Synthesis of thromboxane B2 and prostaglandins by bovine gastric mucosal microsomes

The use of ginger (Zingiber officinale Rosc.) as a potential anti-inflammatory and antithrombotic agent

The effect of an aqueous extract of ginger (Zingiber officinale) on serum cholesterol and triglyceride levels as well as platelet thromboxane-B(2) and prostaglandin-E(2) production was examined. A raw aqueous extract of ginger was administered daily for a period of 4 weeks, either orally or intraperitoneally (IP) to rats. Fasting blood serum was investigated for thromboxane-B(2), prostaglandin-E(2), cholesterol and triglycerides. A low dose of ginger (50 mg/kg) administered either orally or IP did not produce any significant reduction in the serum thromboxane-B(2) levels when compared to saline-treated animals. However, ginger administered orally caused significant changes in the serum PGE(2) at this dose. High doses of ginger (500 mg/kg) were significantly effective in lowering serum PGE(2) when given either orally or IP. However, TXB(2) levels were significantly lower in rats given 500 mg/kg ginger orally but not IP. A significant reduction in serum cholesterol was observed when a higher dose of ginger (500 mg/kg) was administered. At a low dose of ginger (50 mg/kg), a significant reduction in the serum cholesterol was observed only when ginger was administered IP. No significant changes in serum triglyceride levels were observed upon administration of either the low or high dose of ginger. These results suggest that ginger could be used as an cholesterol-lowering, antithrombotic and anti-inflammatory agent.

Role of thromboxane A2 in healing of gastric ulcers in rats

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

Mechanism by which garlic (Allium sativum) inhibits cyclooxygenase activity. Effect of raw versus boiled garlic extract on the synthesis of prostanoids

We have studied the effect of aqueous extract of raw garlic and boiled garlic on cyclooxygenase activity in rabbit tissues. Raw garlic inhibited cyclooxygenase activity non-competitively and irreversibly. A dose-dependent inhibition of cyclooxygenase activity was observed in tissues treated with raw garlic. The garlic concentrations required for 50% inhibition of platelets, lung and vascular aortic cyclooxygenase activities of rabbits were 0.35, 1.10 and 0.90 mg, respectively. Cyclooxygenase activity of rabbit platelets was more sensitive to inhibition by raw garlic than the enzyme from blood vessels or lungs. Boiled garlic was found to have little effect on cyclooxygenase activity as compared to raw garlic in these tissues. This may be because the active component of raw garlic is destroyed upon heating. These results indicate that garlic may be beneficial in the prevention of thrombosis if ingested raw rather in a cooked form.

Two year Cottbus reinfarction study with 30 mg aspirin per day

All 701 heart infarction patients admitted to 15 hospitals in the district of Cottbus between 1981 and 1983 were randomly administered 30, 60 or 1000 mg aspirin daily according to the territorial affiliation of their local hospitals. The physical and drug therapy during the 2 years follow-up was highly standardized; deviations--as far as they occurred--were documented. Lower all-cause mortality was statistically demonstrated in patients over 60 and a lower fatal reinfarction rate in patients over 50 as well as in men. Deaths and fatal reinfarctions were significantly lower among patients with a history of angina pectoris, marked ST-depression, with an infarction location except for the posterior wall and among hypercholesterolemic patients. The preventive effect of 60 mg aspirin daily was less than that of 30 mg in comparison to the 1000 mg group. Side effects were seen in 4 and 8% (first and second year), respectively, of the patients administered 30 mg aspirin as opposed to 22 and 17% in patients allocated 1000 mg. We conclude that the optimum dose of aspirin for preventing reinfarctions could be as low as 30 mg daily.

TXB2: cardiostimulant effect that involves beta-adrenoceptor and Na+ + K+-ATPase activity

The biological properties of Thromboxane B2 (TXB2) on isolated rat heart were studied. Its actions were compared with U-46619 a Thromboxane A2 mimetic compound and with isoproterenol. TXB2 induced a concentration-dependent increase in contractility, that was non-competitively antagonized by propranolol. In addition TXB2 inhibited Na+ + K+-ATPase activity at the same concentrations that influenced the mechanical activity. Inhibition of beta-adrenoceptors efficiently blocked the inhibitory action of TXB2 upon Na+ + K+-ATPase-activity. Isoproterenol simulated the positive inotropic effect and the inhibitory action of TXB2 on Na+ + K+-ATPase-activity. In contrast, U-46619 did not alter the basal dF/dt, neither the enzyme activity. The foregoing results suggest that TXB2 resembles the biological effect of catecholamines-inducing stimulation of myocardial contractility and inhibition of Na+ + K+-ATPase activity.

Vasoactive hormones in the renal response to systemic sepsis

The pathophysiology of renal dysfunction in generalized sepsis remains unknown. In this study, 24 hours after surgical induction of peritonitis in 20 volume-loaded sheep, three patterns of renal function were seen. In group 1 (n = 8), glomerular filtration rate (GFR) decreased by 70%, urine volume by 85%, absolute sodium excretion by 95%, and fractional sodium excretion by 83%. Group 2 (n = 4) exhibited similar sodium retention but GFR did not fall. Group 3 (n = 8) showed no change in GFR or urine volume and only minimally reduced sodium excretion. Mean arterial pressure fell 17% in group 1 only; central venous pressure, pulmonary capillary wedge pressure, and plasma volume were maintained at or above presepsis values in all groups. Cardiac index was either increased or unchanged, and renal plasma flow was maintained in all groups; there was thus no hemodynamic evidence to suggest volume contraction. Histologic examination showed only minor changes with no consistent pattern. Renal functional changes correlated with other manifestations of severe sepsis--GFR and sodium retention correlated significantly with increased cardiac index, decreased systemic vascular resistance, pulmonary arterial hypertension, leukopenia, hypoproteinemia, and hypoglycemia. All of these changes were most marked in group 1. In groups 1 and 2, plasma renin activity (PRA) increased and urinary kallikrein excretion decreased. PRA correlated inversely with GFR, urine volume, and sodium excretion; urinary kallikrein excretion correlated positively with urine volume and sodium excretion. Urinary excretion of 6-keto-PGF1 alpha was increased in groups 1 and 2 and correlated inversely with mean arterial pressure in group 1 animals. During sepsis, urinary thromboxane B2 excretion continued at presepsis values in all groups. The results suggest that unusual reciprocal changes in activity of the renin-angiotensin and renal kallikrein-kinin systems may play a role in the renal response to sepsis. PGI2 synthesis is increased and may affect systemic hemodynamics and renal function; the role of thromboxane A2 in this context is unknown.

Inhibitors of prostaglandin dehydrogenase (Ph CL 28A and Ph CK 61A) increase output of prostaglandins from rat isolated lung

1 Two potent inhibitors of prostaglandin dehydrogenase (PGDH), Ph CL 28A and Ph CK 61A, have been investigated for their effects on prostaglandin catabolism and synthesis in rat isolated lung. 2 Both CL 28A (0.3 microM) and CK 61A (0.5 and 5 microM) markedly increased the survival of prostaglandin E2 (PGE2) and PGF2 alpha on a single passage through the pulmonary circulation. 3 Both inhibitors delayed the efflux of 14C following injection of [14C]-PGE2 through the pulmonary circulation. 4 Output of PGE2 and PGF2 alpha but not that of 6-oxo-PGF1 alpha from exogenous arachidonic acid (AA) was increased by CL 28A. 5 Output of all three prostaglandins from endogenous AA stimulated by calcium ionophore A23187 was increased by CL 28A. 6 With CK 61A, output of 6-oxo-PGF1 alpha from exogenous AA was not increased but that from endogenous AA was increased by either concentration of this inhibitor. 7 We conclude that it is possible to increase output of biologically active prostaglandins from lung by preventing their inactivation in situ. 8 The apparent selectivity of PGI2 synthesis from endogenous AA to potentiation by the inhibitors may have therapeutic possibilities.

Microsomal arachidonate bioconversion in rat small intestine during maturation

This study was designed to compare prostaglandin (PG)-synthesizing activity in rat small intestinal microsomes in the 1st, 3rd, and 6th weeks of life and at maturity (greater than 100 days). When an incubation system was used containing 2 mg microsomal protein, 0.5 mM (-)-epinephrine and 1 mM reduced glutathione, the highest PG-synthesizing activity was achieved by incubating 0.157 mM 1-(14)C-arachidonate (specific activity 2.6 X 10(6) dpm/mumol) at 37 degrees C for 5 min. The labeled metabolites were extracted and then separated with high performance liquid chromatography. The four PGs analyzed were 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha), thromboxane B2, prostaglandin F2 alpha and prostaglandin E2. Enzymatic activity for the synthesis of 6-keto-PGF1 alpha was much higher than that for the other PGs. A significant difference was observed for the bioconversion from arachidonate to 6-keto-PGF1 alpha and total PGs among the four age groups of rats. The postweanling groups (week 6 and adult) showed significantly higher enzymatic activities for the syntheses of 6-keto-PGF1 alpha and total PGs than did the preweanling groups (weeks 1 and 3).

Prostaglandin synthesis along the gastrointestinal tract of the rabbit: differences in total synthesis and profile

In the present study we systematically investigated the synthesis of prostaglandins in the mucosa and the muscle layer along the length of the rabbit gut. Homogenates of mucosa and muscle layer were incubated with (14C)-labelled arachidonic acid, and prostaglandin formation was determined using thin-layer chromatography. With respect to total prostaglandin synthesis the highest values in the mucosa were measured in fundus, antrum and colon, whereas the prostaglandin synthesis in the muscle layer was maximal in the small bowel, particularly the ileum. In the mucosa, the prostaglandins E2 and F2a predominated, and there were minor differences along the gastrointestinal tract. In the muscle layer of the stomach, high amounts of 6-keto prostaglandin F1a, the stable degradation product of prostacyclin were produced, while small and large bowel homogenates synthesized mostly F2a. Consistently the prostaglandins A2/B2 were a major product in most locations. In addition, PG E2 catabolism to 15-keto PG E2 and 13,14-dihydro-15-keto PG E2 in the absence of NAD was slow. No significant changes in total prostaglandin synthesis and prostaglandin profile were detected between 24 hrs fasted and normally fed rabbits at any part of the gastrointestinal tract.

Prostaglandin production in cultured gastric mucosal cells: role of cAMP on its modulation

The effect of cAMP on prostaglandin production may depend on cell types. To clarify the relationship between PG and cAMP, we examined arachidonate's effects on PG synthesis and intracellular cAMP accumulation in monolayers of rat gastric mucosal cells. These cells produced PGE2, PGI2 and thromboxaneA2 (TXA2) in amounts of 316 +/- 18, 100 +/- 7 and 30 +/- 5 pg per 10(5) cells in 10 min, respectively, in response to 10 microM arachidonic acid (AA). The production of these PG, however, leveled off subsequently. Cells initially exposed to AA responded poorly to a subsequent stimulation by AA. AA simultaneously stimulated intracellular cAMP accumulation; this stimulatory effect on cAMP production was abolished by the pretreatment with indomethacin. Nevertheless, the pretreatments with dibutyryl cAMP (0.1-5 mM) did not alter the amount of subsequent AA-induced PGE2 production. Furthermore, the preincubation with 1mM isobutyl methyl xanthine also failed to affect PGE2 synthesis, while it increased intracellular cAMP accumulation. Our studies suggest AA stimulates intracellular cAMP formation in cultured gastric mucosal cells, linked with conversion of AA to cyclooxygenase metabolites, AA-induced PG production is limited in these cells, and it seems, however, unlikely that intracellular cAMP modulates AA metabolism to PG.

Diflunisal protects human gastric mucosa against damage by indomethacin

Mild irritants have been shown to protect the rat gastric mucosa from damage by the subsequent administration of necrotizing agents. The purpose of this study was to determine if a low concentration of a salicyclic acid analog (8 mM diflunisal) was capable of protecting human gastric mucosa from the damage induced by topical indomethacin. Healthy young volunteers were studied in three separate experiments in which gastric transmucosal PD was used as an index of mucosal integrity. In study I (10 subjects) 20 mM aspirin and 2 mM indomethacin were shown to induce a significant (P less than 0.025) fall in PD of 15% and 10%, respectively. In study II (10 subjects) 20 mM diflunisal was found to produce no significant fall in PD nor any reduction in gastric juice PGE2. In study III (5 subjects) 8 mM diflunisal, given 15 min before 2 mM indomethacin, prevented the fall in PD caused by indomethacin alone. These studies demonstrate that in humans, 8 mM diflunisal protects the mucosa from injury induced by the subsequent administration of a known damaging agent. It is possible that the mechanism of this protection may be by stimulation of endogenous mucosal prostaglandins.

The effect of prolonged treatment with sulphinpyrazone on thromboxane A2 and prostacyclin in man

We studied the effect of 3 weeks' treatment with 4 x 200 mg of sulphinpyrazone daily (six healthy volunteers) on proaggregatory thromboxane A2 (TxA2) and antiaggregatory prostacyclin (PGI2). Platelet TxA2 production was evaluated by measuring its stable metabolite, immunoreactive thromboxane B2, from serum, and vessel wall PGI2 production by measuring its stable metabolite, immunoreactive 6-keto-prostaglandin F1 alpha in plasma. The TxA2 production (initially 209.0 +/- 27.1 ng/ml, mean +/- s.e. mean) decreased to about 30% from the second day of the treatment onwards, and it recovered in three days after the discontinuation of the treatment. PGI2 (initially 33.6 +/- 3.6 pg/ml) did not change. The shift of the balance between TxA2 and PGI2 to the dominance of antiaggregatory PGI2 during sulphinpyrazone treatment may be involved with the efficacy of the drug in the secondary prevention of myocardial infarction.

Prostaglandin generation from gastroduodenal mucosa: regional and species differences

Regional and species differences in prostaglandin synthesis from gastroduodenal mucosa were assessed radiometrically. In the presence of excess added arachidonic acid substrate, corporal mucosa generated more prostanoid product per DNA than did antral or duodenal mucosa whether the whole homogenate or the microsomal fraction was used as an enzyme source. This appeared to be secondary to variability in cyclooxygenase activity and could not be explained by regional differences in the activity of enzymes competing for arachidonic acid substrate, in free endogenous arachidonic acid levels, in prostaglandin catabolizing activity, or in homogenate inhibitors. The qualitative product profile differed between species but not between regions within a species.

Immunological and non-immunological synthesis and release of prostaglandins and thromboxanes from isolated guinea pig trachea

Specific radioimmunoassays were used to demonstrate the synthesis by the guinea pig trachea of 6-keto PGF1 alpha, TxB2, and PGF2 alpha in addition to PGE2. The rank order of both spontaneous and stimulated release was PGE2 greater than PGF2 alpha greater than 6-keto PGF1 alpha = TxB2. Ovalbumin-induced prostanoid release from sensitized tissue was antigen-specific. The release was unlikely to be secondary consequence of tracheal contraction since incubations with calcium ionophore A23187, at a concentration which produces an equivalent magnitude of contraction of sensitized trachea, did not induce a significant PG or Tx production. In contrast, significantly higher prostanoid synthesis was induced by A23187 in unsensitized than sensitized trachea. Thus sensitization altered the profile of arachidonic acid metabolism evoked by the ionophore.

Metabolites of arachidonic acid formed by human gastrointestinal tissues and their actions on the muscle layers

1. Gas chromatography-mass spectrometry demonstrated the presence of arachidonic acid (AA), 6-keto-prostaglandin F1 alpha and thromboxane B2 (TxB2) in all extracts of homogenized muscle or mucosa from human stomach, terminal ileum or sigmoid colon. Prostaglandin D2 (PGD2), PGE2 or PGF2 alpha were usually found more often in the mucosal extracts. The 12-hydroxy-derivative of AA (12-HETE) was detected in all extracts of the colon but in only some of the other tissues. 2. Most prostanoids tested contracted the longitudinal muscle, the order of potency being U-46619 (an epoxymethano analogue of PGH2) greater than PGE2 greater than PGF2 alpha greater than PGD2; PGI2 usually caused relaxation, whereas its breakdown products or TxB2 had weak and variable effects. 3. U-46619 or, less potently, PGF2 alpha contracted the circular muscle, whereas PGI2 and usually PGE2 caused relaxation. PGD2, 6-keto-PGF1 alpha, 6,15-diketo-PGF1 alpha or TxB2 usually had little or no effect. 4. PGI2 antagonized contractions to some excitatory prostanoids, without greatly affecting contractions to acetylcholine. 5. For both muscle layers there was a gradient in sensitivity to prostanoids along the gastrointestinal tract. The sensitivities were stomach greater than distal ileum greater than sigmoid colon. 6. The results are discussed in relation to gastrointestinal physiology and pathophysiology.

Mechanisms of Forssman-induced bronchospasm and their inhibition

1 The bronchospasm induced in the guinea-pig by the injection of Forssman antiserum was biphasic in nature in both the sublethal and the lethal reaction. 2 The development of both phases of the bronchospasm in the sublethal reaction was dependent upon the presence of the intact complement system and circulating platelets. In the lethal reaction the phase II bronchospasm did not appear to depend on these factors. 3 The compounds used in this study inhibited phase I bronchospasm of the sublethal reaction in the order, methysergide greater than indomethacin greater than aspirin = sulphinpyrazone and phase II in the order, indomethacin greater than sulphinpyrazone greater than aspirin. Methysergide was inactive. 4 Aspirin, indomethacin and sodium salicylate all prevented the inhibitory action of sulphinpyrazone in reducing the phase II bronchospasm of the sublethal reaction in the order, indomethacin greater than sodium salicylate greater than aspirin, when the drugs were administered prior to sulphinpyrazone. 5 The inhibitory action of aspirin on the sulphinpyrazone effect could be prevented by administering sulphinpyrazone before aspirin. All drug-induced inhibitions of sulphinpyrazone by aspirin, indomethacin and sodium salicylate were dose-dependent.

Synthesis of thromboxane B2 and 6-keto-prostaglandin F1 alpha by bovine gastric mucosal and muscle microsomes

Bovine gastric mucosal and muscle microsomes synthesize prostaglandins and thromboxane b/ (TXB2) from aratchidonic acid (AA). TXB2 and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) were the majro products synthesized by pylorus, body, and cardiac region of the gastric mucosa. Gastric muscle mainly synthesized 6-keto-PGF1 alpha. TXB2 and 6-keto-PGF1 alpha synthesis occurs at an appreciable rate from endogenous precursors but more rapidly with added arachidonate. Prostaglandins E2, F2 alpha and D2 were synthesized in smaller amounts under the conditions studied.

Thromboxane B2: a cardiodepressant of isolated rat hearts and inhibitor of sarcolemma Na+ - K+ stimulated ATPase activity

The actions of thromboxane B2 on various parameters of cardiac performance were studied using the isolated perfused rat heart model. In concentrations from 100 pg/ml to 1 microgram/ml TXB2 significantly reduced the total generated myocardial contractile force. These changes were usually associated with an increase in the coronary perfusion pressure indicating an elevated coronary vascular resitance. Significant coronary pressure alterations were seen with TXB2 concentrations between 1 ng/ml and 1 microgram/ml. No significant changes were seen in either the resting tension or heart rate after TXB2 administration. However TXB2 (10 pg/ml to 10 ng/ml,, significantly reduced the amplitude of the electrical activity as observed in R wave changes of the surface electrocardiogram recording. In another series of experiments the action of TXB2 on rat heart sarcolemmal ATPase activity was studied. TXB2 significantly reduced the activity of the MG++ dependent - Na+ - K+ stimulated ATPase (Na+ - K+ ATPase) in these membrane preparations in concentrations from 10 ng/ml to 1 microgram/ml. Kinetic studies demonstrated that TXB2 reduced Vmax and increased the concentration required of ATP, Na+ and K+ for half-maximal enzyme activity. TXB2 did not inhibit either Ca++ or ouabain-induced depression of Na+ - K+ ATPase activity. The activity of either Mg++ or Ca++ - stimulated ATPase was not affected by TXB2. These results suggest possible important actions of TXB2 on rat heart activity which may be related to Na+ - K+ ATPase inhibition.