Hydralazine-enhanced selective heating of transmissible venereal tumor implants in dogs

This study was designed to test the hypothesis that vasodilator drugs can enhance selective heating of solid tumors by producing a favorable redistribution of blood flow between tumor and normal tissues. Subcutaneous transmissible venereal tumor implants were heated by inductive diathermy using Helmholtz coils in 8 dogs. The temperature rise in tumor and adjacent muscle was measured before and after giving hydralazine (0.5 mg/kg i.v.). Blood flow to the tumors and underlying muscle was measured with radioactive tracer microspheres. Before hydralazine treatment mean muscle blood flow was about one-third tumor blood flow (0.11 +/- 0.02 vs 0.28 +/- 0.09 ml/min/g), and tumor and normal muscle temperatures were not significantly different (40.0 +/- 0.6 vs 39.7 +/- 0.1 degrees C). After hydralazine tumor blood flow decreased and muscle blood flow increased in every dog, and selective heating of the tumors became possible. Muscle blood flow averaged 0.67 +/- 0.13 ml/min/g, 17 times greater than tumor blood flow, which decreased to 0.04 +/- 0.02 ml/min/g. Core tumor temperature was 48.0 +/- 0.9 vs 38.5 +/- 0.5 degrees C for underlying muscle. Blood pressure was maintained at 80 +/- 5.7 mmHg. These results demonstrate that adjuvant treatment with vasodilators is a promising technique to increase the temperature difference between tumors and surrounding normal tissues during local heat therapy.