Increase in tumor microvascular pressure by angiotensin-induced hypertension: implication for pharmacokinetic analysis of drug delivery into tumor tissue

Tumor microvascular pressure was measured by using a newly developed transparent chamber of rat. The pressure of tumor vessels, 20-100 microns in diameter, increased from 9.2 +/- 2.6 cm H2O to 15.4 +/- 3.2 cm H2O when the mean arterial pressure was elevated from 103.3 +/- 8.6 mmHg to 159.2 +/- 7.9 mmHg with continuous infusion of angiotensin II. It was frequently observed that the blood began to flow into the vessels in tumor tissue, where the statis of flow had been seen, when the pressure was elevated from normotension to hypertension by angiotensin II. Based on the results obtained, the mechanism of drug delivery into tumor tissue was discussed in correlation with the enhancement of chemotherapeutic effects in both animal experiments and cancer patients by induced hypertension chemotherapy.