renal vasoconstrictive effect. Twelve healthy subjects (Controls: albuminuria < 10 micrograms min-1), 13 normoalbuminuric type 1 diabetic patients (DNormo: albuminuria < 10 micrograms min-1) and 13 microalbuminuric type 1 diabetic patients (DMicro: albuminuria 10-200 micrograms min-1) performed a fixed bicycle workload (600 kpm for 20 min+urine collection 40 min post exercise). None of the patients suffered from autonomic neuropathy or hypertension. Fractional albumin clearance (FalbCl) rose in DNormo (p = 0.02) and DMicro (p = 0.01) but not in the Controls (p = 0.40). Basal plasma adrenaline and noradrenaline were not different in the three groups. The increments in noradrenaline were more pronounced in DNormo and DMicro than in Control (Controls < DNormo, p < 0.05; Controls < DMicro, p < 0.01). The changes in FalbCl were significantly correlated with the changes in noradrenaline (all subjects r = 0.65, p < 0.001). The increments in adrenaline were not different in the diabetic groups compared to the controls, and were not related to the changes in FalbCl. Multiple regression analysis showed that changes in plasma noradrenaline (p < 0.002) and in mean arterial pressure (p < 0.005) independently contributed to the changes in FalbCl (multiple r = 0.73). It is concluded that the exercise-induced plasma noradrenaline response is increased in normo- and microalbuminuric type-1 diabetic patients. Noradrenaline appears to contribute in the exercise-induced changes in renal protein handling, possibly by its effect on renal haemodynamics.

Screening for microalbuminuria: which measurement?

It now seems worth while to identify Type 1 diabetic patients with microalbuminuria, as improved blood glucose control and reduction of arterial blood pressure will slow if not prevent the progression to persistent proteinuria. Measurement of albumin excretion rate (AER) in a timed urine sample remains the gold standard for the definition of microalbuminuria, but is not a practical screening procedure. Thus attempts have been made to relate the albumin concentration of albumin:creatinine ratio in random or first morning urine samples to AER. There is a weak correlation of albumin concentration (r = 0.32 to 0.68) and albumin:creatinine ratio (r = 0.43 to 0.54) in a random urine sample with AER, and low sensitivity and specificity of a variety of different albumin concentrations and albumin:creatinine ratios to predict microalbuminuria. The correlation of albumin concentration (r = 0.86 to 0.90) and albumin:creatinine ratio (r = 0.74 to 0.91) in an early morning urine sample with AER is stronger. Measurement of albumin:creatinine ratio in an early morning urine sample appears to be the most reliable method of screening for microalbuminuria, with sensitivity of 88 to 100% and specificity 81 to 100% depending on the cut-off ratio chosen and the definition of microalbuminuria used. If the albumin:creatinine ratio in an early morning urine sample is less than or equal to 3.5 mg mmol-1, the patient can be classed as normoalbuminuric and re-screened annually. If the ratio is greater than or equal to 10.0 mg mmol-1, confirmation of microalbuminuria should be sought in a timed urine collection and appropriate therapy begun.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased urinary transferrin excretion in exercising normoalbuminuric insulin-dependent diabetic patients

The median rate of urinary transferrin excretion is greatly increased by exercise in subjects with uncomplicated type 1 (insulin-dependent) diabetes. This increase is proportionally far greater than that seen in urinary albumin excretion rate after the same exercise. Non-diabetic control subjects showed no rise in urinary transferrin excretion rate following exercise. N-acetyl-beta-D-glucosaminidase excretion rate was higher in diabetic than control groups but did not rise with exercise. Our results suggest that patients with apparently uncomplicated diabetes have abnormal renal function. In this group an elevated urinary transferrin excretion rate appears to be a more sensitive indicator of altered renal function than is elevated albumin excretion rate. The mechanism underlying exercise-induced urinary loss of transferrin remains to be elucidated.

A study of exercise-induced microalbuminuria in type I (insulin-dependent) diabetes mellitus

Microalbuminuria is thought to be an important prognostic factor in diabetes mellitus. To study the influence of changes in blood pressure on the development of microalbuminuria during exercise, two exercise tests were carried out. A total of 32 insulin dependent diabetic men whose age at onset was less than 30 years, mean duration of diabetes 14 years (range 7 to 21) and mean age 29 years (range 21 to 40), and who did not have albuminuria (N-labstix negative) were studied. The diabetic patients were compared with a total of 29 age-matched male control subjects. Urinary albumin excretion was measured during two exercise tests: at a standardised workload (150 W) for 30 min, and at a standardised heart rate for 25 min. The diabetic patients had higher albumin excretion rates during both exercise tests compared with the control subjects. Blood pressure and heart rate during exercise were significantly higher in diabetic patients compared with control subjects in the standardised workload test. If the test was individualised to achieve the same standardised heart rate there was no significant difference in blood pressure between the diabetic patients and the control subjects. These results indicate that the diabetic kidneys were more sensitive than the healthy kidneys to similar degrees of haemodynamic stress induced by exercise.

Natural history of diabetic complications: early detection and progression

Until recently Type 1 diabetes has been characterized by a considerable degree of mortality, mainly associated with the development of diabetic nephropathy. Diabetic nephropathy is characterized by persistent proteinuria, decreasing glomerular filtration rate (GFR), increasing blood pressure, and morphological changes. Proteinuria represents a late stage in a prolonged process, which begins at the onset of Type 1 diabetes, when urinary albumin excretion is at the lower end of its normal range (less than 10 mg 24-h-1). However, in those patients who will later develop persistent proteinuria, urinary albumin excretion increases exponentially at about 20% per year. These patients also tend to have rising blood pressure and falling GFR, higher rates of proliferative retinopathy and coronary heart disease, and elevated levels of cardiovascular risk factors. As intervention is possible in all these areas, identification of such patients is required and especially as the imposition of strict metabolic control may postpone or arrest progression to overt nephropathy. Where patients deteriorate despite such control the institution of early antihypertensive therapy and the effective management of end stage renal disease will bring further improvements in the prognosis of diabetic nephropathy.

Glycemic control and longitudinal testing for exercise microalbuminuria in subjects with type I diabetes

There is a need for better and earlier markers of clinical renal damage in subjects with Type I diabetes. In this prospective study, exercise albumin excretion rates (AERs) were studied longitudinally for a 4-year period in 187 young subjects with Type I diabetes. For this time period, 54% of subjects continued to have normal overnight and exercise AERs, 11% had continuously elevated exercise and overnight AERs, 11% developed an elevated exercise AER with the overnight AER remaining normal, and 12% had a normal overnight AER throughout the study, with initially elevated exercise levels later decreasing to normal. This improvement in exercise AER was associated with improved glycosylated hemoglobin (HbA1) values for 64% of the subjects (p = 0.0004, paired t test). Five percent of subjects, who initially had only an elevated exercise AER, developed a consistently elevated overnight AER. Seven of these nine subjects showed either worsening (greater than 10%) or no improvement in their HbA1 values from the initial to the final study periods. Five percent of subjects continued to have an elevated exercise and normal overnight AER throughout the study. These results show that the elevated exercise AER represents a definite transitional stage between a normal and an abnormal (greater than 30 micrograms/min) overnight AER. In addition, a "window" exists during which an elevated exercise AER may be reversed by improved glucose control, but if this improvement does not occur, progression to an increased overnight AER is likely to result.

Nephrotoxicity of cyclosporin A in patients with newly diagnosed type 1 diabetes mellitus

Renal function was studied in 18 patients with Type 1 diabetes mellitus. All were participating in the Canadian-European randomized placebo-controlled cyclosporin trial in newly diagnosed Type 1 diabetic patients, nine being randomized to placebo, and nine to cyclosporin A. During treatment for 12 to 18 months, cyclosporin A caused significant reductions in the glomerular filtration rate (before drug withdrawal, cyclosporin 97 +/- 18 vs placebo 125 +/- 16 ml min-1 1.73-m-2, p less than 0.05), renal plasma flow (454 +/- 83 vs 536 +/- 70 ml min-1 1.73-m-2, p less than 0.05), and lithium clearance (17 +/- 3 vs 28 +/- 5 ml min-1 1.73-m-2, p less than 0.05). The fractional proximal reabsorption was increased (0.82 +/- 0.03 vs 0.78 +/- 0.03, p less than 0.05), and the fractional distal sodium reabsorption reduced (0.88 +/- 0.03 vs 0.94 +/- 0.02, p less than 0.05). These results are in accordance with the hypothesis that the nephrotoxic effect of cyclosporin A results from a preferential constriction of afferent glomerular vessels. One year after withdrawal of the drug, all variables were similar in the two groups, except for blood glucose control which was worse in the cyclosporin A treated group. When corrected for differences in blood glucose control it appeared that in three out of nine patients glomerular filtration rate had not completely returned to the reference range of the placebo group. We conclude that the nephrotoxic side-effects of cyclosporin A treatment for 1 year are reversible. There are, however, signs of minor and perhaps chronic renal injury.

The role of hypertension in the development of nephropathy in type 1 (insulin-dependent) diabetes mellitus

Which comes first when developing clinical diabetic nephropathy, the blood pressure rise or the increasing urinary albumin excretion? This issue is discussed based on recent literature of studies in humans with Type 1 (insulin-dependent) diabetes mellitus. We conclude that hypertension has a central role in the progression of diabetic nephropathy and has deleterious effects on the life expectancy of patients who already have signs of diabetic renal disease in terms of elevated urinary albumin excretion. However, blood pressure is preceded by small increments of urinary albumin excretion rates, an indicator of universally increased vascular leakiness, and thus does not seem to be the cause of diabetic nephropathy.

Effects of exercise on glomerular passage of macromolecules in patients with diabetic nephropathy and in healthy subjects

The effects of exercise on glomerular permeability were investigated in 12 proteinuric insulin-dependent diabetic patients and in 12 healthy controls by measuring the fractional protein and dextran clearances at rest and after exercise. Exercise significantly reduced the glomerular filtration rate (GFR) and the renal plasma flow (RPF) and markedly increased the filtration fraction (FF) in both diabetics and controls. The fractional clearances of albumin and IgG increased significantly during exercise in diabetics. Exercise also significantly increased the fractional clearance of albumin in healthy controls. The changes in the fractional protein clearances correlated significantly with the changes in the FF. In diabetics the fractional dextran clearances of molecules with a radius greater than or equal to 4.8 nm were significantly elevated after exercise. This was not found in healthy controls. It is concluded that exercise increases glomerular permeability by influencing the renal haemodynamics. Probably partial depletion of negative charges on the glomerular capillary wall plays a role in exercise-induced proteinuria in both healthy and diabetic subjects. In addition, the altered glomerular permeability during exercise is associated with increased size of the filtering pores in diabetic nephropathy.

Glomerular function and microalbuminuria in children with insulin-dependent diabetes

Renal function has been evaluated in 45 diabetic children (age 12.5 +/- 4 years) with a mean diabetes duration of 4.9 +/- 3.5 years. Glomerular filtration rate (GFR; inulin and creatinine clearances), renal plasma flow (RPF; PAH clearance), resting urinary albumin excretion (UAE) were measured and compared with indexes of metabolic control: Hb A1C and blood glucose values (mean, post-prandial and maximal excursion) on the same day. GFR (inulin clearance) and RPF were significantly increased in the diabetic group (171 +/- 31 and 778 +/- 172 ml/min per 1.73 m2) compared with controls (124 +/- 18 and 631 +/- 128 ml/min per 1.73 m2). Both parameters were strongly correlated (r = 0.73; P less than 0.001). Creatinine clearance was not correlated to inulin clearance. Hyperfiltration (inulin clearance above 160 ml/min per 1.73 m2) was noted in 61% of the patients and was independent of diabetes duration. Five diabetic children had a UAE level above 15 micrograms/min. No relationship could be established between UAE and any of the metabolic indexes; GFR was weakly correlated to HbA1C (r = 0.35; P less than 0.05), to mean (r = 0.37; P less than 0.05) and post-prandial blood glucose (r = 0.37; P less than 0.05). In contrast, there was a strong correlation between GFR and the maximal blood excursion (r = 0.62; P less than 0.001). The study shows that renal abnormalities can be detected with a high frequency in diabetic subjects characterized by both an early onset and a short duration of diabetes and suggests the need for a more systematic evaluation of renal parameters in this population.

An acceptable exercise test to study microalbuminuria in type 1 diabetes

A modified test for studying the response of urinary albumin excretion (UAV) to exercise in diabetic patients is described. It is designed to produce a standardized increase in pulse rate (by 90-110%) rather than a standardized workload. Thirty-three normotensive Type 1 diabetic patients with normal pre-exercise UAV (less than 10 micrograms min-1) on the day of the test were compared with 25 non-diabetic subjects matched for age and sex. The patients developed a significantly greater increase in the median UAV (p less than 0.05) and systolic blood pressure (p less than 0.01) during exercise, despite the use of lower workloads (p less than 0.05). During exercise, the albumin excretion in the patients was not related to their heart rate, blood pressure, workload or fall in blood glucose; nor was it related to duration of diabetes, glycosylated haemoglobin or insulin dose. An exercise UAV greater than 15 micrograms min-1 was found in 10 of the 33 patients; it was significantly correlated (p less than 0.01) with the frequency of previous overnight microalbuminuria (greater than 10 micrograms min-1), and was associated with a greater progression of microalbuminuria (p less than 0.05) over a mean period of 24 months. Retinol-binding protein excretion rate was also measured as an indicator of proximal tubular function and did not increase in either group.

Effect of the exercise test on albuminuria, blood pressure and blood glucose in type I (insulin-dependent) diabetic patients

Twenty-nine male type I diabetic patients (age range 16-46 years) and thirteen healthy men (age range 18-43 years) were exercised on a cycling ergometer at 75 W and 100 W after having achieved a steady state of water diuresis. Diabetic patients were subdivided into Group A (n = 19, resting urinary albumin excretion rate - UAER less than or equal to 16 micrograms/min) and Group B (n = 10, 16 less than resting UAER less than 126 micrograms/min). The groups were comparable in weight, serum creatinine, duration of diabetes and glycosylated hemoglobin. Group B showed the highest elevation of UAER at the work load of 100 W, with no correlation between increase in UAER and increase in systolic blood pressure (SBP) at both work loads. The only correlation between these parameters was found in Group A at the work load of 100 W (p less than 0.05). No correlation was found between exercise UAER and actual blood glucose in either group. The difference in UAER between healthy subjects and Group B patients (p less than 0.001) remained on the same level during exercise as at rest, but the difference between Group A and Group B (p less than 0.001) decreased with increasing work load (p less than 0.05). The highest exercise-induced systolic and diastolic blood pressure (DBP) was found in Group B, although there was no difference between the diabetic groups in pre-exercise blood pressure and in mean SBP and DBP from previous outpatient check-ups. Blood glucose did not change significantly during exercise in either diabetic group. Working capacity of diabetic patients was lower than that of healthy subjects. The test revealed some diabetic patients with strong elevation of UAER and with abnormally raised systolic and diastolic BP during exercise. The value of the findings reported is to be clarified in a further longitudinal study.

Impaired aerobic work capacity in insulin dependent diabetics with increased urinary albumin excretion

To assess whether decreased aerobic work capacity was associated with albuminuria in insulin dependent diabetics aerobic capacity was measured in three groups of 10 patients matched for age, sex, duration of diabetes, and degree of physical activity. Group 1 comprised 10 patients with normal urinary albumin excretion (less than 30 mg/24 h), group 2 comprised 10 with incipient diabetic nephropathy (urinary albumin excretion 30-300 mg/24 h, and group 3 comprised 10 with clinical diabetic nephropathy (urinary albumin excretion greater than 300 mg/24 h). Ten non-diabetic subjects matched for sex, age, and physical activity served as controls. Oxygen uptake was similar in the four groups at rest and during a 75 W workload. Maximal oxygen uptake was also similar in the control subjects and group 1 (median 41.7, (range 29.1-53.0) ml/kg/min v 38.5 (26.6-59.2) ml/kg/min, respectively), but was significantly lower in group 2 (27.7 (13.9-44.3) ml/kg/min) and group 3 (22.6-36.7) ml/kg/min). The difference in maximal oxygen uptake between groups 1 and 2 was 10.8 ml/kg/min (95% confidence interval 3.6 to 23.4 ml/kg/min) and between groups 1 and 3, 11.7 ml/kg/min (4.9 to 22.5 ml/kg/min). These differences were not explained by differences in metabolic control or the degree of autonomic neuropathy. Thus the insulin dependent diabetics with only slightly increased urinary albumin excretion had an appreciably impaired aerobic work capacity which could not be explained by autonomic neuropathy or the duration of diabetes. Whether the reduced capacity is due to widespread microangiopathy or another pathological process affecting the myocardium remains to be established.

Glomerular size and charge selectivity in insulin-dependent diabetes mellitus

The pathogenesis of clinical nephropathy in Type 1 (insulin-dependent) diabetes was investigated by measuring renal fractional clearances of albumin, total IgG, IgG4 and beta 2-microglobulin, four plasma proteins which differ in size and charge. Seventy patients and eleven control subjects were studied. In diabetic patients with normal urinary albumin excretion (less than 30 mg/24 hr), fractional IgG clearance was two to three times higher than in control subjects, whereas fractional clearance of the anionic plasma proteins IgG4 and albumin was similar to that of control subjects. These alterations indicate an increase in anionic pore charge within the glomerular basement membrane concomitant with an increase in either pore size or impairment of tubular reabsorption. Diabetic patients, whose urinary albumin excretion has started to rise (30 to 100 mg/24 hr), had unchanged fractional IgG compared to patients with normal albumin excretion, while fractional IgG4 and albumin clearances were increased three- to fourfold; indicating unchanged glomerular pore size, but a decrease in anionic pore charge. In patients demonstrating urinary albumin excretion of greater than 100 mg/24 hr fractional IgG clearance increased to the same extent as fractional albumin clearance, indicating an increase in large pore area. Fractional beta 2-microglobulin clearances were similar to that of control subjects in the different patient groups indicating unchanged tubular reabsorption of proteins. Thus, the increase in large pore area seen in patients with clinical nephropathy is preceded by loss of anionic charge in the glomerular basement membrane. It is likely that this loss of anionic charge is due to loss of heparan sulphate-proteoglycan.

Comparison of overnight, morning and 24-hour urine collections in the assessment of diabetic microalbuminuria

With the aim of comparing different urine collection periods in the assessment of micro-albuminuria, urinary albumin excretion rates (AERs) were measured in samples from 24 h, overnight, and morning urine collections in 54 patients aged 17 to 62 years with insulin-dependent diabetes mellitus with a mean duration of 15 years. The AER in overnight urine was found to be reduced by 25% compared to the rate in 24 h and morning urine. Assessing the ability to predict a 24 h AER within the microalbuminuric range (20-200 micrograms/min) we found a sensitivity of 90% and a specificity of 88% for both overnight and morning urine samples. These values were slightly improved by relating AER to the excretion of creatinine and it is concluded that overnight as well as morning urine collections can be used when diagnosing microalbuminuria in insulin-dependent diabetics. Furthermore the results show that the albumin to creatinine ratio in morning urine is a reliable estimate of 24 h AER and better than measurement of the albumin concentration alone.

Immunoturbidimetric assay for the determination of microalbuminuria using the Hitachi analyser

A sensitive and specific immunoturbidimetric method is described for the determination of low concentrations of urinary albumin using a Hitachi 704 or 705 analyser. The sensitivity was 1 mg/l and the precision attained was good (CV 15%, 7% and 6% for low, medium and higher albumin concentrations). The assay was used to determine urinary albumin excretion rates in healthy controls (less than 15 micrograms/min) and in type I diabetics. Since microalbuminuria (30-200 micrograms/min) seems to be a good predictor for the development of diabetic nephropathy and other late diabetic complications, this assay is suitable for the necessary screening and follow-up of diabetic nephropathy. In contrast to RIA methods, no radioactive tracers are needed.

Microalbuminuria in insulin-dependent diabetes: prevalence and practical consequences

Urinary albumin excretion in a representative sample of 679 patients with Type I (insulin-dependent) diabetes, 18 to 50 years of age, was investigated. Patients on antihypertensive therapy were excluded. Urinary albumin excretion was examined in one 24 hour urine sample using an ELISA technique. Twenty-three per cent of the patients had microalbuminuria, i.e., 30-300 mg albumin/24 h. The prevalence of microalbuminuria was independent of sex, age, insulin dose and diabetes duration. In the majority of those cases in which microalbuminuria was found during the first 10 years of diabetes, the concentrations were in the lower range, i.e., 30-50 mg/24 h. The prevalence of incipient nephropathy (urinary albumin excretion in a single urine sample of 51-300 mg/24 h) increased with diabetes duration. In patients with incipient nephropathy hemoglobin A1c tended to be, and blood pressure was, elevated compared with age, sex, and duration matched patients with normal urinary albumin excretion rates (p = 0.08 and p less than 0.001, respectively). Urinary albumin excretion and blood pressure were significantly correlated in the total group (n = 401, r = 0.2, p less than 0.001). On the basis of these findings practical guidelines for the handling of patients with microalbuminuria are proposed.

Increased transcapillary escape rate of albumin in type 1 (insulin-dependent) diabetic patients with microalbuminuria

The transcapillary escape rate, intravascular mass and outflux of albumin were measured in 75 Type 1 (insulin-dependent) diabetic patients. The groups were defined as: group 1: normal urinary albumin excretion, less than 30 mg/24 h (n = 21); group 2: microalbuminuria, 30-300 mg/24 h (n = 36); group 3: diabetic nephropathy, less than 300 mg/24 h (n = 18). Fifteen sex- and age-matched non-diabetic persons served as control subjects. The diabetes duration was: group 1: 20 +/- 9 years, group 2: 17 +/- 5 years, group 3: 19 +/- 7 years. The transcapillary escape rate of albumin was similar in controls and group 1 (5.0 +/- 1.8 versus 5.2 +/- 1.5%) and was significantly higher in the microalbuminuric group 2 and group 3 (8.1 +/- 2.2 versus 8.1 +/- 2.3%). The differences were not explained by differences in metabolic control or blood pressure at the time of investigation. The outflux of albumin was also higher in group 2 than in group 1 and controls (7.1 +/- 2.0 versus 5.3 +/- 1.5 and 5.1 +/- 2.0 g/h X 1.73 m2). It was indistinguishable from controls in group 3 (5.8 +/- 1.5 g/h X 1.73 m2) because of a reduced intravascular mass of albumin (p less than 0.01) in group 3. In conclusion, a universal vascular leakage of albumin is an early event in the development of diabetic nephropathy, with the leakage of albumin being fully developed in the microalbuminuric patient. In contrast, long-term diabetic patients with normal urinary albumin excretion have a normal transcapillary escape rate of albumin.

Acute reduction of arterial blood pressure reduces urinary albumin excretion in type 1 (insulin-dependent) diabetic patients with incipient nephropathy

The effect of an acute reduction in arterial blood pressure upon kidney function was studied in 12 patients with Type 1 (insulin-dependent) diabetes and incipient nephropathy (persistent microalbuminuria). Renal function was assessed by measurement of the glomerular filtration rate (single bolus 51Cr-EDTA technique) and by the urinary albumin excretion rate (radioimmunoassay). The study was performed twice within 2 weeks, with the patients receiving a slow intravenous injection of either clonidine (225 micrograms) or saline (154 mmol/l) in random order. Clonidine reduced arterial blood pressure from 125/79 +/- 13/8 to 104/68 +/- 9/7 mmHg (p less than 0.01), urinary albumin excretion rate from 68 (31-369) to 46 (6-200) micrograms/min (median and range) (p less than 0.01), and fractional clearance of albumin in all patients (median 29%) (p less than 0.01). Glomerular filtration rate was 110 +/- 11 before and 106 +/- 13 ml/min/1.73 m2 after clonidine injection. The blood glucose concentration was 15 +/- 4 mmol/l before and 14 +/- 5 mmol/l after clonidine injection. In agreement with findings in animal studies, our results suggest that microalbuminuria is to a large extent pressure-dependent, probably because of glomerular hypertension, and that autoregulation of glomerular filtration rate is normal in most patients with incipient diabetic nephropathy.