Tissue PO2 and arteriolar responses to metabolic stimuli during maturation of striated muscle.

Tissue O2 tension (PO2) and small arteriolar diameter were measured in hamsters aged 32, 60, and 80 days. The cremaster muscle was isolated and superfused with a solution equilibrated with 0, 5, or 10% O2 stimulated to contract at 1 Hz. Resting muscle tissue PO2 was proportional to superfusate PO2 and was not different between age groups. The decrease in tissue PO2 during contraction was greatest in adult animals when the superfusate PO2 was low but was equal in all groups when the superfusate PO2 was high. Elevated superfusate PO2 was correlated with a vasoconstriction, the magnitude of which varied inversely with age. Resting and contraction-induced vascular diameter were largest in the youngest animals, relative to maximum diameter, but absolute resting and contraction-induced diameters were similar in all groups. We suggest that tissue PO2 at rest was similar because of an age-associated decrease in fiber O2 consumption to maintain a constant proportionality between O2 supply and demand. The relative stability of tissue PO2 during contraction in young animals might have reflected superior regulation. However, a simple numerical analysis predicts smaller tissue PO2 decreases during contraction in young animals because of short intercapillary distances and other altered O2 supply parameters, even if regulation had been identical in all age groups.