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

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.