Functional characteristics of tumor vessels: selective increase in tumor blood flow.

This experiment was carried out to elucidate how tumor microcirculation differs from that of normal tissues. Pressure-flow relationship was examined in normal rat tissues, uninvolved tissues in tumor-bearing rats, transplanted AH109A solid tumors, and primary tumors induced by 3-methylcholanthrene. Tumor blood flow was measured by the hydrogen clearance technique. The blood pressure was elevated by continuous iv infusion of angiotensin II. Elevation of blood pressure produced a several-fold increase in tumor blood flow without increasing blood flow in normal tissue and uninvolved tissue in tumor-bearing rats. The increase was selective to tumor tissues as long as the mean arterial blood pressure remained under about 150 mmHg. The lower the resting tumor blood flow, the greater the increase in the flow was at induced hypertension. There were no significant differences in the resting blood flow and in the rate of flow change at induced hypertension between the intramuscularly transplanted tumor, the intrahepatically transplanted tumor, and the sc transplanted tumor. These results indicate that the delivery of systemically administered anticancer drugs could be selectively enhanced in tumor tissues by induced hypertension.