Bj. Behnke et al., Dynamics of microvascular oxygen pressure across the rest-exercise transition in rat skeletal muscle, RESP PHYSL, 126(1), 2001, pp. 53-63
There exists substantial controversy as to whether muscle oxygen (O-2) deli
very ((Q) over dot o(2)) or muscle mitochondrial O-2 demand determines the
profile of pulmonary (V) over dot o(2) kinetics in the rest-exercise transi
tion. To address this issue, we adapted intravascular phosphorescence quenc
hing techniques for measurement of rat spinotrapezius microvascular O-2 pre
ssure (P(o2)m) The spinotrapezius muscle intravital microscopy preparation
is used extensively for investigation of muscle microcirculatory control. T
he phosphor palladium-meso-tetra(4-carboxyphenyl)porphyrin dendrimer (R2) a
t 15 mg/kg was bound to albumin within the blood of female Sprague-Dawley r
ats (similar to 250 g). Spinotrapezius blood flow (radioactive microspheres
) and P(o2)m profiles were determined in situ across the transition from re
st to 1 Hz twitch contractions. Stimulation increased muscle blood flow by
240% from 16.6 +/- 3.0 to 56.2 +/- 8.3 (SE) ml/min per 100 g (P < 0.05). Mu
scle contractions reduced P(o2)m from a baseline of 31.4 +/- 1.6 to a stead
y-state value of 21.0 +/- 1.7 mmHg (n = 24, P < 0.01). The response profile
of P(o2)m was well fit by a time delay of 19.2 +/- 2.8 sec (P < 0.05) foll
owed by a monoexponential decline (time constant, 21.7 +/- 2.1 sec) to its
steady state level. The absence of either an immediate and precipitous fall
in microvascular P-o2 at exercise onset or any P(o2)m undershoot prior to
achievement of steady-state values, provides compelling evidence that O-2 d
elivery is not limiting under these conditions. (C) 2001 Elsevier Science B
.V. All rights reserved.