Involvement of platelet-activating factor and leukotrienes in anaphylactic segmental venoconstriction in ovalbumin sensitized guinea pig livers

The hepatic anaphylactic venoconstriction is partly involved in anaphylactic hypotension, and is characterized by significant post-sinusoidal constriction and liver congestion in guinea pigs. We determined what chemical mediators are involved in anaphylaxis-induced segmental venoconstriction and liver congestion in perfused livers isolated from ovalbumin sensitized guinea pigs. Livers were perfused portally and recirculatingly at constant flow with diluted blood. The sinusoidal pressure was measured by the double occlusion pressure (Pdo), and was used to determine the pre-sinusoidal (Rpre) and post-sinusoidal (Rpost) resistances. An antigen injection increased both the portal vein pressure and Pdo, resulting in 4.1- and 2.3-fold increases in Rpre and Rpost, respectively. Hepatic congestion was observed as reflected by liver weight gain. Pretreatment with TCV-309 (10microM, platelet-activating factor (PAF) receptor antagonist) or ONO-1078 (100microM, human cysteinyl-leukotriene (Cys-LT) receptor 1 antagonist), but not indomethacin (10microM, cyclooxygenase inhibitor), ketanserin (10microM, serotonin receptor antagonist), or diphenhydramine (100microM, histamine H1 antagonist), significantly attenuated this anaphylactic hepatic venoconstriction. Anaphylaxis-induced increases in Rpre and Rpost were significantly inhibited by TCV-309 (by 48%) and ONO-1078 (by 36%), respectively. Combined TCV-309 and ONO-1078 pretreatment exerted additive inhibitory effects on anaphylactic hepatic venoconstriction. Anaphylactic hepatic weight gain was converted to weight loss when post-sinusoidal constriction was attenuated. It is concluded that anaphylaxis-induced pre-sinusoidal constriction is mainly caused by PAF and the post-sinusoidal constriction by Cys-LTs in guinea pig livers.     

PAF potentiates protamine-induced lung edema: role of pulmonary venoconstriction

We studied the synergistic interaction between platelet-activating factor (PAF) and protamine sulfate, a cationic protein that causes pulmonary endothelial injury, in isolated rat lungs perfused with a physiological salt solution. A low dose of protamine (50 micrograms/ml) increased pulmonary artery perfusion pressure (Ppa) but did not increase wet lung-to-body weight ratio after 20 min. Pretreatment of the lungs with a noninjurious dose of PAF (1.6 nM) 10 min before protamine markedly potentiated protamine-induced pulmonary vasoconstriction and resulted in severe lung edema and increased lung tissue content of 6-keto-prostaglandin F1 alpha, thromboxane B2, and leukotriene C4. Pulmonary microvascular pressure (Pmv), measured by double occlusion, was markedly increased in lungs given PAF and protamine. These potentiating effects of PAF were blocked by WEB 2086 (10(-5) M), a specific PAF receptor antagonist. Pretreatment of the lungs with a high dose of histamine (10(-4) M) failed to enhance the effect of protamine on Ppa, Pmv, or wet lung-to-body weight ratio. Furthermore, PAF pretreatment enhanced elastase-, but not H2O2-, induced lung edema. To assess the role of hydrostatic pressure in edema formation, we compared lung permeability-surface area products (PS) in papaverine-treated lungs given either protamine alone or PAF + protamine and tested the effect of mechanical elevation of Pmv on protamine-induced lung edema. In the absence of vasoconstriction, PAF did not potentiate protamine-induced increase in lung PS. On the other hand, mechanically raising Pmv in protamine-treated lungs to a level similar to that measured in lungs given PAF + protamine did not result in a comparable degree of lung edema. We conclude that PAF potentiates protamine-induced lung edema predominantly by enhanced pulmonary venoconstriction. However, a pressure-independent effect of PAF on lung vasculature cannot be entirely excluded.     

Alpha-thrombin-induced pulmonary vasoconstriction

We examined the direct effects of thrombin on pulmonary vasomotor tone in isolated guinea pig lungs perfused with Ringer albumin (0.5% g/100 ml). The injection of alpha-thrombin (the native enzyme) resulted in rapid dose-dependent increases in pulmonary arterial pressure (Ppa) and pulmonary capillary pressure (Ppc), which were associated with an increase in the lung effluent thromboxane B2 concentration. The Ppa and Ppc responses decreased with time but then increased again within 40 min after thrombin injection. The increases in Ppc were primarily the result of postcapillary vasoconstriction. Pulmonary edema as evidenced by marked increases (60% from base line) in lung weight occurred within 90 min after thrombin injection. Injection of modified thrombins (i.e., gamma-thrombin lacking the fibrinogen recognition site or i-Pr2P-alpha-thrombin lacking the serine proteolytic site) was not associated with pulmonary hemodynamic or weight changes nor did they block the effects of alpha-thrombin. Indomethacin (a cyclooxygenase inhibitor), dazoxiben (a thromboxane synthase inhibitor), or hirudin (a thrombin antagonist) inhibited the thrombin-induced pulmonary vasoconstriction, as well as the pulmonary edema. We conclude that thrombin-induced pulmonary vasoconstriction is primarily the result of constriction of postcapillary vessels, and the response is mediated by generation of cyclooxygenase-derived metabolites. The edema formation is also dependent on activation of the cyclooxygenase pathway. The proteolytic site of alpha-thrombin is required for the pulmonary vasoconstrictor and edemogenic responses.     

Effects of platelet-activating factor and thromboxane A2 on isolated perfused guinea pig liver

Lipid mediators, thromboxane A2 (TxA2) and platelet-activating factor (PAF), are potent vasoconstrictors, and have been implicated as mediators of liver diseases, such as ischemic-reperfusion injury. We determined the effects of a TxA2 analogue (U-46619) and PAF on the vascular resistance distribution and liver weight (wt) in isolated guinea pig livers perfused with blood via the portal vein. The sinusoidal pressure was measured by the double occlusion pressure (P(do)), and was used to determine the pre- (R(pre)) and post-sinusoidal (R(post)) resistances. U-46619 and PAF concentration-dependently increased the hepatic total vascular resistance (R(t)). The minimum concentration at which significant vasoconstriction occurs was 0.001 microM for PAF and 0.1 microM for U-46619. Moreover, the concentration of U-46619 required to increase R(t) to the same magnitude is 100 times higher than PAF. Thus, the responsiveness to PAF was greater than that to U-46619. Both agents increased predominantly R(pre) over R(post). U-46619 caused a sustained liver weight loss. In contrast, PAF also caused liver weight loss at lower concentrations, but it produced liver weight gain at higher concentrations (2.5 +/- 0.3 per 10g liver weight at 1 microM PAF), which was caused by substantial post-sinusoidal constriction and increased P(do). In conclusion, both TxA2 and PAF contract predominantly the pre-sinusoidal veins. TxA2 causes liver weight loss, while PAF at high concentrations increases liver weight due to substantial post-sinusoidal constriction in isolated guinea pig livers.     

TNF-alpha augments pulmonary vasoconstriction via the inhibition of nitrovasodilator activity.

We tested the hypothesis that tumor necrosis factor-alpha (TNF-alpha) increases pulmonary vasoconstriction by decreases in nitric oxide- (NO) dependent vasodilation. Lungs were isolated from guinea pigs 18 h after intraperitoneal injection of either TNF-alpha (1.60 x 10(5) U/kg) or control. U-46619 (365 mM/min) caused increases in pulmonary arterial and capillary pressures, pulmonary arterial and venous resistances, and lung weight. TNF-alpha augmented the U-46619-induced increases in pulmonary arterial and capillary pressures, pulmonary arterial and venous resistances, and lung weight. Methylene blue (1 microM), which inhibits the activation of soluble guanylate cyclase by NO, had an effect similar to TNF-alpha on the pulmonary response to U-46619 alone but was not additive to the effect of TNF-alpha. NG-monomethyl-L-arginine (270 microM), an inhibitor of NO generation, also enhanced the response to U-46619. Lung effluent levels of nitrite, the oxidation product of NO, were reduced after treatment with either TNF-alpha or NG-monomethyl-L-arginine compared with U-46619 alone. In addition, lungs isolated after TNF-alpha treatment showed decreased vasodilation in response to acetylcholine (10(-8)-10(-5) M) compared with control; however, vasodilation in response to L-arginine (10 mM) and nitroprusside (10(-6.3) and 10(-6) M), agents that promote NO release, was not decreased in TNF-alpha-treated lungs. The data indicate that TNF-alpha induces an increase in vascular constriction in response to U-46619 and a decrease in vasodilation in response to acetylcholine. The mechanism for the TNF-alpha-induced alteration in pulmonary vascular reactivity may be decreased generation of NO.     

Contraction of guinea pig lung parenchyma by pancreatic type phospholipase A2 via its specific binding site.

Porcine pancreatic group I phospholipase A2 (PLA2-I) induced contraction of guinea pig parenchyma in a concentration-dependent manner. Its EC50 value was similar to the Kd value calculated from the specific binding of 125I-labeled porcine PLA2-I in the membrane fraction of guinea pig lung. Type-specific action of PLA2's and homologous desensitization strongly implicated the involvement of PLA2-I-specific sites in the activation process. Thromboxane A2 was found to be the main product from lung tissue by PLA2-I action and the contractile response by PLA2-I was specifically suppressed by thromboxane A2 receptor antagonists and cyclooxygenase inhibitor, but not by leukotriene receptor antagonist and H1 blocker. These findings indicate that PLA2-I-induced contractile response may depend on the secondarily produced thromboxane A2, thus providing a new aspect of PLA2-I from the pathophysiological standpoint.     

Role of venoconstriction in thromboxane-induced pulmonary hypertension and edema in lambs

We evaluated the dose response to a stable thromboxane (Tx) A2 analogue (sTxA2; 0.3-30 micrograms) in the pulmonary circulation and its effect on the distribution of pressure gradients determined by the occlusion technique in isolated nonblood perfused newborn lamb lungs. The total pulmonary pressure gradient (delta Pt) was partitioned into pressure drops across the relatively indistensible arteries and veins (delta Pv) and relatively compliant vessels. We also evaluated the effects of prostacyclin (PGI2) and a Tx receptor antagonist (ONO 3708) on the sTxA2-induced pulmonary responses. Injection of sTxA2 caused a dose-related increase in the pulmonary arterial pressure, with the primary component of the increase in delta Pt (4.1 +/- 0.8 to 13.9 +/- 0.4 Torr) at 30 micrograms derived from the prominent rise in delta Pv (1.8 +/- 0.3 to 9.8 +/- 0.9 Torr). Infusion of PGI2 (0.4 microgram.kg-1.min-1) reduced the response to sTxA2 mainly by attenuating the delta Pv elevation. Infusion of ONO 3708 (100 micrograms.kg-1.min-1) completely abolished the sTxA2-induced pulmonary hypertension. Injection of sTxA2 resulted in pulmonary edema characterized by a significant increase in wet-to-dry lung weight ratio (9.13 +/- 0.35 vs. 7.15 +/- 0.41 in control lungs). The sTxA2-induced pulmonary edema was increased by PGI2 and inhibited by ONO 3708. We conclude that thromboxane-induced pulmonary hypertension is primarily produced by venoconstriction and prostacyclin may worsen the edema induced by thromboxane.     

Effects of hypoxia on leukotriene activity and vasomotor tone in isolated sheep lungs

To determine whether hypoxic pulmonary vasoconstriction was associated with release of sulfidopeptide leukotrienes (SPLTs) from the lung, we measured SPLT activity by bioassay (guinea pig ileum) and radioimmunoassay in lymph, perfusate, and bronchoalveolar lavage (BAL) fluid from sheep lungs (n = 20) isolated and perfused in situ with a constant flow of autologous blood (100 ml.kg-1.min-1) containing indomethacin (60 micrograms/ml). The protocol consisted of three periods, each at least 1 h in duration. In experimental lungs, inspired O2 concentration (FIO2) was 28.2% in periods 1 and 3 and 4.2% in period 2. In control lungs, FIO2 was 28.2% throughout. Hypoxia increased pulmonary arterial pressure but did not alter peak tracheal pressure, lung lymph flow, or weight gain measured during the last 30 min of each period. SPLT activity was greatest in lung lymph and least in BAL fluid. Hypoxia did not alter SPLT activity in any fluid. Similar results were obtained in lungs not treated with indomethacin (n = 15). These data do not support the hypothesis that hypoxic pulmonary vasoconstriction is mediated by SPLTs.     

Pulmonary microvascular response to LTB4: effects of perfusate composition

We examined the effects of leukotriene B4 (LTB4) on pulmonary hemodynamics and vascular permeability using isolated perfused guinea pig lungs and cultured monolayers of pulmonary arterial endothelial cells. In lungs perfused with Ringer solution, containing 0.5 g/100 ml albumin (R-alb), LTB4 (4 micrograms) transiently increased pulmonary arterial pressure (Ppa) and capillary pressure (Pcap). Pulmonary edema developed within 70 min after LTB4 injection despite a normal Pcap. The LTB4 metabolite, 20-COOH-LTB4 (4 micrograms), did not induce hemodynamic and lung weight changes. In lungs perfused with autologous blood hematocrit = 12 +/- 1%; protein concentration = 1.5 +/- 0.2 g/100 ml), the increases in Ppa and Pcap were greater, and both pressures remained elevated. The lung weight did not increase in blood-perfused lungs. In lungs perfused with R-alb (1.5 g/100 ml albumin) to match the blood perfusate protein concentration, LTB4 induced similar hemodynamic changes as R-alb (0.5 g/100 ml) perfusate, but the additional albumin prevented the pulmonary edema. LTB4 (10(-11)-10(-6) M) with or without the addition of neutrophils to the monolayer did not increase endothelial 125I-albumin permeability. Therefore LTB4 induces pulmonary edema when the perfusate contains a low albumin concentration, but increasing the albumin concentration or adding blood cells prevents the edema. The edema is not due to increased endothelial permeability to protein and is independent of hemodynamic alterations. Protection at higher protein-concentration may be the result of LTB4 binding to albumin.     

Release of prostaglandins and thromboxanes by guinea pig isolated type II pneumocytes

Lung cells have been isolated by enzymatic digestion of guinea pig lungs and mechanical dispersion to obtain a suspension of viable cells (approximately 500 X 10(6) cells). Type II pneumocytes have been purified to approximately 92% by centrifugal elutriation (2000 rpm, 15 ml/min) followed by a plating in plastic dishes coated with guinea pig IgG (500 micrograms/ml). We have investigated the arachidonic acid metabolism through the cyclooxygenase pathway in this freshly isolated type II cells (2 x 10(6) cells/ml). Purified type II pneumocytes produced thromboxane B2 (TxB2) predominantly and to a smaller extent the 6-keto prostaglandin PGF1 alpha (6-keto-PGF1 alpha) and prostaglandin E2 (PGE2) after incubation with 10 microM arachidonic acid. The stimulation of pneumocytes with 2 microM calcium ionophore A23187 released less eicosanoids than were produced when cells were incubated with 10 microM arachidonic acid. There was no additive effect when the cells were treated with both arachidonic acid and the ionophore A23187. Guinea pig type II pneumocytes failed to release significant amounts of TxB2, 6-keto-PGF1 alpha and PGE2 after stimulation with 10 nM leukotriene B4, 10 nM leukotriene D4, 10 nM platelet-activating factor, 5 microM formyl-methionyl-leucyl-phenylalanine, 0.2 microM bradykinin and 10 nM phorbol myristate acetate. Our findings indicate that guinea pig type II pneunomocytes possess the enzymatic machinery necessary to convert arachidonic acid to specific cyclooxygenase products, which may suggest a role for these cells in lung inflammatory processes.     

The endocannabinoid arachidonyl ethanolamide (anandamide) increases pulmonary arterial pressure via cyclooxygenase-2 products in isolated rabbit lungs

Several cannabinoids elicit systemic vasodilation, mainly via CB1 cannabinoid and vanilloid receptors. However, effects in the pulmonary circulation are unknown. Using the isolated, ventilated, buffer-perfused rabbit lung, we have shown that the endocannabinoids arachidonyl ethanolamide (anandamide) and 2-arachidonyl glycerol (2-AG) dose-dependently increase pulmonary arterial pressure (+19.9 +/- 3.4 mmHg, 5 microM, and +39.5 +/- 10.8 mmHg, 0.4 microM, respectively). 2-AG induced lung edema. The CB1 receptor antagonist AM-251 (0.1 and 5 microM) and the VR1 vanilloid receptor antagonist capsazepine (10 microM) failed to reduce anandamide's effects. The metabolically stable anandamide and 2-AG analogs R-methanandamide and noladin ether, Delta9-tetrahydrocannabinol, and the synthetic cannabinoid HU-210, which is no arachidonic acid product, were without effect. The unspecific cyclooxygenase (COX) inhibitor aspirin (100 microM, P < 0.001) and the specific COX-2 inhibitor nimesulide (10 microM, P < 0.01) completely prevented pulmonary hypertension after 5 microM anandamide. COX-2 RNA was detected in rabbit lungs. The synthetic thromboxane receptor antagonist SQ 29,548 was without effect, but the specific EP1 prostanoid receptor antagonist SC-19220 (100 microM) inhibited the pressure increase after anandamide (P < 0.05). PCR analysis detected fatty acid amidohydrolase (FAAH), an enzyme that degrades endocannabinoids, in rabbit lung tissue. Furthermore, the specific FAAH inhibitor methyl arachidonyl fluorophosphonate (0.1 microM) blocked pressure effects of anandamide (P < 0.01). Finally, anandamide (99 +/- 55 pmol/g) and 2-AG (19.6 +/- 8.4 nmol/g) were found in native lungs. We conclude that anandamide increases pulmonary arterial pressure via COX-2 metabolites following enzymatic degradation by FAAH into arachidonic acid products.     

Pulmonary microvascular responses to arachidonic acid in isolated perfused guinea pig lung

We examined the effects of arachidonic acid (AA) on pulmonary hemodynamics and fluid balance in Ringer- and blood-perfused guinea pig lungs during constant-flow conditions. Mean pulmonary arterial (Ppa), venous (Pv), and capillary pressures (Pcap, estimated by the double-occlusion method) were measured, and arterial (Ra) and venous resistances (Rv) were calculated. Bolus AA injection (500 micrograms) caused transient increases (peak response 1 min post-AA) in Ppa, Pcap, and Rv without affecting Ra in both Ringer- and blood-perfused lungs. The response was sustained in blood-perfused lungs. AA had no effect on the capillary filtration coefficient in either Ringer- or blood-perfused lungs. AA stimulated the release of thromboxane B2 and 6-ketoprostaglandin F1 alpha in both Ringer- and blood-perfused lungs, but the responses were sustained only in the blood-perfused lungs. Meclofenamate (1.5 X 10(-4) M), a cyclooxygenase inhibitor, abolished the AA-induced pulmonary hemodynamic responses in both Ringer- and blood-perfused lungs, whereas U-60257 (10 microM), a lipoxygenase inhibitor, attenuated the response only in the blood-perfused lungs. In conclusion, AA does not alter pulmonary vascular permeability to water in either Ringer- or blood-perfused lungs. AA mediates pulmonary venoconstriction and thus contributes to the rise in Pcap. The venoconstriction results from the generation of cyclooxygenase-derived metabolites from lung parenchymal cells and blood-formed elements. Lipoxygenase metabolites may also contribute to the vasoconstriction in the blood-perfused lungs.     

Leukotriene F4 and the release of arachidonic acid metabolites from perfused guinea pig lungs in vitro

Radioimmunoassay and bioassay techniques have been used to investigate the ability of leukotriene (LT)F4 to release products of arachidonic acid metabolism from guinea pig isolated lungs perfused via the pulmonary artery. Also, the abilities of LTC4, LTD4, LTE4 and LTF4 to contract guinea pig ileal smooth muscle (GPISM) was studied. Each of the LT's contracted GPISM. The rank order of potency was LTD4 greater than LTC4 greater than LTE4 much greater than LTF4 in a ratio of 1:7:170:280 respectively. Bioassay of pulmonary effluents indicated the passage of LTF4 through the lungs caused a contraction of rabbit aorta as well as an FPL-55712 sensitive contraction of GPISM. The contractions of rabbit aorta were inhibited by pretreatment of the lungs with Indomethacin but not with the thromboxane synthetase inhibitor Dazoxiben. Radioimmunoassay of the lung effluents indicated LTF4 to cause a 70-fold increase in thromboxane B2 (TXB2), 4-fold increase in prostaglandin (PG)E2 and a 16-fold increase in 6-keto PGF1 alpha levels. The LTF4-induced increments of these immunoreactive metabolites was inhibited by pretreatment of the lungs with Indomethacin. Pretreatment of lungs with Dazoxiben inhibited the LTF4-induced increment in TXB2 and enhanced the effluent levels of PGE2 24-fold (compared with untreated lungs). There were no detectable differences in either immunoreactive LTC4 or immunoreactive LTB4 levels. It is concluded LTF4 is a relatively weak agonist on GPISM and can induce the release of cyclooxygenase products of arachidonic acid metabolism from guinea pig perfused lung.     

Role of thromboxane receptor activation in the bronchospastic response to endothelin

The selective TxA2/PGH2 (TP) receptor antagonist, SQ 30,741, was used to test the hypothesis that TP-receptor activation contributes to the reactivity of airways and isolated trachea to endothelin-1 (ET-1). Dose-dependent contractions of guinea pig tracheal strips to ET-1 in vitro were unaffected by either SQ 30,741 (1 microM) or indomethacin (2.8 microM). In contrast, maximal bronchospastic responses (increases in airways resistance and decreases in dynamic lung compliance) of anesthetized guinea pigs to ET-1 (0.5 and 1.5 nmole/kg i.v.) in vivo were blocked greater than 90% by SQ 30,741 (1 mg/kg i.v.). Concurrent increases in arterial blood pressure and decreases in leukocyte counts induced by ET-1 were unaffected by SQ 30,741. In rats, ET-1 (1.5 nmole/kg i.v.) did not affect lung mechanics, but did cause biphasic blood pressure and leukopenia responses which were unaltered by SQ 30,741. These data demonstrate that there is considerable species variability in the bronchospastic response to ET-1, and that in guinea pigs, this response is caused predominantly by the activation of TP-receptors.     

Mechanism of peptidoleukotriene-induced increases in pulmonary transvascular fluid filtration

We examined the effects of leukotrienes C4 (LTC4) and D4 (LTD4) (1 microgram) on the pulmonary vascular filtration coefficient, a measure of vessel wall conductivity to water, and the alterations in pulmonary vascular resistance (PVR) in isolated-perfused guinea pig lungs. We also assessed whether LTC4 and LTD4 increased the permeability to albumin in cultured monolayers of pulmonary artery endothelial cells. In Ringer-perfused and blood-perfused lungs, LTC4 resulted in increases in pulmonary arterial pressure (Ppa) and the pulmonary capillary pressure (Pcap) measured as the equilibration pressure after simultaneous pulmonary arterial and venous occlusions. Pulmonary venous resistance (Rv) increased to a greater extent than arterial resistance (Ra) in both Ringer-perfused and blood-perused lungs challenged with LTC4. The greater increase in PVR in blood-perfused lungs corresponded with a greater elevation of lung effluent thromboxane B2 (TxB2) concentration. The LTC4-stimulated increase in PVR was prevented by pretreatment with meclofenamate (10(-4) M). LTD4 also induced rapid increases in Ppa and Pcap in both Ringer-perfused and blood-perfused lungs; however, Ppa decreased before stabilizing at a pressure higher than base line. The increases in Rv with LTD4 were greater than Ra. The LTD4-stimulated increases in Ra and Rv also paralleled the elevation in TxB2 concentration. As with LTC4, the increases in Ppa, Pcap, PVR, and TxB2 concentration were greater in blood-perfused than in Ringer-perfused lungs. Pretreatment with meclofenamate reduced the magnitude of the initial increase in Ppa, but did not prevent the response.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of leukotrienes B4, C4, and D4 on segmental pulmonary vascular pressures

Leukotrienes (LTs) C4 and D4 are vasoconstrictors and are thought to increase both systemic and pulmonary vascular permeability. However, we and others have observed that LTC4 and LTD4 cause pulmonary vasoconstriction but do not increase the fluid filtration coefficient of excised guinea pig lungs perfused with a cell-depleted perfusate. To determine what vascular segments were exposed to an LT-induced increase in intravascular hydrostatic pressure we measured pulmonary arterial (Ppa), pulmonary arterial occlusion (Po,a), venous (Po,v) and double occlusion (Pdo) pressures in isolated guinea pig lungs perfused with a cell-depleted buffered salt solution before and after injecting 4 micrograms of LTB4, LTC4, or LTD4 into the pulmonary artery. All three LTs increased airway pressures and also increased Ppa, Po,a, and Pdo. Histamine (15 micrograms) as well as serotonin (20 or 200 micrograms) had the same effect. In excised rabbit lungs, histamine and serotonin increased only Ppa, and Po,a. LTC4 had no vasoactivity. There are marked species variations with regard to the activity and site of action of histamine, serotonin, and LTC4 on the pulmonary circulation.     

Amiloride impairs lung water clearance in newborn guinea pigs

To determine whether epithelial ion transport is physiologically important for lung water clearance after birth, the sodium transport inhibitor amiloride or its vehicle saline was given intratracheally to newborn full-term guinea pigs before the first breath. Guinea pigs given saline intratracheally breathed normally and had arterial O2 saturations (SaO2) greater than 94%. In contrast, guinea pigs that had an estimated 10(-4) M intra-alveolar concentration of amiloride had chest wall retractions and 88 +/- 3.6% (SD) SaO2 (P less than 0.01). Extravascular lung water (EVLW) per gram of dry lung weight 4 h after birth was significantly greater in newborns that received amiloride (8.3 +/- 1.1, n = 5) than in those that received saline (5.6 +/- 0.9, n = 7, P less than 0.01). The degree of perivascular fluid cuffing at 25 cmH2O inflation was quantitatively similar in amiloride- and saline-treated animals. The effect of amiloride was dose dependent. Intratracheal amiloride did not affect EVLW in 9-day-old guinea pigs. This study demonstrates that intratracheal amiloride before the first breath results in respiratory distress, hypoxemia, and an abnormally high EVLW. Epithelial sodium transport contributes normal lung liquid clearance after birth.     

L-NAME augments PAF-induced venoconstriction in isolated perfused livers of rat and guinea pig, but not mouse

Platelet-activating factor (PAF), one of vasoconstrictive lipid mediators, is involved in systemic anaphylaxis. On the other hand, nitric oxide (NO) is known to attenuate anaphylactic venoconstriction of the pre-sinusoids in isolated guinea pig and rat livers. However, it is not known whether NO attenuates PAF-induced hepatic venoconstriction. We therefore determined the effects of L-NAME, a NO synthase inhibitor, on PAF-induced venoconstriction in blood- and constant flow-perfused isolated livers of mice, rats and guinea pigs. The sinusoidal pressure was measured by the double occlusion pressure (Pdo), and was used to determine the pre- (Rpre) and post-sinusoidal (Rpost) resistances. PAF (0.01-1 microM) concentration-dependently caused predominant pre-sinusoidal constriction in all livers of three species studied. The guinea pig livers were the most sensitive to PAF, while the mouse livers were the weakest in responsiveness. L-NAME pretreatment selectively increased the basal Rpre in all of three species. L-NAME also significantly augmented the PAF-induced increases in Rpre, but not in Rpost, in rat and guinea pig livers. This augmentation was stronger in rat livers than in guinea pig livers at the high concentration of 0.1 microM PAF. However, L-NAME did not augment PAF-induced venoconstriction in mouse livers. In conclusion, in rat and guinea pig livers, NO may be released selectively from the pre-sinusoids in response to PAF, and then attenuate the PAF-induced pre-sinusoidal constriction. In mouse liver, PAF-induced venoconstriction is weak and not modulated by NO.     

PMA-induced pulmonary edema: mechanisms of the vasoactive response

We investigated the effect of phorbol myristate acetate (PMA) in isolated guinea pig lungs perfused with phosphate-buffered Ringer solution. Pulmonary arterial pressure (Ppa), pulmonary capillary pressure (Ppc), and change in lung weight were recorded at 0, 10, 25, 40, and 70 min. The capillary filtration coefficient (Kf), an index of vascular permeability, was measured at 10 and 70 min. The perfusion of PMA (0.5 x 10(-7) M) increased Ppa, Ppc, and lung weight at 70 min. The ratio of arterial-to-venous vascular resistance (Ra/Rv) decreased and the Kf did not change with PMA. The perfusion of the lung with 4 alpha-phorbol didecanoate (inactive toward the protein kinase C analogue of PMA) did not affect the lung. The inhibition of TxA2 synthase with dazoxiben inhibited the response to PMA. The inhibition of the 5-lipoxygenase with U-60257 and the SRS-A receptor antagonist FPL 55712 also prevented the response to PMA. The addition of superoxide dismutase (SOD), catalase, or SOD plus catalase (the enzymes that remove O.2 H2O2, and OH., respectively) did not prevent the PMA effect or the release of TxA2; however, dimethylthiourea (DMTU), a scavenger of OH., did prevent the response to PMA. The data indicate that PMA causes a neutrophil-independent increase in lung weight due to increases in Ppc mediated by TxA2 and SRS-A. The protective effect of DMTU may be due to the inhibition of TxA2 generation.     

Substance P-induced effects in guinea pig lungs: effects of thiorphan and captopril

The effects of the neutral metalloendopeptidase inhibitor, thiorphan, and the angiotensin-converting enzyme inhibitor, captopril, on the changes in airway opening pressure (PaO), pulmonary arterial pressure (Ppa), and weight induced by intravascular administration of substance P were examined in isolated perfused and ventilated guinea pig lungs. Administration of 1 nmol substance P without enzyme inhibitors resulted in a significant (P less than 0.01) increase in the peak PaO during ventilation from 12.4 +/- 0.5 to 22.4 +/- 2.2 cmH2O; there were small statistically insignificant increases in Ppa. The changes in PaO peaked approximately 30 s after peptide infusion and returned to preinfusion values by 5 min. In the presence of combined thiorphan (5.6 microM) and captopril (7.7 microM) the magnitude of the Pao response at 30 s (41.5 +/- 3.8 cmH2O) and at 5 min (40.0 +/- 3.6 cmH2O) after peptide infusion was significantly greater than in control lungs (P less than 0.05). The effects of substance P on PaO in the presence of the various inhibitors were not related to amount of peptide recovered in the lung effluent. Reverse-phase high-performance liquid chromatographic analysis of [3H]Pro2,4 substance P perfused through the lungs demonstrated that the major products were consistent with intact substance P, substance P 1-4, and smaller peptides; only minor amounts of products consistent with substance P 1-7, 1-9, or 3-11 were identified. These data support our previous findings showing that the physiological effects of intravascular substance P are limited by peptide degradation; the latter process, once begun, proceeds rapidly to nearly complete peptide degradation.