Characterization of heterogeneous distribution of tumor blood flow in the rat.

Angioarchitectures of ascites hepatoma AH109A and Sato lung carcinoma (SLC) were quantitatively compared by measuring the following morphometric parameters: vascular density, vascular length, distance between tissues and their nearest blood vessel, and total length of microvascular network per unit area. When the vascular networks in these two types of tumors were compared in the initial stage, the morphological parameters were almost identical. Correlations between tumor size and the number of starting vessels and between enlargement of the tumor and the ensuing increase in pressure of the starting vessel were also evaluated with a microcomputer and an apparatus for measuring microvascular pressure. The total length of tumor vascular network to which one starting vessel supplied blood increased exponentially as the tumor increased in size exponentially. There was a positive correlation between tumor size and the number of starting vessels. The range of the blood supply from one starting vessel was evidently limited. The pressure of the starting vessel increased with enlargement of the tumor size. As soon as the pressure of the starting vessel reached a plateau, however, there was a rapid increase in low-flow or no-flow areas in regions within the tumor. From the results obtained, we consider that low-flow or no-flow areas, resistant to delivery of anticancer drugs, inevitably appear with the progression of tumor growth.