To test the hypothesis that PAF partially mediates endotoxin-induced lung dysfunction, we studied the effects of two structurally dissimilar PAF receptor antagonists (SRI 63-441 and WEB 2086) on endotoxin-induced lung dysfunction in chronically instrumented awake sheep. Each animal was studied three times in varied order: infusion of endotoxin alone (Escherichia coli endotoxin 0.5 micrograms/kg over 20 min [E]), infusion of the competitive platelet-activating factor (PAF) receptor antagonist alone, or with endotoxin given 1 h after beginning the 6-h drug infusion (E + SRI, E + WEB). Neither drug alone had significant effects on any of the measured variables, but both were able to abolish the pulmonary pressor effect of a 0.25-micrograms/kg bolus of PAF. SRI 63-441 (10 to 20 mg/kg/h) attenuated the endotoxin-induced pulmonary hypertension (peak pulmonary arterial pressure, 53 +/- 12 versus 65 +/- 7 cm H2O; p greater than 0.05) and fall in dynamic compliance of the lungs (to 65.1 +/- 9.8% baseline versus 32.6 +/- 5.1% baseline). Lung lymph flow increased 6.1- and 5.8-fold at 2 and 5 h for (E) versus 1.9- and 2.5-fold at identical time points for (E + SRI). SRI 63-441 attenuated the acute leukopenia noted after endotoxemia. WEB 2086 (20 mg/kg/h) similarly attenuated the late alterations in lung mechanics and lymph flow caused by endotoxin, but it had little effect on the early pulmonary hypertension and lung mechanic changes. Both agents significantly attenuated the rise in lymph thromboxane B2 levels after endotoxemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Neutrophils have been implicated as important cellular mediators of the pulmonary dysfunction observed following endotoxemia in chronically instrumented awake sheep. Several areas of research suggest that neutrophil-derived proteases may be mediators of this dysfunction. We hypothesized that neutrophil elastase inhibitors would attenuate the effects of endotoxemia in sheep. To test this hypothesis, we studied the effects of two putative neutrophil elastase inhibitors, SC-37698 and SC-39026 (Searle, Skokie, IL), on endotoxin-induced lung dysfunction in awake sheep. Sheep were given intravenous neutrophil elastase inhibitor alone (20 mg/kg/h for 6 h), intravenous endotoxin (E. coli endotoxin, 0.5 microgram/kg over 20 min) 1 h after beginning the 6-h infusion of elastase inhibitor, or endotoxin 1 h after beginning a 6-h infusion of elastase inhibitor vehicle. SC-37698 attenuated the increase in lung lymph flow and lung lymph protein clearance, the alterations in lung mechanics, and the fall in white blood count. Qualitatively similar effects were seen with SC-39026. These data suggest the need for further research examining the role of protease-antiprotease interactions and the potential utility of neutrophil elastase inhibitors in acute lung injury like that observed in the adult respiratory distress syndrome (ARDS) in the human.

BMS182874, an endothelin receptor antagonist, blocks the effects of exogenously administered endothelins in chronically instrumented awake sheep. A possible role for endothelin in endotoxin-induced pulmonary hypertension in sheep was investigated by studying animals given intravenous endotoxin with and without pretreatment with BMS182874. BMS182874 administration alone caused a reduction in pulmonary artery pressure (P[PA]) and systemic arterial pressure (P[SA]). Endotoxin alone caused an acute, nearly threefold increase in P(PA) which was followed, from 2-5 h after endotoxin, by a sustained but less severe increase in P(PA). These changes were accompanied by a threefold increase in lung lymph flow and dramatic increases in plasma and lung lymph thromboxane B2 concentrations. Pretreatment with BMS182874 significantly attenuated the early endotoxin-induced acute increase in P(PA) and completely blocked the late sustained pulmonary hypertension (p < 0.05), while having no affect on the increases in thromboxane levels. BMS182874 shifts the dose response curve for U46619, a prostaglandin H2 analogue, to the right. BMS182874, in addition to functioning as an endothelium receptor antagonist, appears to counteract the action of thromboxane at the receptor level. We theorize that BMS182874 attenuates the early endotoxin-induced pulmonary hypertension by counteracting the effects of thromboxane, since previous studies demonstrated that the early acute rise in P(PA) is caused by thromboxane. The late sustained pulmonary hypertension of endotoxemia, on the other hand, appears to be mediated by endothelin.

Platelet-activating factor (PAF), a potent proinflammatory ether lipid, has been proposed as a potential mediator of airway hyperresponsiveness. We studied the effect of a single intravascular bolus of synthetic PAF (0.5 microgram/kg) on airway responsiveness to aerosolized histamine in 8 chronically instrumented awake sheep. Lung mechanics were assessed by whole-body plethysmography. Histamine dose-response curves were performed before and 4 h after PAF administration. PAF induced a 60% fall in dynamic compliance and a three-fold increase in resistance to air flow across the lung within 5 min. All animals tested became more responsive to aerosol histamine 4 h after PAF as evidenced by a fall in ED65Cdyn from 9.45 mg/ml before to 4.34 mg/ml. There was no correlation between the initial Cdyn or the Cdyn measured just prior to the second bronchial challenge and the calculated alteration in responsiveness. Animals displaying the greatest initial responsiveness to aerosol histamine also manifested the greatest alteration in lung mechanics after intravascular PAF (r = 0.92). We conclude that PAF consistently alters lung mechanics and increases airway responsiveness in awake sheep, and aerosol histamine responsiveness correlates with the maximal response to intravenous PAF.

The effects of a single intravascular bolus injection of platelet-activating factor (PAF) on pulmonary hemodynamics, lung mechanics, and lung fluid and solute exchange were studied in 13 chronically instrumented unanesthetized sheep. Since PAF has profound effects on both platelets and granulocytes, we investigated the effects of platelet and granulocyte depletion on the sheep's response to exogenous PAF. Sheep received PAF when granulocyte and platelets counts were normal and after platelet depletion with rabbit antisheep platelet antibodies (n = 5) or granulocyte depletion with hydroxyurea (n = 5). Sheep served as their own controls, and the order of experimentation was varied. Bolus injections of PAF had reproducible effects on pulmonary hemodynamics (pulmonary arterial pressure increased acutely to 85 +/- 3.7 cmH2O) and lung mechanics (dynamic compliance of the lungs decreased to 24.5 +/- 3.8% of base line and resistance to airflow across the lungs increased greater than 10-fold) and caused marked increases in lung lymph concentrations of thromboxane B2 and 6-ketoprostaglandin F1 alpha. The single bolus injection of PAF also caused marked prolonged elevations in lung lymph flow and increases in the lymph-to-plasma protein concentration ratio for 3 h after PAF. PAF had profound effects despite platelet and granulocyte depletion. Platelet depletion slightly attenuated the pulmonary hypertension observed after PAF injection. Platelet depletion also attenuated the increases in thromboxane B2 concentrations in lung lymph, and lung mechanics normalized more rapidly in platelet-depleted sheep. There were no statistically significant effects of granulocyte depletion to less than 200 granulocytes/mm3 on any of the measured variables.(ABSTRACT TRUNCATED AT 250 WORDS)