Bradykinin-induced airway responses in guinea pig: effects of inhibition of cyclooxygenase and thromboxane synthetase.

We studied the effects of indomethacin (10 mg/kg i.v.), a cyclooxygenase inhibitor, and OKY-046 (1, 10 and 30 mg/kg i.v.), a selective thromboxane synthetase inhibitor, on airflow obstruction and airway plasma exudation induced by bradykinin (150 nmol) instilled by the airway route to anesthetized guinea pigs. To do this, we studied changes in lung resistance (RL) and extravasation of Evans Blue dye respectively. Instilled bradykinin produced an immediate and marked increase in RL which peaked at approximately 30 s. We also observed a delayed increase in RL, reaching a second peak at approximately 3 min. Bradykinin produced airway plasma exudation at all airway levels, measured as extravasation of Evans Blue dye. Indomethacin significantly inhibited both the immediate and the delayed increase in RL after bradykinin. OKY-046 had a similar significant and dose-dependent inhibitory effect on these responses. In addition, both drugs inhibited bradykinin-induced Evans blue dye extravasation in intrapulmonary airways. Bradykinin instilled by the airway route significantly decreased systemic blood pressure but this effect was not altered in animals pretreated with either indomethacin or OKY-046. We conclude that the bronchoconstrictor response and airway plasma exudation induced by instilled-bradykinin may be mediated in part via thromboxane A2 generation.     

Bradykinin-induced airflow obstruction and airway plasma exudation: effects of drugs that inhibit acetylcholine, thromboxane A2 or leukotrienes.

1. The mechanisms behind bradykinin-induced effects in the airways are considered to be largely indirect. The role of cholinergic nerves and eicosanoids, and their relationship in these mechanisms were investigated in guinea-pigs. 2. The role of cholinergic nerves was studied in animals given atropine (1 mg kg-1, i.v.), hexamethonium (2 mg kg-1, i.v.), or vagotomized. To study the role of eicosanoids, animals were pretreated with a thromboxane A2 (TxA2) receptor antagonist (ICI 192,605; 10(-6) mol kg-1, i.v.) or with a leukotriene (LT) receptor C4/D4/E4 antagonist (ICI 198,615; 10(-6) mol kg-1, i.v.). 3. After pretreatment with a drug, bradykinin (150 nmol) was instilled into the tracheal lumen. We measured both airway insufflation pressure (Pi), to assess airway narrowing, and the content of Evans blue dye in airway tissue, to assess plasma exudation. 4. Bradykinin instillation into the trachea caused an increase in Pi and extravasation of Evans blue dye. The increase in Pi was significantly attenuated by atropine or the TxA2 receptor antagonist, but not by hexamethonium, vagotomy or the LT receptor antagonist. 5. The bradykinin-induced exudation of Evans blue dye was significantly attenuated in the intrapulmonary airways by the TxA2 receptor antagonist, but not by atropine, hexamethonium, cervical vagotomy or the LT receptor antagonist. 6. A thromboxane-mimetic U-46619 (20 nmol kg-1, i.v. or 10 nmol intratracheally), caused both an increase in Pi and extravasation of Evans blue dye at all airway levels. Atropine pretreatment slightly attenuated the peak Pi after the intratracheal administration of U-46619, but not after i.v. administration.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of STA(2), a thromboxane A(2) mimetic, in inducing airflow obstruction and airway microvascular leakage in guinea pigs

BACKGROUND: U-46619, a thromboxane A(2) (TXA(2)) mimetic, is shown to cause airway microvascular leakage, although the effects is weak when comparing with that to induce bronchoconstriction in guinea pigs. OBJECTIVE: In order to know the airway effect of TXA(2) more accurately, we have examined the effects of STA(2), a TXA(2) mimetic with higher affinity to TXA(2) (TP) receptors than U-46619, to induce airway microvascular leakage and airflow obstruction. METHODS: Anesthetized and ventilated guinea pigs were i.v. given STA(2) (3-30 nmol/kg) or U-46619 (3-100 nmol/kg) 1 min after i.v. Evans blue dye. STA(2)- and U-46619-induced increases in lung resistance (R(L)) was measured for 6 min. The amount of extravasated Evans blue dye in the lower airways was, then, examined as an index of leakage. In selected animals, specific TP receptor antagonists (10 microg/kg S-1452 or 10 mg/kg ONO-3708) were pretreated i.v. RESULTS: Both STA(2) and U-46619 induced significant increases in leakage and airflow obstruction. However, STA(2) induced a slow and significantly less increase in R(L) but caused a significantly greater increase in extravasation of Evans blue dye compared to U-46619. Specific TP receptor antagonists completely abolished both airway effects induced by STA(2) and U-46619. CONCLUSION: Our present results have supported a possibility that TXA(2) induces microvascular leakage as well as bronchoconstriction in the airways.     

Endothelin-1 enhances vascular permeability in conscious rats: role of thromboxane A2.

The purpose of the present experiments was to study the effects of endothelin-1 (ET-1) on vascular permeability and the involvement of the cyclooxygenase metabolites in the vascular responses to ET-1. Bolus intravenous injection of ET-1 (0.1-1.0 nmol/kg) into conscious rats induced immediate hypotension lasting for 30 s followed by sustained dose-dependent hypertension. A low dose of ET-1 (0.1 nmol/kg) did not modify the hematocrit value but the 1.0-nmol/kg dose increased the hematocrit value from 39.7 to 44.4%. Pretreatment of the animals with BM-13505 (1 mg/kg), a thromboxane A2 (TxA2) receptor antagonist, prolonged the duration of the hypotensive response to ET-1 (1.0 nmol/kg) but had no effect on the pressor response. Pretreatment with OKY-046 (10 mg/kg), a TxA2 synthesis inhibitor, or indomethacin (10 mg/kg), a cyclooxygenase inhibitor, had no significant effect on ET-1-induced changes in blood pressure. Evans blue dye extravasation, a marker of vascular permeability, increased up to 235% over control levels in specific vascular beds including the upper and lower bronchi, stomach, duodenum and kidney of ET-1 (1.0 nmol/kg)-treated animals. Pretreatment of the animals with BM-13505, OKY-046 or indomethacin reduced by 60-100% the Evans blue extravasation in these tissues. These results suggest that the effect of ET-1 on vascular permeability is partly mediated and/or modulated by the secondary release of TxA2, whereas its action on arterial blood pressure appears to be independent from prostanoid release in conscious rats.     

Pharmacological characterization of prostanoid receptors mediating vasoconstriction in human umbilical vein

1. This study was undertaken to characterize pharmacologically the prostanoid receptor subtypes mediating contraction in human umbilical vein (HUV). 2. HUV rings were mounted in organ baths and concentration-response curves to U-46619 (TXA(2) mimetic) were constructed in the absence or presence of SQ-29548 or ICI-192,605 (TP receptor antagonists). U-46619 was a potent constrictor (pEC(50): 8.03). SQ-29548 and ICI-192,605 competitively antagonized responses to U-46619 with pK(B) values of 7.96 and 9.07, respectively. 3. Concentration-response curves to EP receptor agonists: PGE(2), misoprostol and 17-phenyl-trinor-PGE(2) gave pEC(50) values of 5.06, 5.25 and 5.32, respectively. Neither pEC(50) nor maximum of PGE(2) and 17-phenyl-trinor-PGE(2) concentration-response curves were modified by the DP/EP(1)/EP(2) receptor antagonist AH 6809 (1 micro M). However, ICI-192,605 produced a concentration-dependent antagonism of the responses to all the EP receptor agonists. The pA(2) estimated for ICI-192,605 against PGE(2) or misoprostol were 8.91 and 9.22, respectively. 4. Concentration-response curves to FP receptor agonists: PGF(2)(alpha) and fluprostenol gave pEC(50) values of 6.20 and 5.82, respectively. ICI-192,605 (100 nM) was completely ineffective against PGF(2)(alpha) or fluprostenol. In addition, lack of antagonistic effect of AH 6809 (1 micro M) against PGF(2)(alpha) was observed. 5. In conclusion, the findings obtained with TP-selective agonist and antagonists provide strong evidence of the involvement of TP receptors promoting vasoconstriction in HUV. Furthermore, the action of the natural and synthetic EP receptor agonists appears to be mediated via TP receptors. On the other hand, the results employing FP receptor agonists and antagonists of different prostanoid receptors suggest the presence of FP receptors mediating vasoconstriction in this vessel.     

Prostacyclin modulates the responses to leukotrienes C4 and D4 of guinea-pig airway smooth muscle

Superfusion of lung parenchymal strips or tracheal strips from the guinea-pig with effluent from perfused isolated lungs reduced the contractions elicited by leukotriene C4 (LTC4) and leukotriene D4 (LTD4) but not those elicited by acetylcholine (ACh). Incubation of the lung perfusate for 15 min at 37 degrees C removed the inhibitory effect, as did treatment of the lungs with indomethacin (0.5 microgram ml-1) suggesting that a labile cyclo-oxygenase product was causing the inhibition. Addition of prostacyclin (0.8-5.0 ng ml-1) to the fluid superfusing tracheal and parenchymal strips produced a dose-related decrease in leukotriene-induced contractions, whereas 6-oxo-PGF1 alpha and PGE2 were inactive. Contractions of tracheal strips induced by LTC4 were significantly enhanced by infusion of PGF2 alpha. Parenchymal strips usually developed tachyphylaxis to repeated doses of LTC4. This tachyphylaxis has less evident in the presence of indomethacin (2 micrograms ml-1). Contractions of parenchymal and tracheal strips to histamine, acetylcholine and the stable thromboxane mimetic U-46619 were unaffected by infusion of prostacyclin (5 ng ml-1). These results indicate that prostacyclin selectively antagonises airway smooth muscle reactivity to LTC4 and LTD4 by a mechanism which remains to be elucidated.     

The vasoconstrictor effect of 8-epi prostaglandin F2alpha in the hypoxic rat heart

1. 8-epi prostaglandin (PG) F2alpha, a vasoconstrictor isoprostane, is synthesized under conditions of oxidative stress. This study was undertaken to investigate the vasoconstrictor effect of 8-epi PGF2alpha in the coronary circulation before and after a period of oxidative stress. 2. The effects of the isoprostane 8-epi PGF2alpha and the thromboxane mimetic U46619 were compared in the isolated rat heart perfused in the Langendorff mode at a constant pressure of 80 mmHg. 3. In normal hearts U46619 caused a dose-related reduction in coronary flow (ED50 4.7+/-2.2 nmol). In contrast, 8-epi PGF2alpha had no effect. 4. After reducing perfusion pressure to 20 mmHg for 30 min and reperfusing at 80 mmHg, the dose-response curve to U46619 was unaffected. In contrast, 8-epi PGF2alpha caused a dose-dependent drop in coronary flow (ED50 52.6+/-12.7 nmol), producing a similar maximal reduction to U46619. 5. Similarly, after perfusion with xanthine and xanthine oxidase for either 15 or 30 min there was little change in the response to U46619 in comparison to control hearts. In contrast, 8-epi PGF2alpha caused a reduction in coronary flow similar to that produced by U46619, the magnitude of the response being related to the length of xanthine/xanthine oxidase perfusion. 6. Responses to both U46619 and 8-epi PGF2alpha after xanthine/xanthine oxidase perfusion were blocked by the selective thromboxane receptor antagonist SQ29548 10(-7) M. 7. These results show that oxidative stress in the isolated perfused rat heart reveals a potent vasoconstrictor effect of the isoprostane 8-epi PGF2alpha by an action on the thromboxane receptor. 8. The data also suggest that, since 8-epi PGF2alpha is a partial agonist at the thromboxane receptor, thromboxane receptor reserve is increased by oxidative stress.     

BradykMn-induced airway microvasciilar leakage is potentiated by captopril and phosphoramidon

Bradykinin can be inactivated by the peptidases angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP), both of which are present in the airways. We evaluated the role of these enzymes in bradykinin-induced airway microvascular leakage and lung resistance in anesthetized and mechanically ventilated guinea pigs. We studied the effects of captopril (inhaled; 350 nmol), a specific ACE inhibitor, and phosphoramidon (inhaled; 7.5 nmol), a specific NEP inhibitor. Airway microvascular leakage was measured with the albumin marker Evans Blue dye (20 mg/kg i.v.), and airflow obstruction was measured as lung resistance (R_L). Bradykinin was given by inhalation (0.1, 0.3 and 1 mM; 45 breaths), and caused a dose-dependent increase in both R_L and airway microvascular leakage. Inhibition of NEP or ACE potentiated the bradykinin-induced microvascular leakage in main bronchi and proximal and distal intrapulmonary airways. However, only NEP inhibition significantly potentiated the extravasation of Evans Blue dye into the tracheal wall and lumen. The combined inhibition of NEP and ACE significantly potentiated plasma leakage at all airway levels, as well as the increase in R_L induced by inhaled bradykinin. Recovery R_L after one lung inflation significantly correlated with the extravasation of Evans Blue dye in the tissue at all airway levels, indicating that airway edema may have contributed to airway narrowing. We conclude that in the guinea pig, both NEP and ACE modulate bradykinin-induced airway microvascular leakage.     

Bradykinin-induced release of thromboxane B2 into bronchoalveolar lavage fluid of guinea pigs: relationship to airflow obstruction

The aim of this study was to evaluate the role of thromboxane A₂ in bradykinin-induced airflow obstruction in guinea pig in vivo. Airway insufflation pressure (P_i) was measured to assess airflow obstruction and the thromboxane B₂ (a stable metabolite of thromboxane A₂) concentration in bronchoalvelolar lavage fluid was determined by radioimmunoassay. The animals were pretreated with propranolol (1 mg/kg i.v.) and suxamethonium (5 mg i.v.) prior to bradykinin administration. Bradykinin instillation into the trachea (300 nmol) induced a P_i increase (47.5 ± 8.3 cm H₂O versus 23.8 ± 1.5 in sham) and significant thromboxane B₂ release into bronchoalveolar lavage fluid (79 ± 19 pg/ml versus 19 ± 6 in sham). A thromboxane synthase inhibitor (OKY-046, 30 mg/kg i.v.; ((E-E)-3-[p(1H-imidazole-1-yl-methyl) phenyl]-2-propenoic acid hydrochloride mono-hydrate)) or a thromboxane A₂ receptor antagonist (ICI192,605, 0.5 mg/kg i.v.; (4-(Z)-6-(2-o-chloro-phenyl-4-o-hydroxyphenyl-1,3-dioxan-cis-5-yl)hexenoic acid)) reduced the P_i increase evoked by bradykinin (38.7 ± 3.8 and 40.6 ± 3.8 cm H₂O, respectively). OKY-046 abolished the thromboxane B₂ release. A platelet-activating factor receptor antagonist, WEB2086 (1 mg/kg i.v.; (3-[4-(chlorophenyl)-9-methyl-6H-thienol [3,2-f][1,2,4]trizolo-[4,3-a][1,4] diazepin-2-yl]1-4-(4-morpholinyl)-1-propanon) did not significantly affect any measured parameter. We conclude that, in guinea pigs, bradykinin-induced airway effects are associated with a local thromboxane A₂ release.     

Effects of Y-27632, a Rho/Rho kinase inhibitor, on leukotriene D(4)- and histamine-induced airflow obstruction and airway microvascular leakage in guinea pigs in vivo

Recent in vitro studies have shown that the Rho/Rho kinase pathway is involved in the mechanism of not only airway smooth muscle contraction but also vascular endothelial permeability caused by certain stimuli. This suggests that Rho/Rho kinase inhibitors may become useful agents against asthma via reduction of increased airway microvascular leakage, one of the main features of this disease. Thus, we wanted to know the in vivo effect of Y-27632, a selective Rho kinase inhibitor, on airway microvascular leakage caused by leukotriene D(4) (LTD(4)) and histamine, potent mediators of allergic airway inflammation, by comparing its effect against airflow obstruction. For comparison, the effects of procaterol, a beta(2)-adrenoceptor agonist, on these responses were also studied. Tracheostomized guinea pigs were given either aerosolized Y-27632 (3 or 15 mmol/l), procaterol (6 micromol/l) or vehicle (0.9% NaCl) for 5 min under spontaneous breathing. After being mechanically ventilated, the animals were given intravenous Evans blue dye 15 min after the end of inhalation. One minute later, either 2 nmol/kg LTD(4), 300 nmol/kg histamine or vehicle was administered intravenously. After measurements of lung resistance (R(L)) for 6 min, the lungs of animals were taken out, and the amount of extravasated Evans blue dye was examined as an index of leakage. Inhaled Y-27632 dose-dependently attenuated increases in R(L) caused by LTD(4) and histamine. The degree of inhibition was almost similar between 15 mmol/l Y-27632 and 6 micromol/l procaterol. By contrast, only 15 mmol/l, but not 3 mmol/l, Y-27632 partially reduced LTD(4)-induced leakage. Histamine-induced Evans blue dye extravasation was not inhibited by 15 mmol/l Y-27632. Procaterol significantly inhibited the dye extravasation caused by either LTD(4) or histamine. These results suggest that Y-27632 is not a useful agent in attenuating airway microvascular leakage which is seen in asthma, although it is potent in inhibiting airflow obstruction.     

Role of eicosanoids in PAF-induced increases of the vascular permeability in rat airways.

1. Platelet activating factor (PAF; 1.0 and 5.0 micrograms kg-1) injected in the tail vein of unanaesthetized rats dose-dependently increased the vascular permeability of the trachea, upper and lower bronchi (up to 400%) as measured by the extravasation of Evans blue dye. The permeability of the parenchyma was not affected by PAF treatment. 2. Pretreatment of the animals with an intravenous injection of the PAF antagonist BN-52021 (10 mg kg-1) abolished almost totally the vascular permeability changes elicited by PAF injection (5.0 micrograms kg-1). 3. Pretreatment of the animals with intravenous injections of inhibitors of thromboxane formation, indomethacin (10 mg kg-1) and compound OKY-046 (10 mg kg-1), and thromboxane antagonist, compound L-655,240 (5 mg kg-1), partially reduced PAF effects in the airways (from 28 to 69%). The thromboxane mimic U-44069 (5.0 micrograms kg-1) did not modify the vascular permeability of rat airways. The effect of a low dose of PAF (0.1 microgram kg-1) on the vascular permeability of the trachea and bronchi (but not of the parenchyma) was potentiated by compound U-44069 (5.0 micrograms kg-1) or noradrenaline (400 ng kg-1) whereas the effect of a high dose of PAF (5.0 micrograms kg-1) was not affected. 4. Neither the peptidoleukotriene antagonist MK-571 (10 mg kg-1) nor the 5-lipoxygenase inhibitor, L-663,536 (10 mg kg-1) given before the injection of PAF (5.0 micrograms kg-1) affected the protein extravasation in rat lung tissues.(ABSTRACT TRUNCATED AT 250 WORDS)     

Role of thromboxane A2 in healing of gastric ulcers in rats

We investigated the role of thromboxane (TX) A2 in gastric ulcer healing in rats. Acetic acid ulcers were produced in male Donryu rats. TXA2 synthesis in the stomachs with ulcers was significantly elevated in ulcerated tissue, but not in intact tissue, compared with that in the gastric mucosa of normal rats. Indomethacin inhibited both TXA2 and prostaglandin E2 (PGE2) synthesis in ulcerated tissue, while NS-398 (selective cyclooxygenase-2 inhibitor) reduced only PGE2 synthesis. OKY-046 (TXA2 synthase inhibitor) dose-relatedly inhibited only TXA2 synthesis. The maximal effect of OKY-046 (80% inhibition) was found at more than 30 mg/kg. When OKY-046 was administered for 14 days, the drug at more than 30 mg/kg significantly accelerated ulcer healing without affecting acid secretion. The maximal reduction of ulcerated area by OKY-046 was about 30%, compared with the area in the control. Histological studies revealed that regeneration of the mucosa was significantly promoted by OKY-046, but neither maturation of the ulcer base nor angiogenesis in the base were affected. OKY-046 and TXB2 had no effect on proliferation of cultured rat gastric epithelial cells, but U-46619 (TXA2 mimetic) dose-relatedly prevented the proliferation without reducing cell viability. These results indicate that the increased TXA2, probably derived from cyclooxygenase-1 in ulcerated tissue, exerts a weak inhibitory effect on ulcer healing in rats. The effect of TXA2 might be due partly to prevention of gastric epithelial cell proliferation at the ulcer margin.     

Influence of SK&F 96148 on thromboxane-mediated responses in the airways of the cat

The effects of SK&F 96148, a thromboxane receptor blocking agent, on bronchoconstrictor responses were investigated in paralyzed, anesthetized, mechanically ventilated cats. I.v. injections of the thromboxane A2 (TXA2) mimics, U-46619 and U-44069, produced dose-related increases in transpulmonary pressure and lung resistance (RL) and decreases in dynamic compliance (Cdyn). After administration of SK&F 96148, 5 mg/kg i.v., bronchoconstrictor responses to U-46619 and U-44069 were reduced markedly, whereas airway responses to prostaglandin (PG) F2 alpha, serotonin, PGD2, or the PGD2 metabolite, 9 alpha, 11 beta-PGF2, were not altered. The duration of action of SK&F 96148 was greater than 2 h, and the TXA2 receptor blockade was overcome when 10-fold larger doses of the TXA2 mimics were administered. Bronchoconstrictor responses to arachidonic acid, platelet-activating factor (PAF), endothelin-1, and E. coli endotoxin were blocked by SK&F 96148. The present data suggest that SK&F 96148 has selective thromboxane receptor blocking activity in the airways of the cat, and that bronchoconstrictor responses to endothelin-1, arachidonic acid, PAF, and E. coli endotoxin are mediated in part by the formation of TXA2.     

In vivo enhancement of platelet activating factor-induced prostacyclin production by OKY-046, a selective inhibitor of thromboxane A2 synthase.

Platelet-activating factor (PAF), a likely mediator of endotoxin action, causes thromboxane A2 (TXA2) release and pulmonary hypertension in pigs. We examined the effect of selective TXA2 synthase inhibition with OKY-046 on cyclooxygenase metabolites during PAF-induced pulmonary hypertension. Six closed-chest pigs received PAF in escalating doses (0.1, 0.3, 1.0, and 3.0 nmol intravenously, i.v.) before and after (E)-3[4-(1-imidazolyl methyl) phenyl]-Z-propenoic acid hydrochloride monohydrate OKY-046, 10-mg/kg i.v. bolus plus 20-mg/kg/h infusion. Plasma samples at peak PAF effect had radioimmunoassay (RIA) for the stable metabolites of TXA2 (TXB2) and prostacyclin (6-keto-PGF1 alpha). Tachyphylaxis was not noted in 5 control pigs given sequential repeats of the PAF dosing series. Pulmonary vascular resistance (PVR) was 240 +/- 30 (SE) dyne s cm-5 at baseline and increased to 3,100 +/- 1,300 after 1.0 nmol PAF (p less than 0.05). When the same amount of PAF was given after OKY-046, PVR increased only to 820 +/- 280 dynes/s/cm-5. TXB2 was 34 +/- 7 pg/0.1 ml at baseline and increased to 70 +/- 4 pg/0.1 ml with PAF 1.0 nmol (p less than 0.001). TXB2 levels were unchanged from 34 +/- 4 pg/0.1 ml when PAF 1.0 nmol was administered after OKY-046 (NS vs. pre-OKY-046). In contrast, 6-keto-PGF1 alpha, 6 +/- 2 pg/0.1 ml at baseline, increased to 24 +/- 4 pg/0.1 ml after PAF 1.0 nmol and increased further to 50 +/- 8 pg/0.1 ml when PAF 1.0 nmol was given after OKY-046 (p less than 0.05 vs. pre-OKY-046).(ABSTRACT TRUNCATED AT 250 WORDS)     

Attenuation of tachykinin-induced airflow obstruction and microvascular leakage in immature airways.

1. To study the effect of maturation on substance P (SP)- and neurokinin A (NKA)-induced airflow obstruction and airway microvascular leakage (MVL), we have measured changes in both lung resistance (RL) and extravasation of Evans blue dye in anaesthetized immature (aged 14 +/- 1 days) and adult guinea-pigs (aged 80 +/- 3 days). 2. RL and its recovery after hyperinflation at 5 min were measured for 6 min after i.v. SP (0.2, 1 and 30 nmol kg-1), NKA (1 and 10 nmol kg-1) or vehicle (0.9% NaCl). After measurement of RL, MVL in trachea, main bronchi and intrapulmonary airways was also examined. 3. The order of potency in inducing airflow obstruction did not change with age (NKA > SP) but immature animals required a larger dose of SP or NKA than adults to cause a significant increase in RL. 4. The order of potency in inducing airway microvascular leakage was SP > NKA in both immature and adult animals. The amount of extravasated dye after SP was significantly less in immature airways, especially in central airways. 5. Phosphoramidon (2.5 mg kg-1), a neutral endopeptidase (NEP) inhibitor, significantly increased RL after 0.2 nmol kg-1 SP only in adult airways. Phosphoramidon enhanced the dye extravasation after 0.2 nmol kg-1 SP in both immature and adult airways with a significantly greater amount of dye in adult animals, suggesting that mechanisms other than changes in NEP activity may be responsible for this age-related difference.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modulation of eicosanoid-induced contraction of mouse and rat blood vessels by gingerols

The effects of the active principles of crude ginger (a traditional Sino-Japanese medicine), the gingerols, on the contractile responses to eicosanoids were compared using isolated mouse and rat blood vessels. Leukotrienes (LT) C4 and D4, a thromboxane (TX) A2 derivative (U-46619), prostaglandins (PG) F2 alpha, PGI2-Na, PGE2, the stable PGI2 derivative TRK-100, and PGD2 induced contraction in longitudinal segments of mouse mesenteric veins in that order of potency. Exogenous arachidonic acid and PGE1 did not cause contraction. The mesenteric veins also contracted in response to noradrenaline (NA) and phenylephrine (PhE), but not to clonidine. The gingerols alone relaxed the muscle transiently and then augmented the response to PGF2 alpha, PGE2, PGI2-Na, and TRK-100, but suppressed the response to PGD2, U-46619, LTC4, LTD4, NA and PhE. (+/-)-[6]-Gingerol also potentiated the PGF2 alpha-induced contraction in longitudinal segments of rat mesenteric vein and vena cava, but inhibited it in circular segments of rat aorta and longitudinal segments of mouse mesenteric arteries. These results showed that (+/-)-[6]- and (+/-)-[8]-gingerols potentiated the contraction induced by prostanoids (except PGD2) and inhibited that produced by PGD2, TXA2, and LT, suggesting the modulation of eicosanoids-induced responses by (+/-)-[6]- or (+/-)-[8]-gingerol.     

Pinane thromboxane A2 analogues are non-selective prostanoid antagonists in rat and human stomach muscle.

1 Pinane thromboxane A2 (PTxA2) and its epi-OH isomer were studied on rat and human stomach longitudinal muscle. 2 PTxA2 (0.5 micrograms/ml) usually caused a slight contraction of rat gastric fundus. Contractions to PGE2, PGF2 alpha, PGI2 and epoxymethano analogues of PGH2 (U-46619 and U-44069) were substantially inhibited, whereas those to PGD2 and acetylcholine were only slightly reduced. 3 In human stomach, PTxA2 0.5 micrograms/ml rarely stimulated the muscle. Contractions to PGE2, PGF2 alpha and U-46619 were antagonized, with little effect on those to acetylcholine. 4 epi-PTxA2 (0.5 micrograms/ml) did not affect rat gastric tone. It was moderately potent against PGI2 on rat gastric fundus, but was less effective than PTxA2 against U-44069.     

Studies in the guinea-pig with ICI 185,282: a thromboxane A2 receptor antagonist

The effects of ICI 185,282 (5(Z)-7-([ 2,4,5-cis]-4-O-hydroxyphenyl-2-trifluoromethyl-1, 3-dioxan-5-yl)heptenoic acid) have been studied on guinea-pig platelets and pulmonary smooth muscle in-vitro and in-vivo. When tested on guinea-pig lung parenchyma in-vitro. ICI 185,282 (1 x 10(-7) M) produced a significant shift in U-46619 response curves (concentration ratio of 13:3); the antagonist (1 x 10(-5) M) did not modify histamine responses. When tested on guinea-pig trachea in-vitro ICI 185,282 (1 x 10(-7) M) caused significant inhibition of U-46619 and PGD2 responses (concentration ratios of 8.3 and 14.1, respectively); the antagonist (1 x 10(-5) M proved less effective against contractions of PGF2 alpha, LTD4 and histamine (concentration ratios of 7.0, 1.5 and 1.6). When added to guinea-pig platelet rich plasma in-vitro, ICI 185,282 (x 10(-6), 1 x 10(-5) M) caused concentration-dependent parallel shifts to the right of U-46619 aggregation curves, yielding concentration ratios of 13.6 and 141.9, respectively. In-vitro, addition of ICI 185,282 (x 10(-5) M) to indomethacin-treated pulmonary smooth muscle did not modify resting tone, neither did it induce aggregation or swelling in platelet-rich plasma preparations. When administered orally to guinea-pigs ICI 185,282 (0.1, 0.5 mg kg-1) caused a significant inhibition of U-46619-induced platelet aggregation ex-vivo which persisted greater than or equal to 8 h. In-vivo, a single oral dose of ICI 185,282 (1 mg kg-1) inhibited bronchospasm induced by U-46619, PGD2, PGF2 alpha, arachidonic acid, LTD4 and PAF; responses to histamine were unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)     

Differential effects of phosphoramidon on neurokinin A- and substance P-induced airflow obstruction and airway microvascular leakage in guinea-pig.

1. The effects of the inhaled neuropeptides, neurokinin A (NKA) and substance P (SP) on lung resistance (RL) and airway microvascular permeability were studied in anaesthetized guinea-pigs. 2. Single doses of inhaled NKA (3 x 10(-5), 1 x 10(-4), 3 x 10(-4) M; 45 breaths) and SP (1 x 10(-4), 3 x 10(-4), 1 x 10(-3); 45 breaths) caused a dose-dependent increase in both RL and airway microvascular leakage, assessed as extravasation of the albumin marker, Evans blue dye. 3. NKA at 1 x 10(-4) and 3 x 10(-4) M resulted in a significantly higher increase in RL than SP at the same doses. 4. Inhaled SP (3 x 10(-4) M; 45 breaths) caused significantly higher Evans blue dye extravasation in main bronchi and proximal intrapulmonary airways compared to the same dose of NKA. 5. Pretreatment with the specific inhibitor of neural endopeptidase (NEP24.11), phosphoramidon, caused an approximately 100 fold leftward shift of the RL responses to inhaled NKA and SP. 6. Phosphoramidon significantly potentiated both NKA- and SP-induced airway microvascular leakage at proximal intrapulmonary airways, but not at any other airway level. 7. Inhibition of NEP24.11 potentiate both the SP- or NKA-induced airflow obstruction to a larger extent than the induced airway microvascular leakage, suggesting that NEP24.11 is more important in the modulation of the airflow obstruction observed after these mediators.     

Pharmacological actions of S-145, a novel thromboxane A2 antagonist, in various smooth muscles

Antagonistic actions of S-145 ((+-)-5(Z)-7-[3-endo[(phenylsulfonyl)amino]bicyclo[2.2.1] hept-2-exo-yl]heptenoic acid) against U-46619, a thromboxane A2 mimic, were studied using isolated thoracic aorta of the rat and the trachea, lung parenchyma and ileum of the guinea pig. S-145 as well as SQ-29548 and ONO-3708 inhibited the contraction of aorta induced by U-46619 in a concentration-dependent manner. The IC50 value of each compound was 1.4, 14.5 and 52.6 nM. S-145 also inhibited contractions of the aorta induced by high concentrations of PGE1, PGE2 and PGF2 alpha, but failed to affect the responses to K+, Ca2+, NE, 5-HT, and angiotensin II. Contractions of trachea and lung parenchyma of the guinea pig induced by U-46619 were concentration-dependently inhibited by S-145, but those induced by histamine and leukotriene D4 were not affected. Ileac contractions by PGE2 and PGF2 alpha were not inhibited by S-145. The (+)-isomer of S-145 was more potent and the (-)-isomer was less potent than S-145 for antagonistic action against U-46619. These results suggest that S-145 is a potent and specific antagonist to the thromboxane A2 receptor; and in the aorta, the thromboxane A2 receptor may respond to high concentrations of PGs.