Influence of vasoactive drugs on blood flow in subcutaneous tumors – an experimental study in rats

Subcutaneously implanted tumors in Wistar and Lister rats were used as a model for the study of metastatic tumor blood flow and how it is affected by vasoactive drugs. Blood flow measurements were obtained using the labelled microsphere method and the reference organ technique. Microspheres (15-μm) labelled with either ⁹⁹Tc^m or ⁵¹ Cr isotopes were injected intracardially and a reference sample was drawn simultaneously at constant speed. This was performed before and after the infusion of vasoactive drugs, and (as control), saline infusion. The drugs tested (adrenaline, noradrenaline, glucagon, histamine, and vasopressin) showed profound effects on central hemodynamic parameters and on muscle and skin blood flow. The relative tumor blood flow, measured as the ratio between tumor and skin or tumor and muscle blood flow, was calculated. The results show that no enhancement of the relative tumor blood flow could be registered. In fact, a decrease in the tumor-to-muscle-blood-flow ratio was noted when noradrenaline was infused, and in the tumor-to-skin ratio when adrenaline was infused. Blood flow in subcutaneous tumors was four to five times that in muscle or skin. Tumor blood flow was also inversely related to the size of the tumor.