Mechanisms of parenchymal cell death in-vivo after microvascular hemorrhage

Objective: In vitro studies suggest that microhemorrhages with escape of red cells into the tissue may be cytotoxic to parenchymal cells clue to oxygen free radical formation, We examined in the rat mesentery the impact of microhemorrhages on parenchymal cell death, as detected by propidium iodide staining, using an intravital approach. Methods and Results: Postcapillary venules were punctured with a closed-end micropipette, permitting escape of blood cells and plasma into the mesentery interstitium. Over a period of 2 h, no significant increase in parenchymal cell death was encountered in tissues with hemorrhagic sites compared with nonhemorrhagic control sites. Interstitial microinjections of plasma derived from whole blood incubated for several hours with and without a combination of sodium azide (2 mM) and hydrogen peroxide (1 mM) led to significantly increased levels of cell death compared to control experiments. Interventions against the hydroxyl radical with dimethylthiourea (DMTU, 2 mM) or 2,2'-dipyridyl (DPD, 2 mM), a lipid soluble iron chelator, provided no protective effect against the parenchymal cell death. DMTU slightly delayed the cytotoxic reaction. Conclusions: These observations suggest that a newly formed micro hemorrhage is not necessarily cytotoxic to parenchymal tissue cells. Interstitial microinjections of plasma, derived from whole blood after prolonged exposure to oxygen free radicals or just aging under in vitro conditions, may be cytotoxic to mesenteric parenchymal cells without effective blockade by interventions against the hydroxyl radical.