Functional integrity and inflammatory reactions of exchange vessels and lymphatics in X-irradiated tissues.

Local pre-irradiation of the foot (LFI) with 500 to 20,000 rad X-rays and sublethal whole body irradiation (WBI) of rats did not significantly affect development, intensity or resolution of inflammatory oedema induced by subdermal injection of the foot with pharmacological mediators of inflammation or Compound 48/80. LFI and WBI both caused modest increases in swelling induced by carrageenan which are attributed to a combined (additive) effect of slight early oedema from increased vascular permeability induced by radiation and the inflammatory oedema induced by carrageenan. Age of rat did not significantly affect inflammatory oedema induced by various irritants in unirradiated or irradiated rats. The pattern of tissue swelling induced by irradiation was measured. It is concluded that the small exchange vessels (capillaries and venules) and lymphatics which largely regulate the amount and composition of interstitial fluids are highly radioresistant; they remain physiologically intact and react normally to vasoactive substances which mediate inflammatory reactions, even after exposure to doses of radiation which completely eliminate cell reproductive integrity. Inflammatory effects of X-rays (“roentgen reactions”) are largely attributed to the reactions mounted by the mature microvasculature to products of tissue damage, and the anti-inflammatory (“antiphlogistic”) effects to the suppression of regenerative growth of actively proliferating capillaries (angiogenesis) in the repair phase.