Microcirculatory studies in rat mammary carcinoma. I. Transparent chamber method, development of microvasculature, and pressures in tumor vessels.

Fragments of a mammary adenocarcinoma were implanted into transparent tissue chambers in the dorsal skin flaps of female inbred F344 rats. A chamber modification permitted repeated access to the tissue without infection, vessel disruption, or impairment of tumor growth. Tumors completely filled the chambers after 26-30 days. Development of tumor microvasculature was characterized by increase in number, length, and diameter of vessels. These changes were much more pronounced in capillaries and venules than in arterioles. Direct blood pressure measurements were performed in microvessels throughout the tumor during the first 3 weeks of growth as well as in microvessels of tumor-free control preparations containing subcutaneous tissue. Average pressures in arterioles of 40- to 11-micron diameter were between 23.0 and 17.3 cm H2O in tumors versus 25.5 and 16.2 cm H2O in controls. Average pressures in venous capillaries, venules, and veins up to 150-micron diameter were between 9.1 and 8.1 cm H2O in tumors and between 13.4 and 11.0 cm H2O in controls.