Longitudinal Gradients in Periarteriolar Oxygen Tension

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Abstract
The oxygen tension (Po2) on the external surface of arterioles between 8 and 100µ in diameter was measured with oxygen microcathodes (2 to 6µ diameter) in the suffused cheek pouch of hamsters and in the cremaster muscle of hamsters and rats anesthetized with pentobarbital and urethane. Intravascular Po2 was measured in 10 vessels and compared with extravascular Po2. Good agreement was found, with a mean difference of 1.4 ± 0.8 (SE) mm Hg. Significant longitudinal gradients were observed in periarteriolar Po2. Oxygen tension fell from 35 ± 4 mm Hg on the small arteries (ca. 80µ diameter) to 20 ± 3 mm Hg at the end of the terminal arterioles. These measurements were obtained with a suffusion solution Po2 of 39 ± 8 mm Hg, a tissue Po2 of 8 ± 2 mm Hg and femoral arterial blood Po2 of 69 mm Hg. When the suffusion solution Po2 was raised to 79 mm Hg, the resultant measurements were 42 ± 3 on the small arteries and 21 ± 3 mm Hg at the end of the terminal arterioles. Similar experiments were carried out while animals were breathing 95% oxygen and the Po2 of the cheek pouch suffusion solution was 39 mm Hg. Under these conditions, small artery Po2 was 152 ± 13 mm Hg and terminal arteriolar Po2 was 37 ± 9 mm Hg. Femoral artery blood Po2 was 427 ± 12 mm Hg. These data are consistent with the hypothesis that oxygen diffuses from the precapillary vessels and that intravascular Po2 falls progressively along the resistance vessels. This finding suggests a possible mechanism for the involvement of O2 in local regulation of blood flow.