Efficacy of a combination thromboxane receptor antagonist and lipoxygenase inhibitor in traumatic shock

Leukotrienes in the pathogenesis of pulmonary blast injury

Our previous studies demonstrate a significant increase of sulfidopeptide leukotriene concentrations in animals exposed to a free air blast. The aim of this study was to analyze the role of leukotrienes in the local response of lung tissue as well as in the general response of organisms to blast overpressure. The study was conducted on adult rabbits exposed to moderate blast overpressure (four pulmonary contusions characterized as confluent ecchymoses involving 30 to 60% of the lungs), generated in laboratory conditions. One group of experimental animals was treated with 5-lipoxygenase (5-LO) inhibitor, diethylcarbamazine (DEC, Sigma, St. Louis, Missouri) (50 mg/kg, i.v.), immediately before blast. The early posttraumatic period was observed (30 minutes after blast). Hemodynamic parameters (mean arterial pressure, heart rate, blood gases) as well as arterial plasma levels of conjugated dienes were observed. The myeloperoxidase activity, lipid peroxidation products levels, and water contents were measured in the lung tissue of injured rabbits. We observed that 5-LO inhibition reduced edema formation, accumulation of neutrophils, and generation of lipid peroxidation products in injured lungs. In this study, we demonstrated that treatment with DEC inhibits the increased systemic generation of conjugated dienes after blast injury. Although DEC exerts local antioxidant activity with beneficial effects on lung tissue, this 5-LO inhibitor intensifies the blast overpressure caused hemodynamic insufficiency.

Increased renal uptake of gentamicin in endotoxemic rats receiving concomitant thromboxane A2 antagonist therapy

This report describes the effects of endotoxin and a thromboxane receptor antagonist, L-655,240, on kidney function and the intrarenal pharmacokinetics of aminoglycosides. The rationale for these studies was that thromboxane antagonists may eventually be used in combination with aminoglycosides in patients with gram-negative sepsis and endotoxemia. As aminoglycosides are nephrotoxic and endotoxin has already been shown to increase the renal uptake of gentamicin, we investigated the possibility that thromboxane antagonists might interfere with the nephrotoxic potential of both substances. A decrease in the volume of distribution and an increase in the intracortical concentration of gentamicin were observed in animals given endotoxin. Compared with animals given endotoxin alone, those which received endotoxin plus L-655,240 had significant accumulation of gentamicin in the renal cortex and medulla, as determined by the area under the concentration-time curve, and a significant reduction in the total clearance of the antibiotic (P < 0.05). This difference in uptake could not be attributed to hypotension or changes in the glomerular filtration rate or renal plasma flow. L-655,240 alone did not modify gentamicin pharmacokinetics but did decrease p-aminohippuric acid secretion. Thromboxane antagonists in the context of endotoxemia increase intrarenal uptake of aminoglycosides. If these compounds are to be used as therapeutic agents when endotoxin is present, their influence on renal handling of nephrotoxic drugs needs to be considered. Multiple-dosing regimens deserve investigation.

Protective effects of KW-3635, a novel thromboxane A2 antagonist, in murine traumatic shock

Pentobarbital anesthetized rats subjected to Noble-Collip drum trauma developed a shock state characterized by marked hypotension, increases in plasma cathepsin D (9.6-fold), free amino-nitrogen (4.0-fold), and myocardial depressant factor (5.2-fold) activities, and a survival time of 1.90 +/- 0.23 h. Following the induction of traumatic shock, plasma thromboxane B2 (TxB2) concentrations significantly increased from 3.12 +/- 0.68 to 6.78 +/- 0.27 pmol/ml. Treatment with the thromboxane receptor antagonist KW-3635 10 min post-trauma (2 mg/kg + 2 mg/kg per h, i.v.) prolonged survival time to 3.30 +/- 0.39 h (P less than 0.01) and attenuated the accumulation of cathepsin D compared to untreated trauma rats (6.6 +/- 1.1 and 13.6 +/- 1.3 U/ml, P less than 0.01), free amino-nitrogen (6.4 +/- 1.1 and 14.3 +/- 1.2 U/ml, P less than 0.01), and myocardial depressant factor (45 +/- 5 and 94 +/- 13 U/ml, P less than 0.02). However, KW-3635 did not prevent the increase in plasma TxB2 concentration, suggesting a lack of thromboxane synthetase inhibitory activity of this drug. The beneficial effects of thromboxane A2 (TxA2) antagonism in the present study are highly significant, and consistent with the concept that TxA2 is involved in the pathogenesis of traumatic shock.

Involvement of leukotriene C4 in PAF-induced death in mice

The role of leukotrienes (LTs) in the pathogenesis of platelet-activating factor (PAF)-induced death in mice was reinvestigated, since previously reported results are in conflict. A novel 5-lipoxygenase inhibitor, E6080, and a leukotriene antagonist, LY17883, protected mice from PAF-induced death in a dose-dependent manner, while the well-known 5-lipoxygenase inhibitor, AA861, was less effective than E6080. After the intravenous injection of PAF in mice, immunoreactive leukotriene C4 (i-LTC4), which was co-eluted with authentic LTC4 in HPLC, was significantly increased in bronchoalveolar lavage fluid (BALF). Oral administration of E6080 suppressed the increase in i-LTCM4. The results suggest that LTs may play an important role in PAF-induced lethality in mice.

Beneficial effects of a specific leukotriene receptor antagonist in splanchnic artery occlusion shock

The purpose of this study was to examine the effects of a new potent peptidoleukotriene receptor antagonist, SK&F 104353, in splanchnic artery occlusion shock. SK&F 104353 was administered as a 1 mg/kg initial bolus followed by an infusion of 3 mg/kg per h for the entire 2 h post-reperfusion observation period. In a group of conscious rats, this dose of SK&F 104353 shifted the LTD4 dose response curve rightward 10-fold, indicating effective antagonism of peptidoleukotriene responses in the rat. Anesthetized rats subjected to splanchnic artery occlusion shock survived an average of only 98 +/- 8 min whereas all animals receiving SK&F 104353 survived the 2 h reperfusion period (P less than 0.02 from vehicle). Therefore, the survival rate of the splanchnic artery occlusion shock group of rats receiving SK&F 104353 was improved to 100% compared with 50% survival for the vehicle-treated splanchnic artery occlusion shock group (P less than 0.025). In the splanchnic artery occlusion shock + SK&F 104353 group the increase in the plasma activities of the lysosomal hydrolase, cathepsin D, and the cardiotoxic peptide, myocardial depressant factor, were significantly attenuated in comparison to the splanchnic artery occlusion shock + vehicle group (P less than 0.025). These data indicate that the peptidoleukotriene receptor antagonist, SK&F 104353 is beneficial in splanchnic artery occlusion shock, and furthermore suggests that it may be a therapeutically useful agent in bowel ischemic shock.