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.