Longitudinal Gradients in Periarteriolar Oxygen Tension

The oxygen tension (Po 2 ) 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 Po 2 was measured in 10 vessels and compared with extravascular Po 2 . Good agreement was found, with a mean difference of 1.4 ± 0.8 ( SE ) mm Hg. Significant longitudinal gradients were observed in periarteriolar Po 2 . 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 Po 2 of 39 ± 8 mm Hg, a tissue Po 2 of 8 ± 2 mm Hg and femoral arterial blood Po 2 of 69 mm Hg. When the suffusion solution Po 2 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 Po 2 of the cheek pouch suffusion solution was 39 mm Hg. Under these conditions, small artery Po 2 was 152 ± 13 mm Hg and terminal arteriolar Po 2 was 37 ± 9 mm Hg. Femoral artery blood Po 2 was 427 ± 12 mm Hg. These data are consistent with the hypothesis that oxygen diffuses from the precapillary vessels and that intravascular Po 2 falls progressively along the resistance vessels. This finding suggests a possible mechanism for the involvement of O 2 in local regulation of blood flow.