[Urinary albumin excretion and noninvasive assessment of peripheral endothelial dysfunction with high-resolution ultrasound in type 2 diabetic subjects and nondiabetic controls].

BACKGROUND

Recent theory in pathogenesis of atherosclerosis has focused on the pathobiology of the artery wall including the emerging influence of the nitric oxide (NO) system on thrombogenicity and trigger mechanisms leading to morphologic changes culminating in the stenotic plaque. Therefore, diagnostic evaluation of disturbances in NO bioavailability might be of prognostic relevance regarding primary prevention of cardiovascular disease. Disturbances in NO production can be measured noninvasively with conventional high-resolution ultrasound. On the other hand, particularly in individuals with diabetes, microalbuminuria is thought to be associated with an increased risk of cardiovascular events. Thereby it is still unknown, whether an increase in renal albumin excretion can be regarded as an indicator of global endothelial dysfunction, or whether other partial functions such as the nitric oxide system might be disturbed earlier.

PROBANDS AND METHODS

Therefore, the NO system and renal albumin excretion were examined in 129 subjects (56 with type 2 diabetes and 73 nondiabetics). Nitric oxide production was assessed by measuring flow-mediated vasodilatation (FMD) of the brachial artery using a 13-MHz linear array. Comparison was done between subjects with disturbed endothelial NO production (FMD < 5%) and subjects with normal regulation of the vascular tone (FMD > 5%).

RESULTS

In normoalbuminuric individuals (< 20 microg/min, and < 20 mg/l, respectively), neither for the group of subjects with type 2 diabetes nor in the group of nondiabetics, relevant differences could be found in renal albumin excretion (RAE) rate between subjects with disturbed and normal FMD (RAE in diabetics 4.8 +/- 5.5 vs. 4.6 +/- 5.1 mg/l and in nondiabetics 5.1 +/- 2.6 vs. 4.9 +/- 2.7 microg/min). Both groups were well balanced regarding other risk factors of the metabolic syndrome (systolic/diastolic blood pressure, glucose and lipid metabolism). Furthermore, comparison of FMD in subjects with microalbuminuria (20-200 microg/min and 20-200 mg/l, respectively, n = 18) versus normoalbuminuric individuals (n = 111) again did not reveal a significant difference for the diabetic group (FMD median 4.3% [range 1.8-7.6%] vs. 5.0% [range 1.1-9.1%]) nor for the nondiabetic group (FMD median 4.7% [range 3.1-13.3%] vs. 5.2% [range -1.2-31.6%]). However, this analysis underlined the considerable influence of the classic cardiovascular risk factors. Particularly in the nondiabetic group, individuals with microalbuminuria showed higher blood pressure (p = 0.05) and a higher body mass index (p < 0.01).

CONCLUSION

From these results, it is concluded that both procedures (renal albumin excretion rate and the measurement of endothelium-dependent vasodilatation) investigate two independent disturbances of the vascular wall. Furthermore, these results lead to the hypothesis that disturbances in endothelial NO production occur early and may already be operative before renal albumin excretion increases. Thus, for the purpose of actually identifying cardiovascular high-risk subjects early, peripheral endothelial dysfunction should be measured in addition to renal albumin excretion rate.