Cytochrome P450 2C9 plays an important role in the regulation of exercise-induced skeletal muscle blood flow and oxygen uptake in humans

Abstract

Previous studies show that exercise-induced hyperaemia is unaffected by systemic inhibition of nitric oxide synthase (NOS) and it has been proposed that this may be due to compensation by other vasodilators. We studied the involvement of cytochrome P450 2C9 (CYP 2C9) in the regulation of skeletal muscle blood flow in humans and the interaction between CYP 2C9 and NOS. Seven males performed knee extensor exercise. Blood flow was measured by thermodilution and blood samples were drawn frequently from the femoral artery and vein at rest, during exercise and in recovery. The protocol was repeated three times on the same day. The first and the third protocols were controls, and in the second protocol either the CYP 2C9 inhibitor sulfaphenazole alone, or sulfaphenazole in combination with the NOS inhibitor N(omega)-monomethyl-L-arginine (L-NMMA) were infused. Compared with control there was no difference in blood flow at any time with sulfaphenazole infusion (P > 0.05) whereas with infusion of sulfaphenazole and L-NMMA, blood flow during exercise was 16 +/- 4 % lower than in control (9 min: 3.67 +/- 0.31 vs. 4.29 +/- 0.20 l min(-1); P < 0.05). Oxygen uptake during exercise was 12 +/- 3 % lower (9 min: 525 +/- 46 vs. 594 +/- 24 ml min(-1); P < 0.05) with co-infusion of sulfaphenazole and L-NMMA, whereas oxygen uptake during sulfaphenazole infusion alone was not different from that of control (P > 0.05). The results demonstrate that CYP 2C9 plays an important role in the regulation of hyperaemia and oxygen uptake during exercise. Since inhibition of neither NOS nor CYP 2C9 alone affect skeletal muscle blood flow, an interaction between CYP 2C9 and NOS appears to exist so that a CYP-dependent vasodilator mechanism takes over when NO production is compromised.

Figure 1. Thigh blood flow and vascular conductance in subjects at rest, during knee extensor exercise (30 W) and in recovery

Measurements were performed during control conditions, with infusion of the CYP 2C9 inhibitor sulfaphenazole, and with infusion of sulfaphenazole in combination with the NO synthase inhibitor N^ω-monomethyl-l-arginine (l-NMMA). Blood flow during control conditions (○) and infusion of sulfaphenazole (•) (A). Blood flow during control conditions (○) and infusion of l-NMMA and sulfaphenazole (•) (B). Vascular conductance during control conditions (○) and infusion of sulfaphenazole (•) (C). Vascular conductance during control conditions (○) and infusion of l-NMMA and sulfaphenazole (•) (D). #P < 0.05 vs. pre-infusion; *P < 0.05vs. control.

Figure 2. Muscle oxygen extraction and oxygen uptake determined from measurements of arterial and venous oxygen content differences and blood flow in subjects at rest, during knee extensor exercise (30 W) and in recovery

Measurements were performed during control conditions, with infusion of the CYP 2C9 inhibitor sulfaphenazole, and with infusion of sulfaphenazole in combination with the NO synthase inhibitor N^ω-monomethyl-l-arginine (l-NMMA). Oxygen extraction during control conditions (○) and infusion of sulfaphenazole (•) (A). Oxygen extraction during control conditions (○) and infusion of l-NMMA and sulfaphenazole (•) (B). Oxygen uptake during control conditions (○) and infusion of sulfaphenazole (•) (C). Oxygen uptake during control conditions (○) and infusion of l-NMMA and sulfaphenazole (•) (D). *P < 0.05vs. control.

Figure 3. Muscle lactate release determined from measurements of arterial and venous lactate differences and blood flow in subjects at rest, during knee extensor exercise (30 W) and in recovery

Measurements were performed during control conditions, with infusion of the CYP 2C9 inhibitor sulfaphenazole, and with infusion of sulfaphenazole in combination with the NO synthase inhibitor N^ω-monomethyl-l-arginine (l-NMMA). Lactate release during control conditions (○) and infusion of sulfaphenazole (•) (A). Lactate release during control conditions (○) and infusion of l-NMMA and sulfaphenazole (•) (B). *P < 0.05vs. control.

Figure 4. Distribution of CYP 2C9 in microvascular endothelium (white arrows) of human skeletal muscle

Inset shows negative control. Scale bar represents 50 μm.