Correlation between erythrocyte aldose reductase activity and the width of skeletal-muscle capillary basement membrane in insulin-dependent diabetes mellitus

Pericapillary basement membrane thickening in human skeletal muscles

The basement membrane (BM) surrounding capillaries in skeletal muscles varies physiologically in thickness according to age, physical fitness, and anatomical site in humans. Furthermore, the pericapillary BM thickness (CBMT) increases pathophysiologically during several common disease states, including peripheral arterial disease and diabetes mellitus. This review on CBM thickening in human skeletal muscles is two pronged. First, it addresses the advantages/disadvantages of grid- and tablet-based measuring and morphometric techniques that are implemented to assess the CBMT on transmission electron micrographs. Second, it deals with the biology of CBM thickening in skeletal muscles, particularly its possible causes, molecular mechanisms, and functional impact. CBM thickening is triggered by several physical factors, including diabetes-associated glycation, hydrostatic pressure, and inflammation. Increased biosynthesis of type IV collagen expression or repetitive cycles in pericyte or endothelial cell degeneration/proliferation appear to be most critical for CBM accumulation. A thickened CBM obviously poses a greater barrier for diffusion, lowers the microvascular elasticity, and impedes transcytosis of inflammatory cells. Our own morphometric data reveal the CBM enlargement to be not accompanied by the pericyte coverage. Owing to an overlap or redundancy in the capillary supply, CBM thickening in skeletal muscles might not be such a devastating occurrence as in organs with endarterial circulation (e.g., kidney and retina). CBM growth in skeletal muscles can be reversed by training or administration of antidiabetic drugs. In conclusion, CBM thickening in skeletal muscles is a microvascular remodeling process by which metabolic, hemodynamic, and inflammatory forces are integrated together and which could play a hitherto underestimated role in etiology/progression of human diseases.

Increased forearm blood flow in longstanding Type 1 diabetic patients without microvascular complications

AIMS

According to the 'haemodynamic hypothesis', chronic hyperglycaemia induces an increase in tissue perfusion that predisposes to microangiopathy. We hypothesized that patients with longstanding diabetes mellitus (DM), who have not developed microvascular complications, would have normal tissue perfusion.

METHODS

In six Type 1 diabetic patients (age 43.4 +/- 1.1 years; DM duration 25.3 +/- 2.6 years.; HbA(1c) 8.5 +/- 0.7%), who had no evidence of microvascular complications, and six age- and gender-matched healthy volunteers (Control) we measured haemodynamic parameters including forearm blood flow (FBF; plethysmography) and sympathetic tone, an important regulator of blood flow, by the combination of plasma sampling (catecholamine levels), microneurography and power spectral analysis of blood pressure and heart rate.

RESULTS

FBF was increased in the diabetic compared with control subjects (4.8 +/- 1.2 vs. 2.2 +/- 0.3 ml/dl per min, P < 0.05) and forearm vascular resistance (FVR) was decreased (25 +/- 6 and 43 +/- 3 arbitrary units, P < 0.05). Heart rate was higher in diabetic subjects (77 +/- 10 vs. 57 +/- 2 beats/min, P < 0.05). All parameters of sympathetic tone were similar in diabetic and control subjects.

CONCLUSIONS

In patients with Type 1 diabetes, without signs of microvascular complications and with diabetes duration of > 20 years, skeletal muscle blood flow was increased while sympathetic tone was normal. These results suggest that increased blood flow does not inevitably lead to microvascular complications and challenge the hypothesis that it has a causative role in the pathophysiology of complications.