MODULATION OF SPATIAL O-2 TENSION DISTRIBUTION IN EXPERIMENTAL-TUMORSBY INCREASING ARTERIAL O-2 SUPPLY

Tumor oxygenation has been measured polarographically in s.c. implante d DS-sarcomas on the dorsum of the hind foot of male Sprague-Dawley ra ts, pO(2) was determined in all 3 spatial dimensions and 3-dimensional pO(2) distributions as well as the mean extent of confluent areas wit h pO(2) < 5 mmHg were calculated. Finally, the effect of elevating art erial pO(2) (by carbogen breathing) as well as of increasing tumor blo od flow (by angiotensin infusion) on the spatial pO(2) distribution wa s analyzed. Depending on the tumor volume, the spatial pO(2) distribut ion is more or less anisotropic. In smaller tumors, areas with physiol ogical pO(2) values are found adjacent to large hypoxic areas whereas larger tumors are almost completely hypoxic/anoxic. With carbogen brea thing, the mean tissue pO(2) is elevated although hypoxia is not eradi cated in larger tumors. In small tumors, angiotensin leads to a vasoco nstriction of tumor vessels followed by a worsening of tumor oxygenati on whereas in large tumors the increased systemic perfusion pressure r esulted in an improvement of oxygenation. Thus, carbogen predominately affects pO(2) diffusion by increasing the arterial pO(2) whereas angi otensin influences tumor perfusion and leads to an increased oxygen su pply to the tumor tissue.