Influence of a prostaglandin synthesis inhibitor and of thrombocytopenia on tumor blood flow and tumor vascular permeability. Experimental studies in the rat.

The intratumor distribution of vascular permeability in two transplantable rat tumors was studied by calculating tissue-plasma ratios of two intravenously injected labeled albumins with an interval of five hours between albumin injections. The data were calculated and presented as the capillary permeability surface area product (PS) in multiple tumor biopsies. Furthermore, the intratumor distribution of blood flow was studied by the intratumor uptake of intravenously injected 86Rb. The same parameters were also studied in normal striated muscle. Prolonged administration of a prostaglandin synthesis inhibitor, diclofenac-sodium (Voltaren) changed significantly the tumor blood flow towards higher values. A similar change was observed in animals with induced thrombocytopenia. Tumor PS values were increased by administration of diclofenac-sodium, but not by induced thrombocytopenia. The intratumor distribution of plasma volume, calculated from tissue-plasma values of albumin injected 5 minutes before the animals were killed, was not significantly changed as well as blood flow, plasma volume and PS in normal muscle. There was no significant correlation between separate tumor blood flow and PS values, while such a significant correlation was found in normal muscle. The observations made in this study suggest that a release of both prostaglandins and serotonin might be included in the regulation of tumor blood flow and vascular permeability.