Longitudinal and radial gradients of PO(2) in the hamster cheek pouch microcirculation

Objectives: The aim of this study was to determine longitudinal and radial gradients in oxygen tension (PO(2)) in microvessels of the hamster check pouch. Methods: We measured PO(2) using the phosphorescence-quenching method in two orders of arterioles (45.8 +/- 5.5 and 19.9 +/- 1.8 mu m diameter), capillaries, and two orders of venules (50.5 +/- 3.4 and 21.4 +/- 2.0 mu,m diameter) in order to determine the longitudinal PO(2) gradient. At the arteriolar and venular sites, we also measured PO(2) at four different sites for an analysis of radial PO(2) 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 1.0 Hz, with a rectangular diaphragm limiting the excitation field to 5 x 25 mu m. Results: In the longitudinal direction, intravascular PO(2) decreased significantly (P < 0.01) from large arterioles (39.5 +/- 2.3 mm-nHg) to small arterioles (32.2 +/- 0.3 mmHg), then to capillaries (30.2 +/- 1.8 mmHg), and on to small ventiles (27.3 +/- 2.1, mmHg) and large venules (25.5 +/- 2.2 mmHg). In the radial direction, PO(2) 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 PO(2) gradient, longitudinal or radial, associated with venules. The PO(2) difference from the centerline to the outside wall in large arterioles was 8.3 +/- 1.4 mmHg, and most of the decline in PO(2) 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 transitional difference. Conclusions: Our data show that there are large intra-arteriolar radial PO(2) gradients, but no large transmural PO(2) differences, suggesting that the oxygen consumption of the microvessel wall is not exceptionally high.