Mechanisms of parenchymal cell death in-vivo after microvascular hemorrhage

Objective: In vitro studies suggest that microhemorrhages with escape of re d cells into the tissue may be cytotoxic to parenchymal cells clue to oxyge n free radical formation, We examined in the rat mesentery the impact of mi crohemorrhages on parenchymal cell death, as detected by propidium iodide s taining, 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 mesente ry interstitium. Over a period of 2 h, no significant increase in parenchym al cell death was encountered in tissues with hemorrhagic sites compared wi th nonhemorrhagic control sites. Interstitial microinjections of plasma der ived from whole blood incubated for several hours with and without a combin ation of sodium azide (2 mM) and hydrogen peroxide (1 mM) led to significan tly increased levels of cell death compared to control experiments. Interve ntions against the hydroxyl radical with dimethylthiourea (DMTU, 2 mM) or 2 ,2'-dipyridyl (DPD, 2 mM), a lipid soluble iron chelator, provided no prote ctive effect against the parenchymal cell death. DMTU slightly delayed the cytotoxic reaction. Conclusions: These observations suggest that a newly formed micro hemorrhag e is not necessarily cytotoxic to parenchymal tissue cells. Interstitial mi croinjections of plasma, derived from whole blood after prolonged exposure to oxygen free radicals or just aging under in vitro conditions, may be cyt otoxic to mesenteric parenchymal cells without effective blockade by interv entions against the hydroxyl radical.