iloprost and linsidomine

Topics: Amino Acid Sequence; Blood Platelets; Blood Proteins; Calcium; Cyclic AMP; GTP-Binding Proteins; Humans; Iloprost; Molecular Sequence Data; Molsidomine; Phosphatidylinositol Diacylglycerol-Lyase; Phosphoric Diester Hydrolases; Phosphorylation; Platelet Activation; Prostaglandins; Protein Processing, Post-Translational; rap GTP-Binding Proteins; Signal Transduction; Vasodilator Agents

Many diseases of the heart and circulatory system have been linked with both dysfunction of vascular endothelium and insufficient deformability of erythrocytes. Using shear stress laser diffractometry we investigated whether deformability of erythrocytes would be regulated endogenously by generation of two endothelial secretogogues: prostacyclin and nitric oxide. Experiments were performed in rats ex vivo and with whole blood or isolated erythrocytes in vitro. Iloprost--a stable analogue of prostacyclin (10 microg/kg i.v.) and SIN-1 (NO-donor) at a dose of 2 mg/kg/min i.v induced a significant improvement of deformability of erythrocytes ex vivo. Improvements of deformability by these two compounds were also evident in vitro when they were applied at a range of concentrations of 1 microM and 3 microM, respectively. Cyclooxygenase (indomethacin 20 mg.kg i.v.) and nitric oxide synthase (L-NAME 10 mg/kg i.v.) inhibitors while worsening deformability ex vivo, they did not affect (3 mM and 10 microM, respectively) rheological functions of erythrocytes in vitro. Aggravating effects of these inhibitors on erythrocyte deformability ex vivo were reversed by prostacyclin and nitric oxide supplemented exogenously. Aspirin at a low (1 mg/kg i.v.) and high dose (50 mg/kg i.v.), contrary to indomethacin and L-NAME, aggravated erythrocyte deformability either ex vivo or in vitro. It is concluded that autocrine function of vascular endothelium plays an important role in regulation of rheology of red blood cells in flowing blood. The mechanism of this phenomenon is unclear but some possible explanations are discussed. In addition, in our experiments aspirin revealed unique erythrocyte damaging properties, possibly independent of inhibition of cyclooxygenase, but related to a direct protein acetylation.

Topics: Animals; Endothelium, Vascular; Enzyme Inhibitors; Epoprostenol; Erythrocyte Deformability; Iloprost; Male; Molsidomine; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Rats; Rats, Wistar

Nitric oxide and prostacyclin are endothelial-derived vasodilators which inhibit platelet aggregation in a synergistic manner. Experiments were designed to examine whether 3-morpholino-sydnonimine (SIN-1) and iloprost have synergistic cardioprotective actions and whether their effects on infarct size are related to inhibition of platelet aggregation. Anaesthetized rabbits (n = 9-10 per group) were subject to 40 min myocardial ischaemia followed by 3 h reperfusion. Infarct size (percentage of area at risk) was not altered significantly by 3 microg kg(-1) min(-1) SIN-1 (29.7 +/- 1.9%), but was reduced by 0.03 microg kg(-1) min(-1) iloprost (24.6 +/- 1.6%) and to a greater extent by the combination of SIN-1 and iloprost (18.8 +/- 1.7%), compared to controls (33.6 +/- 4.7%). In control rabbits, there were reductions in the ex vivo aggregation of platelets in response to ADP or collagen after ischaemia and reperfusion. SIN-1 and iloprost caused some alterations in platelet responses, but combined administration of both drugs did not produce greater effects. Although the reduction in myocardial infarct size was greatest with both drugs, this did not appear to be a synergistic interaction and was not dependent on the effects of the drugs on haemodynamics or platelet aggregation.

Topics: Animals; Arrhythmias, Cardiac; Creatine Kinase; Drug Synergism; Electrocardiography; Hemodynamics; Iloprost; Male; Molsidomine; Myocardial Infarction; Platelet Aggregation; Rabbits

Although many diseases of the heart and circulatory system have been linked with insufficient deformability and increased aggregability of red blood cells, there are only a few drugs which can modulate these biological functions of erythrocytes. Here, we show evidences that iloprost, stable prostacyclin analogue and SIN-1, active metabolite of molsidomine which spontaneously releases NO, may be sufficient pharmacological tools for modulating red blood cell deformability and aggregability. Deformability of red blood cells was measured by shear stress laser diffractometer (Rheodyn SSD) and expressed in percent of red blood cell deformability index (DI). MA-1 (Myrenne) erythrocyte aggregometer was used for photometric measurements of aggregability in arbitrary units (MEA) of mean extent of aggregation. Experiments were carried out on rats ex vivo and in vitro using whole rat blood or isolated erythrocytes. Ex vivo SIN-1 (infusion 2 mg/kg/min i.v.) and iloprost (bolus injection 10 microg/kg i.v.) significantly improved erythrocyte deformability and aggregability at 5-15 min after administration. L-NAME (10 mg/kg i.v.)- inhibitor of nitric oxide synthase, and aspirin (1 mg/kg i.v.) caused worsening of deformability of erythrocytes in experiments ex vivo. Studies in vitro also revealed improvement of red blood cell deformability and aggregability by SIN-1 (3 microM, 15 min incubation at 22 degrees C) or iloprost (1 microM, 15 min incubation at 22 degrees C) and this phenomenon appeared not only in whole blood but also in isolated red cells. It is concluded that NO- and prostacyclin-induced improvement of red blood cell deformability and aggregability results from direct action of these compounds on erythrocytes. NO-donors and iloprost could be useful in the treatment of disorders of blood fluidity.

Topics: Animals; Aspirin; Drug Interactions; Enzyme Inhibitors; Epoprostenol; Erythrocyte Aggregation; Erythrocyte Deformability; Iloprost; In Vitro Techniques; Male; Molsidomine; NG-Nitroarginine Methyl Ester; Nitric Oxide; Platelet Aggregation Inhibitors; Rats; Rats, Wistar

Vascular endothelial cells respond to external stimuli by altering the secretion of several bioactive molecules, including von Willebrand factor (vWf), prostacyclin (PGI2) and nitric oxide (NO). The release of all three molecules is regulated by a rise in cytosolic calcium ([Ca2+]i). In the present study we investigated whether cAMP-dependent signaling provides differential regulation of these effector systems by modulating the effect of [Ca2+]i in cultured human endothelial cells. The stable PGI2 analog iloprost, like other cAMP-raising agents (forskolin and adenosine), caused an acute dose-dependent increase in vWf release and potentiated the secretory response to thrombin. In contrast, iloprost, forskolin and adenosine failed to induce PGI2 release and inhibit thrombin-induced release. Our findings indicate cAMP-raising agents have opposite effects on [Ca2+]i-mediated vWf secretion and PGI2 release. PGI2 may potentiate vWf release and inhibit its own release in an autocrine manner.

Topics: Adenosine; Cells, Cultured; Colforsin; Cyclic AMP; Endothelium, Vascular; Epoprostenol; Exocytosis; Humans; Iloprost; Molsidomine; Nitric Oxide; Nitroprusside; Thrombin; von Willebrand Factor

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 hyperpolariza

Topics: Animals; Apamin; Biological Factors; Charybdotoxin; Endothelium, Vascular; Hepatic Artery; Iloprost; In Vitro Techniques; Molsidomine; Muscle Relaxation; Muscle, Smooth, Vascular; Nitric Oxide; Potassium Channel Blockers; Potassium Chloride; Rats; Rats, Sprague-Dawley; Vasodilator Agents

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.

Topics: 1-Methyl-3-isobutylxanthine; 8-Bromo Cyclic Adenosine Monophosphate; Angiotensin II; Animals; Bradykinin; Cardiomegaly; Cells, Cultured; Coculture Techniques; Cyclic GMP; Endothelium, Vascular; Heart; Iloprost; Indomethacin; Male; Molsidomine; Myocardium; Nitric Oxide; Nitric Oxide Donors; Nitroprusside; omega-N-Methylarginine; Phenylalanine; Protein Biosynthesis; Rats; Rats, Sprague-Dawley

Phosphorylation of rap 1b in human platelets correlates with both an upward shift of the protein on sodium dodecyl sulfate polyacrylamide gels and the translocation of the phosphorylated protein to the cytosolic fraction of platelets. We reported that this phenomenon occurs in platelets in response to agents that stimulate adenylate cyclase and thereby activate the cyclic AMP-dependent protein kinase. We now have evidence that phosphorylation of rap1b in platelets is also induced by nitric oxide generating compounds through stimulation of guanylate cyclase and activation of the cyclic GMP-dependent protein kinase. We observed time-dependent phosphorylation of rap1b and dose-dependent inhibition of collagen-stimulated aggregation in washed platelets incubated with S-nitroso serum albumin. In the presence of a combination of iloprost and 3-morpholinosydnonimine, when both PKA and PKG are activated, phosphorylation of rap1b increased synergistically to a level three times higher than the sum of their individual actions.

Topics: Blood Platelets; Electrophoresis, Polyacrylamide Gel; GTP-Binding Proteins; Humans; Iloprost; Kinetics; Molsidomine; Nitric Oxide; Penicillamine; Phosphoproteins; Phosphorylation; Platelet Aggregation; Platelet Aggregation Inhibitors; rap GTP-Binding Proteins; S-Nitroso-N-Acetylpenicillamine

Topics: Animals; Arginine; Aspirin; Blood Pressure; Cats; Epoprostenol; Extracorporeal Circulation; Fibrinolysis; Heparitin Sulfate; Iloprost; Infusions, Intravenous; Injections, Intravenous; Molsidomine; Nitric Oxide; Nitroarginine; Platelet Aggregation; Streptokinase; Thrombosis; Vasodilator Agents

Human platelets suspended in plasma or buffer were incubated with low concentrations of the nitric oxide (NO)-donor 3-morpholino-syndnonime (SIN-1; 100 nM to 1 microM) and the stable prostacyclin analogue iloprost (50 or 100 pM) and analyzed for cyclic nucleotide levels and protein phosphorylation. SIN-1 and iloprost synergistically stimulated the phosphorylation of rap1B and the 50 kDa vasodilator-stimulated phosphoprotein. SIN-1 stimulated platelet cyclic GMP and cAMP-levels and enhanced the increase in cyclic AMP elicited by iloprost. It was found that the mechanism underlying the synergistic phosphorylation of the 50 kDa protein and rap1B was different: synergistic phosphorylation of the 50 kDa protein seemed to be mediated by activation of both protein kinases A and G, whereas the synergistic rap1B phosphorylation could be attributed entirely to activation of protein kinase A. Measurement of rap1B phosphorylation might be a useful tool to monitor the action of systemically applied prostacyclin-analogues and nitrovasodilators in pharmacological studies.

Topics: Autoradiography; Blood Platelets; Blotting, Western; Cells, Cultured; Cyclic AMP; Cyclic GMP; Drug Synergism; GTP-Binding Proteins; Humans; Iloprost; Molsidomine; Nitric Oxide; Phosphorylation; Platelet Aggregation Inhibitors; rap GTP-Binding Proteins

When whole blood is stirred there is a "spontaneous" platelet aggregation (SPA) which is presumed to be caused by proaggregatory factors released from platelets and other blood cells. Adding streptokinase (SK) to stirred whole blood frequently increases the rate and extent of the platelet aggregation that occurs; this is likely to be via immune complex formation between SK and natural anti-SK antibodies leading to increased release of pro-aggregatory factors. In this investigation we have examined the effects of several inhibitors and antagonists in an attempt to identify the proaggregatory factors that contribute to both SPA and SK-induced aggregation (SKA) and to evaluate different means of inhibiting both processes. The effects of the inhibitors/antagonists were determined in vitro after adding them to citrated whole blood obtained from healthy volunteers. Platelet aggregation was measured using a platelet counting technique. Inhibition of both SPA and SKA by apyrase and by FPL 66096 (a P2T receptor antagonist) demonstrated the involvement of ADP in both processes. Inhibition by chlorpromazine indicated that the most likely source of the ADP is red cells. The effects of sulotroban (a TXA2 antagonist) indicated involvement of TXA2 in SKA but not in SPA. The lack of effect of specific antagonists at S2, alpha 2 and PAF receptors suggested lack of involvement of serotonin, catecholamines and platelet-activating factor in either SPA or SKA. Both SPA and SKA were potently inhibited by low concentrations of iloprost (a PGI2 analogue), but a high concentration of SIN-1 (a NO donor) was much less effective.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adenosine Diphosphate; Amino Acid Sequence; Hirudins; Humans; Iloprost; Magnesium Chloride; Molecular Sequence Data; Molsidomine; Platelet Aggregation; Platelet Aggregation Inhibitors; Reference Values; Streptokinase; Thromboxane A2

The molecular mechanism of the synergistic platelet inhibition by activators of adenylate cyclase and guanylate cyclase in human platelets was investigated. The adenylate cyclase activators iloprost and prostaglandin E1 and the guanylate cyclase activator 3-morpholino-syndnonimine (SIN-1) dose-dependently inhibited thrombin-induced aggregation of washed human platelets. Furthermore, SIN-1 at a concentration inhibiting platelet aggregation by only 10% shifted the IC50 values of iloprost and prostaglandin E1 by one order of magnitude to the left, indicating a synergistic action of adenylate cyclase and guanylate cyclase activators. Iloprost and prostaglandin E1 dose-dependently elevated platelet cAMP without a significant influence on cGMP. In contrast, the platelet cGMP level was dose-dependently elevated by SIN-1. In addiiton, SIN-1 markedly increased cAMP level induced by low concentrations of adenylate cyclase activators (0.1-0.3 nM iloprost or 10-150 nM prostaglandin E1). In contrast, the rise in cAMP induced by higher adenylate cyclase activator concentrations (3 nM iloprost or 30 microM prostaglandin E1) was significantly reduced in the presence of SIN-1. The same biphasic mode of action of SIN-1 was observed with forskolin, an adenylate cyclase stimulator acting receptor independently, indicating a prostacyclin-receptor independent mechanism. The cAMP elevating effect of SIN-1 in the presence of low prostanoid concentrations was completely abolished by piroximone, a selective inhibitor of phosphodiesterase type III. Therefore, the inhibition of phosphodiesterase III by cGMP seems to be the mechanism for the elevation of cAMP levels by SIN-1 in the presence of low concentration of adenylate cyclase activators in human platelets.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Adenylyl Cyclases; Alprostadil; Blood Platelets; Cyclic AMP; Cyclic GMP; Drug Synergism; Enzyme Activation; Guanylate Cyclase; Humans; Iloprost; In Vitro Techniques; Molsidomine; Nitric Oxide; Platelet Aggregation; Platelet Aggregation Inhibitors

The interaction of three antiplatelet drugs was studied in vitro: aspirin, an inhibitor of the cyclooxygenase pathway of platelet activation; iloprost, a stable analog of prostacyclin that increases platelet cAMP; and the nitrix oxide donors SIN-1 and sodium nitroprusside (SNP), which both raise platelet cGMP. Platelet adhesion and aggregation evoked by collagen/ADP were measured in anticoagulated blood under physiological flow conditions using the new Thrombostat. Aggregation was also measured in platelet-rich plasma (PRP) upon stimulation by a low (2.5 micrograms/ml) and high (20 micrograms/ml) dose of collagen, ADP, or thrombin-receptor activating peptide (TRAP). We found a synergism between iloprost and aspirin in inhibiting platelet adhesion/aggregation in flowing blood and aggregation of PRP stimulated by collagen. The mean inhibitory concentrations (IC50) of iloprost in the presence of aspirin were much lower (0.7 nM and 0.5 nM in flowing blood and low-dose collagen-stimulated PRP, respectively) than in the absence of aspirin (3 and 3.6 nM, respectively). Synergism between SIN-1 and aspirin was observed in inhibiting platelet activation in flowing blood but was much less pronounced in inhibiting collagen-induced aggregation of PRP. SIN-1/SNP and iloprost synergistically inhibited the aggregation of PRP induced by collagen as well as platelet adhesion/aggregation in blood. We found that two protein substrates of cAMP- and cGMP-dependent protein kinases, rap1B and a 50 kD protein, were associated with the functional synergism between SIN-1 and iloprost and were synergistically phosphorylated by platelet treatment with both iloprost and SIN-1. Platelet inhibition by SIN-1, iloprost, and aspirin was synergistic when measured in blood. In contrast, only additive effects of SIN-1 and iloprost were observed when platelet aggregation was measured in aspirin-treated PRP stimulated by ADP, TRAP, or collagen. Our study defines the basis for a more effective antiplatelet therapy using a combination of cGMP- and cAMP-elevating and cyclooxygenase-inhibiting drugs. The results also emphasize the importance of using various methods for the evaluation of antiplatelet drugs.

Topics: Adenosine Triphosphate; Aspirin; Blood Platelets; Cyclic AMP; Cyclic GMP; Drug Interactions; Humans; Iloprost; In Vitro Techniques; Iodine Radioisotopes; Molsidomine; Nitric Oxide; Nitroprusside; Phosphorylation; Platelet Activation; Platelet Adhesiveness; Platelet Aggregation; Platelet Aggregation Inhibitors

The aim of our study was to evaluate the platelet antiaggregatory and hemodynamic effects of the stable prostacyclin analog iloprost and the NO-donor SIN-1, an active metabolite of molsidomine. The number of circulating platelets was determined in anesthetized male Wistar rats as a measure of in vivo platelet aggregation. Platelet count decreased from 648 +/- 25 to 476 +/- 15 x 10(3) platelets/microliter and from 578 +/- 36 to 411 +/- 40 (mean +/- SEM) in response to two repetitive injections of collagen (70 micrograms/kg body weight). Treatment with SIN-1 bolus injections (0.3 or 1 mg/kg bw) and/or continuous i.v. infusion of iloprost (0.2 or 0.4 micrograms/kg bw/min) was initiated 15 min before the second collagen bolus. As a single agent, SIN-1 did not influence platelet count. Iloprost at 0.2 micrograms/kg/min reduced platelet aggregation (PA) by 15.5%, and at 0.4 micrograms/kg/min by 27.1% (p = n.s.). When iloprost (0.2 micrograms/kg) and SIN-1 (0.3 mg/kg) were administered simultaneously, PA was suppressed by 56.2%, iloprost at 0.4 micrograms/kg/min and SIN-1 at 0.3 mg/kg were even more effective and inhibited PA synergistically by 64.9% (p < 0.05). A statistically significant decrease in mean arterial blood pressure (MABP) was seen in response to all SIN-1 and iloprost groups. However, the vasorelaxant effect of both agents given simultaneously was not synergistic but less than additive. In conclusion, iloprost and SIN 1 exert synergistic platelet inhibitory effects in vivo. In contrast, the decrease in MABP is less then additive. These results are of major interest for the therapeutic regimen with NO-donors (nitrovasodilators).

Topics: Adenylyl Cyclase Inhibitors; Animals; Antihypertensive Agents; Blood Pressure; Drug Synergism; Enzyme Activation; Guanylate Cyclase; Iloprost; Male; Molsidomine; Nitric Oxide; Platelet Aggregation; Platelet Aggregation Inhibitors; Rats; Rats, Wistar; Signal Transduction

This study was designed to determine vasodilator activities of two endothelium-derived relaxing factors: prostacyclin (PGI2) and nitric oxide (NO) in human umbilical arteries. Isolated vessel segments were contracted by submaximal concentrations of serotonin and bradykinin. These contractions were enhanced after inhibition of prostaglandin formation by the cyclooxygenase inhibitor indomethacin and after removal of the endothelium, both resulting in a pronounced decrease in PGI2 formation. Contractions remained unchanged after treatment of the vessels with nitro-L-arginine, a selective inhibitor of endogenous NO biosynthesis. The efficacy of inhibition of NO biosynthesis was established by a more than 60% reduction in cyclic GMP accumulation. Even inhibition of stimulated NO formation by histamine did not change vascular tone. These data suggest that PGI2 rather than NO is an endothelium-derived relaxing factor in human umbilical arteries.

Topics: Arginine; Bradykinin; Cyclic GMP; Epoprostenol; Female; Histamine; Humans; Iloprost; In Vitro Techniques; Indomethacin; Molsidomine; Muscle Contraction; Nitric Oxide; Nitroarginine; Serotonin; Umbilical Arteries; Vasodilation

We investigated the possible involvement of reduced nitric oxide (NO) formation in development of nitrate tolerance in an intact organ circulation. NO formation was measured spectrophotometrically on-line in the coronary effluent of Langendorff hearts of rabbits. Short-term (3 min) infusion of glyceryl trinitrate (GTN, 40 microM) or a sydnonimine (SIN-1, 2.3 microM), the active metabolite of molsidomine, into the coronary inflow tract resulted in a decrease in coronary vascular resistance and NO release into the coronary effluent. Pretreatment with 250 microM GTN for 30 min resulted in considerably reduced NO formation and coronary vasodilation, whereas NO release and coronary vasodilation subsequent to SIN-1 remained unchanged. In hearts pretreated with 250 microM SIN-1 for 30 min, there was no effect on GTN- or SIN-1-induced vasodilation and NO release. Studies of cyclic GMP formation in rat lung fibroblasts further indicated that GTN bioconversion rather than desensitization of the soluble guanylate cyclase is involved in GTN tolerance. These data suggest metabolic, endothelium-independent NO release from GTN during passage through the coronary circulation. This NO release is reduced in nitrate-tolerant cells and appears to be the major cause of nitrate tolerance in intact circulatory systems.

Topics: Animals; Bradykinin; Cell Line; Coronary Vessels; Cyclic GMP; Drug Tolerance; Fibroblasts; Heart; Iloprost; Lung; Molsidomine; Myocardium; Nitrates; Nitric Oxide; Nitroglycerin; Rabbits; Rats; Vasodilator Agents

1. The interactions between carbenoxolone and nitric oxide (NO) were examined by investigating their effects on human platelet aggregation, on rat aortic strips precontracted by phenylephrine and on protection of rat gastric mucosa against ethanol-induced injury. 2. Carbenoxolone (100-300 microM) caused a significant and concentration-dependent potentiation of rat peritoneal neutrophil (RPN)- 3-morpholino-syndnonimine (SIN-1)- or iloprost-induced inhibition of platelet aggregation. Higher concentrations (500 microM) of carbenoxolone alone markedly inhibited platelet aggregation. Pretreatment with carbenoxolone (100-300 microM) antagonized the reversal of the RPN- or SIN-1-induced antiaggregatory effect by oxyhaemoglobin (10 microM). 3. Rat aortic strips with intact endothelium precontracted by phenylephrine (0.1-0.3 microM) were relaxed by carbenoxolone (100-300 microM) in a concentration-dependent manner. Relaxations were abolished by mechanical removal of the endothelium or by incubation with methylene blue (10 microM) or NG-nitro-L-arginine (L-NNA, 100 microM). Sodium nitroprusside (10 nM)-induced relaxations of endothelium-denuded rat aortic strips were potentiated by carbenoxolone (100 microM). . The carbenoxolone (200 mg kg-1, p.o.)-induced gastroprotection against ethanol was antagonized by L-NNA (5-40 mg kg-1) in a dose-dependent manner. Pretreatment of rats with indomethacin (10 mg kg-1, s.c.) increased the effect of L-NNA. 5. The results suggest that the activity of carbenoxolone in the experimental systems tested is due to phosphodiesterase inhibition, although radical scavenging properties of the drug could contribute to some of the effects observed. In the rat gastric mucosa both increased prostaglandin levels and effects on the NO system could contribute to the protective action of carbenoxolone.

Topics: Animals; Aorta; Arginine; Carbenoxolone; Gastric Mucosa; Humans; Iloprost; In Vitro Techniques; Male; Methylene Blue; Molsidomine; Muscle Relaxation; Muscle Tonus; Neutrophils; Nitric Oxide; Nitroarginine; Nitroprusside; Oxyhemoglobins; Rats; Rats, Inbred Strains; Stomach Ulcer; Vasodilator Agents

The release of NO from SIN-1, the active metabolite of molsidomine, was measured in vitro in Langendorff-perfused rabbit hearts. NO in the coronary effluent was determined on-line using the oxyhemoglobin technique. Left ventricular and coronary perfusion pressure were also recorded continuously. Glyceryl trinitrate and iloprost were used as reference compounds. Infusion of SIN-1 or glyceryl trinitrate into the coronary inflow resulted in a significant and dose-dependent NO release. An apparently identical response was seen when SIN-1 was infused into the coronary effluent while the response to glyceryl trinitrate was greatly reduced or abolished. The glyceryl trinitrate-induced coronary vasodilation was only slightly diminished in presence of oxyhemoglobin whereas the response to SIN-1 was abolished. This is explained by complete scavenging of NO by oxyhemoglobin within the vessel lumen. In isolated porcine aortic endothelial cells, SIN-1 induced a significant and dose-dependent increase in cyclic GMP, whereas glyceryl trinitrate was ineffective. This would argue against biotransformation of glyceryl trinitrate to NO by endothelial cells. Finally, glyceryl trinitrate-tolerant heart preparations exhibited a considerably reduced or even undetectable release of NO, whereas the response to SIN-1 was unchanged.

Topics: Animals; Cells, Cultured; Coronary Circulation; Coronary Vessels; Cyclic GMP; Dose-Response Relationship, Drug; Endothelium, Vascular; Enzyme Activation; Iloprost; Molsidomine; Nitric Oxide; Nitroglycerin; Oxyhemoglobins; Rabbits; Vasodilator Agents