Adenosine infusion does not improve maximal O2 uptake in isolated working dog muscle

We asked whether maximally working muscle could increase O2 extraction at fixed O2 delivery [i.e., improve maximal O2 uptake (VO2max)] when vascular resistance was decreased with adenosine (A) infusion. We postulated that a reduction in vascular resistance at the same blood flow (Q) might result in more uniform vascular perfusion and also possibly increase red blood cell transit time, thereby potentially improving the ability of the tissue to extract O2. Pump-perfused isolated dog gastrocnemius muscle (n = 6) was stimulated maximally at each of two levels of Q: 110 +/- 3 and 54 +/- 4 (SE) ml.100 g-1.min-1 [normal control (C) and ischemia (I), respectively], both before and after giving 10(-2) M of A solution in each case. Arterial and venous blood samples were taken to measure blood gases, and the Fick principle was used to calculate O2 uptake. Resistance decreased significantly after A treatment in both groups (1.2 +/- 0.1 vs. 0.9 +/- 0.1 and 1.3 +/- 0.1 vs. 1.1 +/- 0.1 mmHg.ml-1.100 g.min for C vs. C + A and I vs. I + A, respectively; P < 0.01). O2 delivery was lower with I but did not change at either perfusion rate when A was infused. VO2max also decreased significantly with I but was no different when A was added (13.8 +/- 0.7 vs. 13.8 +/- 0.9 and 8.4 +/- 0.5 vs. 8.2 +/- 0.6 ml.100 g-1.min-1 for C vs. C + A and I vs. I + A, respectively). These results show that the decrease in resistance with A did not lead to changes in VO2max.(ABSTRACT TRUNCATED AT 250 WORDS)