Vascular density profile of rat mammary carcinomas induced by 1-methyl-1-nitrosourea: Implications for the investigation of angiogenesis

Abstract

Given the mounting interest in studying the effects of various cancer preventive regimes on the angiogenic process in autochthonously growing mammary tumors, the experiment reported here was conducted to identify factors that should be considered in the collection of data from experiments in which a primary endpoint is the measurement of blood vessel density as a reflection of angiogenic activity. Female Sprague-Dawley rats were injected i.p. with 50 mg 1-methyl-1-nitrosourea (MNU)/kg body weight at 21 days of age. Tumor-bearing rats were killed 35 days post-carcinogen. Immunohistochemical detection of blood vessels using antiserum directed against the CD31 epitope was performed on paraffin sections of 36 carcinomas representing four histological types. Census counting was used to detect all blood vessels that were subsequently divided into one of five vessel size categories. Vessels were counted in both the intra-tumoral region and in a 50 μm width band of mammary tissue circumscribing each tumor; the circumscribed area was referred to as the extra-tumoral region. Vascular density was reported in units of vessel counts or vessel area per unit of assessed area. Overall, vascular density was observed to be highly variable and was not affected by tumor histology. Vascular density in the extra-tumoral region was significantly higher than in the intra-tumoral region. Correlation analyses indicated that similar information was obtained when vascular density was reported as either vessel counts or vessel area; however, correlations across vessel size categories and between the intra-tumoral and extra-tumoral regions were low and generally not statistically significant. Collectively, the data provide a complete description of vascularization in autochthonously growing mammary tumors, and a reference for comparison in studies of various cancer preventive agents that modulate the angiogenic process. © Oxford University Press 2002.