[Development of the angioarchitecture and microcirculatory characteristics in rat tumor].

Using a rat transparent chamber and a device for measurement of microvascular pressure, we observed tumor vascularization process in vivo and measured the daily change in pressure of a "starting vessel" which supplies blood to the tumor vascular network. Results were summarized as follows: (1) The position from which tumor vessels originated was usually the terminal portion of a terminal arteriole (starting vessel). The frequency with which new capillaries originated from vein and venule was very low. (2) Pressure of a starting vessel increased from 30-40 cm H2O (22-30 mmHg) to 120-130 cm H2O (88-96 mmHg) with enlargement of the tumor vascular network. As soon as pressure of a starting vessel reached a plateau, no-flow vessels appeared in places within a tumor. (3) Pressure of a starting vessel was elevated by angiotensin II. In turn, the elevated pressure of a starting vessel brought about a marked increase in tumor blood flow, resulting in the blood flow in no-flow vessels.