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Department of Molecular and Integrative Physiology, University of Kansas Medical Center, Kansas City, Kansas 66160-7401
Systemic hypoxia (SHx) produces microvascular inflammation in mesenteric, cremasteric, and pial microcirculations. In anesthetized rats, SHx lowers arterial blood pressure (MABP), which may alter microvascular blood flow and microvascular PO2 (PmO2) and influence SHx-induced leukocyte-endothelial adherence (LEA). These experiments attempted to determine the individual contributions of the decreases in PmO2, venular blood flow and shear rate, and MABP to the hypoxia-induced increase in LEA. Cremaster microcirculation of anesthetized rats was visualized by intravital microscopy. PmO2 was measured by a phosphorescence-quenching method. SHx [inspired PO2 of 70 Torr for 10 min, MABP of 65 ± 3 mmHg, arterial PO2 (PaO2) of 33 ± 1 Torr] and cremaster ischemia (MABP of 111 ± 7 mmHg, PaO2 of 86 ± 3 Torr) produced similar PmO2: 7 ± 2 and 6 ± 2 Torr, respectively. However, LEA increased only in SHx (1.9 ± 0.9 vs. 11.2 ± 1.1 leukocytes/100 µm, control vs. SHx, P < 0.05). Phentolamine-induced hypotension (MABP of 55 ± 4 mmHg) in normoxia lowered PmO2 to 26 ± 6 Torr but did not increase LEA. Cremaster equilibration with 95% N2-5% CO2 during air breathing (PaO2 of 80 ± 1 Torr) lowered PmO2 to 6 ± 1 Torr but did not increase LEA. On the other hand, when cremaster PmO2 was maintained at 60-70 Torr during SHx (PaO2 of 35 ± 1 Torr), LEA increased from 2.1 ± 1.1 to 11.1 ± 1.5 leukocytes/100 µm (P < 0.05). The results show a dissociation between PmO2 and LEA and support the idea that SHx results in the release of a mediator responsible for the inflammatory response.
leukocyte-endothelial interactions; cremaster muscle; microcirculation; ischemia; local hypoxia; tissue PO2
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