Limb Ischemia-Induced Increase in Permeability Is Mediated by Leukocytes and Leukotrienes

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Abstract
This study tests the role of white blood cells (WBC) and leukotrienes in mediating the increased microvascular permeability following ischemia and reperfusion. Anesthetized dogs (n = 23) underwent 2 hours of hind limb ischeima induced by tourniquet inflation to 300 mmHg. In untreated animals (n = 7), tourniquet release led after 5 minutes to a rise in plasma thromboxane (Tx) B2 levels from 360 to 1702 pg/ml (p < 0.05); after 2 hours, lymph TxB2 concentration had risen from 412 to 1598 pg/ml (p > 0.05). There were decreases in circulating WBC from 11,766 to 6550/mm3 and platelets from 230 to 155 .times. 103/mm3. During reperfusion, popliteal lymph flow (.ovrhdot.QL) increased from 0.07 to 0.24 ml/hour (p < 0.05), while the lymph/plasma (L/P) protein ratio was unchanged from 0.39, changes consistent with increased microvascular permeability. WBC depletion (n = 7) to 302/mm3 by hydroxyurea or nitrogen mustard attentuated (p < 0.05) the reperfusion induced rise in plasma TxB2 from 91 to 248 pg/ml and prevented the increase in lymph TxB2 concentration. Within 5 minutes of tourniquet release WBC counts further decreased to 191/mm3 (p < 0.05) and platelets declined from 175 to 93 .times. 103/mm3 (p < 0.05). .ovrhdot.QL increased from 0.07 to 0.12 ml/hour (p < 0.05), lower than untreated animals (p < 0.05), and the L/P protein ratio decline from 0.49 to 0.37 (p < 0.05), dilutional changes consistent with increased filtration pressure but not permeability to protein. Pretreatment with the lipoxygenase inhibitor diethylcarbamazine (DEC) (n = 8) prevented the reperfusion-induced increase in plasma and lymph TxB2 levels (p < 0.05) and the fall in WBC counts (p < 0.05), while platelet counts declined from 381 to 210 .times. 103/mm3 (p < 0.05). .ovrhdot.QL rose from 0.09 to 0.23 ml/hour (p < 0.05) during reperfusion, and the L/P protein ratio of 0.3 remained unchanged, a value lower than in untreated dogs (p < 0.05). In two animals of each group, vascular recruitment was induced by tourniquet inflation to 50 mmHg. This led to a high .ovrhdot.QL of 0.25 ml/hour and a low L/P ratio of 0.18. In untreated animals during reperfusion, .ovrhdot.QL further increased to 1.3 ml/hour, and L/P ratio rose to 0.44, documenting increased vascular permeability. In contrast, reperfusion in leukopenic or diethylcarbamazine (DEC)-treated dogs with vascular recruitment, was not associated with increases in .ovrhdot.QL or the L/P protein ratio. These data indicate that circulating leukocytes and leukotrienes mediate the reperfusion-induced injury to the vasular barrier.