Failure of histamine type mediators to enhance vascular permeability in experimental liver metastases

The effects of histamine, bradykinin, serotonin and reactive hyperemia on vascular permeability in Walker carcinosarcomas and host liver tissue were studied in rats. A quantitative Evans blue technique was used to assess vascular permeability. While the expected increases in permeability occurred in the liver five minutes after the administration of the histamine type drugs, the drugs failed to increase vascular permeability in the tumors at all the time periods studied. The liver responded variably at 30 minutes after drug administration, and all effects had disappeared at six hours. The only increase in vascular permeability seen in the tumors was that occurring five minutes after the establishment of reactive hyperemia. Results of these studies demonstrate further differences between newly formed tumor vessels and well established vessels of the host tissue.