Capillary blood flow in the amelanotic melanoma of the hamster after isovolemic hemodilution.

In malignant tumors, spontaneous arteriolar vasomotion disappeared already during earliest tumor growth (tumor weight less than 200 mg) suggesting that arterioles supplying a malignant tumor with blood are maximally dilated from the very beginning of tumor growth. As a result, the viscosity of blood becomes a limiting factor of tissue perfusion. To evaluate the effects of isovolemic hemodilution in a malignant tumor, a transparent chamber model was used in conjunction with a subcutaneously growing amelanotic melanoma of the hamster. Quantitative intravital microscopy (video image analysis) and a platinum multiwire electrode were utilized to study the tumor microcirculation. Isovolemic hemodilution was performed by exchange of blood vs. Dextran 60 to lower the systemic hematocrit to 30% in 21 animals. Capillary flow increased significantly and improved tissue pO2 on the tumor's surface without any change in capillary density. Since tumor growth was accelerated after hemodilution, these data suggest to combine with hemodilution other treatment modalities to improve blood-mediated tumor therapy.