Aging impacts microvascular oxygen pressures during recovery from contractions in rat skeletal muscle

Aging-induced alterations in peripheral circulatory control during contractions reduce the microvascular partial pressure of O-2 (P-O2 mv: which reflects the dynamic balance in the O-2 delivery-to-O-2 uptake ratio), resulting in exaggerated intramuscular metabolic disturbances and premature fatigue. However, the extent to which this altered P-O2 mv during contractions is associated with prolongated muscle metabolic recovery is not known. We tested the hypothesis that the aging-induced speeding of the P-O2 mv on-kinetics would presage slowed P-O2 mv off-kinetics. The spinotrapezius muscle was exposed in six young (6-8 months) and seven old (26-28 months) male Fischer 344 x Brown Norway F1-hybrid rats. The P-O2 mv kinetic profile was measured via phosphorescence quenching at rest, during electrically stimulated contractions (1 Hz, 7-9 V. 2 ms pulse duration, 180 s), and throughout recovery (180 s). Aged rats which evidenced faster P-O2 mv on-kinetics (reduced mean response time (MRTon), young: 27.3 +/- 3.6 s, old: 19.2 +/- 1.6 s; P < 0.05) exhibited markedly slowed P-O2 mu off-kinetics (increased MRT off, young: 46.5 +/- 5.9 s, old: 84.8 +/- 7.9 s; P < 0.05). Accordingly, a greater degree of P-O2 mv on-off asymmetry (MRT off-MRT on) in the aged muscle was observed (young: 19.1 +/- 4.5 s, old: 65.6 +/- 8.6 s; P < 0.01). We conclude that aging-induced speeding of the P-O2 mv on-kinetics does indeed presage a slowed P-O2 mv off-kinetics, which likely compromises muscle metabolic recovery and may reduce subsequent contractile performance. Moreover, the greater degree of P-O2 mv on-off asymmetry in the aged muscle suggests a mechanistic link between impaired microvascular oxygenation and altered muscle metabolic responses during exercise transitions. (C) 2009 Elsevier B.V. All rights reserved.