The rate of O₂loss from mesenteric arterioles is not unusually high

Abstract

Golub AS, Song BK, Pittman RN. The rate of O2 loss from mesenteric arterioles is not unusually high. Am J Physiol Heart Circ Physiol 301: H737-H745, 2011. First published June 17, 2011 doi:10.1152/ajpheart.00353.2011The O 2 disappearance curve (ODC) recorded in an arteriole after the rapid arrest of blood flow reflects the complex interaction among the dissociation of O 2 from hemoglobin, O 2 diffusivity, 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 O 2 transport and O2 consumption 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 O 2 photoconsumption in stationary media. The observed ODC signatures were close to linear, in contrast to the reported exponential decline of intra-arteriolar PO 2. The rate of PO2 decrease was 0.43 mmHg/s in 20-m-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 O 2 disappearance rate of 0.73 mmHg/s. The O 2 flux from arterioles, calculated from the average O 2 disappearance rate, was 0.21 nl O2·cmϪ2 ·s Ϫ1 , two orders of magnitude lower than reported in the literature. The physical upper limit of the O 2 consumption rate by the arteriolar wall, calculated from the condition that all O 2 is consumed by the wall, was 452 nl O 2·cm Ϫ3 ·s Ϫ1 . From consideration of the microvascular tissue volume fraction in the rat mesentery of 6%, the estimated respiration rate of the vessel wall was ϳ30 nl O 2·cm Ϫ3 ·s Ϫ1 . This result was three orders of magnitude lower than the respiration rate in rat mesenteric arterioles reported by other investigators. Our results demonstrate that O 2 loss from mesenteric arterioles is small and that the O2 consumption by the arteriolar wall is not unusually large. microcirculation; arterioles; oxygen consumption; phosphorescence quenching microscopy CAPILLARIES PLAY A CENTRAL ROLE in the diffusive O 2 supply to parenchymal cells, as envisioned by Krogh (18,19). For half a century after Krogh's breakthrough, this concept stood as a pillar of experimental research and mathematical modeling of O 2 transport to tissue. Forty years ago, the experimental findings of a longitudinal gradient of PO 2 in arterioles undermined the absolutism of the central role of capillaries and demonstrated the possibility of substantial O 2 loss from blood before it enters the capillaries (5). Longitudinal gradients of O 2 content and partial pressure in arteriolar blood were reported by independent researchers with different measuring techniques (20,21,25,26,37) and were reviewed in Refs. 17 and 38. The contribution of arterioles to the diffusion of O 2 from blood to tissue was established experimentally and received theoretical substantiation (24). Fur...

Oxygen Transport in the Microcirculation and Its Regulation

“…Recent reports by Golub et al . have demonstrated that the transmural gradient in PO 2 for arterioles is small , only a few mmHg confirming the original report by Duling and Berne , and that the rate of loss of oxygen from mesenteric arterioles is not unusually high .…”

“…Thus, the large transmural gradient in PO 2 reported by Tsai et al . appears to be the failure to apply a large correction, for the oxygen consumption by the method, to their measurements and so the conclusion that the arteriolar wall is a major sink for oxygen consumption is called into question .…”

Effects of a hemoglobin-based oxygen carrier (HBOC-201) and derivatives with altered oxygen affinity and viscosity on systemic and microcirculatory variables in a top-load rat model

“…The measurement of ISF PO 2 was undertaken because, had vasoconstriction been measured after HBOC-201 or its modifications, then it would have determined whether or not the test fluid was providing adequate oxygen to the tissue despite the vasoconstriction (Golub & Pittman, 2012). The observed interstitial PO 2 values for skeletal muscle were consistent with other studies indicating adequate accuracy in our tissue oxygenation technique (Shibata et al, 2001; Golub et al, 2007; Golub et al, 2011; Song et al, 2013). …”

“…PO 2 was related to the rate of phosphorescence decay, K, according to the Stern-Volmer equation, K = Ko + Kq PO 2 , where the values of the calibration constants for Oxyphor R2 were Ko = 1.53×10 −4 μs −1 and Kq = 4.3×10 −4 μs −1 mmHg −1 . Details of the phosphorescence quenching microscopy technique have been previously published (Golub et al, 2007; Golub et al, 2011, Golub & Pittman, 2012). …”

Update on innovative initiatives for the American Journal of Physiology-Heart and Circulatory Physiology

“…We produced several podcasts in the field of vascular biology and microcirculation (7, 8, 10, 23,33,34,39,41,53,57,58,67,76,105,106,115,116), and we wish to highlight several key podcasts here. We discussed a human study that looked at the central blood pressure response to the cyclooxygenase inhibitor indomethacin in both old and young healthy adults (5), which addressed the question: What happens when you combine nonsteroidal anti-inflammatory drug-type pain medication and aging-induced arterial stiffening?…”