Early effects of ionizing radiation on the microvascular networks in normal tissue

Microvascular networks, which control the delivery of oxygen and nutrients and the removal of metabolic waste, are the most sensitive part of the vasc ular system to ionizing radiation, Structural and functional changes in mic rovascular networks were studied in locally irradiated (single 10-GS dose) hamster cremaster muscles observed 3, 7 and 30 days postirradiation. Networ ks were selected in reference to a well-defined location in the tissue to r educe heterogeneity due to spatial variations. Intravital microscopy was us ed to measure structural and functional parameters in vivo. A factorial des ign was used to examine the effects of radiation status, time postirradiati on, and network vessel type on the structure and function of microvascular network. While the diameter of microvessels in control animals increased si gnificantly with age, vessel diameter in irradiated vessels decreased signi ficantly with age. Red blood cell velocity in irradiated networks at 3 and 30 days postirradiation was significantly lower than in control networks. T here was a significant decrease in capillary surface area and a significant increase in vessel hematocrit in irradiated animals, Blood dow in irradiat ed vessels was significantly lower than in control vessels, Changes in func tional parameters were evident at 3 days postirradiation while changes in s tructural parameters occurred later. All vessel types were not damaged equa lly by radiation at every time examined, (C) 1999 by Radiation Research Soc iety.