PERIVASCULAR OXYGEN-TENSIONS IN A TRANSPLANTABLE MAMMARY-TUMOR GROWING IN A DORSAL FLAP WINDOW CHAMBER

Fischer 344 rats with R3230 Ac mammary carcinomas implanted in dorsal flap window chambers served as a model to obtain measurements of perivascular and stromal oxygen tension in normal and tumor tissues using Whalen recessed-tip microelectrodes (3- to 6-μm tip). Perivascular measurements were made adjacent to vessels with continuous blood flow. Thus the measurements and models provided are reflective of conditions leading to chronic hypoxia. Perivascular oxygen tensions averaged 72 ± 13 mmHg in normal tissue vessels adjacent to tumor, 26 ± 5 mmHg in tumor periphery, and 12 ± 3 mmHg in tumor central vessels. There was a significant trend toward lower perivascular oxygen tensions in the tumor center (Kruskal-Wallis test, P = 0.002). A similar tendency was seen with a limited number of stromal measurements. Krogh cylinder models, which incorporate these data for perivascular oxygen tension, along with morphometric data obtained from the same tumor model suggest that hypoxic regions will exist between tumor vessels in the tumor center unless O2 consumption rates are well below 0.6 ml/100 g/min. The low perivascular measurements observed near the tumor center combined with the theoretical considerations suggest, for this model at least, that tissue oxygenation may best be improved by increasing red cell velocity and input pO2 and reducing oxygen consumption. The low perivascular oxygen tensions observed near the center also suggest that conditions conducive to increased red cell rigidity exist, that drugs which can decrease red cell rigidity could improve tumor blood flow and oxygenation, and that the endothelium of those vessels may be susceptible to hypoxia-reoxygenation injury.