The rate of O2loss from mesenteric arterioles is not unusually high

Abstract

The O2disappearance curve (ODC) recorded in an arteriole after the rapid arrest of blood flow reflects the complex interaction among the dissociation of O2from hemoglobin, O2diffusivity, and rate of respiration in the vascular wall and surrounding tissue. In this study, the analysis of experimental ODCs allowed the estimation of parameters of O2transport and O2consumption in the microcirculation of the mesentery. We collected ODCs from rapidly arrested blood inside rat mesenteric arterioles using scanning phosphorescence quenching microscopy (PQM). The technique was used to prevent the artifact of accumulated O2photoconsumption in stationary media. The observed ODC signatures were close to linear, in contrast to the reported exponential decline of intra-arteriolar Po2. The rate of Po2decrease was 0.43 mmHg/s in 20-μm-diameter arterioles. The duration of the ODC was 290 s, much longer than the 12.8 s reported by other investigators. The arterioles associated with lymphatic microvessels had a higher O2disappearance rate of 0.73 mmHg/s. The O2flux from arterioles, calculated from the average O2disappearance rate, was 0.21 nl O2·cm−2·s−1, two orders of magnitude lower than reported in the literature. The physical upper limit of the O2consumption rate by the arteriolar wall, calculated from the condition that all O2is consumed by the wall, was 452 nl O2·cm−3·s−1. From consideration of the microvascular tissue volume fraction in the rat mesentery of 6%, the estimated respiration rate of the vessel wall was ∼30 nl O2·cm−3·s−1. This result was three orders of magnitude lower than the respiration rate in rat mesenteric arterioles reported by other investigators. Our results demonstrate that O2loss from mesenteric arterioles is small and that the O2consumption by the arteriolar wall is not unusually large.