Hyperpolarization and slowing of the rate of contraction in human uterus in pregnancy by prostaglandins E2 and f2alpha: involvement of the Na+ pump

1. The effects of prostaglandins E2 (PGE) and F2alpha (PGF) on membrane potential and isometric tension and cytoplasmic free calcium concentration ([Ca2+]i) and tension were studied in strips of uterine smooth muscle obtained from women undergoing Caesarean delivery at term and during established labour. 2. Prostaglandins (PGs) evoked a biphasic response. The excitatory component consisted of depolarization of the membrane, which initiated spike action potentials, an increase in [Ca2+]i and tension development. The membrane remained depolarized at -19 +/- 1 mV for about 2 min, then repolarized abruptly, [Ca2+]i promptly returned to basal levels, and tension development ceased. 3. This component of the response to PGE or PGF was followed by a slow hyperpolarization which reached -85 +/- 2 mV (n = 22) at term and -70 +/- 2 mV (n = 9) during labour, and during which spontaneous action potentials and tension development did not occur. 4. Nifedipine (10-6 M) abolished spontaneous activity, abolished PG-induced action potentials and reduced the increase in [Ca2+]i (9 +/- 3 %, n = 6), the depolarization (10 +/- 1 mV, n = 14), the tension (2 +/- 1 %, n = 14) and the hyperpolarization (9 +/- 1 mV, n = 14, at term). 5. A variety of K+ channel blockers were without effect on the peak amplitude of the PG-induced hyperpolarization but the latter did not occur in the presence of ouabain (10-6 M) or in K+-free or low-Na+ solutions, suggesting an involvement of the Na+-K+-ATPase pump. 6. In conclusion, a substantial dependence on Ca2+ influx through voltage-operated Ca2+ channels accounts for the importance of membrane potential in regulating contractions in human uterine smooth muscle. The classical excitatory effect of PGE and PGF is followed by hyperpolarization involving the Na+-K+-ATPase pump. The hyperpolarization restricts the response to a single contraction and decreases the frequency of subsequent contractions. The amplitude of the hyperpolarization decreases during labour, allowing contraction frequency to increase. Its persistence at this time ensures complete relaxation between each single robust contraction, preventing spasm of the uterus that would restrict blood flow to the fetus during delivery.

Endothelium-dependent hyperpolarization in resting and depolarized mammary and coronary arteries of guinea-pigs

1. The membrane potential responses in guinea-pig coronary and mammary arteries attributable to endothelium-derived nitric oxide (NO), prostaglandin (PG) and hyperpolarizing factor (EDHF), and to exogenous NO and the prostacyclin analogue, iloprost, were compared at rest and when depolarized with the thromboxane analogue, U46619. 2. In the coronary artery, stimulation of the endothelium with acetylcholine (ACh) evoked hyperpolarization attributable to NO and a PG with similar pD2s at rest and in the presence of U46619. However, in depolarized tissues, the pD2 of the response attributed to EDHF required a 10 fold lower concentration of ACh compared with at rest. 3. In the mammary artery, lower concentrations of ACh were required to evoke NO- and EDHF-dependent hyperpolarizations in depolarized mammary artery compared with at rest, while PG-dependent hyperpolarization did not occur until the concentration of ACh was increased some 10 fold both at rest and in U46619. 4. The smooth muscle of the coronary artery of guinea-pigs was some 4 fold more sensitive to exogenous NO and iloprost than was the mammary artery. 5. In conclusion, the membrane potential response in arteries at rest, that is, in the absence of constrictor, may be extrapolated to events in the presence of constrictor when NO and PG are under study. However, the sensitivity to ACh and the magnitude of the hyperpolarization attributed to EDHF obtained in tissues at rest may underestimate these parameters in depolarized tissues.

Selective formation of Gsalpha-MHC I complexes after desensitization of human platelets with iloprost

Prolonged treatment of human platelets with the adenylate cyclase-stimulating prostacyclin analog iloprost leads to reduction in cAMP formation. Previous studies have demonstrated that this may be ascribed to modification of both receptor and Gsalpha function rather than of the catalytic component of adenylate cyclase [Mollner, S., Deppisch, H. & Pfeuffer, T. (1992) Eur. J. Biochem. 210, 539-544]. Iloprost-induced desensitization was accompanied by the formation of a Gsalpha-containing 90-kDa product in membranes treated with the bifunctional cross-linker 1,6-bismaleimidohexane. The cAMP-inducing prostanoid PGD2, which does not promote desensitization, did not cause formation of the 90-kDa species either. The long-term effect of the common G-protein activator [AlF4]- on human platelet adenylate cyclase was shown in many respects to be comparable with that of iloprost. However, [AlF4]- treatment also failed to induce the 90-kDa species, showing that different mechanisms of desensitization were operating. Treatment of the cross-linked 90-kDa complex with PNGase F demonstrated the glycoprotein nature of the Gsalpha-associated component. The 90-kDa cross-linked product was purified by consecutive immunoaffinity chromatography and preparative PAGE to apparent homogeneity. Analysis of the purified protein by MS suggested that, besides Gsalpha, the heavy chain of MHC I (HLA-A2) was part of the complex. This was confirmed by coprecipitation of Gsalpha by the monoclonal anti-(MHC I) antibody W6/32.

Antithrombin reduces ischemia/reperfusion injury of rat liver by increasing the hepatic level of prostacyclin

We investigated whether antithrombin (AT) can reduce ischemia/reperfusion (I/R)-induced injury of rat liver by promoting prostacyclin release from endothelial cells. Although intravenous administration of AT (250 U/kg) markedly reduced hepatic injury, neither dansyl-Glu-Gly-Arg-chloromethyl ketone-treated factor Xa (DEGR-Xa), a selective inhibitor of thrombin generation, nor Trp49-modified AT, which lacks affinity for heparin, had any effect. Hepatic levels of 6-keto-PGF1, a stable prostacyclin (PGI2) metabolite, were increased significantly after I/R of the rat liver. AT significantly increased the hepatic level of 6-keto-PGF1, whereas neither DEGR-Xa nor Trp49-modified AT increased it. Hepatic tissue blood flow was markedly reduced after I/R. Although AT significantly increased the hepatic tissue blood flow after I/R, neither DEGR-Xa nor Trp49-modified AT increased the blood flow. Hepatic levels of cytokine-induced neutrophil chemoattractant (CINC) and myeloperoxidase (MPO) were significantly increased after hepatic I/R. The levels of these two indicators were reduced by AT but were unaffected by either DEGR-Xa or Trp49-modified AT. Pretreatment of animals with indomethacin (IM) completely inhibited the protective effects of AT on the I/R-induced hepatic damage and the leukocyte activation as well as the AT-induced increase in hepatic 6-keto-PGF1 levels after I/R. Iloprost, a stable analog of PGI2, exhibited effects similar to those of AT and also significantly inhibited the exacerbation of liver injury, the decrease in hepatic tissue blood flow, and the increases in hepatic CINC and MPO levels seen in rats subjected to I/R but pretreated with IM. These findings suggest that AT may prevent I/R-induced hepatic injury by increasing the hepatic levels of PGI2 through the interaction of AT with cell-surface glycosaminoglycans, thus increasing hepatic tissue blood flow and inhibiting leukocyte activation in animals subjected to I/R.

Expression of prostacyclin receptors in luteinizing hormone-releasing hormone immortalized neurons: role in the control of hormone secretion

PGs of the E series are involved in the control of LHRH secretion. The present experiments were conducted to clarify whether PGI2 (prostacyclin) might be also involved in such a control, using multiple methodological approaches on immortalized LHRH-secreting neurons. A RT-PCR procedure to detect mouse PGI2 receptor (IP) messenger RNA was first applied, and the results obtained showed the presence of a specific transcript in two cell lines of immortalized LHRH neurons (GT1-1 and GN11 cell lines). Receptor binding assays on membrane preparations from GT1-1 cells showed the presence of a single specific and saturable class of binding sites (Kd = 4.6 nM; 10,000 sites/cell) for [3H]iloprost, a stable analog of PGI2. Competition experiments showed that the binding sites labeled by [3H]iloprost possess the pharmacological characteristics of IP receptors. In functional studies, PGI2 and its analogs, iloprost and cicaprost, were able to stimulate LHRH release from the GT1-1 cells with elevated potencies (EC50 = 0.6-4.3 nM); PGE1 was only slightly less active (EC50 = 28.5 nM), whereas PGE2, considered the major PG involved in LHRH secretion, was poorly effective (EC50 = 921 nM). The relative potencies (EC50) of these compounds in stimulating the intracellular accumulation of cAMP were in line with their LHRH-releasing activities. In conclusion, these results indicate that immortalized LHRH-secreting neurons express IP receptors through which PGI2 may exert relevant effects on LHRH release.

Prostaglandins prevent inducible nitric oxide synthase protein expression by inhibiting nuclear factor-kappaB activation in J774 macrophages

We investigated the effect of PGE2 and iloprost (a prostacyclin analogue) on inducible nitric oxide synthase (iNOS) protein expression and nuclear factor-kappaB (NF-kappaB) activation in lipopolysaccharide (LPS)-stimulated J774 macrophages. Incubation of J774 cells with LPS (10 microg/ml) caused an increase of iNOS protein expression which was prevented in a concentration-dependent fashion by PGE2 (0.1, 1, 10 microM) and iloprost (0.01, 0.1, 1 microM). Electrophoretic mobility shift assay indicated that both prostanoids blocked the activation of NF-kappaB, a transcription factor necessary for NO synthase induction. PGE2 and iloprost also blocked disappearance of I kappaB-alpha from cytosolic fraction and nuclear translocation of NF-kappaB subunits p50 and p65. These results show for the first time that PGE2 and iloprost down-regulate iNOS protein expression by inhibiting NF-kappaB activation and suggest a negative feed-back mechanism that may be important for limiting excessive or prolonged NO production in pathological events.

Influence of low- and high-dose aspirin treatment on thrombin generation in whole blood

The effects of two doses of aspirin (75 and 500 mg/day during 1 week) on thrombin generation was investigated in healthy volunteers. Thrombin generation in whole blood was monitored by repeated measurements of prothrombin fragment 1+2 (F1+2) in plasma prepared from untreated whole blood left to clot at 37 degrees C. Experiments with a platelet inhibiting agent (iloprost, a prostacyclinanalogue) and platelet-activating compounds (collagen and a thromboxane analogue), indicated that the formation of thrombin in this system is partly dependent on platelet function. High dose aspirin (500 mg daily) attenuated thrombin generation, whereas low-dose treatment (75 mg daily) failed to attenuate thrombin formation significantly. Collagen-induced platelet aggregation in whole blood, used to monitor antiplatelet effects of aspirin, showed profound inhibition of platelet aggregation already at 75 mg of aspirin; 500 mg did not inhibit platelet aggregation further. Our results show that aspirin suppresses thrombin formation in whole blood in a dose-dependent fashion and that the "antithrombin" effects of aspirin require higher doses than the antiaggregating effects. The mechanism(s) behind the "antithrombin" effects of aspirin is at present unclear but may involve thromboxane-independent mechanisms, such as acetylation of platelet membrane receptors or coagulation factors.

Angiotensin II-induced hypertrophy of adult rat cardiomyocytes is blocked by nitric oxide

The aim of the present study was to test the hypothesis that bradykinin-stimulated release of nitric oxide (NO) and/or prostacyclin from endothelium blocks myocyte hypertrophy in vitro. Angiotensin II increased [3H]phenylalanine incorporation by 21 +/- 2% in myocytes cocultured with endothelial cells; this was abolished by bradykinin in the presence of endothelial cells. Bradykinin increased cytosolic concentrations of cGMP by 29 +/- 4% in myocytes cocultured with endothelial cells. This was abolished by inhibition of NO synthase and by a cyclooxygenase inhibitor. Angiotensin II also increased [3H]phenylalanine incorporation by 28 +/- 3% in myocytes cultured in the absence of endothelial cells. This effect of angiotensin II in monoculture was abolished by donors of NO but not by bradykinin. Neither the stable analog of prostacyclin (iloprost) nor the prostacyclin second messanger analog 8-bromo-cAMP (8-BrcAMP) blocked the effect of angiotensin II. Furthermore, 8-BrcAMP and iloprost individually increased [3H]phenylalanine incorporation. The antihypertrophic effects of bradykinin are critically dependent on endothelium-derived NO.

Evidence that Ca2+-activated K+ channels play a major role in mediating the vascular effects of iloprost and cicaprost

The role of K+ channels in mediating vasorelaxation induced by two prostacyclin analogues was investigated in guinea-pig aorta. Iloprost caused substantial relaxation of tissues contracted with phenylephrine or 25 mM K+ but not 60 mM K+. In endothelial-denuded tissues, maximal relaxations to iloprost, cicaprost or isoprenaline were inhibited by approximately 40-50% with tetraethylammonium or iberiotoxin, both blockers of large conductance Ca2+-activated K+ (BKCa) channels. In contrast, the response to forskolin, an activator of adenylate cyclase was marginally inhibited by tetraethylammonium. The K(ATP) channel blocker, glibenclamide significantly augmented the response to iloprost but not cicaprost. These effects were largely inhibited by the EP1 receptor antagonist, 8-chlorodibenz[b,f][1,4]oxazepine-10(11H)-carboxylic acid 2-[1-oxo-3(4-pyridinyl)propyl]hydrazide, monohydrochloride (SC-51089) and partially by indomethacin, suggesting that iloprost relaxation is counterbalanced by activation of EP1 receptors, in part through a constrictor prostaglandin. We conclude that BKCa channels play an important role in mediating the effects of iloprost and cicaprost and raises the possibility that cyclic AMP-independent pathways might be involved.

Phosphorylation of the prostacyclin receptor during homologous desensitization. A critical role for protein kinase c

Agonist-induced phosphorylation of an epitope-tagged prostacyclin receptor (HAhIP) is mediated primarily by PKC (Smyth, E. M., Nestor, P. V., and FitzGerald G. A. (1996) J. Biol. Chem. 271, 33698-33704). Based on the two consensus sites for protein kinase C (PKC) phosphorylation in the C-terminal region mutant HAhIPs were generated: S328A and S374A, in which an alanine replaced Ser-328 or Ser-374, respectively, S328A/S374A and C-DEL, in which the C-terminal portion was truncated at amino acid 313. Mutant receptors, stably expressed in HEK293 cells, coupled normally to cAMP production. Substantially less coupling to inositol phosphate was apparent with S328A, S328A/S374A, and C-DEL compared with HAhIP or S374A. Point mutants resolved by SDS-polyacrylamide gel electrophoresis as a broad band with a molecular mass of 44-62, indicating that the receptors are glycosylated, and immunofluoresence staining demonstrated their membrane localization. C-DEL demonstrated a substantial reduction in glycosylation; bands with molecular masses of 38-54 (glycosylated), 30, and 27 kDa (unglycosylated) were apparent. Although membrane localization was evident, cellular localization was more diffuse. HAhIP and S374A underwent iloprost- and PMA-induced phosphorylation (1 and 5 microM, respectively, for 10 min). S328A and S328A/S374A showed a markedly less iloprost- and no PMA-induced phosphorylation. Phosphorylation of C-DEL was completely absent with either agonist. Electrospray mass spectrometry indicated that a peptide, including Ser-328, was phosphorylated in vitro by PKC, whereas one including Ser-374 was not. Iloprost (1 microM, 10 min) desensitized HAhIP- and S374A-mediated adenylyl cyclase activation. A less impressive desensitization was evident with S328A and S328A/S374A, and no desensitization of C-DEL coupling was apparent. Exposure of transfected cells to iloprost (1 microM) for increasing times induced a rapid desensitization of subsequent iloprost-induced (1 microM) HAhIP and S374A adenylyl cyclase coupling. In contrast, no significant time-dependent desensitization of S328A, S328A/S374A, or C-DEL coupling was evident. These results indicate that PKC-dependent phosphorylation is of critical importance to homologous regulation of hIP. Ser-328 is a primary site for PKC phosphorylation of hIP.

Venous levels of shear support neutrophil-platelet adhesion and neutrophil aggregation in blood via P-selectin and beta2-integrin

BACKGROUND

After activation, platelets adhere to neutrophils via P-selectin and beta2-integrin. The molecular mechanisms and adhesion events in whole blood exposed to venous levels of hydrodynamic shear in the absence of exogenous activation remain unknown.

METHODS AND RESULTS

Whole blood was sheared at approximately 100 s(-1). The kinetics of neutrophil-platelet adhesion and neutrophil aggregation were measured in real time by flow cytometry. P-selectin was upregulated to the platelet surface in response to shear and was the primary factor mediating neutrophil-platelet adhesion. The extent of neutrophil aggregation increased linearly with platelet adhesion to neutrophils. Blocking either P-selectin, its glycoprotein ligand PSGL-1, or both simultaneously by preincubation with a monoclonal antibody resulted in equivalent inhibition of neutrophil-platelet adhesion (approximately 30%) and neutrophil aggregation (approximately 70%). The residual amount of neutrophil adhesion was blocked with anti-CD11b/CD18. Treatment of blood with prostacyclin analogue ZK36374, which raises cAMP levels in platelets, blocked P-selectin upregulation and neutrophil aggregation to baseline. Complete abrogation of platelet-neutrophil adhesion required both ZK36374 and anti-CD18. Electron microscopic observations of fixed blood specimens revealed that platelets augmented neutrophil aggregation both by forming bridges between neutrophils and through contact-mediated activation.

CONCLUSIONS

The results are consistent with a model in which venous levels of shear support platelet adherence to neutrophils via P-selectin binding PSGL-1. This interaction alone is sufficient to mediate neutrophil aggregation. Abrogation of platelet adhesion and aggregation requires blocking Mac-1 in addition to PSGL-1 or P-selectin. The described mechanisms are likely of key importance in the pathogenesis and progression of thrombotic disorders that are exacerbated by leukocyte-platelet aggregation.

Preservation of myocardial metabolism in acute coronary artery occlusions with retrograde coronary sinus perfusion and iloprost

A total of 12 healthy mongrel dogs were subjected to the study. The left anterior descending artery was occluded. The occlusion was done for 15 min. At the end of this period, without removing the occlusion, the heart was retroperfused for 3 h. Then, occlusion was removed and reperfusion was supplied. Animals were divided into two equal groups. Six animals received iloprost and the other six control did not receive any additional treatment. In the iloprost group, the drug was administered into the coronary sinus. After 15 min following occlusion, iloprost was infused at a rate of 50 microg/min continuously. Cardiac output (CO), mean arterial pressure (MAP), mean pulmonary arterial pressure (MPAP), heart rate (HR), pulmonary capillary wedge pressure (PCWP), right atrium pressure (RAP), myocardial oxygen extraction (MOE) and myocardial lactate extraction (MLE) parameters were examined in the two groups, before and during retroperfusion and during the reperfusion (1-4 h). Iloprost retroperfusion (50 microg/min) was started at the fifteenth minute of occlusion and continued till the end of the observation period (3 h). The measured hemodynamic data showed that the hearts treated with iloprost had satisfactory preservation of cardiac function. At the end of the reperfusion period cardiac output was 1.5 +/- 0.06 L/min in the control and 1.7 +/- 0.04 L/min in the iloprost group (P < 0.05). At the end of the reperfusion period, tumor necrosis factor level was raised significantly in the control group (P < 0.05). Myocardial lactate release was also high in the control group (P < 0.05). CPK-MB release was low in the iloprost group (P < 0.05). We conclude that retrogradely administered iloprost reduced the risk of myocardial injury and it is probable that this drug effectively distributes to the area of myocardium at risk.

A single amino-acid substitution in the EP2 prostaglandin receptor confers responsiveness to prostacyclin analogs

A high degree of homology between the four Gs-coupled prostaglandin (PG) receptors [EP2, EP4, prostacyclin (IP), PGD2 (DP)] and the four Gq/Gi-coupled receptors [EP1, EP3, PGF2alpha (FP), thromboxane A2 (TP)] suggests that prostaglandin receptors evolved functionally from an ancestral EP receptor before the development of distinct binding epitopes. If so, ligand selectivity should be determined by a limited number of amino acids. EP2 receptor transmembrane domain residues that are similar to those in the EP4 receptor but differ from those in the IP receptor were mutated to the corresponding IP receptor residue. Activation of the mutant receptors by PGE2 (EP2 ligand), iloprost (stable prostacyclin analog), and PGE1 (EP2/IP ligand) was determined using a cAMP-dependent reporter gene assay. A Leu304-to-tyrosine substitution in the seventh transmembrane domain enhanced iloprost potency approximately 100-fold. A glycine substitution at Ser120 in the third transmembrane domain had no effect on drug potency but improved the response of the Tyr304 mutant. The potency of the natural prostaglandins PGF2alpha and PGD2 was not enhanced by the mutations. In contrast, the potency of all prostaglandins was reduced 10- to 100-fold when arginine 302, which is thought to be a counterion for the prostaglandin carboxylic acid, was mutated. Thus, a single amino acid change resulted in a selective gain of function for iloprost, which is consistent with the proposed phylogeny of the prostaglandin receptors.

Evidence that adenosine diphosphate can activate adenylate cyclase via conversion to adenosine in platelet-rich plasma containing magnesium

When adenosine diphosphate (ADP) is added to hirudinized platelet-rich plasma (PRP) in which the level of platelet cAMP has been pharmacologically elevated, there is an initial rapid fall in the level of cAMP brought about by inhibition of adenylate cyclase. This may be followed by a subsequent activation of adenylate cyclase that does not occur when citrated PRP is used in place of hirudinized PRP, and is more pronounced in the presence of added Mg2+. Here we provide evidence that a) the Mg2+-dependent activation of adenylate cyclase seen in hirudinized PRP is mediated by adenosine, b) the adenosine produced synergizes with forskolin and with DN9693 to raise the level of cAMP in platelets. but not with iloprost, c) Mg2+ does not influence directly the rate or extent of cAMP production and so is more likely to influence the rate of adenosine production, and d) activation of adenylate cyclase by adenosine can lead to inhibition of platelet aggregation. ARL 66096, a P2T purinoceptor antagonist which inhibits ADP-induced platelet aggregation, prevented inhibition of adenylate cyclase by ADP. Conversely, ARL 66096 did not appear to inhibit conversion of ADP to adenosine and subsequent activation of adenylate cyclase.

Interactions between endothelium-derived relaxing factors in the rat hepatic artery: focus on regulation of EDHF

1. In rat isolated hepatic arteries contracted with phenylephrine, acetylcholine and the calcium ionophore A23187 each elicit endothelium-dependent relaxations, which involve both nitric oxide (NO) and endothelium-derived hyperpolarizing factor (EDHF). However, the contribution of prostanoids to these responses, and the potential interaction between EDHF and other endothelium-derived relaxing factors have not been examined. 2. In the presence of the NO synthase inhibitor N(G)-nitro-L-arginine (L-NOARG, 0.3 mM) and a mixture of charybdotoxin (0.3 microM) and apamin (0.3 microM), inhibitors of the target potassium (K) channel(s) for EDHF, acetylcholine and A23187 each induced a concentration-dependent and almost complete relaxation, which was abolished in the additional presence of indomethacin (10 microM). Thus, in addition to EDHF and NO, a relaxing factor(s) generated by cyclo-oxygenase (COX) contributes to endothelium-dependent relaxation in the rat hepatic artery. 3. The resting membrane potentials of endothelium-intact and endothelium-denuded vascular segments were -57 mV and -52 mV, respectively (P>0.05). In intact arteries, the resting membrane potential was not affected by L-NOARG plus indomethacin, but reduced to -47 mV in the presence of charybdotoxin plus apamin. Acetylcholine and A23187 (10 microM each) elicited a hyperpolarization of 13 mV and 15 mV, respectively. The hyperpolarization induced by these agents was not affected by L-NOARG plus indomethacin (12 mV and 14 mV, respectively), but reduced in the presence of charybdotoxin plus apamin (7 mV and 10 mV, respectively), and abolished in the combined presence of charybdotoxin, apamin and indomethacin. 4. The NO donor 3-morpholino-sydnonimine (SIN-1) induced a concentration-dependent relaxation, which was unaffected by charybdotoxin plus apamin, but abolished by the selective soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ, 10 microM). SIN-1 (10 microM) did not alter the resting membrane potential in endothelium-denuded vascular segments. 5. The COX-dependent relaxation induced by acetylcholine was abolished following exposure to 30 mM KCl, but unaffected by glibenclamide (10 microM). The prostacyclin analogue iloprost induced a concentration-dependent relaxation, which was also abolished in 30 mM KCl and unaffected by the combined treatment with glibenclamide, charybdotoxin and apamin. Iloprost (10 microM) induced a glibenclamide-resistant hyperpolarization (8 mV with and 9 mV without glibenclamide) in endothelium-denuded vascular segments. 6. Exposure to SIN-1 or iloprost did not affect the EDHF-mediated relaxation induced by acetylcholine (i.e. in the presence of L-NOARG and indomethacin). Replacement of L-NOARG with the NO scavenger oxyhaemoglobin (10 microM) or the soluble guanylate cyclase inhibitor ODQ (10 microM) or methylene blue (10 microM), which all significantly inhibited responses to endothelium-derived NO, did not affect the acetylcholine-induced relaxation in the presence of indomethacin, indicating that endogenous NO also does not suppress EDHF-mediated responses. 7. These results show that, in addition to EDHF and NO, an endothelium-derived hyperpolarizing factor(s) generated by COX contributes significantly to endothelium-dependent relaxation in the rat heptic artery. Neither this factor nor NO seems to regulate EDHF-mediated responses. Thus, EDHF does not serve simply as a 'back-up' system for NO and prostacyclin in this artery. However, whether EDHF modulates the NO and COX pathways remains to be determined.

PTX-sensitive G proteins and permissive action of prostacyclin in newborn pig cerebral circulation

The present study of newborn pig cerebral circulation investigated the role of pertussis toxin (PTX)-sensitive GTP binding proteins in the permissive action of prostacyclin in specific dilator responses. Pial arterioles of anesthetized piglets were observed through closed cranial windows. The piglets were treated topically with PTX and intravenously with indomethacin. The effects of hypercapnia (10% CO2 ventilation) and topical 5,6-epoxyeicosatrienoic acid (5,6-EET) on pial arteriolar diameter were noted before and after the intervention. Samples of the artificial cerebrospinal fluid (aCSF) were collected from beneath the cranial windows for determination of the cAMP concentration. After administration of PTX, indomethacin still abolished pial arteriolar dilation to both hypercapnia and 5, 6-EET and also inhibited the cAMP elevation caused by hypercapnia. The addition of phorbol 12-myristate 13-acetate (PMA), but not iloprost, restored the increase in cAMP and vascular responses to hypercapnia and 5,6-EET. Therefore, in the newborn pig cerebral microvasculature, PTX appears to inhibit a G protein involved in the permissive action of prostacyclin. However, the protein kinase C (PKC) activator PMA appears to act downstream from the block, and, therefore, the permissive action of PMA is not affected by PTX. We suggest that the prostacyclin IP receptor may be coupled to phospholipase C via a PTX-sensitive G protein that normally permits vasodilation to specific stimuli via activation of a PKC, resulting in phosphorylation of a component of the adenylyl cyclase pathway.

Antiischemic effect of ZK-118.182 in rabbits: a comparative study with iloprost

The effects of ZK-118.182, a stable analogue of PGD2, were evaluated in an endothelin-1-induced cerebral ischemia rabbit model. Ischemia was induced by endothelin-1 injection (0.25 ng bolus) into subcavian artery and ischemic changes were assessed histologically by the number of ischemic neurons in the brain stem. ZK-118.182 (2 micrograms/kg, bolus into subclavian artery) reduced the number of ischemic neurons when injected 20 min after endothelin-1 injection, Iloprost, a stable analogue of PGI2, was also effective in reducing the number of ischemic neurons in a dose of 0.5 microgram/kg (bolus into subclavian artery). The results suggested that ZK-118.182 has a potent antiischemic effect which is comparable to that of iloprost in rabbits.

Site-specific delivery of iloprost during experimental angioplasty suppresses smooth muscle cell proliferation

PURPOSE

The authors have previously reported that intramural delivery of iloprost during angioplasty suppresses local platelet aggregation at 1 hour in undiseased porcine arteries. In this study, the authors sought to quantify the effect of such treatment on medial vascular smooth muscle cell proliferation, an event implicated in the development of intimal hyperplasia.

MATERIALS AND METHODS

Three Yorkshire pigs underwent percutaneous transluminal angioplasty with hydrogel-coated balloons for a total of 10 iloprost-treated (experimental) and 10 saline-treated (control) arterial sites. The balloons were prepared with previously reported techniques and loaded with 2.25 microg of iloprost for the experimental sites. On the eighth day after angioplasty, these sites were harvested and prepared for immunohistochemical staining. Thin (4 microm) sections of the specimens were stained with use of monoclonal antibody to proliferating cell nuclear antigen (PCNA). Appropriate positive and negative controls were used. Approximately 350-500 vascular smooth muscle cells were randomly counted under high power (100x) by an experienced physician who was blinded to the origin of the specimen. A PCNA index (%) was calculated as follows: [(#PCNA [+] cells)/(#PCNA [+] cells + #PCNA [-] cells)]x 100. A paired t test was used for statistical comparison.

RESULTS

The PCNA indices for eight (n = 8) paired large vessels (iliac, carotid, subclavian) were 7.98 (+/- 1.8)%, for the iloprost-treated experimental sites, and 14.58 (+/- 3.8)% for the saline-treated control sites. This difference was statistically significant (P = .003). One large vessel pair was not available for analysis. When the pair of renal arteries of animal 3 were included (n = 9), the PCNA indices were 8.32 (+/- 2.3)% for the experimental sites, and 13.79 (+/- 4.2)% for the control sites. The differences were again significant (P = .01).

CONCLUSION

Intraarterial site-specific delivery of iloprost during angioplasty with drug-loaded, hydrogel-coated balloons significantly suppresses medial smooth muscle cells in swine at the expected peak period of proliferation of 7 days after angioplasty.

Prostaglandin I2 analogue, iloprost, down regulates mitogen-activated protein kinases of macrophages

OBJECTIVE

Vascular endothelial cells (EC) play a pivotal role in diffuse organ injury seen in ARDS and MOFS. On exposure to cytokines or endotoxin (LPS) EC are stimulated to express adhesion molecules as well as proinflammatory and procoagulant activity. However, the potential feedback control of EC on macrophages (M-theta) is not clear. We studied the cellular mechanism of iloprost, a PGI2 analogue, in regulation of TNF production by LPS-stimulated M-theta.

METHODS

Rabbit alveolar M-theta and mouse M-theta RAW 264.7 cells were exposed to Escherichia coli LPS in the presence of various concentrations of iloprost. TNF production was measured by L929 bioassays. To further study the cellular mechanism of iloprost on M-theta activation, RAW 264.7 cells were stimulated by LPS (10 micrograms/ml) in the presence of either iloprost or specific mitogen-activated protein kinase (MAPK) inhibitors, either PD98059 or SB202190. P44/P42 and P38 MAPK activation were evaluated by Western blot assays with anti-phospho MAPK antibodies.

RESULTS

LPS induced M-theta TNF production, which was inhibited by iloprost. Iloprost also attenuated the activation of P44/P42 and P38 induced LPS. Inhibition of P44/P42 with PD98059 or P38 with SB202190 significantly reduced TNF production by LPS-stimulated RAW cells.

CONCLUSIONS

The regulatory mechanism of EC on M-theta activation is dependent on PGI2. The effect of PGI2 on M-theta is, at least in part, mediated through inhibiting MAPKs.