High level of cholesterol increases coronary vasomotor tone during exercise

Tetrahydrobiopterin restores impaired coronary microvascular dysfunction in hypercholesterolaemia

PURPOSE

Tetrahydrobiopterin (BH4) is an essential co-factor for the synthesis of nitric oxide (NO), and BH4 deficiency may cause impaired NO synthase (NOS) activity. We studied whether BH4 deficiency contributes to the coronary microcirculatory dysfunction observed in patients with hypercholesterolaemia.

METHODS

Myocardial blood flow (MBF; ml min(-1) g(-1)) was measured at rest, during adenosine-induced (140 microg kg(-1) min(-1) over 7 min) hyperaemia (mainly non-endothelium dependent) and immediately after supine bicycle exercise (endothelium-dependent) stress in ten healthy volunteers and in nine hypercholesterolaemic subjects using 15O-labelled water and positron emission tomography. Measurements were repeated 60 min later, after intravenous infusion of BH4 (10 mg kg(-1) body weight over 30 min). Adenosine-induced hyperaemic MBF is considered to represent (near) maximal flow. Flow reserve utilisation was calculated as the ratio of exercise-induced to adenosine-induced hyperaemic MBF and expressed as percent to indicate how much of the maximal (adenosine-induced) hyperaemia can be achieved by bicycle stress.

RESULTS

BH4 increased exercise-induced hyperaemia in controls (2.96+/-0.58 vs 3.41+/-0.73 ml min(-1) g(-1), p<0.05) and hypercholesterolaemic subjects (2.47+/-0.78 vs 2.70+/-0.72 ml min(-1) g(-1), p<0.01) but had no influence on MBF at rest or during adenosine-induced hyperaemia in controls (4.52+/-1.10 vs 4.85+/-0.45 ml min(-1) g(-1), p=NS) or hypercholesterolaemic subjects (4.86+/-1.18 vs 4.53+/-0.93 ml min(-1) g(-1), p=NS). Flow reserve utilisation remained unchanged in controls (70+/-17% vs 71+/-19%, p=NS) but increased significantly in hypercholesterolaemic subjects (53+/-15% vs 66+/-14%, p<0.05).

CONCLUSION

BH4 restores flow reserve utilisation of the coronary microcirculation in hypercholesterolaemic subjects, suggesting that BH4 deficiency may contribute to coronary microcirculatory dysfunction in hypercholesterolaemia.

Cholesterol lowering with statins reduces exercise-induced myocardial ischemia in hypercholesterolemic patients with coronary artery disease

Coronary flow reserve is mainly influenced by the combination of luminal stenosis and vascular dilation capacity. Thus, after statin treatment, the reduction of ischemic threshold in patients submitted to exercise testing could be intensely influenced by angiographic severity. In this study, we verify the effect of statin treatment on exercise-induced myocardial ischemia in hypercholesterolemic patients with a broad range of coronary angiographic severities. Patients with 2 consecutive positive exercise tests, coronary stenosis > or =70%, total cholesterol > or =300 mg/dl, and triglycerides < or =200 mg/dl were randomly assigned to a 16-week treatment period with either diet alone (n = 39) or diet plus statins (simavastatin, n = 31 and pravastatin, n = 10). Statin-treated patients had a significant variation in total cholesterol (-46% vs -2.7%; p <0.01), low-density lipoprotein cholesterol (-58% vs 0.8%; p <0.01), and high-density cholesterol (+28% vs -6%; p <0.05) in comparison with the diet-only group. After 16 weeks of treatment, 36 patients (92%) in the diet group still had positive exercise tests, whereas only 7 patients (15%) of the statin group had a positive test (p <0.01). The proportion of positive tests was significantly reduced in subgroups of patients with 1-, 2-, or 3-vessel disease. Regarding the severity of coronary stenosis, the proportion of positive tests was significantly reduced in patients with stenosis between 70% and 90% and in patients with stenosis > or =90%. Moreover, the proportion of positive tests tended to decrease to a greater extent in patients with mild coronary disease. In conclusion, cholesterol-lowering treatment with statins reduces exercise-induced myocardial ischemia in hypercholesterolemic patients with mild or severe epicardial coronary stenosis.