title: Effects of aging on microvascular oxygen pressures in rat skeletal muscle.
abstract: Aging alters skeletal muscle vascular geometry and control such that the dynamics of muscular blood flow (Q) and O2 delivery (Q(O2)) may be impaired across the rest-exercise transition. If, at the onset of muscle contractions, Q dynamics are slowed disproportionately to those of muscle O2 uptake (V(O2), microvascular PO2 (PO2m) would be reduced and blood-tissue O2 transfer compromised. This investigation determined the effects of aging on PO2m (a direct reflection of the Q(O2)-to-V(O2) ratio), at rest and across the rest-contractions transition in the spinotrapezius of young (approximately 6 months, n = 9) and old (>24 months, n = 10) male Fisher 344/Brown Norway hybrid rats. Phosphorescence quenching techniques were used to quantify PO2m, and test the hypothesis that, across the rest-contractions (twitch, 1 Hz; 4-6 V, 240 s) transition, aging would transiently reduce the Q(O2)-to-V(O2) ratio causing a biphasic profile in which PO2m fell below steady-state contracting values. Old rats had a lower pre-contraction baseline PO2m than young (27.1+/-1.9 versus 33.8+/-1.6 mmHg, P<0.05, respectively). In addition, in old rats PO2m demonstrated a pronounced difference between the absolute nadir and end-contracting values (2.5+/-0.9 mmHg), which was absent in young rats. In conclusion, unlike their young counterparts, old rats exhibited a transiently reduced PO2m across the rest-contractions transition that may impair blood-tissue O2 exchange and elevate the O2 deficit, thereby contributing to premature fatigue.
authors.affiliation: Department of Health and Kinesiology, Texas A&M University, College Station, TX, USA.
authors.forename: Brad J
authors.initials: BJ
authors.lastname: Behnke
authors.forename: Michael D
authors.initials: MD
authors.lastname: Delp
authors.forename: Patrick J
authors.initials: PJ
authors.lastname: Dougherty
authors.forename: Timothy I
authors.initials: TI
authors.lastname: Musch
authors.forename: David C
authors.initials: DC
authors.lastname: Poole
mesh_terms: D000367:Age Factors; D000375:Aging / Q000502:physiology*; D000818:Animals; D002950:Citrate (si)-Synthase / Q000378:metabolism; D008163:Luminescent Measurements / Q000379:methods; D008297:Male; D008833:Microcirculation / Q000378:metabolism*; D008954:Models, Biological; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000502:physiology*; D010100:Oxygen / Q000097:blood*; D010101:Oxygen Consumption / Q000502:physiology*; D010313:Partial Pressure; D051381:Rats; D011916:Rats, Inbred F344; D012039:Regional Blood Flow; D013997:Time Factors
chemical_list: D002950:Citrate (si)-Synthase; D010100:Oxygen