Investigation of microvessel density after irradiation

It is believed that malignant cell populations need the development of micr ovessels to grow and metastasize. The aim of our investigation was to find out whether gamma irradiation can affect proliferation of endothelial cells and thus fan affect microvessel density in vivo. We used fertilized chicke n eggs. The vascularized part of the yolk sac membrane (area vasculosa) of the eggs received single doses of 2 to 10 Gy, Forty-eight hours after irrad iation, the area vasculosa was photographed in vivo, and prints of known ma gnification were evaluated to determine the density of the blood vessels. M icrovessel count is the well-established marker used to determine vascular density. In addition, the proliferative activity of endothelial cells in th e yolk sac membrane was determined by estimating the expression of prolifer ating cell nuclear antigen (PCNA), PCNA immunostaining was assessed immunoh istochemically. After a single dose of 10 Gy, a statistically significant i ncrease in vascular density was found compared to values determined at 0, 2 , 4 and 8 Gy (P < 0.05). Twenty-four hours after 10 Gy irradiation, 44.8% ( mean) of the endothelial cells were PCNA-positive, This was significantly h igher (P < 0.05) compared to the results 24 h after 4.0 Gy (22.7%) and comp ared to control (19.4%). Twenty-four hours later, i.e. 48 h after irradiati on with 10 Gy, the endothelial cells also showed a significantly (P < 0.05) higher PCNA positivity with a mean of 34.1% compared to the nonirradiated area vasculosa (18.1%) and compared to the results after 4.0 Gy irradiation (12.0%), The prerequisite for blood vessel formation is the proliferation of endothelial cells. Thus a single-dose irradiation with 10 Gy induces end othelial cell. proliferation and subsequent neovascularization in the area vasculosa of the fertilized egg. (C) 1999 by Radiation Research Society.