The effects of antioxidants on microvascular oxygenation and blood flow in skeletal muscle of young rats.

Alterations of skeletal muscle redox state via antioxidant supplementation have the potential to impact contractile function and vascular smooth muscle tone. The effects of antioxidants on the regulation of muscle O-2 delivery-O-2 utilization ((Q) over dot(O2m)/(V) over dot(O2m)) matching (which sets the microvascular partial pressure of O-2; P-O2mv) in young healthy muscle are not known. Therefore, the purpose of this study was to test the effects of acute antioxidant supplementation on rat spinotrapezius muscle force production, blood flow, (V) over dot(O2m) and P-O2mv (phosphorescence quenching). Anaesthetized male Fischer 344 x Brown Norway rats (6-8 months old) had their right spinotrapezius muscles either exposed for measurement of blood flow and P-O2mv (n = 13) or exteriorized for measurement of muscle force production (n = 6). Electrically stimulated 1 Hz twitch contractions (similar to 7-9 V) were elicited for 180 s, and measurements were made before and after acute intra-arterial antioxidant supplementation (76 mg kg(-1) ascorbic acid, 52 mg kg(-1) tempol) dissolved in saline and infused over 30 min. The principal effects of antioxidants were a similar to 25% decrease (P < 0.05) in contracting spinotrapezius muscle force production concurrent with reductions in muscle blood flow and (V) over dot(O2m) at rest and during contractions (P < 0.05 for both). Antioxidant supplementation reduced the resting baseline P-O2mv (before, 29.9 +/- 1.2 mmHg; after, 25.6 +/- 1.3 mmHg; P < 0.05), and this magnitude of depression was sustained throughout the rest-to-exercise transition (steady-state value before, 16.4 +/- 0.7 mmHg; after, 13.6 +/- 0.9 mmHg; P < 0.05). In addition, the time constant of the P-O2mv decrease was reduced after antioxidant supplementation (before, 23.4 +/- 4.3 s; after, 15.6 +/- 2.7 s; P < 0.05). These results demonstrate that antioxidant supplementation significantly impacts the control of (Q) over dot(O2m)/(V) over dot(O2m) in young rats at rest and during contractions.