Correlation of regional disease and in vivo PO2 in rat mammary adenocarcinoma.

A knowledge of the distribution of oxygen tension (PO2) and vascularization in neoplasia has been fundamental to understanding relationships between tumor growth, hypoxia, and therapy. We have combined recessed oxygen microcathode and freeze-substitution techniques to correlate in situ PO2 profiles and morphologic features in 7,12-dimethylbenz(a)anthracene (DMBA) tumors in rats. Overlying connective tissue of transplanted tumor was exposed by a 1-2 mm incision and a cross-stitch pattern demarcated electrode puncture sites for histologic reference. Three buffered salt solutions (BSS) with different PO2 were each allowed to flow through a well over the tumor where electrodes were placed for calibration. Zero electrode oxygen current was recorded from a buffered yeast-agar mixture of zero torr. PO2 was recorded at 5-mu intervals to approximately 1-2 mm. Atmospheric contamination was eliminated by continuous well flow of BSS, 30 torr. Finally, the tumor and surrounding tissues were quick-frozen in vivo with Freon 22 and liquid nitrogen. The tissue block was freeze-substituted and sectioned. PO2 profiles were superimposed onto correspondingly scaled photomicrographs. A viable periphery with a PO2 range of 50-82 torr and a transition to necrotic areas of PO2, 2-13 torr were observed. This transition was characterized by PO2 gradients within distances of 50-300 mu at variable puncture depths. This technique should be useful in further studies of growth, necrosis, and therapy.