Exercise Hyperemia in the Absence of a Tissue PO2 Decrease

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Abstract
The relationship between contraction-induced arteriolar vasodilation, estimated blood flow (BF), and tissue oxygen tension (PtO2) in skeletal muscle of young rats was investigated. Arteriolar diameters, BF, and PtO2 were measured during cremaster muscle stimulation at 2, 4, and 8 Hz. At a suffusate PO2 (PsO2) of 5–10 mm Hg, the caliber of second-order arterioles (2A, > 30 µm diameter) did not significantly increase after 8 Hz stimulation. In contrast, with the same PsO2, third-order arterioles (3A, < 30 µm diameter) significantly dilated to 127 ± 9 (SE), 135 ± 12, and 160 ± 13% of control, respectively at 2, 4, and 8 Hz stimulation. Third-order arteriolar BFs at the end of the stimulation periods were: 119 ± 18, 176 ± 14, and 258 ± 43% of control, respectively. PtO2 remained essentially constant during and following 4 and 8 Hz stimulation if the systemic arterial blood pressure exceeded 80 mm Hg. When PsO2 was increased to 65–70 mm Hg, neither 3A diameters nor PtO2 during 8 Hz stimulation differed from paired comparisons of the response at low PsO2. These data indicate that dilation of small arterioles during increased muscle metabolic activity can occur without a mandatory change in PtO2. This circumstance is unaffected by a substantially increased supply of oxygen to the tissue.