The role of prostaglandin E2 in human vascular inflammation

Prostaglandins (PG) are the product of a cascade of enzymes such as cyclooxygenases and PG synthases. Among PG, PGE2 is produced by 3 isoforms of PGE synthase (PGES) and through activation of its cognate receptors (EP1-4), this PG is involved in the pathophysiology of vascular diseases. Some anti-inflammatory drugs (e.g. glucocorticoids, nonsteroidal anti-inflammatory drugs) interfere with its metabolism or effects. Vascular cells can initiate many of the responses associated with inflammation. In human vascular tissue, PGE2 is involved in many physiological processes, such as increasing vascular permeability, cell proliferation, cell migration and control of vascular smooth muscle tone. PGE2 has been shown to contribute to the pathogenesis of atherosclerosis, abdominal aortic aneurysm but also in physiologic/adaptive processes such as angiogenesis. Understanding the roles of PGE2 and its cognate receptors in vascular diseases could help to identify diagnostic and prognostic biomarkers. In addition, from these recent studies new promising therapeutic approaches like mPGES-1 inhibition and/or EP4-antagonism should be investigated.

PGE(2) receptor (EP(4)) agonists: potent dilators of human bronchi and future asthma therapy?

BACKGROUND

Asthma and chronic obstructive pulmonary disease are characterized by inappropriate constriction of the airway smooth muscle. In this context, the physiological response of the human airways to selective relaxant agonists like PGE(2) is highly relevant. The aim of this study was thus to characterize the PGE(2) receptor subtypes (EP(2) or EP(4)) involved in the relaxation of human bronchial preparations.

METHODS

Human bronchial preparations cut as rings were mounted in organ baths for isometric recording of tension and a pharmacological study was performed using selective EP(2) or EP(4) ligands.

RESULTS

In the presence of a thromboxane TP receptor antagonist and indomethacin, PGE(2) induced the relaxation of human bronchi (E(max) = 86 ± 04% of papaverine response; pEC(50) value = 7.06 ± 0.13; n = 6). This bronchodilation was significantly blocked by a selective EP(4) receptor antagonist (GW627368X, 1 and 10 μmol/L) with a pK(B) value of 6.38 ± 0.19 (n = 5). In addition, the selective EP(4) receptor agonists (ONO-AE1-329; L-902688), but not the selective EP(2) receptor agonist (ONO-AE1-259), induced potent relaxation of bronchial preparations pre-contracted with histamine or anti-IgE.

CONCLUSION

PGE(2) and EP(4) agonists induced potent relaxations of human bronchial preparations via EP(4) receptor. These observations suggest that EP(4) receptor agonists could constitute therapeutic agents to treat the increased airway resistance in asthma.

Differential reactivity of human mammary artery and saphenous vein to prostaglandin E(2) : implication for cardiovascular grafts

BACKGROUND AND PURPOSE

Human internal mammary arteries (IMA) and saphenous veins (SV) are frequently used for coronary artery bypass graft surgery. Intra- and postoperatively, the bypass grafts are exposed to inflammatory conditions, under which there is a striking increase in the synthesis of prostaglandin E(2) (PGE(2) ). In this context, the physiological response of these vascular grafts to PGE(2) is highly relevant. The aim of this study was thus to characterize the PGE(2) receptor subtypes (EP(1) , EP(2) , EP(3) or EP(4) ) involved in modulation of the vascular tone in these two vessels.

EXPERIMENTAL APPROACH

Rings of IMA and SV were prepared from 48 patients. The rings were mounted in organ baths for isometric recording of tension, and a pharmacological study was performed, together with associated reverse transcriptase PCR and immunohistochemistry experiments.

KEY RESULTS

PGE(2) induced contractions of IMA (E(max) = 1.43 ± 0.20 g; pEC(50) = 7.50 ± 0.10); contractions were also observed with the EP(3) receptor agonists, sulprostone, 17-phenyl-PGE(2) , misoprostol or ONO-AE-248. In contrast, PGE(2) induced relaxation of the precontracted SV (E(max) =-0.22 ± 0.02 g; pEC(50) = 7.14 ± 0.09), as did the EP(4) receptor agonist, ONO-AE1-329. These results were confirmed by the use of selective EP receptor antagonists (GW627368X, L-826266, ONO-8713, SC-51322) and by molecular biology and immunostaining.

CONCLUSIONS AND IMPLICATIONS

PGE(2) induced potent and opposite effects on the human vascular segments used for grafting, namely vasoconstriction of the IMA and vasodilatation of the SV via EP(3) and EP(4) receptors respectively. These observations suggest that EP(3) and EP(4) receptors could constitute therapeutic targets to increase vascular graft patency.

Vasorelaxation induced by prostaglandin E2 in human pulmonary vein: role of the EP4 receptor subtype

BACKGROUND AND PURPOSE

PGE2 has been shown to induce relaxations in precontracted human pulmonary venous preparations, while in pulmonary arteries this response was not observed. We investigated and characterized the prostanoid receptors which are activated by PGE2 in the human pulmonary veins.

EXPERIMENTAL APPROACH

Human pulmonary arteries and veins were cut as rings and set up in organ baths in presence of a TP antagonist. A pharmacological study was performed using selective EP1-4 ligands. The cellular localization of the EP4 receptors by immunohistochemistry and their corresponding transcripts were also investigated in these vessels.

KEY RESULTS

PGE2 and the EP4 agonists (L-902688, ONO-AE1-329) induced potent vasodilatation of the human pulmonary vein, pEC50 values: <7.22+/-0.20, 8.06+/-0.12 and 7.80+/-0.09, respectively. These relaxations were inhibited by the EP(4) antagonist GW627368X and not modified in presence of the DP antagonist L-877499. Higher concentrations (>or=1 microM) of the EP2 agonist ONO-AE1-259 induced relaxations of the veins. The EP4 agonists had no effect on the precontracted arteries. Finally, the EP(1) antagonists ONO-8713 and SC-51322 potentiated the relaxation of the veins induced by PGE2. EP4 and EP1 receptors were detected by immunohistochemistry in the veins but not in the arteries. EP4 mRNA accumulation was also greater in the veins when compared with the arterial preparations.

CONCLUSIONS AND IMPLICATIONS

Of the 4 EP receptor subtypes, smooth muscle cells in the human pulmonary vein express the EP4 and EP1 receptor subtypes. The relaxations induced by PGE2 in this vessel result from the activation of the EP4 receptor.

A new mRNA splice variant coding for the human EP3-I receptor isoform

The cellular localization of prostaglandin E2 receptors (EP) and their corresponding transcripts were investigated in human gastric and vascular tissues. A strong staining of the EP3 receptor on the gastric glands, mucous cells, media of the mammary and pulmonary arteries was observed by immunohistochemistry. We identified a new mRNA splice variant of the EP3 gene in human gastric fundic mucosa, mammary artery and pulmonary vessels. This EP3-Ic transcript contains exons 1, 2, 3, 5 and 6 of the EP3 gene and should be translated in the EP3-I isoform. In addition, the EP3-Ib, EP3-II, EP3-III, EP3-IV and EP3-e mRNAs were detected in these tissues.

Modulation of vascular tone and reactivity by nitric oxide in porcine pulmonary arteries and veins

Isolated porcine pulmonary vessels were studied in order to evaluate the role of nitric oxide in arteries and veins. Leukotriene C4 and noradrenaline contracted porcine pulmonary arteries but induced only negligible contractions of porcine pulmonary veins. After treatment with the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine (L-NOARG), significant contractions to leukotriene C4 and noradrenaline were uncovered in pulmonary veins. In arterial preparations, L-NOARG caused a less marked potentiation of noradrenaline-induced contractions and did not alter leukotriene C4-induced contractions. Endothelium-dependent relaxations to acetylcholine were greater in veins compared with arteries whereas the endothelium-independent relaxations to the nitric oxide donor sodium nitroprusside (SNP) and the cyclic nucleotide analogue 8-bromo-cGMP were similar in the two preparations. Taken together these data suggest that the apparent insensitivity of porcine pulmonary veins to leukotriene C4 and noradrenaline was because of release of nitric oxide. The effect of nitric oxide synthase inhibition was less pronounced in porcine pulmonary arteries, suggesting a preferential functional role of nitric oxide in porcine pulmonary veins, originating in a greater production of nitric oxide by veins as opposed to arteries.

The muscarinic receptor subtypes in human blood vessels

Acetylcholine (ACh) may induce the relaxation and the contraction of human blood vessels. These effects involve the activation of muscarinic receptors located on endothelial or smooth muscle cells. In humans and animals, five subtypes of muscarinic receptors (M1-M5) have been identified. In the particular case of human blood vessels, the M3 subtype seems to be prevalent on endothelial cells as well as on smooth muscle cells. However, the M1 subtype may be specific for the pulmonary vascular endothelium. In contrast, the M4 subtype has not been described in human vessels. These conclusions are, however, based on a limited number of studies and further work is needed in this area of research. Although muscarinic receptors may not be the only receptors involved in hypertension, the development of specific agonists for M1 receptors may be useful to counteract any elevation of blood pressure in the pulmonary circulation.

Prostacyclin modulation of contractions of the human pulmonary artery by cysteinyl-leukotrienes

The contractile response to cysteinyl-leukotrienes was studied in isolated human pulmonary arterial rings. Concentration-response curves for leukotriene C(4) were significantly potentiated by the cyclooxygenase inhibitor indomethacin (1.7 microM) and after endothelial denudation. Measurements of 6-keto prostaglandin F(1alpha) showed that cysteinyl-leukotrienes stimulated the release of prostacyclin. A single concentration (1 microM) of either leukotriene C(4) or leukotriene D(4) resulted in both contraction and relaxation. Indomethacin abolished the relaxant phase and enhanced the amplitude of the contraction, supporting that cysteinyl-leukotriene-induced contractions of the human pulmonary artery may be functionally antagonised by the release of prostacyclin. The contractions induced by leukotriene C(4) were resistant to the two cysteinyl-leukotriene receptor antagonists MK 571 ((3-(-2(7-chloro-2-quinolinyl)ethenyl)phenyl)((3-(dimethylamino-3-oxo propyl)thio)methyl)thio propanoic acid, 1 microM) and BAY u9773 (6(R)-(4'-carboxyphenylthio)-5(S)-hydroxy-7(E),9(E), 11(Z)14(Z)-eicosatetrenoic acid, 3 microM), both in the absence and presence of indomethacin. These findings suggest a functional cysteinyl-leukotriene receptor in the human pulmonary artery with antagonist properties not previously described in human tissue.

Antagonist resistant contractions of the porcine pulmonary artery by cysteinyl-leukotrienes

The contractile response to cysteinyl-leukotrienes was studied in isolated porcine pulmonary arterial rings. In endothelium-denuded preparations, the concentration-response curves for leukotriene C(4) and leukotriene D(4) were identical, whereas leukotriene E(4) did not contract these tissues. The response to leukotriene C(4) was not blocked by either CysLT(1)/CysLT(2) receptor antagonism or by pre-treatment with leukotriene E(4). In preparations with an intact endothelium, leukotriene C(4) was somewhat more potent than leukotriene D(4) and the concentration-response curves were only slightly depressed in the presence of either ICI 204,219 (4-(5-cyclopentyloxycarbonylamino-1-methylindol-3-ylmethy l)-3-methoxy -N-o-tolylsulfonylbenzamide, 1 microM) or BAY u9773 (6(R)-(4'-carboxyphenylthio)-5(S)-hydroxy-7(E),9(E), 11(Z)14(Z)-eicosatetrenoic acid, 3 microM). Indomethacin (1.7 microM) significantly reduced the response to leukotriene C(4) whereas the response to leukotriene D(4) was unchanged. These findings suggest that a CysLT receptor subtype resistant to current antagonists mediated the major part of the contractions to leukotriene C(4) and leukotriene D(4) in intact preparations, and was the sole receptor associated with contractions of endothelium-denuded preparations.

Functional studies of leukotriene receptors in vascular tissues

The paradoxical effects of cysteinyl-leukotrienes, namely contraction and relaxation, are now well documented in a number of vascular preparations from various species. The vascular smooth muscle contractions are associated with activation of a single receptor subtype and in some vascular smooth muscles with activation of two receptor subtypes. However, the receptors implicated in the contraction of vessels such as pig pulmonary arteries and veins, dog inferior vena cava, and dog splenic and mesenteric veins remain to be established. There are sufficient data concerning some vascular tissues to suggest that relaxations induced by cysteinyl-leukotrienes are via the stimulation of specific receptors present on the endothelium. The endothelium in human pulmonary arteries has one receptor (CysLT2) and activation induced the release of NO. However, in isolated human pulmonary veins two receptors are present, CysLT1 and CysLT2 (Figure 1). Activation of the former induced the release of a contractile factor whereas activation of the CysLT2 receptor released NO. In guinea pig pulmonary artery and guinea pig thoracic aorta, one receptor has been demonstrated since the relaxations are blocked by ICI-198615. These data suggest the presence of a CysLT1 receptor. Activation of this receptor leads to the release of a relaxant factor, namely, nitric oxide. In contrast, in human pulmonary arteries and veins activation of a receptor that is resistant to ICI-198615 is associated with NO release. These results suggest that there may be species differences even when analogous vascular preparations are examined. While the cysteinyl-leukotrienes are known to relax vascular smooth muscle in a variety of preparations from different species, there are presently two pathways known to be involved in this response. One involves the metabolites of arachidonic acid via the cyclooxygenase enzymatic pathway and the other implicates products of the L-arginine enzymatic pathway. Although both pathways may be present and active in the endothelium of the vascular preparations only one of these enzymatic pathways may be dominant and responsible for the relaxations observed. Ortiz and coworkers have demonstrated that in pulmonary veins the dominant pathway for cysteinyl-leukotriene relaxations is the NO pathway. There are some reports from animal studies that support a dominant role for NO in pulmonary veins. In contrast, Allen and co-workers demonstrated that the LTC4-induced relaxations in isolated human saphenous veins were not modified by treatment of tissues with an NO inhibitor but were significantly enhanced after treatment with indomethacin. These authors suggested that a contracting factor derived from the arachidonic acid pathway was released in preparations challenged with LTC4. In addition, these investigators demonstrated that the NO inhibitor had no effect on the LTC4 relaxations. Together, these results suggest that cysteinyl-leukotriene effects in human pulmonary veins are dominated by the NO pathway whereas in human systemic veins these mediator effects are modified by metabolites of the cyclooxygenase pathway. Unfortunately, most studies involving the actions of cysteinyl-leukotrienes on vessels have been performed in the presence of indomethacin, making interpretation of the relative contribution of the cyclooxygenase and NO pathways difficult. In any event, the cysteinyl-leukotrienes may have a prominent role in the activation of these pathways and the receptors involved have not been clearly established.

Cysteinyl-leukotriene receptors in pulmonary vessels

Two categories of cysteinyl-leukotrienes have been proposed, namely, CysLT1 and CysLT2. These receptors are found not only on the vascular smooth muscle but also on the endothelium. Activation of the receptor(s) on vascular smooth muscle provokes contraction whereas activation of the receptors on the endothelium produces contraction and/or relaxation. These endothelium dependent effects are due to the release of both contractile and relaxant factors derived from the endothelium. While factors derived from either the cyclooxygenase or nitric oxide pathways are involved, in some vascular preparations other mediators such as endothelin may be involved. However, in isolated human pulmonary vascular preparations, this appears not to be the case and presently the nature and origin of the contractile factor remains to be established.

Prostanoid receptors involved in the relaxation of human bronchial preparations

1. Iloprost and cicaprost (IP-receptor agonists) induced relaxations in the histamine- (50 microM) contracted human bronchial preparations (pD2 values, 6.63+/-0.12 and 6.86+/-0.08; Emax values, 90+/-04 and 65+/-08% of the papaverine response for iloprost (n=6) and cicaprost (n=3), respectively). 2. Prostaglandin E2 (PGE2) and misoprostol (EP-receptor agonist) relaxed the histamine-contracted human bronchial preparations (pD2 values, 7.13+/-0.07 and 6.33+/-0.28; Emax values, 67+/-04 and 57+/-08% of the papaverine response for PGE2 (n=14) and misoprostol (n=4), respectively). In addition, both relaxations were inhibited by AH6809 (DP/EP1/EP2-receptor antagonist; 3 microM; n=5-6). 3. The PGE2-induced relaxations of human bronchial preparations were not modified by treatment with AH23848B (TP/EP4-receptor antagonist; 30 microM; n=4). 4. The contracted human bronchial preparations were significantly relaxed by prostaglandin D2 (PGD2) or by BW245C a DP-receptor agonist. However, these responses did not exceed 40% of the relaxation induced by papaverine. In addition, the relaxations induced by PGD2 were significantly inhibited by treatment with a DP-receptor antagonist BWA868C (0.1 microM; n=3). 5. These data suggest that the relaxation of human isolated bronchial preparations induced by prostanoids involved IP-, EP2- and to a lesser extent DP-receptors but not EP4-receptor.

Cholinergic control of human and animal pulmonary vascular tone

The regulation of pulmonary vascular tone by acetylcholine (ACh) involves the activation of different subtypes of muscarinic receptors as well as the cholinesterase activities which are responsible for ACh degradation. Most of the studies on the cholinergic control of the pulmonary vascular tone have been performed in vessels derived from animals. The ability of ACh to induce pulmonary vasoconstriction is species dependent. In vessels derived from sheep lung, ACh induced contractions in veins but not in arteries whereas in human pulmonary vessels the reverse was observed. The subtype(s) of the muscarinic receptors involved in the pulmonary vasoconstrictions is also dependent on the species which are studied. M1 receptors are implicated in the rabbit pulmonary vasoconstrictions, M3 in humans, whereas M1 and M2 receptors are involved in the dog. The cholinesterases are implicated in the vasoconstriction produced by ACh in human and rabbit pulmonary arteries. However, in these studies while acetylcholinesterase (EC 3.1.1.7) and butyrylcholinesterase (EC 3.1.1.8) activities were detected in human vessels only acetylcholinesterase activity was found in rabbit vessels. The endothelium-dependent relaxation induced by ACh has been reported in isolated pulmonary vessels from different animals including man. However, the muscarinic receptors involved in the ACh-induced vasodilatation of rat and rabbit pulmonary artery are of the M3 subtype while those characterized in the human pulmonary artery are of the M3 and M1 subtypes. Together these results concerning the cholinergic control of the pulmonary vascular tone indicate that extrapolation of the data obtained in animal models to human vessels requires some caution. In addition, there is considerable evidence to demonstrate that ageing may modify cholinergic responses. However, little information is available concerning the pulmonary vascular bed during ageing.

Leukotriene D4 contractions in human airways are blocked by SK&F 96365, an inhibitor of receptor-mediated calcium entry

In human bronchial muscle preparations, nifedipine (3 microM) significantly inhibited the histamine, ACh and KCl contractions. However, the dihydropyridine did not modify the contractile responses induced by either leukotriene D4 (LTD4) or anti-human IgE (a-IgE). In human airways, SK&F 96365 (30 microM and 100 microM) markedly reduced the KCl and, at the higher concentration, LTD4 maximal contractions. In addition, when preparations were treated with nifedipine (3 microM), SK&F 96365 (100 microM) significantly blocked responses to both LTD4 and a-IgE. The calcium chelating agent ethylene glycol-bis (beta-amino-ethyl ether) N,N,N',N'-tetraacetic acid (4 mM) also inhibited the a-IgE-induced contractions. These data demonstrate that the nifedipine-resistant component of the LTD4 and a-IgE contractions was inhibited by SK&F 96365 and suggest that the cysteinyl-leukotriene receptor in human airways may be intimately linked with a receptor-operated calcium-entry mechanism.

Cholinesterase activity in human pulmonary arteries and veins

1. Human isolated pulmonary vessels were treated with cholinesterase (ChE) inhibitors to determine the role of these enzymes in regulating vascular muscle tone. In addition, kinetic parameters were determined for acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) in human pulmonary vessel homogenates. 2. Carbachol (CCh) and acetylcholine (ACh) were equipotent contractile agonists in human pulmonary arteries (pD2 values, 5.28 +/- 0.05 and 5.65 +/- 0.16; Emax, 0.91 +/- 0.26 and 0.98 +/- 0.30 g wt. for CCh and ACh, respectively; n = 7). In venous preparations, ACh was ineffective and CCh induced small contractions (Emax, 0.08 +/- 0.04 g wt; n = 13). 3. In human pulmonary arteries following pretreatment with tetraisopropylpyrophosphoramide (iso-OMPA, 100 microM), an increased sensitivity to the contractile agonist ACh was observed (pD2 values, 5.80 +/- 0.13 and 6.37 +/- 0.19 for control and treated preparations, respectively; n = 5). This pretreatment had no effect on the CCh concentration response curve. In contrast, human pulmonary veins pretreated with iso-OMPA failed to elicit a contractile response to ACh. 4. Neither Iso-OMPA nor neostigmine elicited concentration-dependent contractions in human isolated pulmonary arteries or veins. These results suggest the absence of sufficient spontaneous release of ACh to modulate human pulmonary vessel basal tone. 5. CCh was less potent than ACh in relaxing precontracted human isolated pulmonary arteries (pD2 value, CCh: 6.55 +/- 0.15 and ACh: 7.16 +/- 0.13, n = 4) and veins (pD2 value, CCh: 4.95 +/- 0.13; n = 5 and ACh: 5.56 +/- 0.17; n = 6). Pretreatment of vessels with either iso-OMPA or neostigmine did not modify ACh relaxant responses in either type of preparation. 6. In human pulmonary veins, the ChE activity was two fold greater than in arteries (n = 6). Vmax for AChE was 1.73 +/- 0.24 and 3.36 +/- 0.26 miu mg-1 protein in arteries and veins, respectively, whereas Vss for BChE was 1.83 +/- 0.22 and 4.71 +/- 0.17 miu mg-1 protein, in these respectively. 7. In human pulmonary arteries, BChE activity may play a role in the smooth muscle contraction but not on the smooth muscle endothelium-dependent relaxation induced by ACh. A role for ChE activity in the control of venous tone is presently difficult to observe, even though this tissue contains a greater amount of enzyme than the artery.

Cholinesterase activity in pig airways and epithelial cells

Acetylcholinesterase (AChE, EC 3.1.1.7) and butyrylcholinesterase (BChE, EC 3.1.1.8) activities were detected in bronchial and bronchial epithelial cell homogenates of the pig. In the bronchial homogenates, the maximal upstroke velocity (Vmax) of AChE and the maximal velocity after second substrate fixation (Vss) of BChE were 5.70 +/- 0.46 and 7.87 +/- 0.81 mU/mg protein, respectively. In the epithelial cell homogenates, a smaller amount of cholinesterase (ChE) was found: Vmax was 0.62 +/- 0.29 and Vss was 1.56 +/- 0.33 mU/mg protein for AChE and BChE, respectively. AChE activity was increased by 21 +/- 5% in the bronchial homogenates and by 54 +/- 14% in the epithelial cell homogenates, when intact bronchial segments were incubated with a cyclooxygenase inhibitor, indomethacin (INDO). These results suggest that prostanoids may be involved in the regulation of AChE activity in pig airways.

Role of nitric oxide on cholinergic component of bronchial tone in pig

In vitro studies demonstrated that stimulation of intrinsic nerves of airway smooth muscle results in a predominantly contractile response, followed by a relaxant response which involves cholinergic, adrenergic and non-adrenergic non-cholinergic (NANC) nerve activation. Thus, in this paper it is determined whether endogenous nitric oxide (NO) modulates cholinergic neurotransmission in isolated pig airway smooth muscle. Bronchial rings were suspended in organ baths for isometric measurement of tension and the contractions were induced using electrical field stimulation (EFS) techniques. Then, the effects of L-NG-nitroarginine (L-NOARG, 10 microM), an inhibitor of NO synthase, and L-arginine (L-ARG, 1 mM), a precursor of NO synthesis, were evaluated. The cholinergic contractions induced by electrical field stimulation (EFS: 60 V, 2 ms, 60 Hz) of pig lobar bronchial preparations increased (29%) in the presence of L-NOARG (10 microM). This effect may be released by nerves in pig large airways during EFS.

M1 and M3 muscarinic receptors in human pulmonary arteries

1. Acetylcholine (ACh) and the M1 agonists (McN-A-343 or PD142505) relaxed human isolated pulmonary arteries which were pre-contracted with noradrenaline (10 microM). In preparations where the endothelium had been removed ACh induced a contractile response whereas the M1 agonists (McN-A-343 or PD142505) had no effect. 2. ACh- and McN-A-343-induced relaxations were abolished after treatment of endothelium-intact preparations with the drug combination NG-nitro-L-arginine (L-NOARG: 0.1 mM) and indomethacin (1.7 microM). 3. The affinity (pKB value) for pirenzepine was higher in human pulmonary arteries when tissues were relaxed with McN-A-343 as compared with ACh (pKB values, 7.71 +/- 0.30 (n = 4) and 6.68 +/- 0.15 (n = 8), respectively). In addition, the affinity for pFHHSiD against McN-A-343- and ACh-induced relaxations was 6.86 +/- 0.13 (n = 3) and 7.35 +/- 0.11 (n = 9) respectively. 4. The low affinities for methoctramine in human isolated pulmonary arteries with the endothelium either intact or removed, suggested the lack of involvement of M2 and M4 receptors in the Ach responses. 5. Phenoxybenzamine (3 microM: 30 min) abolished both ACh contraction and relaxation in human pulmonary artery. The ACh contraction was present when the phenoxybenzamine treatment was preceded by incubation with pFHHSiD (2 microM) but not with pirenzepine (1 microM). In addition, the ACh relaxation was present when preparations were treated with either pFHHSiD (2 microM) or pirenzepine (1 microM), before exposure to phenoxybenzamine. 6. These results in human isolated pulmonary arteries support the notion that only M3 receptors, on smooth muscle, mediate the ACh-induced contraction whereas M3 and M1 receptors are involved in the endothelium-dependent ACh-induced relaxation.

Leukotriene synthesis inhibition and anti-ige challenge of human lung parenchyma

The leukotriene (LT) synthesis inhibitors BAY x1005 and MK-886 were evaluated in human lung parenchyma challenged with an anti-IgE. The anti-IgE-induced LTE4 release was time- and dose-dependent. Treatment of the parenchyma with indomethacin (3 microM) prior to anti-IgE challenge inhibited the 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha) release and enhanced (36%) the quantities of LTE4 detected during IgE-stimulations. BAY x1005 and MK-886 were assessed in the presence of indomethacin (3 microM) and the IC50 values for both inhibitors were similar (0.13 microM). BAY x1005 (1 microM) produced the same percent of inhibition of anti-IgE-induced LTE4 release in the presence or absence of indomethacin. BAY x1005 (1 microM) did not alter the 6-keto PGF1 alpha release during anti-IgE challenge. The results indicate that BAY x1005 and MK-886 are potent inhibitors of LT synthesis when human lung parenchyma were stimulated by an anti-IgE.

Endothelin-1 modulates cyclic GMP production and relaxation in human pulmonary vessels

The aim of this study was to examine the effects of endothelin-1 (ET-1) on sodium nitroprusside (SNP) induced relaxation and cyclic 3',5'-guanosine monophosphate (cGMP) accumulation in human pulmonary vessels. The basal levels of cGMP were similar in arteries (2.48 +/- 0.24 pmol/mg protein; n = 7) and veins (3.25 +/- 0.24 pmol/mg protein; n = 7). In tissues (n = 7) treated with N omega-nitro-L-arginine and indomethacin, cGMP values were significantly reduced (arteries, 1.30 +/- 0.24 pmol/mg protein and veins, 1.95 +/- 0.28 pmol/mg protein). In treated tissues, SNP (10 microM) increased the cGMP level by 10-fold in arteries and veins. ET-1 (0.02 and 0.2 microM) reduced significantly the cGMP increase in SNP-stimulated vessels. This inhibition was greater in veins (76%) when compared with arteries (34%). Norepinephrine (10 microM) did not affect the cGMP levels. The sensitivity and the maximal relaxation induced by SNP in veins contracted with ET-1 (0.2 microM) was significantly diminished (in comparison with norepinephrine; 10 microM). In arteries, SNP relaxations were not altered by ET-1 contraction. Inasmuch as 8-bromo-cyclic 3',5' guanosine monophosphate curves were not altered by ET-1 treatment in either arteries or veins, the relaxant mechanisms that are downstream of guanylate cyclase activation apparently are not affected. These results suggest that ET-1 may play a role in the control of muscle tone in the human pulmonary vascular bed by modifying cGMP levels associated with vasorelaxant agonist stimulation.

Effects of beta 2-adrenoceptor agonists on anti-IgE-induced contraction and smooth muscle reactivity in human airways

1. The beta 2-adrenoceptor agonists, salbutamol, salmeterol and RP 58802 relaxed basal tone of human isolated bronchial smooth muscle. Salmeterol- and RP 58802-induced relaxations persisted for more than 4 h when the medium was constantly renewed after treatment. 2. Salbutamol, salmeterol and RP 58802 reversed histamine-induced contractions in human airways (pD2 values: 6.15 +/- 0.21, 6.00 +/- 0.19 and 6.56 +/- 0.12, respectively). 3. Anti-IgE-induced contractions were significantly inhibited immediately after pretreatment of preparations with beta 2-adrenoceptor agonists (10 microM). However, when tissues were treated with beta 2-agonists and then washed for a period of 4 h, salmeterol was the only agonist which significantly inhibited the anti-IgE response. 4. Histamine response curves were shifted to the right immediately after pretreatment of tissues with the beta 2-adrenoceptor agonists (10 microM; 20 min), but maximal contractions were not affected. After a 4 h washing period, the histamine curves were not significantly different from controls. Concentration-effect curves to acetylcholine (ACh) or leukotriene C4 (LTC4) were not significantly modified after beta 2-agonist pretreatment. 5. These results suggest that beta 2-adrenoceptor agonists may prevent anti-IgE-induced contraction by inhibition of mediator release rather than alterations of those mechanisms involved in airway smooth muscle contraction.

(R)-2-[4-(quinolin-2-yl-methoxy)phenyl]-2-cyclopentyl] acetic acid (BAY x1005), a potent leukotriene synthesis inhibitor: effects on anti-IgE challenge in human airways

Anti-IgE at a fixed dilution (1:1000) contracted human airways that had been pretreated with atropine (1 microM), indomethacin (3 microM) and chlorpheniramine (1 microM). This response was blocked by the potent leukotriene synthesis inhibitor BAY x 1005 ((R)-2-[4-(Quinolin-2-yl-methoxy)phenyl)-2-cyclopentyl acetic acid]. The leukotriene synthesis inhibitor MK-886 also blocked the contraction, but BAY x1005 was approximately 10-fold more potent than MK-886 (the IC50 values were 0.27 microM and 3.4 microM for BAY x1005 and MK-886, respectively). BAY x1005 (1 microM) did not alter LTD4 cumulative concentration-effect curves on human airways. Bronchial muscles derived from different levels of the respiratory tract released small quantities of LTE4 (proximal, 7.99 +/- 1.25 ng/g tissue wet wt.; distal, 13.12 +/- 4.46 ng/g tissue wet wt.). These basal levels were significantly increased when the preparations were challenged with a fixed dilution (1:1000) of anti-IgE (proximal, 21.84 +/- 5.33 ng/g tissue wet wt.; distal 72.13 +/- 30.70 ng/g tissue wet wt.). Indomethacin (3 microM) did not alter either the basal amounts or the levels of LTE4 measured during anti-IgE stimulation. However, BAY x1005 or MK-886 in the presence of indomethacin prevented the increase in LTE4 levels that were observed during anti-IgE challenge. In these protocols the IC50 values obtained were 0.18 microM and 1.42 microM for BAY x1005 and MK-886, respectively. These data demonstrate that BAY x1005 is a potent leukotriene synthesis inhibitor in human airways.

Cholinesterase inhibition by vecuronium and pancuronium in human airways

Vecuronium (100 microM) but not pancuronium (100 microM) increased the sensitivity of human isolated bronchial preparations (HBP) to exogenous acetylcholine (ACh). The pD2 values obtained from concentration-dependent contractions were: control, 4.59 +/- 0.29 vecuronium, 5.86 +/- 0.31. Vecuronium or pancuronium (100 microM) significantly decreased (50%) the neostigmine contractions in HBP. In addition, vecuronium was more potent than pancuronium in preventing exogenous ACh degradation. These results suggest that vecuronium and pancuronium may have physiological effects in human airways by inhibiting both the tissue cholinesterases and muscarinic (M3) receptors.

Degradation of acetylcholine in human airways: role of butyrylcholinesterase

1. Neostigmine and BW284C51 induced concentration-dependent contractions in human isolated bronchial preparations whereas tetraisopropylpyrophosphoramide (iso-OMPA) was inactive on airway resting tone. 2. Neostigmine (0.1 microM) or iso-OMPA (100 microM) increased acetylcholine sensitivity in human isolated bronchial preparations but did not alter methacholine or carbachol concentration-effect curves. 3. In the presence of iso-OMPA (10 microM) the bronchial rings were more sensitive to neostigmine. The pD2 values were, control: 6.05 +/- 0.15 and treated: 6.91 +/- 0.14. 4. Neostigmine or iso-OMPA retarded the degradation of acetylcholine when this substrate was exogenously added to human isolated airways. A marked reduction of acetylcholine degradation was observed in the presence of both inhibitors. Exogenous butyrylcholine degradation was prevented by iso-OMPA (10 microM) but not by neostigmine (0.1 microM). 5. These results suggest the presence of butyrylcholinesterase activity in human bronchial muscle and this enzyme may co-regulate the degradation of acetylcholine in this tissue.

Response to anti-human IgE in human pulmonary arteries. Regulation by endothelium

Initial reports concerning anaphylactic reactions in the lung have demonstrated that histamine is released, and this mediator may be responsible for the severe hypotension observed in vivo in sensitized animals. However, those mechanisms involved in the antigen-vascular interactions have not been elucidated. Human isolated pulmonary arterial preparations relaxed when challenged with anti-human IgE (a-IgE). This response was associated with a release of histamine and PGI2. Both the relaxation and the release of PGI2 were attenuated by removal of the endothelium or by prior treatment of the tissues with chlorpheniramine. Indomethacin also significantly reduced the relaxations produced by a-IgE. In addition, L-NOARG in the presence of indomethacin blocked the a-IgE-dependent relaxation. Stimulation of these tissues with histamine also induced relaxations which were endothelium dependent and blocked by chlorpheniramine and L-NOARG in the presence of indomethacin. These results suggest that the relaxations via products of the cyclooxygenase and NO pathways were mediated by histamine release which stimulated the endothelium.

Contraction of bovine isolated bronchial airways: effects of epithelium removal

The influence of the epithelium on the contractile responses of bovine bronchial rings to acetylcholine, carbachol, 5-hydroxytryptamine and histamine was studied. Epithelium removal caused a significant leftward shift of the acetylcholine concentration-effect curve, pD2 values were 2.86 +/- 0.11 and 3.34 +/- 0.18 for intact and rubbed tissue, respectively (P < 0.05). However, there was no change in the acetylcholine maximal response. The sensitivity and responsiveness of the bovine bronchus to the other spasmogens were not significantly altered by removal of the epithelium. These results suggest that the epithelium of bovine bronchi modulates only acetylcholine-induced contraction.

A second cysteinyl leukotriene receptor in human lung

Leukotrienes (LT) are potent spasmogenic agents in human isolated bronchial and pulmonary venous muscle preparations. Treatment of human isolated pulmonary veins with the L-serine borate complex (45 mM; 30 min) did not alter the LTC4 pD2 values in these preparations. The cysteinyl LT antagonists, ICI 198615, MK 571 and SKF 104353, significantly shifted to the right the LT concentration-effect curves in airways with pKB values against LTC4 of 8.4 for ICI 198615, 8.6 for MK 571 and 8.0 for SKF 104353. Similar results were found against LTD4. In contrast, these antagonists did not inhibit the LTC4 and LTD4 contractions in human pulmonary veins. LTE4 was a partial agonist on the human pulmonary veins and blocked the contractions with a pKp value of 6.3 against LTD4 and 6.6 against LTC4. An LT analog, BAY u9773, also blocked the LT contractions in bronchial and venous muscle preparations with pKp values against LTD4 and LTC4 of 6.5 and 6.7, respectively. These data provide pharmacological evidence for a second cysteinyl LT receptor in the human lung. One LT receptor (LT-1) is stimulated by all cysteinyl LT, found on airways and inhibited by the LT-1 antagonists, and a second receptor (LT-2) can also be stimulated by all cysteinyl LT and is found on pulmonary veins, resistant to LT-1 antagonists but blocked by LTE4 and the dual LT-1/LT-2 antagonist BAY u9773.

Histamine receptors on human isolated pulmonary arterial muscle preparations: effects of endothelial cell removal and nitric oxide inhibitors

Human isolated intact pulmonary arterial muscle ring preparations which were precontracted with serotonin (10 microM) relaxed when stimulated with low concentrations of histamine, 2-[2-thiazolyl]ethylamine or 2-[pyridyl]ethylamine (pD2 values: 8.66 +/- 0.22, 7.10 +/- 0.06 and 6.20 +/- 0.26, respectively) or contracted at higher concentrations of these agonists. This relaxant response was obliterated in endothelial denuded tissues. Chlorpheniramine (H1-antagonist; 0.25 and 2.5 microM) induced a small contractile response in the tissues at resting tone (0.08 +/- 0.03 g and 0.10 +/- 0.10 g, respectively). Chlorpheniramine also shifted the histamine relaxation curves to the right (pD2 values: control, 8.85 +/- 0.31; 0.25 microM, 6.90 +/- 0.41; and 2.5 microM, 5.58 +/- 0.30; N = 6). Dimaprit (H2-agonist) induced a small relaxation (20%) in both intact and denuded tissues. Treatment of the tissues with cimetidine (H2-antagonist; 50 microM), burimamide (H2/H3-antagonist; 10 microM) and impromidine (H2-agonist/H3-antagonist; 1 microM) did not alter histamine-induced relaxation or contraction. Indomethacin (1.7 microM) caused a small contraction in these tissues and significantly reduced the histamine relaxation. The nitric oxide inhibitors (L-NG-monoethyl-L-arginine, 30 and 300 microM; or L-NG-nitroarginine, 30 and 300 microM) induced a slight and variable contraction in the preparations. However, these inhibitors, only in the presence of indomethacin, inhibited the relaxant effects of histamine and potentiated the contractions induced by this amine. These data suggest that a dual endogenous vasodilatory mechanism is present in human isolated pulmonary arterial muscle preparations and that products of the cyclooxygenase and endothelium-derived relaxing factor-nitric oxide pathway may interact to regulate histamine stimulation of H1-receptors.

Inhibitory effects of BAY u3405 on prostanoid-induced contractions in human isolated bronchial and pulmonary arterial muscle preparations

1. The thromboxane-mimetic, U46619, was a more potent contractile agonist than prostaglandin D2 (PGD2), PGF2 alpha or histamine in human isolated bronchial and pulmonary arterial muscle preparations. 2. Human isolated proximal bronchial muscles were less sensitive to contractile agents than distal bronchial preparations. However, the former tissues developed a greater contractile force (Emax) when compared with results obtained in the latter tissues. 3. BAY u3405 attenuated the contractions induced by U46619, PGF2 alpha and PGD2 in both human isolated bronchial and pulmonary arterial muscle preparations. 4. BAY u3405 did not alter histamine concentration-effect curves nor the relaxation induced by Butaprost (TR4979) in human isolated bronchial muscle preparations. In addition BAY u3405 did not modify the relaxation induced by PGI2 in isolated pulmonary arterial muscle preparations. 5. The contractions induced by different prostaglandins were blocked by BAY u3405, suggesting a common functional site for these agents found both on human bronchial and pulmonary arterial muscles.

Antigen-induced contraction of human isolated lung preparations passively sensitized with monoclonal IgE: effects of indomethacin

Human isolated lung preparations were passively sensitized using mouse monoclonal dinitrophenyl (DNP)-specific IgE antibodies. The contractile response to antigen (DNP-bovine serum albumin; DNP-BSA) was approximately 80% of the histamine response (50 microM: 0.20 +/- 0.03 g/mm2) in bronchial muscle preparations. In passively sensitized pulmonary vascular and parenchymal preparations, the contraction to antigen was negligible. Indomethacin (1.7 microM; 30 min) did not alter the contractile response to DNP-BSA (5 micrograms/ml) in bronchial tissues. In passively sensitized bronchial muscle preparations stimulated with DNP-BSA, there was a significant increase (2-fold) in prostanoid production. This production was inhibited by indomethacin. These data suggest that endogenous prostaglandins may not play a role in the regulation of human isolated bronchial muscle contraction to antigen in vitro.

Vasorelaxant effects of atrial peptide II on isolated human pulmonary muscle preparations

Isolated human pulmonary arterial preparations were approximately 10-fold more sensitive to atrial peptide II than venous preparations (pD2 values: 7.11 +/- 0.14 and 6.17 +/- 0.14, respectively). Atrial peptide II did not relax isolated human bronchial muscle preparations (pD2 value: greater than 5.5). These data demonstrate that atrial peptide II is a selective relaxant agent in isolated human pulmonary vascular muscle preparations with no effect on isolated human airway muscle preparations.

Antigenic contraction of guinea pig tracheal preparations passively sensitized with monoclonal IgE: pharmacological modulation

Spirally cut guinea pig tracheal preparations were passively sensitized using a mouse monoclonal IgE antibody against dinitrophenol (DNP). Maximal contraction observed following challenge with DNP-bovine serum albumin (DNP-BSA, 5 micrograms/ml; n = 20) response was approximately 46% of the histamine response (0.52 +/- 0.09 g/mm2; n = 53). Indomethacin (1.7 microM) increased and PGE2 (1 microM) decreased the response to the antigen. FPL 55712 (10 microM), atropine (0.1 microM), L 651392 (5 microM) or tripelennamine (1 microM) always reduced the maximal DNP-BSA response, but not BN 52021 (100 microM). This model may be used for rapid detection of compounds with antiallergic properties on IgE-dependent lung pathological states.

Effects of various pharmacological agents on isolated human bronchial and pulmonary arterial and venous muscle preparations contracted by leukotriene D4

The response of isolated human bronchial muscle preparations to leukotriene D4 (LTD4, 0.1 microM; 0.22 +/- 0.03 g/mm2) was similar to that of histamine (50 microM; 0.21 +/- 0.02 g/mm2). Isolated pulmonary venous preparations also contracted to these same concentrations of both agonists (LTD4, 0.32 +/- 0.19 g/mm2; and histamine, 0.36 +/- 0.07 g/mm2). However, pulmonary arterial preparations responded to histamine (50 microM, 0.59 +/- 0.10 g/mm2) but exhibited a reduced response to LTD4 (0.3 microM, 0.06 +/- 0.01 g/mm2). Bronchial and pulmonary venous muscle preparations from the human lung had the same sensitivities to LTD4 (pD2 values: bronchus, 7.95 +/- 0.08 and vein, 7.76 +/- 0.07). When bronchial or pulmonary venous muscle preparations were incubated for 30 min with either diltiazem (10 microM), indomethacin (1.7 microM) or L-cysteine (3 microM), the LTD4 cumulative concentration-effect curves following these drug treatments were similar to controls. However, FPL-55712 (10 microM) significantly shifted the LTD4 concentration-effect curves produced in bronchial preparations to the right. In isolated pulmonary arterial preparations none of these drug treatments enhanced the LTD4 response. These results show that isolated human pulmonary arterial preparations are less responsive to LTD4 than bronchial or venous preparations. In addition, the data obtained subsequent to the various drug treatments indirectly suggest that the LTD4 contraction is not modified by a calcium channel blocker or by inhibition of the endogenous products of the cyclooxygenase pathway.

Platelet-activating factor-acether-induced relaxation of guinea pig airway muscle: role of prostaglandin E2 and the epithelium

A fixed concentration of paf-acether (platelet-activating factor; 4 microM) relaxed isolated guinea pig tracheal preparations which had been contracted with histamine (50 microM), serotonin (1 microM) or leukotriene D4 (0.1 microM). The relaxations were approximately 43, 100 and 57%, respectively. We did not observe any relaxant effect of paf-acether (4 microM) in tissues contracted with acetylcholine (50 microM). Both lyso paf-acether (10 microM) and bovine serum albumin (25 micrograms/ml) were without effect on histamine-contracted preparations. In the presence of indomethacin (1.7 microM; 30 min) or aspirin (0.1 mM; 30 min) the relaxant effect of paf-acether (4 microM) in tissues contracted with histamine was significantly reduced to approximately 10 and 12%, respectively. When paf-acether (4 microM) was added to histamine-contracted tracheal preparations in the presence of noradrenaline (0.1 microM) or prostaglandin E2 (PGE2, 10 nM) the relaxations were 62 and 82%, respectively. Noradrenaline and PGE2 alone had only a slight relaxant effect in these tissues (7 and 14%, respectively). In the presence of indomethacin (1.7 microM) the synergistic effect of paf-acether and PGE2 was still observed. The basal production of PGE2 in isolated guinea pig tracheal preparations was 4.6 +/- 1.4 pg/mg of tissue. In the presence of paf-acether (4 microM) increased levels of this prostanoid were detected (11.2 +/- 2.4 pg/mg of tissue). Isolated guinea pig tracheal preparations when contracted with histamine released PGE2 (17.6 +/- 4.1 pg/mg of tissue). In the presence of histamine and paf-acether there was a significant increase in detectable levels of PGE2 (48.6 +/- 13.2 pg/mg of tissue).(ABSTRACT TRUNCATED AT 250 WORDS)

Relaxation of isolated human pulmonary muscle preparations with prostacyclin (PGI2) and its analogs

The effects of PGI2 and two analogs Iloprost and ZK 96480 were examined on isolated human pulmonary muscle preparations. High concentrations of these agents reduced the basal tone in all types of preparations. In addition, they relaxed tissues which had been maximally contracted with histamine (50 microM). PGI2 was more potent on pulmonary arterial muscle preparations (pD2 value: 6.33, n = 3) than on bronchial muscles. The relaxations induced by PGI2 in bronchial preparations were quite variable, that is, some tissues relaxed while others did not. The analogs also relaxed arterial preparations and the pD2 values were approximately the same (Iloprost: 7.42, n = 4 and ZK 96480: 7.48, n = 4). The isolated human pulmonary vascular preparations were approximately 10-fold more sensitive to the analogs than bronchial muscle preparations. In bronchial tissues we noted that the PGI2 relaxant effect was spontaneously reversed with time, an activity not observed with both analogs. A pretreatment of the bronchial tissues with indomethacin (1.7 microM) did not reduce the variations observed with PGI2 nor modify the transient relaxation observed with this agent. These data demonstrate that vascular tissues from the human lung are considerably more sensitive to these relaxant agonists than bronchial preparations.

Specific inhibition of PAF-acether-induced platelet activation by BN 52021 and comparison with the PAF-acether inhibitors kadsurenone and CV 3988

BN 52021 is a chemically defined substance extracted from Ginkgo biloba leaves. Its inhibitory potency was tested on washed human platelets prepared so as to render them specifically sensitivity either to adenosine 5'-diphosphate (ADP), arachidonic acid (AA) or PAF-acether. Its activity and specificity were compared with those of two other reported inhibitors of PAF-acether effects: Kadsurenone and CV 3988. PAF-acether-induced aggregation of washed human platelets was concentration dependently inhibited by BN 52021 (IC50: 2.22 +/- 0.79 microM against 7.5 nM PAF-acether (n = 3)). Under the same experimental conditions the aggregation triggered by ADP was not modified and that induced by AA was marginally affected. The PAF-acether EC50 in platelet-rich plasma was increased 5- and 46-fold with 1 microM and 5 microM of BN 52021 respectively. This strongly suggested that the mechanism of action of BN 52021 is of the competitive type. Analysis of [3H]PAF-acether binding showed that BN 52021 as well as unlabelled PAF-acether prevented [3H]PAF-acether binding to intact washed platelets. In washed human platelets Kadsurenone affected only PAF-acether-induced aggregation (IC50: 0.8 +/- 0.4 microM (n = 3)), whereas CV 3988 inhibited the aggregation induced by ADP, AA and PAF-acether (IC50 were 10.2 +/- 2.3 microM; 2.2 +/- 0.1 microM; 1.0 +/- 0.1 microM respectively (n = 3). In contrast, up to 30 microM, CV 3988 was a specific antagonist of PAF-acether-induced platelet aggregation in plasma.(ABSTRACT TRUNCATED AT 250 WORDS)