To investigate the suggestion of A. S. Popel, R. N. Pittman, and M. L. Ellsworth [Am. J. Physiol. 256 (Heart Circ. Physiol. 25): H921-H924, 1989] that Krogh's diffusion coefficient for O2 in vivo might be an order of magnitude higher than in vitro, O2 diffusion coefficient (DO2) and resting O2 consumption were measured on hamster retractor muscle in vitro and under near in vivo conditions where the muscle remained attached to the animal but the arterial inflow was occluded just before measurement. Experiments were performed on two groups of animals, differing in weight and age. We found that DO2 determined in vitro (extrapolated to 37 degrees C) was 1.81 +/- 0.12 x 10(-5) cm2/s for group I (smaller and younger), which was not significantly different from the value (2.00 +/- 0.08 x 10(-5) cm2/s) determined in group II. In both groups, DO2 under near in vivo conditions tended to be 10-15% larger than the value in vitro, although this trend did not reach statistical significance. It is unlikely that this trend is large enough to reconcile the inconsistency between theoretical and experimental determinations of O2 diffusion from the arteriolar network of this tissue.
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