Exposure of bovine pulmonary arterial endothelial cells to the oxidant tert-butyl hydroperoxide (t-bu-OOH) caused a dose-dependent increase in the release of [14C]arachidonic acid and synthesis of the cyclooxygenase products, thromboxane, prostaglandin E2, prostaglandin D2, and prostacyclin. There was no detectable production of peptide leukotrienes before or after administration of t-bu-OOH. Pretreatment with the oxygen radical scavenger 4-hydroxy-2,2,6,6-tetramethylpiperidino radical (HTP) or the antioxidants vitamin E and dithiothreitol prevented the increased arachidonic acid (AA) release caused by t-bu-OOH. t-bu-OOH increased the activity of phospholipase A2 by increasing its apparent maximum velocity without affecting its Michaelis constant. The increased AA release caused by t-bu-OOH did not appear to require new RNA or protein synthesis, because pretreatment of the cells with actinomycin D or cycloheximide did not reduce the increased release of AA or activation of phospholipase A2 caused by t-bu-OOH. Dexamethasone pretreatment of the cells prevented the increase in phospholipase A2 activity, and AA release produced by t-bu-OOH. t-bu-OOH increased the activity of phospholipase A2 and release of AA in both the presence and absence of extracellular calcium (Ca2+). Pretreatment with a nominal Ca2+-free buffer, the Ca2+ chelator ethylene glycolbis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, nifedipine, or verapamil did not reduce t-bu-OOH-stimulated AA release. In contrast, treatment with the intracellular Ca2+ chelator 8-N,N-diethyamino octyl 3,4,5-trimethoxybenzoate (TMB-8) prevented t-bu-OOH-stimulated AA release in both the presence and absence of extracellular Ca2+. Treatment with calmodulin antagonists also prevented the increased release of AA caused by t-bu-OOH.

We have previously shown that phosgene markedly increases lung weight gain and pulmonary vascular permeability in rabbits. The current experiments were designed to determine whether cyclooxygenase- and lipoxygenase-derived mediators contribute to the phosgene induced lung injury. We exposed rabbits to phosgene (1,500 ppm/min), killed the animals 30 min later, and then perfused the lungs with a saline buffer for 90 min. Phosgene markedly increased lung weight gain, did not appear to increase the synthesis of cyclooxygenase metabolites, but increased 10-fold the synthesis of lipoxygenase products. Pre- or posttreatment with indomethacin decreased thromboxane and prostacyclin levels without affecting leukotriene synthesis and partially reduced the lung weight gain caused by phosgene. Methylprednisolone pretreatment completely blocked the increase in leukotriene synthesis and lung weight gain. Posttreatment with 5,8,11,14-eicosatetraynoic acid (ETYA), a nonmetabolized competitive inhibitor of arachidonic acid metabolism, or the leukotriene receptor blockers, FPL 55712 and LY 171883, also dramatically reduced the lung weight gain caused by phosgene. These results suggest that lipoxygenase products contribute to the phosgene-induced lung damage. Because phosgene exposure did not increase cyclooxygenase synthesis or pulmonary arterial pressure, we tested whether phosgene affects the lung's ability to generate or to react to thromboxane. Infusing arachidonic acid increased thromboxane synthesis to the same extent in phosgene-exposed lungs as in control lungs; however, phosgene exposure significantly reduced pulmonary vascular reactivity to thromboxane but not to angiotension II and KCl.

Infusion of the oxidant lipid peroxide tert-butyl hydroperoxide (t-bu-OOH) causes pulmonary vasoconstriction and increases vascular permeability in isolated perfused rabbit lungs. We have previously shown that t-bu-OOH stimulates arachidonic acid metabolism, increasing the synthesis of the cyclooxygenase products. The current experiments were designed to determine the role that cyclooxygenase- and lipoxygenase-derived mediators play in the lung injury caused by t-bu-OOH. In the present experiments, we found that t-bu-OOH not only increased the synthesis of the cyclooxygenase-derived products thromboxane and prostacyclin but also increased the synthesis of the lipoxygenase-derived products leukotrienes B4, C4, D4, and E4. To determine the role that these arachidonic acid metabolites play in the increase in pressure and vascular permeability caused by t-bu-OOH, we studied the effect that inhibitors of arachidonic acid metabolism or a leukotriene receptor blocker had on the pulmonary edema. We compared an uninjured control group with 4 groups of lungs given t-bu-OOH: a t-bu-OOH control group; a group pretreated with the cyclooxygenase inhibitor indomethacin (14 microM); a group pretreated with an analogue of arachidonic acid, 5-, 8-, 11-, 14-eicosatetraynoic acid (ETYA) (100 microM), that inhibits both the cyclooxygenase and lipoxygenase pathways; and a group pretreated with the leukotriene receptor antagonist FPL 55712 (38 microM). To produce lung injury, t-bu-OOH (300 microM) was infused throughout the first minute of 4 successive 10-min periods.(ABSTRACT TRUNCATED AT 250 WORDS)

Our objectives were 1) to quantify the magnitude of the hypoxic pulmonary vasoconstrictor (HPV) response in conscious dogs by utilizing pulmonary vascular pressure-cardiac index (P/Q) plots and 2) to assess the extent to which the autonomic nervous system (ANS) modulates the HPV response. Multipoint P/Q plots were constructed in conscious dogs during normoxia and during bilateral alveolar hypoxia by stepwise constriction of the thoracic inferior vena cava to reduce Q. With the ANS intact, the pulmonary vascular pressure gradient (pulmonary arterial pressure-pulmonary capillary wedge pressure) increased (P less than 0.01) approximately twofold during hypoxia over a broad range of Q. The absolute magnitude of the HPV response was related (P less than 0.01) to the level of Q. We hypothesized that if ANS activation reduces the magnitude of HPV in intact dogs, then we would expect the magnitude of HPV to be increased both after combined sympathetic alpha-(phentolamine) and beta-(propranolol) adrenergic block and after total autonomic ganglionic block (hexamethonium). A marked HPV response (P less than 0.01) was observed after both combined sympathetic block and ganglionic block over a broad range of Q during alveolar hypoxia. The magnitude of the HPV response with the ANS intact, however, was not significantly different from the magnitude of HPV after combined sympathetic block (P = 0.45) or after ganglionic block (P = 0.64) at any level of Q. Thus, during bilateral alveolar hypoxia, the ANS does not appear to attenuate the HPV response of intact conscious dogs.