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Effects of antioxidants on contracting spinotrapezius muscle microvascular oxygenation and blood flow in aged rats

¹Departments of Kinesiology and Anatomy and Physiology, Kansas State University, Manhattan, Kansas; ²Department of Physiology, University of Kentucky, Lexington, Kentucky; and ³Department of Human Nutrition, Kansas State University, Manhattan, Kansas

Submitted 13 May 2008 ; accepted in final form 1 October 2008

Aged rats exhibit a decreased muscle microvascular O₂ partial pressure (Pmv_O2) at rest and during contractions compared with young rats. Age-related reductions in nitric oxide bioavailability due, in part, to elevated reactive O₂ species, constrain muscle blood flow (m). Antioxidants may restore nitric oxide bioavailability, m, and ameliorate the reduced Pmv_O2. We tested the hypothesis that antioxidants would elevate m and, therefore, Pmv_O2 in aged rats. Spinotrapezius muscle Pmv_O2 and m were measured, and oxygen consumption (m_O2) was estimated in anesthetized male Fisher 344 x Brown Norway hybrid rats at rest and during 1-Hz contractions, before and after antioxidant intravenous infusion (76 mg/kg vitamin C and 52 mg/kg tempol). Before infusion, contractions evoked a biphasic Pmv_O2 that fell from 30.6 ± 0.9 Torr to a nadir of 16.8 ± 1.2 Torr with an "undershoot" of 2.8 ± 0.7 Torr below the subsequent steady-state (19.7 ± 1.2 Torr). The principal effect of antioxidants was to elevate baseline Pmv_O2 from 30.6 ± 0.9 to 35.7 ± 0.8 Torr (P < 0.05) and reduce or abolish the undershoot (P < 0.05). Antioxidants reduced m and m_O2 during contractions (P < 0.05), while decreasing force production 16.5% (P < 0.05) and elevating the force production-to-m_O2 ratio (0.92 ± 0.03 to 1.06 ± 0.6, P < 0.05). Thus antioxidants increased Pmv_O2 by altering the balance between muscle O₂ delivery and m_O2 at rest and during contractions. It is likely that this effect arose from antioxidants reducing myocyte redox below the level optimal for contractile performance and directly (decreased tension) or indirectly (altered balance of vasoactive mediators) influencing O₂ delivery and m_O2.

aging; antioxidant supplementation; muscle tension

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