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Paradoxical decrease in plasma NOx by L-arginine load in diabetic and non-diabetic subjects.
Katsuyuki Maejima1, Mariko Himeno, Takaharu Ishibashi
1Department of Internal Medicine, Kanazawa Medical University, Uchinada, Ishikawa, Japan.
Summary
Diabetic patients show a reduced blood pressure response to L-arginine, indicating endothelial dysfunction. Plasma NOx levels unexpectedly decreased in both groups, challenging its use as a sole marker for nitric oxide formation.
Area of Science:
- Cardiovascular Physiology
- Metabolic Disorders
Background:
- Endothelial dysfunction is a hallmark of type 2 diabetes.
- L-arginine is a precursor to nitric oxide (NO), crucial for vasodilation.
Purpose of the Study:
- To investigate if impaired L-arginine response in type 2 diabetes correlates with altered plasma NOx levels.
- To assess the utility of plasma NOx as a marker of NO formation after L-arginine infusion in diabetic and non-diabetic individuals.
Main Methods:
- Intravenous infusion of L-arginine (30 g/300 ml/30 min) in patients with and without type 2 diabetes.
- Measurement of blood pressure, plasma NOx (nitrite and nitrate), and plasma cGMP levels.
- Monitoring of urinary NOx excretion.
Main Results:
- Diabetic patients exhibited a significantly smaller decrease in blood pressure following L-arginine infusion compared to non-diabetic controls.
- Increases in plasma cGMP levels were blunted and delayed in diabetic patients.
- Plasma NOx levels decreased similarly in both groups, despite no change in urinary NOx excretion.
Conclusions:
- The attenuated depressor response to L-arginine in type 2 diabetes suggests significant endothelial dysfunction.
- Plasma NOx levels may not solely reflect nitric oxide formation after L-arginine loading due to potential redistribution to other compartments.
- Further research is needed to understand the paradoxical decrease in plasma NOx and its implications.