Thromboxane B2 Production Research Articles

Effect of chloroquine on arachidonic acid pathway in isolated mast cells

Chloroquine (CQ) interacts with the arachidonic acid (AA) pathway in many cells and tissues as a result of phospholipase A2 inhibition. Previously, we reported the inhibitory effect of CQ on stimulated secretion from isolated rat mast cells along with the inhibition of stimulated AA liberation and thromboxane B2 (TXB2) production from membrane phospholipids [1, 2]. In this study we investigated the effect of CQ on prostagiandin D2 (PGD2) generation (a major cyclooxygenase metabolite of arachidonic acid in mast cells) [3], in compound 48/80 stimulated isolated mast cells and evaluated the relationship between AA liberation, PGD2 and TXB2 generation from membrane phospholipids.

Synthesis of [[(benzenesulfonamido)alkyl]phenyl]alkanoic acid derivatives containing pyridyl or imidazolyl groups and their thromboxane A2 receptor antagonistic and thromboxane A2 synthase inhibitory activities.

As part of our search for a dual inhibitor possessing both thromboxane A2 (TXA2) receptor antagonistic and TXA2 synthase inhibitory activities, some [[(benzenesulfonamido)alkyl]phenyl]alkanoic acid derivatives possessing a pyridyl or imidazolyl group were synthesized. Their TXA2 receptor antagonistic and TXA2 synthase inhibitory activities were evaluated in terms of the inhibitory effects on U-46619-induced guinea-pig platelet aggregation and on thromboxane B2 (TXB2) production in human platelets, respectively. It was found that 3-[4-[2-(1-imidazolyl)-1-(4-chlorobenzenesulfonamido)ethyl]phenyl] propionic acid (22a), containing an imidazolyl group, is a well-balanced dual inhibitor having both TXA2 receptor antagonistic activity (IC50 = 0.31 microM) and TXA2 synthase inhibitory activity (IC50 = 0.39 microM).

Platelet Reactivity In Vitro in Relation to Thromboxane in Healthy Pregnancy

There is substantial evidence of increased platelet reactivity in vivo and in vitro during pregnancy. Previous in vitro studies suggest that platelets from pregnant women show increased sensitivity to agonists, the response to which has a thromboxane dependent component. The aim of this study was to determine whether this is due to increased activity of the thromboxane biosynthetic pathway or to increased platelet sensitivity to the effects of thromboxane. During pregnancy, platelets were more sensitive to the pro-aggregatory effects in vitro of the thromboxane mimetic U46619, in whole blood and in platelet rich plasma, compared to those from non-pregnant controls. The difference in extent of U46619-induced platelet aggregation between groups was abolished in the presence of a high concentration of the specific thromboxane antagonist ICI 192605, but not by prior incubation of blood with aspirin. Platelets from pregnant women were significantly less sensitive to inhibition of arachidonic acid induced activation by the thromboxane synthetase inhibitor dazmegrel, but there was no change in platelet cyclic AMP accumulation under these conditions. Arachidonic acid induced platelet thromboxane B2 production was similar in pregnant and non-pregnant subjects. In conclusion, platelets are more sensitive to the activating effects of thromboxane during pregnancy, but there is no change in the intrinsic reactivity of the thromboxane biosynthetic pathway.

Pulmonary Pharmacology of DT-TX 30 SE, a Potent Selective Combined Thromboxane Synthetase Inhibitor and Receptor Antagonist, in Guinea Pigs

A novel chemical compound, DT-TX 30 SE (E-6-(4-(2-(4-chlorobenzenesulphonylamino)-ethyl)phenyl)-6-(3-pyridyl)-hex-5-enoic acid), was studied in various models of guinea pig pulmonary function. The compound was a potent inhibitor (ED50 0.019 mg/kg, i.v.) of bronchospasm induced by the thromboxane receptor agonist U-46619, indicating thromboxane receptor antagonism. At even lower doses (ED50 0.0036 mg/kg, i.v.), it blocked arachidonic acid-induced bronchospasm. Interpretation of the latter results as evidence for additional thromboxane synthetase inhibitory activity was supported by the inhibition of arachidonic acid- or bradykinin-induced thromboxane B2 production in an isolated lung preparation, although prostaglandin E2 and prostaglandin 6-oxo-F1α production measured at the same time were not inhibited. The potency of DT-TX 30 SE was compared with thromboxane receptor antagonists and synthetase inhibitors described in the literature. As a receptor antagonist, DT-TX 30 SE was significantly more potent than BM 13505 and BM 13177 (assessed by antagonism of U-46619-induced bronchospasm), but less potent than SQ 29548, while as a thromboxane synthetase inhibitor, it was significantly more potent than OKY 046 and UK 37248 as assessed by antagonism of arachidonic acid-induced bronchospasm or (OKY 046) inhibition of thromboxane production in isolated lung. The compound was active by the oral route as shown by its ability, at 10 mg/kg, p.o., to significantly reduce the immediate allergic response of sensitized guinea pigs to an ovalbumin aerosol.

Substance P and stress-induced changes in macrophages.

The present paper further links nervous-endocrine-immune systems by describing influences of SP on the immune system, and more specifically, on macrophage function. We have discussed how macrophages are important to immune responses in that much of cellular and humoral responses depend on macrophage function. Macrophages are sensitive to stress in that cold-water stress causes increased cytokine production, either spontaneously (IL-1), or after induction with LPS (IL-6, TNF alpha). Increased cytokine levels (IL-1, IL-6) may induce acute phase reactants in the liver, which is presumably the mechanism operative in the studies indicating increases in acute phase reactants after certain stressors in animals. SP is a likely candidate to affect immune function. Previous data show that macrophages from various species have receptors for and respond to SP in vitro. SP stimulates phagocytic and chemotactic capacity, as well as increased cytokine, PGE2, and thromboxane B2 production. SP is also involved in neurogenic inflammation and is likely to be involved in the pathogenesis of several inflammatory diseases. Present data indicate SP's involvement in macrophage responses to stress. We have shown that stress induced differential SP receptor binding to peritoneal macrophages, although the precise nature of binding differences has not yet been clearly elucidated. Stress also induces more immunoreactive SP in the peritoneal fluid that bathes the peritoneal macrophages. We hypothesize that the two events, altered SP binding and concomitant increased ligand, are causally related. In addition to other correlational data showing concomitant increased SP binding plus ligand concentrations, there is more direct evidence that SP ligand may induce SP receptor expression since the SP antagonist, CP-96,345, prevents the induction of SP receptor mRNA in the staphylococcal toxin A-induced gastroenteritis (C. Pothoulakis and S. E. Leeman, personal communication). Further supporting our notion for a causal relationship we have found the elimination of SP in vivo (via capsaicin pretreatment) reduced SP binding, as has been previously reported. We have also examined the role of SP on stress-induced altered macrophage function in vitro. SP greatly enhanced the LPS-induced macrophage TNF alpha production from stressed animals; in contrast, it produced relatively little effect on macrophages from control animals. Capsaicin pretreatment diminished the enhanced cytokine production in response to stress, such that levels of TNF alpha and IL-6 approximated those of control mice. Taken together, past and present data suggest that (1) stress may initiate, or at least contribute to, an inflammatory response, and that (2) SP is involved in the macrophage stress response. SP has long been known to be involved in inflammatory processes; our data further suggest its role in mediating stress-induced cytokine alterations.

Select dietary fatty acids attenuate cardiopulmonary dysfunction during acute lung injury in pigs.

We examined the effect of substituting linoleic acid (LA) with eicosapentaenoic acid (EPA) and gamma-linolenic acid (gamma-LA), precursors of trienoic and monoenoic eicosanoids, respectively, on acute lung injury (ALI). Three groups (n = 8/group) of pigs were fed enteral diets containing LA (diet A), EPA (diet B), or EPA+gamma-LA (diet C) for 8 days. ALI was then induced with a 0.1 mg/kg bolus of Escherichia coli endotoxin followed by a continuous infusion for 4 h (0.075 mg.kg-1.h-1). Pulmonary arterial and capillary wedge pressures, cardiac index (CI), arterial blood gases, arterial O2 content, and plasma thromboxane B2 (TxB2) were measured. Arterial PO2 decreased at 20 min in animals fed diet A. This change was attenuated with diets B and C. The EPA- and EPA + gamma-LA-enriched diets attenuated the fall in O2 delivery at 20 min, an improvement that was sustained throughout the 4-h study period with the EPA+gamma-LA-enriched diet only. This improvement in O2 delivery was due not only to the improved arterial PO2, but also to the maintenance of CI at 20 min in animals fed diets B and C and throughout the 4-h study period in animals fed diet C. At 4 h, TxB2 increased 10-fold over baseline in animals fed diet A, whereas in animals fed diets B and C the increase was only 3-fold. These decreased TxB2 levels in animals fed diets B and C correlate with an attenuation in the increase in pulmonary vascular resistance that was observed at 20 min after endotoxin infusion in animals fed diet A. These data suggest that specialized enteral diets enriched in EPA+gamma-LA improve gas exchange and O2 delivery, presumably in part through a modification of TxB2 production with a decrease in pulmonary vascular resistance and an increase in CI, during ALI.

The Effect of Selenium Compounds (Selenite, Selenate, Ebselen) on the Production of Thromboxane and Prostacyclin by the Human Term Placenta in Vitro

Selenium not only has an important role in controlling lipid hydroperoxides through glutathione peroxidase (GPX) activity, but also can produce oxidative stress through exposure to selenite. Because levels of lipid hydroperoxides affect the production of thromboxane A2 (TxA2) and prostacyclin (PGI2), selenium compounds may be able to influence the production of these two vasoactive substances. Late-gestation pregnancy reduces the half-life of PGI2; therefore, pregnancy itself may enhance susceptibility to changes in the production of TxA2 and PGI2. The objective of this investigation was to determine if different selenium compounds, selenite, selenate, and ebselen, can influence the human term placental production of thromboxane B2 (TxB2) and 6-keto-prostaglandin F1α (6-keto-PGF1α), the inactive hydrolysis products of TxA2 and PGI2. Although selenate exposure (40 μM 24 hr) increased TxB2 production, and ebselen (an organic selenium compound with GPX activity) exposure (40 μM, 24 hr) decreased both TxB2 and 6-keto-PGF1α production, only selenite had a significant effect on the TxB2/6-keto-PGF1α, ratio. Three exposures to selenite at 6 μM (32 hr) significantly decreased 6-keto-PGF1α production with no effect on TxB2 production or tissue GPX activity. Following two exposures to selenite at 20 and 40 μM (24 hr), TxB2 production was significantly increased, while tissue 6-keto-PGF1α production and tissue GPX activity were significantly decreased. These results indicate that selenite, but not selenate or ebselen, can directly affect the human placenta by producing changes in the TxB2/6-keto-PGF1α ratio, which may be related to increased vasoconstriction and blood coagulation.

Effects of Fish Oil Supplementation on Atherosclerosis in Different Regions of the Aorta of Rabbits with Diet-Induced Hypercholesterolaemia

1. The effects of fish oil supplementation on atherosclerosis in different regions of the aorta in rabbits with diet-induced hypercholesterolaemia were studied. Control and experimental rabbits were fed a 1% cholesterol-enriched diet with or without 10% fish oil supplementation (seven in each group), and were killed after 2 weeks of feeding. The ascending, descending and abdominal aortas as well as the pulmonary artery were harvested for analyses of prostanoid production, malondialdehyde, superoxide dismutase activity and cholesterol levels. The tissues from the other seven rabbits of each group were obtained after 6 weeks of feeding for the identification of atherosclerotic lesions by a Sudan IV stain. 2. The cholesterol-fed rabbits had a significantly higher thromboxane B2 production, a lower 6-keto-prostaglandin1 alpha/thromboxane B2 ratio and a higher malondialdehyde level than the other two groups in the ascending and abdominal aortas as well as the pulmonary artery; this finding paralleled the severity of atherosclerotic lesions. These manifestations were most prominent in the ascending aorta. The fish oil-supplemented rabbits had the most beneficial aortic prostanoid production, attenuated lipid peroxidation and significantly suppressed atherosclerosis. 3. These results suggest that a high-cholesterol diet induces more atherosclerotic lesions, especially on the ascending aorta, in rabbits. A fish oil supplement favours prostanoid production and attenuates lipid peroxidation on all four regions of the great arteries, thus suppressing atherosclerosis in diet-induced hypercholesterolaemic rabbits.

Secretion of Prostaglandins Elicited by Lipopolysaccharide and Ethanol in Cultured Rat Kupffer Cells

Prostaglandins (PGs) released by cultured rat Kupffer cells in response to stimulation with lipopolysaccharide (LPS) or ethanol were extracted from culture media, separated by HPLC and measured by radioimmunoassay. LPS (0.5-5 μg/ml) enhanced. after a 3-4 hrs lag period, the production of PGE2 (7-10 fold by 24 hrs), thromboxane B2 (2-3 fold) and PGD2, PG 6-keto-F1α. PGF2α (20-50% each): This effect was not inhibited by 30 μM aspirin but was reduced by dexamethasone. Ethanol (25-85 mM) gradually increased the release of PGE2 (40-90% by 24 hrs) and other PGs (10-30%), with 30 μM aspirin eliminating this effect. When added together with LPS, ethanol potentiated the endotoxin action. We suggest that LPS causes synthesis of the inducible cyclooxygenase-2 form in Kupffer cells, whereas ethanol exerts its effect via the preexisting cyclooxygenase-1 mainly by increasing the free arachidonic acid content.

Effects of age on the pharmacodynamics of naproxen in the rat.

The pharmacodynamics of naproxen were evaluated in 5- and 24-month-old male Fischer 344 rats. Plasma naproxen concentrations and thromboxane B2 (TxB2) concentrations were measured as a function of time after intravenous administration of 25 mg/kg naproxen. Age-dependent alterations in naproxen pharmacokinetics were attributed to significant reductions in free plasma clearance (CLfree) and free steady-state volume of distribution (VSSfree), suggesting a decline in metabolic activity and naproxen binding to tissue components in aged rats, respectively. The time course of TxB2 production as a function of unbound naproxen concentrations was described by a sigmoid Emax model. Age had no significant effect on the pharmacodynamic parameter Emax, the maximum percent inhibition of TxB2 formation. Age also had no statistically significant effect on EC50, the drug concentration producing 50% of the maximum effect, however, average EC50 values were 35% higher in the aged rats. The duration of TxB2 inhibition was unaffected by age, possibly owing to similar relative decreases in receptor sensitivity (increased EC50) and increases in free naproxen concentrations (decreased free clearance and volume of distribution). Alternatively, the age-related changes in pharmacokinetic parameters were not of sufficient magnitude to produce a significant change in drug response, naproxen, pharmacokinetics, pharmacodynamics, age, rats, thromboxane B2, nonsteroidal anti-inflammatory drugs.

Purified ??-3 fatty acids retard the development of proteinuria in salt-loaded hypertensive rats

To determine whether purified omega-3 and omega-6 fatty acids influence the progression of hypertensive renal failure in salt-loaded stroke-prone spontaneously hypertensive rats (SHRSP) with established hypertension or during the developmental stage of their hypertension. Groups of eight SHRSP aged 1 or 4 months were fed, for 12 weeks, synthetic diets containing 2% sodium (wt:wt) and either 5% olive oil or 4.5% gamma-linolenic acid (omega-6), eicosapentaenoic acid (omega-3) or docosahexaenoic acid (omega-3). Urinary protein excretion and blood pressure were measured after 6, 9 and 12 weeks. The rats were killed and their tissues were collected for fatty acid and eicosanoid analysis. Young rats (aged 1 month) fed diets containing gamma-linolenic acid or olive oil developed marked proteinuria by 9 weeks, whereas no change was observed after 12 weeks in rats fed docosahexaenoic acid or eicosapentaenoic acid. Blood pressure was lower in those fed docosahexaenoic acid or eicosapentaenoic acid than in the gamma-linolenic acid or olive oil groups. Adult rats (aged 4 months) fed the docosahexaenoic acid diet had significantly lower proteinuria than those fed gamma-linolenic acid, eicosapentaenoic acid or olive oil, but there were no differences in blood pressure among the groups. Kidneys from rats fed omega-3 fatty acids had increased levels of docosahexaenoic acid or eicosapentaenoic acid, or both, whereas those from rats fed gamma-linolenic acid and olive oil contained virtually no omega-3 fatty acids. Thromboxane B2 and 12-hydroxyeicosatetraenoic acid production in renal cortex extracts was lowest in rats fed docosahexaenoic acid and eicosapentaenoic acid. Dietary omega-3 fatty acids retard the development of hypertension-induced proteinuria. This may be caused by a favourable influence on fatty acid and eicosanoid metabolism and reduction of blood pressure.

The effects of opioid and α2 adrenergic blockade on non‐steroidal anti‐inflammatory drug analgesia in sheep

The analgesic effects of the non-steroidal anti-inflammatory drugs (NSAIDs) flunixin and dipyrone were assessed in healthy sheep with no pre-existing inflammation, and in sheep with a chronic inflammatory lesion, using a mechanical noxious stimulus. Saline and dexamethasone were given as controls. Blood taken from healthy sheep after NSAID administration was assayed for thromboxane B2 (TxB2) to compare the ability of these drugs to inhibit cyclo-oxygenase. Both flunixin and dipyrone produced a small but statistically significant rise in pain thresholds (18% and 21% of maximum possible effect respectively) in the healthy sheep which peaked at 30 min and had returned to pre-drug values by 2-3 h. In the lame sheep a similar effect occurred but the response was smaller, much more variable and tended to be prolonged. Saline and dexamethasone had no effect on thresholds over 6 h in either group of sheep. The rise in thresholds was prevented by pre-treatment with naloxone (an opioid antagonist) or atipamezole (an alpha 2-adrenergic antagonist) in the healthy sheep. Naloxone and atipamezole had no effect on thresholds when given alone to healthy sheep. Both NSAIDs inhibited the production of TxB2 to a similar extent. These results indicate that central mechanisms may be involved in NSAID analgesia.

The Effects of Short-Term Treatment with the Prostaglandin E1 (PGE1) Analog Misoprostol on Inflammatory Mediator Production in Murine Lupus Nephritis

MRL-lpr/lpr mice spontaneously develop an autoimmune disease with nephritis similar to human systemic lupus erythematosus. In these animals, treatment with E-series prostaglandins ameliorates renal disease and prolongs survival, perhaps by modulating production of cytokines or eicosanoids. To further define the mechanisms of action of E-series prostaglandins in established murine lupus nephritis, we administered the prostaglandin E1 (PGE1) analog misoprostol to 20-week-old MRL-lpr/lpr mice by twice-daily subcutaneous injection. After 2 days of treatment, misoprostol reduced renal cortical interleukin-1β (IL-1β) mRNA levels compared to vehicle-treated controls (0.19 ± 0.06 (misoprostol) vs 0.50 ± 0.04 (vehicle) densitometry units; P < 0.005). A similar reduction in cortical IL-1β mRNA levels was found in left kidneys harvested from MRL-lpr/lpr mice following 2 days of treatment with misoprostol compared to right kidneys harvested from the same animal prior to the first dose of PGE1 analog (0.12 ± .05 (left) vs 0.39 ± 0.18 (right) densitometry units; P < 0.05). This reduction in cortical IL-1β mRNA levels was not associated with alterations in renal production of thromboxane B2, PGE2, or leukotriene B4 or with significant changes in the severity of renal inflammatory cell infiltrates. Timecourse studies indicated that IL-1β mRNA levels were decreased within 24 hr of initiating misoprostol therapy. This reduction in IL-1β mRNA levels was transient because levels were not reduced after 1 week of treatment with the PGE1 analog. Thus, while the beneficial effects of chronic treatment with E-series prostaglandins in MRL-lpr/lpr mice may be mediated by other mechanisms, these data suggest than an important short-term effect of misoprostol in this model may be suppression of renal cortical IL-1β mRNA levels.

Eicosanoid production and levels of newly characterized eicosanoid‐forming enzymes in glomeruli and tubules of rat kidneys

Summary: We examined the production of prostaglandin (P0) E2, 6‐keto PGF1α and thromboxane (Tx) B2, the mass of cyclooxygenase (COX) isoenzymes and the activities of phospholipases A2 and C in glomeruli, cortical tubules and medullary tubules of rat kidneys. Medullary tubules produced significantly greater amounts of PGE2, 6‐keto PGF1α. and TxB2 than glomeruli or cortical tubules. the most abundant eicosanoid in medullary tubules was 6‐keto PGF1α. By contrast, glomeruli and cortical tubules predominantly produced POE2 (glomeruli &gt; cortical tubules). Levels of COX 1 were markedly greater in medullary tubules than in glomeruli or cortical tubules. Glomeruli had significantly greater amounts of COX 1 than cortical tubules. Detectable amounts of COX 2 were not present in the three preparations. the activity of phospholipase (PL) A2 against phosphatidyicholine (PC) was significantly greater in tubules (medullary tubules &gt; cortical tubules) than in glomeruli. By contrast, there was a significant increase in the activity of PLA2 against phosphatidylethanolamine (PE) in glomeruli as compared to tubules (medullary tubules &gt; cortical tubules). the activity of PLC was the Weatest in medullary tubules. Glomeruli had significantly greater activity of PLC than cortical tubules. the order of magnitude for the total activity of the three phospholipases in membranes was medullary tubules&gt; glomeruli&gt; cortical tubules. the total production rate of POE2, 6‐keto PGF1α and TxB2 was in parallel with the amount of COX 1 and the total activity of membranous phospholipases A2 and C in the three preparations. In conclusion, there are differences in the production of PGE2, 6.‐keto PGF1α and TxB2, the ainount of COX 1 and the activities of phospholipases A2 andC among glomeruli, cortical tubules and medullary tubules of rat kidneys; and the different aspects of COX 1 and phospholipases A2 and C have a key role in the control of eicosanoid production in the three preparations.

A possible role for platelet-activating factor in the hydrogen peroxide-induced TXB2 and PGE2 glomerular synthesis.

Hydrogen peroxide stimulates both prostanoid and platelet-activating factor (PAF) biosynthesis in cultured rat mesangial cells and isolated rat glomeruli. The present experiments were designed to try to establish some relationship between prostanoid and PAF synthesis in these renal structures, in the presence of hydrogen peroxide. Cells and glomeruli were incubated with hydrogen peroxide under different experimental conditions, and thromboxane B2 (TXB2), the stable metabolite of thromboxane A2 (TXA2), and prostaglandin E2 (PGE2) concentrations were measured in the supernatants of the cells or glomeruli. Moreover, H2O2-dependent PAF synthesis was measured by high performance liquid chromatography (HPLC) ([3H]acetate incorporation) and radioimmunoassay. H2O2 induced increased TXB2 and PGE2 production in cultured rat mesangial cells and isolated rat glomeruli. This effect was blocked by incubation in the presence of a PAF-receptor antagonist, BN-52021. This antagonist has no intrinsic effect either in basal prostanoid synthesis or in arachidonic acid-stimulated glomerular TXB2 synthesis. Alprazolam, another PAF antagonist, nonchemically related to BN-52021, also completely blocked the H2O2-induced production of TXB2 by isolated rat glomeruli. Moreover, H2O2 was also able to induce an increased [3H]acetate incorporation into a fraction comigrating with a PAF standard in HPLC in isolated glomeruli, and this effect was dependent on the H2O2 concentration tested. Moreover, H2O2 was also able to induce an increased [3H]acetate incorporation and increased synthesis of radioimmunoassayable PAF in cultured mesangial cells. These results suggest that the increased synthesis of PGE2 and TXB2 induced by H2O2 could be dependent on platelet-activating factor production.

Effects of ditazol on the vascular retinal pattern in experimental diabetes in rats.

Platelets from diabetic patients are hypersensitive to aggregating agents. An imbalance in thromboxane/prostacyclin synthesis has been postulated as an antecedent to the development of diabetic retinopathy. We studied 3-month streptozotocin-diabetic rats (SDR) treated with 200 mg/kg/day p.o. of ditazol, an antiplatelet drug that inhibits thromoboxane formation. Thromboxane B2 (TxB2) production was higher and 6-keto-PGF1 alpha synthesis lower in SDR than nondiabetic rats (NDR). In treated animals, ditazol inhibited platelet aggregation by 66%, and TxB2 production by 58%, and increased vascular 6-keto-PGF 1 alpha by 45%. Furthermore, 13% of the retinal surface was covered by peroxidase-labelled vessels in NDR, 2.1% in nontreated SDR, and 8.9% in SDR treated with ditazol. We postulate that ditazol may prevent or reduce diabetic retinopathy.

Clostridium difficilesuppresses colonic vasoactive intestinal peptide associated with altered motility

We investigated whether Clostridium difficile toxin alters colonic tissue levels of vasoactive intestinal peptide (VIP) at the expense of changes in colonic motility in the isolated perfused rabbit left colon. Colonic inflammation was induced by the intracolonic administration of 10−8 M C. difflcile toxin. Strain gauge transducers were sewn onto the serosal surface of the colon to evaluate colonic motility. C. difflcile administration produced histologic changes consistent with epithelial damage. This was associated with an increased production of prostaglandin E2 and thromboxane B2. Tissue levels of VIP but not substance P were significantly reduced. This was associated with an increased number of contractions per minute and an average force of each colonic contraction. These results suggest that tissue levels of VIP are suppressed by C. difflcile and may participate in colonic dysmotility during active inflammation.

Regulation of TXB2and PGE2production by TGF-β1inin vitrosilica dust-exposed rat alveolar macrophage

We investigated the effect of transforming factor factor-β1 (TGF-β1) on thromboxane B2 (TXB2) and prostaglandin E2 (PGE2) production in in vitro silica dust-exposed rat alveolar macrophages (AM). In the presence of 5 μg of anti-TGF-β1 antibodies, TXB2 production decreased, but PGE2 production increased. Addition of 2 ng of TGF-β1 to the culture medium potentiated TXB2 production, but PGE2 production apparently did not change. At 50 ng of TGF-β1, TXB2 production decreased, and PGE2 production varied. Our data suggest that in rat AM: (1) both endogenous and exogenous TGF-β1 regulate TXB2 production; and (2) in the absence of endogenous TGF-β1 the liberation of PGE2 increases; however, exogenous TGF-β1 does not have a regulatory effect on PGE2.

Effects of Ticlopidine Administered to Healthy Volunteers on Platelet Function in Whole Blood

Ticlopidine is thought to be a selective inhibitor of ADP-induced platelet function. Here we have investigated the effects of ticlopidine on platelet function in whole blood induced by ADP and by other platelet agonists. Whole blood was used because it was considered that ADP derived from red cells might act synergistically with other platelet agonists to enhance platelet responses, and that ticlopidine might interfere with this process. Measurements were performed using blood from 16 healthy volunteers before ticlopidine administration, after taking ticlopidine 250 mg daily for 10 days, after taking ticlopidine 250 mg twice daily for a further 10 days, and after 14 days off treatment. Ticlopidine proved to be a very effective inhibitor of the platelet aggregation induced by ADP; it was most effective in enhancing the reversibility of the aggregation response. The drug modestly but significantly reduced streptokinase, adrenaline, collagen, sodium arachidonate, PAF and U46619 - induced platelet aggregation. The drug significantly reduced the extent of the release reaction (14C-5HT release) induced by ADP, streptokinase, PAF, ristocetin and sodium arachidonate, and also reduced the extent of the synergistic 14C-5HT release induced by combinations of ADP and PAF, ADP and adrenaline and PAF and adrenaline. The various inhibitory effects of ticlopidine were evident after treatment with 250 mg daily but were more pronounced after 250 mg twice daily. All values had returned to normal after 14 days off treatment. Ticlopidine had no effect on serum thromboxane B2 production nor on several parameters of coagulation and fibrinolysis. We conclude that ticlopidine is an effective inhibitor of ADP-induced platelet aggregation and also the platelet aggregation and 14C-5HT release induced in whole blood by a number of platelet agonists and combinations of agonists. These latter effects are probably mainly via a selective effect on ADP. The inhibitory effects of the drug are dose-related.

Hirudin - A new anticoagulant in haemodialysis (HD)

Heparin is the most widely used anticoagulant drug for prevention and treatment of thrombosis. However, inhibition of blood coagulation might not fully explain the antithrombic activity of this drug. The present study shows that different heparin preparations (50 nM) completely human platelet aggregation, serotonin release and thromboxane B2 production induced by purified neutrophil-derived cathepsin G (E.C. No. 3.4.21.20). This inhibitory effect was not related to the anticoagulant property of the compounds, since a heparin preparation with an activated active site for antithrombin II was also effective. Heparins inhibited the protease activity of the enzyme over the same range of concentrations. Since the effect of cathepsin G on platelets requires an intact proteolytic active site, the inhibitory effect of the drugs on cathepsin G-induced platelet activation may be explained by a blockade activity. Heparins were also shownto reduce platelet activation induced by cathepsin G released from activated polymorphonuclear leucocytes in mixed cell suspensions. As polymorphonuclear leucocytes might contribute to both arterial and venous thrombosis through platelet activation induced by the release of cathepsin G, this novel property of heparin could be used its antithrombotic efficacy.