Longitudinal and Radial Gradients of PO₂ in the Hamster Cheek Pouch Microcirculation

Abstract

Objectives: The aim of this study was to determine longitudinal and radial gradients in oxygen tension (PO₂) in microvessels of the hamster cheek pouch.

Methods: We measured PO₂ using the phosphorescence-quenching method in two orders of arterioles (45.8 ± 5.5 and 19.9 ± 1.8 μ m diameter), capillaries, and two orders of venules (50.5 ± 3.4 and 21.4 ± 2.0 μ m diameter) in order to determine the longitudinal PO₂ gradient. At the arteriolar and venular sites, we also measured PO₂ at four different sites for an analysis of radial PO₂ gradients: centerline, inside wall (larger arteriole and venule only), outside wall, and interstitium. We used 10 hamsters weighing 115 ± 27 g anesthetized with pentobarbital intraperitoneally and maintained with alpha-chloralose intravenously. The cheek pouch was everted and a single-layered preparation was studied by intravital microscopy. Albumin-bound Pd-porphyrin was infused into the circulation and excited by flash illumination at 10 Hz, with a rectangular diaphragm limiting the excitation field to 5 × 25 μ m.

Results: In the longitudinal direction, intravascular PO₂ decreased significantly (P < 0.01) from large arterioles (39.5 ± 2.3 mmHg) to small arterioles (32.2 ± 0.3 mmHg), then to capillaries (30.2 ± 1.8 mmHg), and on to small venules (27.3 ± 2.1 mmHg) and large venules (25.5 ± 2.2 mmHg). In the radial direction, PO₂ decreased significantly (P < 0.01) in and around larger arterioles, and to a lesser extent, around the smaller ones (P < 0.05). There was no significant PO₂ gradient, longitudinal or radial, associated with venules. The PO₂ difference from the centerline to the outside wall in large arterioles was 8.3 ± 1.4 mmHg, and most of the decline in PO₂ in the radial direction was contributed by the intravascular difference (4.7 ± 2.1 mmHg) and only about 1.0 ± 2.7 mmHg by the transmural difference.

Conclusions: Our data show that there are large intra-arteriolar radial PO₂ gradients, but no large transmural PO₂ differences, suggesting that the oxygen consumption of the microvessel wall is not exceptionally high.

Key words:

• convection
• diffusion
• microvessels
• oxygen transport
• phosphorescence quenching

ACKNOWLEDGEMENTS

The authors thank Lei Zheng for expert technical assistance during the initial stage of this study. Drs. Aleksander S. Golub and Aleksander S. Popel provided valuable comments on the manuscript.

This work was supported by Grant HL18292 from the National Heart, Lung and Blood Institute and by a fellowship from CAPES–Brasília/Brasil.