The Effects on Platelet Aggregation and Prostanoid Biosynthesis of two Parenteral Analgesics: Ketorolac Tromethamine and Dipyrone

The pharmacokinetics and effects on platelet function of dipyrone (1.0 g; 2.5 g; i. v.) and ketorolac tromethamine (30 mg; i.m.) were studied in a three-way crossover study in twelve healthy subjects. The biosynthesis of thromboxane A2 in clotting whole blood ex vivo as well as collagen-induced platelet aggregation were determined before and up to 48 h after administration. Both prostanoid biosynthesis and platelet aggregation were inhibited by ketorolac tromethamine for a significantly longer period of time than by both doses of dipyrone. The changes in platelet functions correlated well with the serum concentrations of ketorolac or 4-methylaminoantipyrine and 4-aminoantipyrine. Using the sigmoidal Emax model the mean serum concentration (SD) of ketorolac, 4-methylaminoantipyrine and 4-aminoantipyrine inhibiting platelet TXB2 generation by 50% (EC50) in vitro was found to be 0.088 ± 0.031, 1.2 ± 0.3 and 10.2 ± 3.4 µg ml-1, respectively. In conclusion the recovery of platelet function after dipyrone administration is faster as compared to ketorolac tromethamine. This is in line with clinical observations and may be an advantage when these drugs are given as postoperative analgesics at the doses tested.

A novel antagonist of CRTH2 blocks eosinophil release from bone marrow, chemotaxis and respiratory burst

BACKGROUND

Chemoattractant receptor-homologous molecule expressed on Th2 cells (CRTH2) has been revealed to be a novel receptor for prostaglandin (PG) D(2), which is a major mast cell product released during the allergic response. The aim of this study was to analyze the effects of a newly developed small molecule antagonist of CRTH2, Cay10471, on eosinophil function with respect to recruitment, respiratory burst and degranulation.

METHODS

Chemotaxis of guinea pig bone marrow eosinophils and human peripheral blood eosinophils were determined using microBoyden chambers. Eosinophil release from bone marrow was investigated in the in situ perfused guinea pig hind limb preparation. Respiratory burst and degranulation were measured by flow cytometry.

RESULTS

Cay10471 bound with high affinity to recombinant human and guinea pig CRTH2, but not DP, receptors. The antagonist prevented the PGD(2)-induced release of eosinophils from guinea pig bone marrow, and inhibited the chemotaxis of guinea pig bone marrow eosinophils and human peripheral blood eosinophils. Pretreatment with PGD(2) primed eosinophils for chemotaxis towards eotaxin, and this effect was prevented by Cay10471. In contrast, PGD(2) inhibited the C5a-induced up-regulation of CD63, a cellular marker of degranulation, in a Cay10471-sensitive manner. Finally, Cay10471 abolished the respiratory burst of eosinophils upon stimulation by PGD(2).

CONCLUSION

These data further emphasize the importance of CRTH2 in eosinophil function and show that Cay10471 is a highly potent and selective antagonist of PGD(2)-induced eosinophil responses. Cay10471 might hence be a useful compound for the treatment of allergic diseases.

Effect of endotoxin treatment on the expression of cyclooxygenase-2 and prostaglandin synthases in spinal cord, dorsal root ganglia, and skin of rats

Peripheral inflammation causes upregulation of cyclooxygenase in the spinal cord and subsequent increase in prostaglandin biosynthesis. However, prostaglandin synthases, which are downstream of cyclooxygenase control the type of prostaglandin that is formed predominantly. Since there is little known about the regulation of prostaglandin synthases, the present study was conducted in order to determine the effect of endotoxin treatment on the expression of messenger RNA encoding interleukin 1beta, cyclooxygenase-2, and prostaglandin synthases mediating the formation of prostaglandin E(2) (membrane bound prostaglandin E synthase) and prostaglandin D(2) (lipocalin prostaglandin D synthase) in spinal cord, dorsal root ganglia and skin of rats. Endotoxin (2 mg/kg i.p.) induced the expression of interleukin-1beta, cyclooxygenase-2, and membrane bound prostaglandin E synthase messenger RNA in spinal cord, dorsal root ganglia, and skin as determined by reverse transcription polymerase chain reaction. In contrast, basal expression of lipocalin prostaglandin D synthase messenger RNA in spinal cord and dorsal root ganglia was not significantly altered by endotoxin. Dexamethasone (1 mg/kg s.c. at -18 h and -1 h) attenuated the effect endotoxin on the expression of interleukin-1beta, cyclooxygenase-2, and membrane bound prostaglandin E synthase messenger RNA in all tissues investigated, but did not significantly influence expression of lipocalin prostaglandin D synthase mRNA in spinal cord and dorsal root ganglia. In situ hybridisation histochemistry showed endotoxin-induced expression of cyclooxygenase-2 and membrane bound prostaglandin E synthase messenger RNA throughout gray and white matter of spinal cord sections. In dorsal root ganglia, expression of membrane bound prostaglandin E synthase seemed primarily located to non-neuronal cells, while cyclooxygenase-2 messenger RNA was not detectable. The results show that the immune response elicited by endotoxin induced cyclooxygenase-2 and membrane bound prostaglandin E synthase, but not lipocalin prostaglandin D synthase messenger RNA in spinal cord and dorsal root ganglia of rats. The distribution of cyclooxygenase-2 and membrane bound prostaglandin E synthase messenger RNA expressing cells suggests major involvement of non-neuronal cells in spinal prostaglandin biosynthesis. Determination of the regulation of enzymes downstream of cyclooxygenase at the messenger RNA level may represent a valuable tool to investigate effects of analgesic/anti-inflammatory drugs on the regulation of spinal prostaglandin biosynthesis.

Ketoprofen-induced cyclooxygenase inhibition in renal medulla and platelets of rats treated with caffeine

It has been suggested that caffeine can augment analgesic activity and aggravate side effects of nonsteroidal anti-inflammatory drugs (NSAIDs). The aim of the present study was to investigate a possible interaction between ketoprofen and caffeine on prostaglandin (PG) biosynthesis and cyclooxygenase (COX) mRNA expression in the rat renal medulla ex vivo. Treatment of rats with ketoprofen (60 min before) resulted in a dose-dependent (estimated ID(50) 0.3 mg/kg p.o.) reduction of PGE(2) biosynthesis in renal medulla ex vivo. Ketoprofen (0.3 mg/kg)-induced inhibition of PGE(2) biosynthesis was stable between 30 and 180 min and still detectable 300 min after drug administration. Caffeine (10 mg/kg) did not cause a detectable effect on its own, nor did it significantly affect ketoprofen-induced inhibition of renal medullary PGE(2) biosynthesis. Similar results were obtained with repeated daily drug administration for 1 week: there was no significant effect of caffeine on ketoprofen-induced inhibition of renal medullary PGE(2) biosynthesis. The absence of significant caffeine effects on ketoprofen-induced inhibition of renal medullary PGE(2) biosynthesis was paralleled by experiments showing no significant effect of caffeine on ketoprofen-induced inhibition of platelet thromboxane (TX)B(2) biosynthesis. Additional experiments showed increased COX-2 mRNA expression in the renal medulla 60 min after ketoprofen administration, that was not significantly influenced by concomitant caffeine treatment. Treatment of rats with ketoprofen for 1 week had no significant effects on COX-2 mRNA expression. The present results show that ketoprofen caused inhibition of PGE(2) biosynthesis in the rat renal medulla ex vivo with a potency similar to that reported for in vivo models suggesting that the ex vivo approach is a valid model to test a possible interference of caffeine with ketoprofen-induced COX inhibition. The absence of detectable effects of caffeine on time course or magnitude of ketoprofen-induced suppression of PGE(2) biosynthesis in this model indicates, therefore, that possible adverse actions of co-administered caffeine on renal function are not related to interference with renal COX inhibition.

Sodium salicylate enhances the expression of cyclooxygenase-2 in endotoxin-stimulated human mononuclear cells

The effects of salicylate on the expression of cyclooxygenases, and on prostaglandin E(2) biosynthesis were examined in human peripheral blood mononuclear cells. Peripheral blood mononuclear cells were incubated in the presence of endotoxin, which induced expression of cyclooxygenase-2 protein, and caused a time-dependent increase of immunoreactive prostaglandin E(2) in the supernatant. The cycooxygenase-2 selective inhibitor N-(2-cyclohexyloxy-4-nitrophenyl)methanesulfonamide (NS-398, 1 microM) suppressed the endotoxin-induced increase of prostaglandin E(2), without significantly affecting the expression of cyclooxygenase-1 or cyclooxygenase-2. In peripheral blood mononuclear cells exposed to endotoxin (18 h), 1.0 and 3.0 mM sodium salicylate reduced the prostaglandin E(2) concentration of the supernatant, and, at the same time, stimulated cyclooxygenase-2 expression. After a subsequent 2 h incubation of peripheral blood mononuclear cells in drug-free medium, prostaglandin E(2) concentrations in samples that had been exposed to endotoxin together with 1.0 or 3.0 mM salicylate were significantly higher than in samples exposed to endotoxin alone. These results show that salicylate can enhance the expression of cyclooxygenase-2 in endotoxin-exposed peripheral blood mononuclear cells and at the same time reduce prostaglandin E(2) formation. After washout and removal of salicylate-induced cyclooxygenase inhibition, increased cyclooxygenase-2 expression resulted in enhanced prostaglandin E(2) formation. It seems possible that under certain conditions salicylate-induced stimulation of cyclooxygenase-2 expression may contribute to its clinical pharmacological profile.

Cholera toxin induces prostaglandin synthesis via post-transcriptional activation of cyclooxygenase-2 in the rat jejunum

The mechanisms of diarrhea in Asiatic cholera have been studied extensively. Cyclic AMP, 5-hydroxytryptamine, prostaglandins, and the function of neuronal structures have been implicated in the pathogenesis of cholera. To elucidate the role of the different isoforms (COX-1 and COX-2) of cyclooxygenase in cholera toxin (CT)-induced fluid secretion and intraluminal prostaglandin E(2) (PGE(2)) release in the rat jejunum in vivo, the effects of the COX-2 inhibitors NS-398 ([N-(2-cyclohexaloxy-4-nitrophenyl)methanesulfonamide]) and DFU [5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulfonyl)phenyl-2(5H)-furanone], and of the COX-1 inhibitor SC-560, were studied. Net fluid transport was measured gravimetrically and PGE(2) by radioimmunoassay. COX-1 and COX-2 mRNA expression were determined by reverse transcription-polymerase chain reaction (RT-PCR) and COX-2 protein by Western blot analysis in mucosal scrapings. CT caused profuse net fluid secretion in all control rats. The COX-2 inhibitors NS-398 and DFU, but not the COX-1 inhibitor SC-560 or dexamethasone, dose-dependently inhibited CT-induced fluid secretion and PGE(2) release. RT-PCR showed expression of COX-1 and of COX-2 mRNA in control rats. CT did not induce an increase and dexamethasone did not reduce COX-2 mRNA, whereas lipopolysaccharide caused a marked induction of COX-2 mRNA, which was inhibited by dexamethasone. A weak band of COX-2 protein was observed in controls; however, CT enhanced COX-2 levels, which remained unaffected by dexamethasone. It can be assumed that post-transcriptional modulation is responsible for CT-induced increase in COX-2 protein. COX-1 does not seem to be involved. Therefore, PGE(2) produced by COX-2 seems to be responsible for the profuse fluid secretion induced by CT, and COX-2 appears to be a specific target for the treatment of Asiatic cholera.

Effects of terbutaline on NGF formation in allergic inflammation of the rat

1. The aim of this study was to determine the effects of the beta adrenergic agonist terbutaline on NGF increase caused by allergic inflammation in rats. 2. Intraplantar antigen injection in sensitized rats increased paw volume and stimulated NGF biosynthesis in the skin of the injected paw as determined 3 and 6 h after injection. Treatment of rats with terbutaline (0.1 - 0.3 mg kg(-1), s.c.) had no significant effect on the NGF concentration in non-inflamed skin, but reduced oedema, and at 0.3 mg kg(-1) also NGF mRNA and immunoreactive NGF in the skin of the inflamed paw in a propranolol-reversible manner. In carrageenan-induced inflammation, terbutaline did not significantly reduce the inflammation-induced increase of NGF in paw skin. 3. Exposure of sensitized rats to aerosolized antigen (twice, 24 h interval) increased protein content, eosinophil leukocytes, and immunoreactive NGF in the bronchoalveolar lavage fluid (BAL, obtained 16 h after the second antigen exposure). Treatment of rats with terbutaline (0.3 mg kg(-1), s.c. 30 min before the second antigen challenge) suppressed antigen-induced elevation of protein and eosinophil leukocytes, and reduced the concentration of NGF in BAL to values similar to those found in non-sensitized rats. 4. The present results demonstrate anti-allergic properties of terbutaline in rats that were accompanied by a marked reduction of antigen-induced NGF increase in skin and BAL, respectively. These results are compatible with the assumption that terbutaline primarily suppressed the immune response to antigen thereby attenuating the release of vasoactive mediators and the stimulation of NGF biosynthesis.

Effects of COX-1 and COX-2 inhibitors on eicosanoid biosynthesis and the release of substance P from the guinea-pig isolated perfused lung

OBJECTIVE

In the guinea-pig isolated perfused lung, co-administration of bradykinin (BK) and histamine causes the release of pro-inflammatory neuropeptides, an effect that is largely dependent on BK-induced formation of prostaglandins. Since it is known that at least two isoenzymes, cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) catalyse the conversion of arachidonic acid to prostaglandins (PGs) and thromboxanes, the present study aimed at investigating the effect of selective COX-1 and COX-2 inhibitors on the evoked release of substance P (SP).

MATERIAL AND METHODS

Lungs were vascularly perfused with oxygenated physiological salt solution containing peptidase inhibitors. BK (0.1 microM) and histamine (100 microM) were added to the perfusate for 10 min and 5 min, respectively. The concentrations of 6-keto-PGF1alpha, cysteinyl-leukotriene (LT), and SP were determined in the outflow by radioimmunoassay.

RESULTS

In non-stimulated preparations, indomethacin (2 microM) and the selective COX-1 inhibitor SC-560 (0.03-1 microM) reduced basal release of 6-keto-PGF1alpha, without significantly affecting the release of cysteinyl-LT and SP. The selective COX-2 inhibitors NS-398 (1 microM) or DFU (10 microM) had no significant effect on the basal release of eicosanoids or SP. Co-administration of BK and histamine caused a pronounced increase in the concentration of 6-keto-PGF1alpha and cysteinyl-LT, and SP in the effluate. Under these conditions, indomethacin as well as SC-560 reduced the release of 6-keto-PGF1alpha, enhanced cysteinyl-LT release, and attenuated the release of SP. In contrast, the selective COX-2 inhibitors NS 398 and DFU had no significant effect on the stimulated release of eicosanoids or SP.

CONCLUSIONS

These results suggest that in the isolated guinea-pig lung, basal prostanoid biosynthesis as well as BK-induced stimulation of prostanoid formation and subsequent facilitation of histamine-induced SP release is primarily mediated by COX-1 without detectable involvement of COX-2.

Eicosanoid release in the endotoxin-primed isolated perfused rat lung and its pharmacological modification

OBJECTIVE

Recent observations have demonstrated a central role of the "inducible" isoform of the cyclooxygenase (COX), COX-2, in the rat lung. Therefore, the reported capacity of selective COX-2 inhibitors to potentiate the formation of leukotriene (LT) B4 may raise concern about pro-inflammatory side effects of such drugs in the respiratory system. The present study was aimed at determining the effects of the COX-2 inhibitor NS-398 on the release of COX and 5-lipoxygenase (LOX) metabolites of arachidonic acid in isolated perfused lungs obtained from endotoxin-treated rats before and after stimulation with the leukocyte secretagogue N-formyl-methionyl-leucyl-phenylalanine (FMLP).

METHODS

Two hours after rats had received endotoxin i.v., the lung was dissected and perfused via the pulmonary artery with physiological salt solution. After an equilibration period of 20 min the outflow was collected (5-min fractions). In the respective treatment groups, indomethacin, NS-398, or the 5-LOX inhibitor MK886 were present throughout the experiment, while FMLP was added to the perfusate during a single 5-min period. The concentration of eicosanoids in the outflow was determined by radioimmunoassay.

RESULTS

Endotoxin treatment of rats resulted in increased expression of COX-2 mRNA in lung tissue, and an elevated basal release of the prostaglandin (PG)I2 metabolite 6-keto PGF1alpha, without a detectable increase of leukotriene (LT) formation. In-vitro exposure to FMLP stimulated LT and prostanoid release, which was significantly enhanced in endotoxin-primed lungs, and was suppressed by the 5-LOX inhibitor MK-886 (3 microM) and the COX-inhibitor indomethacin (5 microM), respectively. Either compound showed selective inhibition of the respective pathway of arachidonic acid metabolism. In endotoxin-primed lungs, the COX-2 inhibitor NS-398 (0.3-1.0 microM) depressed basal as well as FMLP-stimulated release of 6-keto PGF1alpha, but did not cause a significant increase of LTB4 or cysteinyl-LT release.

CONCLUSIONS

These results suggest that FMLP, presumably acting on inflammatory cells trapped in the pulmonary circulation of endotoxin treated rats, induced prostanoid formation mainly via the COX-2 pathway, and that its inhibition by NS-398 had no detectable potentiating effect on LTB4 or cysteinyl-LT biosynthesis.

Lack of effect of a selective vasopressin V1A receptor antagonist SR 49,059, on potentiation by vasopressin of adrenoceptor-mediated pressor responses in the rat mesenteric arterial bed

The vasopressin receptor subtype involved in the enhancement by vasopressin of adrenoceptor-mediated vasoconstriction was investigated in rat isolated perfused mesenteric arteries. [Arg8]vasopressin (1-10 nM) dose-dependently increased the perfusion pressure and enhanced the pressor response to the adrenoceptor agonist methoxamine (40 nmol) or electrical stimulation of periarterial nerves (16 Hz), at the concentration of 10 nM of [Arg8]vasopressin up to 4 and 3 fold, respectively. During prolonged exposure (45 min) the direct vasoconstrictor effect of [Arg8]vasopressin (10 nM) rapidly declined whereas the potentiation of methoxamine-induced vasoconstriction was maintained. The selective vasopressin V1A receptor antagonist SR 49,059 (1-3 nM) and the non-selective V1A/B and oxytocin receptor antagonist [deamino-Pen1,Tyr(Me)2,Arg8]vasopressin (15-45 nM) inhibited the direct vasoconstrictor action of [Arg8]vasopressin but had no effect on the enhancement of the pressor response to methoxamine or electrical stimulation. The V1B receptor agonist [deamino-Cys1,beta-(3-pyridyl)-D-Ala2,Arg8]vasopressin (100-1000 nM) and the V2 receptor agonist [deamino-Cys1,D-Arg8]vasopressin (1-10 nM) were devoid of any pressor activity and did not potentiate methoxamine-evoked vasoconstriction. In contrast, [1-triglycyl,Lys8]vasopressin (100 - 1000 nM) potentiated the methoxamine responses without per se inducing vasoconstriction. In arteries precontracted with methoxamine (7.5 microM) pressor responses to [Arg8]vasopressin (3-10 nM) were not inhibited by a dose of SR 49,059 (3 nM) which abolished the peptide's vasoconstrictor effect under control conditions. These data show that the direct vasoconstrictor effect of [Arg8]vasopressin is mediated by V1A receptors while the enhancement of adrenoceptor-mediated pressor responses is insensitive to V1A, V1B, and oxytocin receptor antagonists and is not mimicked by selective agonists of V1B and V2 receptors. In conclusion, an unusual interaction of vasopressin with V1A receptors, or even the existence of a novel receptor subtype, has to be considered.

Bradykinin-evoked sensitization of neuropeptide release from afferent neurons in the guinea-pig lung

1. It has been shown that bradykinin (BK) causes sensitization of airway sensory neurons and an enhancement of the cough reflex in guinea-pigs. In the present study, the guinea-pig isolated perfused lung was used to investigate the possible enhancement by BK of histamine-evoked neuropeptide release from peripheral terminals of primary afferent neurons, and to determine the contribution of cyclooxygenase products of arachidonate metabolism to this effect. 2. The lung was perfused with oxygenated physiological salt solution containing peptidase inhibitors (thiorphan, bestatin and captopril, 1 microM each). BK and histamine were added to the perfusate for 10 and 5 min, respectively. 3. BK alone (0.1 microM) evoked the release of 10.35+/-2.4 fmol immunoreactive calcitonin gene-related peptide (CGRP), histamine alone (100 microM) evoked the release of 12.7+/-1.6 fmol CGRP. Stimulation with 100 microM histamine in the presence of 0.1 microM BK (added 5 min before histamine and present during histamine) evoked the release of 67.1+/-5.3 fmol CGRP. 4. Prostaglandin (PG) release was stimulated by BK (418+/-71 pmol 15-keto-13,14-dihydro-PGF2alpha and 345+/-59 pmol 6-keto-PGF1alpha), and, to a lesser extent, by histamine (36.1+/-7.4 pmol 15-keto-13,14-dihydro-PGF2alpha, and 24.6+/-3.9 pmol 6-keto-PGF1alpha). Prostaglandin release induced by histamine in the presence of BK was not significantly higher than with BK alone. 5. Indomethacin (5 microM) as well as the bradykinin B2 receptor antagonist HOE140 (icatibant, 1 microM) inhibited prostaglandin release following stimulation with histamine in combination with BK. CGRP release evoked by histamine in combination with BK was attenuated by indomethacin and HOE140 to 22.1+/-7.8 fmol and 16.4+/-3.8 fmol, respectively, significantly less than the value obtained in control experiments (67.1+/-5.3 fmol). 6. The results suggest that BK-induced stimulation of prostaglandin synthesis results in facilitation of histamine-evoked release of pro-inflammatory neuropeptides from afferent neurons, a mechanism that probably becomes relevant during inflammation, and that can be blocked by a bradykinin B2 receptor antagonist.

Antiinflammatory effect of tepoxalin: blood and synovial tissue studied in patients with knee arthrosis

Our aim was to determine the amounts of eicosanoids in blood and synovial tissue of patients with knee arthrosis and to examine the effects of 2 doses of tepoxalin (50 mg twice, 200 mg twice), administered p.o. for 3.5 days. Concentrations of leukotriene B4 (LTB4, LTC4, and thromboxane B2 (TXB2) were measured in blood before and after oral administration of tepoxalin and release of prostaglandin E2 (PGE2), 6-keto-PGF1alpha, and LTC4 was measured in incubation media of synovial tissue, taken at surgery from patients treated with tepoxalin. Radioimmunoassay (RIA) was used to determine the levels of the eicosanoids. LT and TXB2 release was reduced by tepoxalin in both doses used. Under these conditions, PGE2, 6-keto-PGF1alpha, and LTC4 release from synovial tissue was detectable only after stimulation with calcium ionophore A23187. Washed synovial tissue, in which tepoxalin concentrations should be reduced, released higher amounts of all eicosanoids measured than directly incubated synovial tissue did. Pain after tepoxalin administration was significantly reduced. Relevant drug concentrations were detected in plasma and synovial fluid. Tepoxalin was well tolerated and had no marked adverse effects. At 400 mg, tepoxalin is a dual inhibitor of cyclooxygenase (CO) and 5-lipoxygenase (5-LO) in blood and synovial tissue.

Effects of the cyclooxygenase-2 inhibitor NS-398 on thromboxane and leukotriene synthesis in rat peritoneal cells

OBJECTIVE

Inhibition of inducible cyclooxygenase (COX)-2 has been suggested to offer therapeutic advantages without some side effects associated with the inhibition of constitutive COX activity. These side effects encompass asthmatic responses that can be induced by analgesic/ antiphlogistic drugs and are possibly related to increased leukotriene (LT) biosynthesis. We have therefore investigated whether or not the selective COX-2 inhibitor NS-398, similar to indomethacin, stimulates leukotriene (LT) biosynthesis in rat peritoneal cells.

METHODS

Three hours after rats had received intraperitoneal injections of bacterial lipopolysaccharide (LPS) or saline, cells were obtained by peritoneal lavage. Northern blot analysis confirmed induction of COX-2 mRNA by LPS treatment. For determination of eicosanoid biosynthesis, peritoneal cells were incubated in the presence of various concentrations of test compounds for 60 min. The supernatants were used for radioimmunological determination of immunoreactive eicosanoids.

RESULTS

In cells from LPS treated rats, but not in controls, NS-398 (10-300nM) reduced the amount of TXB2-like immunoreactivity (IR) in the supernatants, the maximum effect being a 25% inhibition. At these concentrations, there was no detectable effect of NS-398 on the amount of LTB4-IR or LTC4-IR in the supernatants. At higher concentrations (1-10 microM), NS-398 caused further inhibition of TXB2 synthesis, an effect that was observed also in non-LPS treated preparations. A significant increase of LTB4-IR was caused by 3-10 microM NS-398. Indomethacin (3-100 nM) reduced the amount of TXB2-IR, and at >10 nM increased the amount of LTB4- and LTC4-IR in the supernatant.

CONCLUSIONS

The results show that concentrations of NS-398 that selectively inhibited COX-2 activity, produced no detectable increase in LT biosynthesis, thus raising the possibility that COX-2 inhibitors are less likely than non-selective COX inhibitors to produce LT- related side effects.

Effects of prostaglandin E1 metabolites on the induction of arterial thromboresistance

Prostaglandin (PG) E1 has been shown to induce arterial thromboresistance in experimental animals and in man. It is known to be degraded in vivo to metabolites which have comparable (13,14-dihydro-PGE1) or no (15-keto-PGE1, 15-keto-13,14-dihydro-PGE1) biological activity. It was the goal of this study to examine whether 13,14-dihydro-PGE1 and its derivatives might share biological activity in rendering the arterial wall less thrombogenic. Using a cross-perfusion technique the aorta and iliac artery surface were exposed to a donor rabbits' blood. We examined the intact endothelial lining and a surface which had been deendothelialized before by means of a Fogarty catheter. Donor animals and/or receiver animals were treated daily for 1 week with 13,14-dihydro-PGE1, PGE1, 15-keto-PGE1, 15-keto-13,14-dihydro-PGE1, or the vehicle only, respectively. From the group of the receiver animals, a subgroup of 6 animals each was treated for the same period of time with either 13,14-dihydro-PGE1, PGE1, 15-keto-PGE1, 15-keto-13,14-dihydro-PGE1, or the vehicle. Immediately after the last administration of the respective PG or solvent, native blood from a donor rabbit was circulated [30 mL/min. under in vivo flow conditions (60 Hz)] over an arterial segment of a receiver animal. Deposition of 111Indium-oxine labeled autologous platelets per surface unit was quantitatively assessed. In vitro perfusion data were morphometrically analysed. In animals pretreated with 13,14-dihydro-PGE1 the thromboresistance was almost comparable to that achieved with PGE1. In contrast, pretreatment of the donor animals (platelet) had only minor effects on the thromboresistance. The other compounds showed no effects. In vitro perfusion of human saphenous vein segments revealed PGE1 and 13,14-dihydro-PGE1 again to be of comparable potency, while 15-keto-PGE1 and 15-keto-13,14-dihydro-PGE1 were only active at concentrations being several orders of magnitude higher. Not only PGE1 but also its in vivo formed metabolite PGE0 may play an important role in inducing improvement of haemostatic balance via the vascular wall rather than the platelets. The other metabolites, however, are unlikely to exhibit an effect at biologically relevant concentrations.

Alteration of rat cerebral microvascular eicosanoid formation by isradipine, a calcium channel blocker

We studied the influence of the calcium channel blocker isradipine on cerebral microvascular and aortic eicosanoid synthesis. The rat cerebral microvascular eicosanoid formation was assessed by means of bioassay, radioimmunoassay and radio thin layer chromatography from endogenous as well as from exogenous (20:4) radiolabelled substrate. The in vitro as well as the in vivo (0.3 mg/kg/day for 1 week) effect of isradipine was examined. Isradipine increased significantly (P < 0.01) both conversion to and formation of PGI2 and its derivative 6-oxo-PGF1alpha respectively, as well as PGD2-production, while TXB2-synthesis was diminished. The conversion to the other metabolites was not affected to a significant extent. These findings indicate that isradipine enhances PGI2-generation in aorta and cerebral microvessels from both exogenous and endogenous substrate and PGD2 from endogenous substrate, a phenomenon shown to underlie the antiatherosclerotic actions of this calcium channel blocker.

Dilatation by angiotensin II of the rat femoral arterial bed in vivo via pressure/flow-induced release of nitric oxide and prostaglandins

1. The haemodynamic effects of angiotensin II (AII) and, for comparison, arginine vasopressin (AVP) in the femoral and superior mesenteric artery of urethane-anaesthetized rats were analysed with the ultrasonic transit time shift technique. 2. I.v. bolus injection of AII (0.1-3 nmol kg-1) and AVP (0.03-1 nmol kg-1) increased blood pressure which was accompanied by a decrease in blood flow through the superior mesenteric artery and an increase in femoral blood flow. The femoral hyperaemia was in part due to vasodilatation as indicated by a rise of femoral vascular conductance up to 200% relative to baseline. The femoral vasodilatation caused by AVP, but not AII, was followed by vasoconstriction. 3. Blockade of angiotensin AT1 receptors by telmisartan (0.2-20 mumol kg-1) prevented all haemodynamic responses to AII. 4. The femoral dilator responses to AII and AVP depended on the increase in vascular perfusion pressure since vasodilatation was reversed to vasoconstriction when blood pressure was maintained constant by means of a gravity reservoir. However, the AII-evoked femoral vasodilatation was not due to an autonomic or neuroendocrine reflex because it was not depressed by hexamethonium (75 mumol kg-1), prazosin (0.25 mumol kg-1) or propranolol (3 mumol kg-1). 5. The AII-induced femoral vasodilatation was suppressed by blockade of nitric oxide (NO) synthesis with NG-nitro-L-arginine methyl ester (L-NAME, 40 mumol kg-1) and reversed to vasoconstriction when L-NAME was combined with indomethacin (30 mumol kg-1), but was left unaltered by antagonism of endothelin ETA/B receptors with bosentan (37 mumol kg-1). 6. These results demonstrate that the effect of AII to increase systemic blood pressure and the resulting rise of perfusion pressure in the femoral artery stimulates the formation of NO and prostaglandins and thereby dilates the femoral arterial bed. This local vasodilator mechanism is sufficient to mask the direct vasoconstrictor response to AII.

PGE1-induced arterial thromboresistance is a vascular property as identified by cross-perfusion technique

Prostaglandin (PG) E1 has been shown to improve thromboresistance. This experiment was designed to examine whether an effect on the arterial wall or the platelets is responsible for this phenomenon. Using a cross-perfusion model, the aortic and iliac artery endothelium of rabbits was removed by a balloon catheter before being perfused with blood of donor rabbits. Donor and/or receiver animals were treated with 20 microg PGE1 or vehicle (cyclodextrin) intravenously daily for 1 week. After the last administration of PGE1 or its vehicle, the animals were killed and native blood from a donor rabbit was recirculated (30 ml/min) via a deendothelialized segment of a receiver rabbit. The contact (C) and spread (S) platelets as well as the denuded surface covered with platelet aggregates (> 5 microm in height) were quantified by morphometry. Deposition of (111)In-oxine labeled autologous platelets was quantitatively determined per surface unit. In addition, PGI(2)- and TXB2-formation by the denuded aortic and iliac artery segments was determined. Pretreatment of receiver rabbits with PGE1 resulted in morphometrically assessed decreased platelet adhesion and aggregation, even when the donor rabbit was vehicle-treated. A vehicle-treated receiver rabbit, in contrast, shows platelet deposition comparable to controls, even if the donor rabbit was PGE1-pretreated. Treatment of donor animals with PGE1 did not result in a reduction in thrombogenicity. The beneficial in vivo PGE1 action of decreased arterial thrombogenicity is thus mediated by an effect on the vascular wall rather than on circulating platelets.

Determination of nociceptin-like immunoreactivity in the rat dorsal spinal cord

An endogenous ligand for the opioid receptor-like (ORL1) receptor has been characterized recently. This 17 amino acid peptide, nociceptin, has potent effects on pain processing in experimental animals. In the present study, we describe the development of a radio-immunoassay for nociceptin, suitable for quantification of immunoreactivity in the rat spinal cord. in the dorsal spinal cord we found 641 fmol nociceptin-like immunoreactivity (IR)/mg protein, while in the ventral spinal cord the amount was below the detection limit of the assay (11 fmol/mg protein). High pressure liquid chromatography (HPLC) showed that the immunoreactive material was heterogeneous with the major part eluting at the position of synthetic nociceptin. The presence of nociceptin in the dorsal spinal cord is compatible with its proposed involvement in modulating afferent transmission.

Release of calcitonin gene-related peptide in cardiac anaphylaxis

We have investigated the antigen-stimulated release of calcitonin gene-related peptide (CGRP) from ovalbumin-sensitized guinea-pig isolated hearts and the interaction with other mediators of anaphylaxis released concomitantly. It was found that antigen challenge caused a significant increase of CGRP release (from basal 31.2 +/- 2.9 to 51.6 +/- 4.9 fmol/5 min). Anaphylactic CGRP release was significantly attenuated in the presence of the cyclooxygenase inhibitor indomethacin while the 5-lipoxygenase inhibitor Bay-X1005 ((R)-2-[4-quinolin-2-yl-methoxy)phenyl]-2-cyclopentyl acetic acid) had no significant effect. Combined treatment with the histamine receptor (H1,H2) antagonists mepyramine and cimetidine also significantly attenuated anaphylactic release of CGRP. Under control conditions antigen injection increased release of cysteinyl-leukotrienes (LT), thromboxane (TXB2) and 6-keto-prostaglandin (PG)F1 alpha from basal values of 0.96 +/- 0.09, 2.7 +/- 0.7 and 3.4 +/- 0.28 ng/5 min respectively, to 5.9 +/- 0.9, 48.4 +/- 3.4 and 6.9 +/- 1.4 ng/5 min. Indomethacin abolished the release of cyclooxygenase products of arachidonate metabolism and simultaneously increased cysteinyl-LT release significantly (8.8 +/- 1.4 ng/5 min). Conversely Bay-X1005 completely abolished cysteinyl-LT release and had no significant effect on anaphylactic release of TXB2 and 6-keto-PGF1 alpha. Simultaneous blockade of H1 and H2 receptors abolished release of 6-keto-PGF1 alpha, while release of TXB2 and cysteinyl-LT was not significantly affected. The results indicate that CGRP is not a primary mediator of the immediate hypersensitivity reaction of the heart, but is in turn released by arachidonic acid metabolites of the cyclooxygenase pathway and histamine. In contrast, LT obviously do not contribute to anaphylactic CGRP release. CGRP is a potent coronary vasodilator and could act as endogenous functional antagonist of vasoconstrictor mediators also released during cardiac anaphylaxis such as cysteinyl-LT, platelet activating factor and TXA2.

The prostacyclin stimulating plasma factor activity improves thromboresistance only if vascular PGI2-production is intact

PGI2 is important in regulating platelet vessel wall interaction (1). In perfusion chamber experiments the amount of PGI2 formed was inversely related to the amount of platelets deposited (2). In 1978 a plasma factor was described which stimulates vascular PGI2-production (3). In later years, this activity has been monitored in different patient groups (for review see 4). Interestingly, it has been found that diseases associated with an increased bleeding tendency such as uraemia (5) or hepatic failure (6) were associated with an increased PF-activity while others with an enhanced thrombophilia sometimes show an absence of PF-activity (7). Recently, the PGI2 stimulating plasma factor has been purified and cloned (8). It was the aim of these experiments to assess whether PF-activity plays a role in local hemostasis regulation under in-vivo flow conditions and whether this is dependent on the presence of an intact PGI2-formation.

The effects on platelet aggregation and prostanoid biosynthesis of two parenteral analgesics: ketorolac tromethamine and dipyrone

The pharmacokinetics and effects on platelet function of dipyrone (1.0 g; 2.5 g; i.v.) and ketorolac tromethamine (30 mg; i.m.) were studied in a three-way crossover study in twelve healthy subjects. The biosynthesis of thromboxane A2 in clotting whole blood ex vivo as well as collagen-induced platelet aggregation were determined before and up to 48 h after administration. Both prostanoid biosynthesis and platelet aggregation were inhibited by ketorolac tromethamine for a significantly longer period of time than by both doses of dipyrone. The changes in platelet functions correlated well with the serum concentrations of ketorolac or 4-methylaminoantipyrine and 4-aminoantipyrine. Using the sigmoidal Emax model the mean serum concentration (SD) of ketorolac, 4-methylaminoantipyrine and 4-aminoantipyrine inhibiting platelet TXB2 generation by 50% (EC50) in vitro was found to be 0.088 +/- 0.031, 1.2 +/- 0.3 and 10.2 +/- 3.4 micrograms ml-1, respectively. In conclusion the recovery of platelet function after dipyrone administration is faster as compared to ketorolac tromethamine. This is in line with clinical observations and may be an advantage when these drugs are given as postoperative analgesics at the doses tested.

Inhibition of eicosanoid release from synovial organ culture by incubation with tepoxalin and its acid metabolite

The pharmacological profile of a novel dual inhibitor, tepoxalin and of its carboxylic acid metabolite on cyclooxygenase and lipoxygenase pathways was evaluated by in vitro incubation with synovial tissue. Tissue specimens obtained at surgery in rheumatoid arthritis (RA, n = 10) or osteoarthritis (OA, n = 11) patients were incubated. Tepoxalin (10(-7), 10(-6), 10(-5) M) decreased eicosanoid release calculated in % of tyrode control for OA: LTC4 to 71-33%, 6-keto-PGF1a to 37-20%, PGE2 to 29-6%. For RA: LTC4 to 56-22%, 6-keto-PGF1a to 43-22%, PGE2 to 57-32%. Similarly, its metabolite (10(-7), 10(-5)M) decreased release in OA: LTC4 to 99 and 60%, PGE2 to 42 and 20%, 6-keto-PGF1a to 54 and 25%. In RA:LTC4 to 81 and 45%, PGE2 to 61 and 30%, 6-keto-PGF1a to 46 and 18%. Significance (P < 0.05) was achieved for all but 1 group (LTC4 metabolite at 10(-7)M vs tyrode). In summary a marked and dose dependent decrease of LT and PG release was obtained when incubating the dual inhibitor tepoxalin and its active carboxylic acid metabolite with synovial tissue at doses expected to be reached in the joint during therapy.

Effect of a 5-lipoxygenase inhibitor on nerve growth factor-induced thermal hyperalgesia in the rat

Intraplantar injection of mouse beta (2.5S) nerve growth factor (NGF) caused thermal hyperalgesia and stimulated release of immunoreactive leukotriene B4 from the rat paw skin. Both effects of NGF were prevented by the 5-lipoxygenase inhibitor, (R)-2-[4-quinolin-2-yl-methoxy)phenyl]-2-cyclopentyl acetic acid (BAY X1005). BAY X1005 did not affect bradykinin-induced thermal hyperalgesia. These results suggest the participation of 5-lipoxygenase products of arachidonate in NGF-induced local thermal hyperalgesia.

Passive smoking and platelet thromboxane

While active smoking is known to enhance platelet thromboxane production, no data on passive smoking is available yet. The influence of single and repeated exposure to passive smoke for 60 minutes in a 18 m3 room was assessed in non-smokers as compared to sex and age matched smokers. All the evaluated measures (malondialdehyde, plasma thromboxane B2, 11-dehydro-thromboxane B2, serum thromboxane B2, conversion of exogenous arachidonic acid to thromboxane B2 and to hydroxy-5, 8,10-heptadecatrienoic acid) were higher in smokers than non-smokers at baseline, immediately and 6 hours after passive exposure to cigarette smoke. Repeated exposure of non-smokers rendered their platelets more activated becoming close to the behaviour of smokers. These results indicate that passive smoking may activate thromboxane A2 release from the platelets, contributing to the development of hemostatic imbalance.

Effects of single oral doses of lysine clonixinate and acetylsalicylic acid on platelet functions in man

Lysine clonixinate is an analgesic drug with a so far unknown mechanism of action. We have determined its effect on platelet cyclooxygenase in man. Biosynthesis of thromboxane (TX)B2 and prostaglandin (PG)F2 alpha in clotting whole blood ex vivo as well as collagen-induced platelet aggregation measured before and at various time points after oral administration of 125 mg lysine clonixinate were compared to results obtained with 500 mg acetylsalicylic acid (ASA). While biosynthesis of both TXB2 and PGF2 alpha measured radioimmunologically was inhibited significantly 2.5 h, but not 6 h, after administration of lysine clonixinate, inhibition by ASA was much greater and still highly significant after 48 h. Similarly, collagen-induced aggregation of platelet-rich plasma was inhibited for a longer period and to a greater extent after administration of ASA than after lysine clonixinate. Our results indicate that lysine clonixinate is a cyclooxygenase inhibitor of moderate potency. It remains to be investigated whether mechanisms other than inhibition of cyclooxygenase contribute to the analgesic activity of lysine clonixinate.

Mediation by prostaglandins of the nitric oxide-induced neurogenic vasodilatation in rat skin

1. Intraplantar administration of the nitric oxide (NO) donor, sodium nitroprusside (SNP), induces hyperaemia in the rat paw skin, which is in part due to release of calcitonin gene-related peptide (CGRP) from afferent nerve fibres. The present study examined whether prostaglandins or other inflammatory mediators participate in the neurogenic vasodilatation caused by SNP. Blood flow in the plantar hindpaw skin of urethane-anaesthetized rats was measured by laser Doppler flowmetry. 2. The hyperaemic responses to intraplantar administration of the NO donors SNP (150 pmol) and 3-morpholino-sydnonimine (SIN-1, 15 nmol) were attenuated by 45% and 61%, respectively, after injection of the CGRP antagonist, CGRP8-37 (50 nmol kg-1, i.v.) which did not significantly change baseline blood flow. 3. The NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME, 15 mg kg-1, i.v.), the bradykinin antagonist Hoc-140 (100 nmol kg-1, i.v.) and the histamine antagonists, pyrilamine (2 mg kg-1, i.v.) plus cimetidine (10 mg kg-1, i.p.) were without effect on baseline blood flow and the vasodilatation caused by SNP. 4. The cyclo-oxygenase inhibitors, indomethacin (10 mg kg-1, i.p.) and flurbiprofen (5 mg kg-1, i.p.) depressed the SNP-induced hyperaemia by 65% and 42%, respectively, without altering baseline blood flow. The ability of CGRP8-37 to inhibit the vasodilator response to SNP was lost in indomethacin-treated rats. 5. Intraplantar administration of prostaglandin E2 (PGE2, 15 pmol) evoked cutaneous vasodilatation which was attenuated by 66% after administration of CGRP8-37 but remained unaltered by indomethacin or L-NAME. 6. These data indicate that the neurogenic hyperaemia which in rat skin is induced by intraplantar administration of NO donors involves the formation of prostaglandins which in turn cause release of the vasodilator peptide, CGRP, from perivascular afferent nerve fibres.

Interaction of 5-aminosalicylic acid with nitric oxide on rat aortic strips and human platelets

We have examined the interactions of 5-aminosalicylic acid with nitric oxide (NO). Phenylephrine-precontracted rat aortic strips with intact endothelium were further contracted by 5-aminosalicylic acid (50-200 microM) in a concentration-dependent manner. Removal of endothelium, inhibition of guanylate cyclase by methylene blue, inhibition of NO biosynthesis by NG-nitro-L-arginine as well as in inactivation of NO by oxyhemoglobin abolished the effect of 5-aminosalicylic acid. The antiaggregatory effects of 3-morpholinosydnonimine and rat peritoneal neutrophils, which are due to release of NO, were diminished in a concentration-dependent manner by 5-aminosalicylic acid (50-250 microM). In both experimental models the effects of 5-aminosalicylic acid were significantly reduced by superoxide dismutase in a concentration which alone exhibited no effect. Since NO might act as a cytotoxic and vasodilating mediator, our results suggest that inactivation of NO by 5-aminosalicylic acid could contribute to the therapeutic activity of the drug in inflammatory bowel disease.

Effects of lysine clonixinate and ketorolac tromethamine on prostanoid release from various rat organs incubated ex vivo

The release of prostanoids from rat brain, gastric mucosa, lungs and kidneys incubated ex vivo has been investigated for up to 5 h after oral administration of 10 mg/kg lysine clonixinate or 1 mg/kg ketorolac tromethamine. Additionally, 60 min after drug administration, a time point of near-maximal inhibition of prostanoid release, the effects of 2.5, 10 and 30 mg/kg lysine clonixinate and of 0.0225, 0.15 and 1 mg/kg ketorolac tromethamine were compared. In all organs investigated both drugs inhibited fatty acid cyclooxygenase (COX) in a dose-dependent manner, but ketorolac tromethamine was more potent and had a longer-lasting effect than lysine clonixinate. While the ID50 values for lysine clonixinate were in the same order of magnitude for all 4 organs investigated, ketorolac tromethamine exhibited some organ selectivity with a particularly high activity in the kidneys. This effect might be related to the renal toxicity of ketorolac tromethamine. On the other hand, the difference in potency was smallest in brain suggesting that inhibition of central prostanoid biosynthesis could contribute to the rapid and effective inhibition of pain by both drugs. IC50 values for inhibition of purified COX-1 and COX-2 in vitro were slightly lower for lysine clonixinate (2.4 and 24.6 micrograms/ml, respectively) than for ketorolac tromethamine (3.7 and 25.6 micrograms/ml, respectively).

A neutrophil-derived NO-synthase (NOS) inhibitor

In the present work we have demonstrated that the low NOS activity of circulating blood neutrophils is related to an endogenous inhibitory factor. This factor inhibits constitutive NOS (cNOS) of cerebellum and inducible NOS (iNOS) of macrophages in a concentration-dependent manner. Boiling only partially diminished its activity. The inhibition of cNOS was specific, since to some degree NADPH (0.5-4 mM) and more effectively L-arginine (0.1-1 mM), but not D-arginine, reversed the inhibition.

Modulation of nitric oxide effects by flurbiprofen enantiomers and nefopam and its relation to antinociception

We have examined the interactions of the analgesics, R- and S-flurbiprofen and nefopam, with nitric oxide (NO) in several experimental systems. Phenylephrine-precontracted rat aortic strips with intact endothelium were relaxed by R- and S-flurbiprofen and nefopam in a concentration-dependent manner. Removal of endothelium, inhibition of guanylate cyclase, inhibition of NO biosynthesis and inactivation of NO significantly reduced these relaxations. R- and S-flurbiprofen as well as nefopam enhanced the inhibition of platelet aggregation caused by rat peritoneal neutrophils or 3-morpholinosydnonimine. The antinociceptive effects of R- and S-flurbiprofen in the mouse writhing test as well as those of nefopam in the hot plate test were not significantly affected by administration of NO synthase inhibitors. We conclude that the increase in the biological activity of NO by R- and S-flurbiprofen and nefopam does not play a major role in the antinociceptive activity of the drugs, but might contribute to acute hypotension, a side-effect occasionally seen with flurbiprofen and nefopam.

Pharmacokinetics of vasoactive substances administered into the human corpus cavernosum

The pharmacokinetics of vasoactive substances injected into the corpus cavernosum for the treatment of erectile dysfunction have not been investigated to date. We measured the local intracavernous and peripheral venous concentration curves of papaverine and prostaglandin E1, and its primary metabolite 15-keto-13,14-dihydro-prostaglandin E1 in an intra-individual comparison after intracavernous injection. Papaverine was measured with high performance liquid chromatography and prostaglandin E1 was measured with a specially adapted radioimmunoassay. The results demonstrate that papaverine is slowly draining into the systemic circulation, showing slightly elevated levels in the peripheral blood 30 and 60 minutes after injection. Prostaglandin E1 shows a much faster decrease in local concentrations with no measurable increase in the periphery, probably due to the short half-time after lung passage. Measurement of the primary metabolite proves a local degradation of prostaglandin E1 in the corpus cavernosum into the biologically inactive 15-keto-13,14-dihydro-prostaglandin E1, which also shows a slight increase in the peripheral circulation due to the longer half-time of approximately 8 minutes. The data provide good explanation for the clinical finding of a markedly decreased incidence of priapism with the use of prostaglandin E1, which can be shown to be locally metabolized, compared to papaverine, which is retained in the corpus cavernosum in cases of nonvenogenic impotence.

Isradipine decreases arterial thrombogenicity in rabbits. A morphometric and radioisotopic study

The effect of isradipine, a calcium antagonist, on aortic and iliac wall thrombogenicity was examined in rabbits. After one week of dosing, the abdominal aortic and iliac artery endothelium was abraded using a Fogarthy catheter. One group of animals (n = 8) was dosed for one week with isradipine 0.3 mg/kg. A second group of animals received 10 mg acetylsalicylic acid (ASA)/kg daily in addition, while a third group received the vehicle only. Finally, a fourth group of animals (n = 8) was treated with ASA only. The percentage denuded surface covered with contact (unspread) platelets decreased significantly (p < 0.01) from 14.7 +/- 2.0 to 9.3 +/- 2.1 (6.2 +/- 0.8 to 3.7 +/- 0.4). The amount of contact and spread platelets was diminished from 84.9 +/- 5.6 to 71.4 +/- 4.4 (91.8 +/- 5.3 to 75.2 +/- 4.6). Platelet thrombi decreased from 7.4 +/- 0.9 to 4.6 +/- 1.4 (9.4 +/- 1.9 to 5.2 +/- 0.7) in the aortic and the iliac artery, respectively. In-platelet deposition decreased by 39.9 and 41.9%. Concomitant ASA therapy not only abolished the effect of isradipine but enhanced thrombogenicity, probably as a result of almost complete blockade of vascular PGI2-production.

Effects on platelet functions and pharmacokinetics of azapropazone and ketorolac tromethamine given as single parenteral doses

The biosynthesis of thromboxane (TX) B2 and immunoreactive prostaglandin (PG) F2 alpha in clotting whole blood ex vivo as well as collagen-induced platelet aggregation were determined before and up to 72 h after intravenous injection of 600 mg azapropazone 2H2O and intramuscular injection of 30 mg ketorolac tromethamine in six healthy subjects. The drug doses were selected on the basis of comparable analgesic activity (maximal recommended analgesic dose). Both platelet aggregation and prostanoid biosynthesis were inhibited by racketorolac to a significantly greater extent and for a longer period of time than by azapropazone. Correlations between serum concentrations and the inhibitory effects on TXB2 biosynthesis were observed for both drugs. Using the sigmoidal Emax model the mean serum concentration of azapropazone inhibiting platelet TXB2 generation by 50% (EC50) was found to be 98.1 +/- 41.9 (s.d.) micrograms ml-1, a value 1000 times higher than that for rac-ketorolac. The moderate inhibition of platelet function by azapropazone as compared with rac-ketorolac might be an advantage with regard to its use as a post-operative analgesic.

Gastro-protective effects by extracts of Petasites hybridus: the role of inhibition of peptido-leukotriene synthesis

Extracts from Petasites hybridus are in therapeutic use for more than 2000 years. They have been claimed to improve gastrointestinal pain, lung-diseases such as asthma and cough, as well as spasms of the urogenital-tract. We have investigated these claims in animal models of gastro-intestinal ulcers and confirmed that alcoholic extracts of Petasites hybridus block the ethanol-induced gastric damage and reduce small intestinal ulcerations induced in rats by indomethacin. Searching for a possible mode of action, we found that ethanolic extracts of Petasites hybridus inhibit the peptido-leukotriene biosynthesis in mouse peritoneal macrophages but leave prostaglandin biosynthesis unimpaired. We conclude that the active principle could be useful in the treatment of gastro-intestinal human diseases and that Petasites hybridus may contribute to the inhibition of calcium-dependent processes such as leukotriene biosynthesis.

In vitro release of prostaglandins and leukotrienes from synovial tissue, cartilage, and bone in degenerative joint diseases

OBJECTIVE

To determine the major source of eicosanoid release in arthritic joint tissues and to examine the modulation of this release by indomethacin and diclofenac.

METHODS

Release of prostaglandin E2 (PGE2), 6-keto-PGF1 alpha, leukotriene B4 (LTB4), and LTC4 was measured in supernatants of synovial tissue, cartilage, and bone incubates from patients with osteoarthritis, active rheumatoid arthritis (RA), inactive RA, and pseudogout. Radioimmunoassay (RIA) was used to determine the levels of the eicosanoids.

RESULTS

Addition of the divalent cation ionophore A23187 resulted in significant release of all eicosanoids measured from synovial tissue, but not from cartilage, cortical bone, or cancellous bone. PG release was significantly inhibited by the addition of indomethacin or diclofenac at either 10(-5) moles/liter or 10(-7) moles/liter. The amount of LTC4 released from cartilage and bone was only slightly above the detection limit of the RIA, whereas large amounts were released from synovial tissue. Neither indomethacin nor diclofenac had an effect on LTC4 release. LTC4 release from synovial tissue of patients with inactive RA was significantly decreased in comparison with the levels from synovial tissue of patients with the other joint diseases. There was no significant difference in PG release among patients in the various disease groups.

CONCLUSION

Synovial tissue appears to be the major source of eicosanoids in synovial fluid. Indomethacin and diclofenac inhibit the release of PG, but not LT, from various joint tissues.

Effect of prostaglandin (PG) E1 and its initial metabolites on neutrophil-induced inhibition of human platelet aggregation

We have investigated the effects of PGE1, 15-keto-PGE1, 15-keto-13,14-dihydro-PGE1 and 13,14-dihydro-PGE1 on inhibition of human platelet aggregation by rat peritoneal neutrophils (RPN) and human polymorphonuclear neutrophils (PMN). Both RPN and PMN are known to synthesize nitric oxide (NO). In the presence of a threshold concentration of RPN or PMN the inhibitory effects of PGE1 and 13,14-dihydro-PGE1 on thrombin- or collagen-induced platelet aggregation were significantly increased as compared to the absence of cells, while 15-keto-PGE1 and 15-keto-13,14-dihydro-PGE1 were inactive. Oxyhemoglobin (oxy-Hb) abolished the synergistic effect of RPN and either PGE1 or 13,14-dihydro-PGE1 on thrombin-induced platelet aggregation, but under the experimental conditions used had much less effect on inhibition of collagen-induced aggregation. Potentiation of the antiaggregatory effect of PGE1 and 13,14-dihydro-PGE1 by NO might contribute to the therapeutic efficacy of exogenous PGE1. This view is supported by the fact that plasma levels of PGE1 and its active metabolite in patients receiving infusions of PGE1 for treatment of peripheral arterial occlusive disease are in the order of magnitude acting synergistically with neutrophil-derived NO, while direct inhibition of platelet aggregation requires considerably higher concentrations of PGE1 and 13,14-dihydro-PGE1.

Transient ventilatory responses to endotoxin infusion in the cat are mediated by thromboxane A2

We tested the hypothesis that ventilatory responses to endotoxin infusion in the anesthetized cat are mediated by thromboxane A2 (TxA2). Intravenous infusion of endotoxin (1.6 mg/kg of E. coli, strain 05:B55, delivered over 1 min) in six cats elicited increases in right ventricular blood pressure (Prv) and a transient systemic hypotension. These hemodynamic changes were accompanied by an abrupt apnea, followed by a transient period of rapid, shallow breathing, Cardiorespiratory changes coincided with large increases (> 10-fold) in the plasma concentration of TxB2, the stable metabolite of TxA2. These effects and the release of TxA2 did not occur if endotoxin was infused a second time into the same animal. In addition, animals that were pretreated with either indomethacin (n = 3; 3.0 mg/kg) or the TxA2 receptor antagonist, daltroban, (n = 4; 7.5 mg/kg) exhibited no change in Prv, arterial blood pressure, or respiration when given equivalent doses of endotoxin. We conclude that the release of TxA2 is responsible for the early pulmonary hypertension and rapid, shallow breathing observed during endotoxin infusion in the anesthetized cat. These TxA2-mediated responses are severe but transient in nature.

13,14-Dihydro-prostaglandin E1 decreases low-density lipoprotein influx into rabbit aorta

The effect of 4-week daily administration of 13,14-dihydro-prostaglandin E1 (13,14-DH-PGE1; 2 micrograms/kg) on LDL influx into the rabbit aortic wall was examined versus the effect of the same dose of PGE1 and sham-treatment in 108 male animals fed an 1% cholesterol supplemented diet. Treatment was started after de-endothelialization of the abdominal aorta with a Fogarty catheter. After the 1-month treatment period the animals were injected with 10 microCi 125I-low-density lipoprotein (LDL; 0.5 mg protein/ml). Uptake of the radiolabelled LDL was measured in morphologically verified endothelialized, re-endothelialized and de-endothelialized abdominal aortic segments. The LDL influx into the aorta was significantly (P less than 0.001) lower in 13,14-DH-PGE1- and PGE1-treated rabbits than in the controls. This reduction was most pronounced in re- and de-endothelialized segments. No significant difference between effect of PGE1 and of its biologically active derivative, 13,14-DH-PGE1, on arterial LDL entry was found. These data demonstrate a comparable beneficial effect of 13,14-DH-PGE1 and PGE1 on vascular wall lipid metabolism by decreasing LDL entry into the aortic wall in vivo.

Effect of prostaglandin E2 and 3-morpholinosydnonimine (SIN-1) on arachidonic acid metabolism in fMLP-stimulated rat neutrophils and on thrombin-induced human platelet aggregation

The effects of prostaglandin (PG) E2 and the nitric oxide (NO) donor SIN-1 on leukotriene (LT) release from formyl-methionyl-leucyl-phenylalanine (fMLP) (100 nM)-stimulated rat peritoneal neutrophils (RPN) and on thrombin-induced aggregation of washed human platelets were investigated. Both PGE2 (1-100 nM) and SIN-1 (30-300 microM) inhibited release of LTB4 and cysteinyl-LT from RPN in a concentration-dependent manner. The combined effects of PGE2 and SIN-1 were not greater than expected by summation. On the other hand, the inhibitory effect of SIN-1 (0.5 or 1.0 microM) on platelet aggregation was potentiated by PGE2 (0.3-5 microM) in a concentration-dependent manner, while PGE2 alone in the concentrations used had only marginal effects. The results suggest differential regulation of platelet and leukocyte functions by the mediators PGE2 and NO, which could be relevant for various physiological and pathophysiological conditions.

Synergism between PGE1-metabolites(13,14-dihydro-prostaglandin E1, 15-keto prostaglandin E1, 15-keto-13,14-dihydro-prostaglandin E1) and nitric oxide (NO) on platelet aggregation

A synergistic antiplatelet effect between prostaglandins (PG), cAMP-stimulators and nitric oxide (NO), a cGMP-stimulator, has already been described. Data on a synergism between NO and the metabolites of PGE1, however, are lacking so far. We therefore tested the antiplatelet activity of the metabolites of PGE1 alone and their synergism with NO on human platelets of 8 healthy volunteers in vitro. 13,14-DH-PGE1 (ID 50 = 10.8 ng/ml platelet rich plasma (PRP)) was the only PGE1 metabolite inhibiting the ADP-induced platelet aggregation, its efficacy being 76.4% of the parent compound PGE1 (ID 50 = 8.25 ng/ml PRP). NO (ID 50 = 0.52 microM) also inhibited platelet aggregation. The combined addition of 13,14-dihydro-prostaglandin E1 (13,14-DH-PGE1) and NO caused an additive effect. The other PGE1-metabolites tested, 15-keto prostaglandin (15-K-PGE1) (ID 50 = 16.2. micrograms/ml PRP) and 15-keto-13,14-dihydro-prostaglandin(15-K-13,14-DH-PGE1) (ID 50 = 14.8 micrograms/ml PRP), neither had any relevant antiaggregatory capacity themselves nor a synergistic effect with NO. These findings could be of clinical relevance as a NO-synergism may occur not only with therapeutically administered PGE1 but also with its biologically active metabolite 13,14-DH-PGE1.

Release of endothelin in the oleic acid-induced respiratory distress syndrome in rats

Rats injected intravenously with oleic acid developed pulmonary edema leading to hypoxia and hypercarbia. These changes were accompanied by an increase in immunoreactive endothelin (ir-ET) in plasma as early as 15 min after injection. At 45 min after injection plasma levels peaked at 114 +/- 19 pg/ml plasma (n = 8) and reached basal levels again after 240 min. In contrast, much larger amounts of ir-ET were found in the bronchoalveolar lavage fluid, with a peak at 120 min (2878 +/- 258 pg/lung, n = 7) preceding the maximum hypoxia observed at 180 min. In both plasma and bronchoalveolar lavage fluid samples ir-ET was characterized by reverse-phase HPLC as a mixture consisting mainly of ET-1 and smaller amounts of big ET-1, ET-2 and ET-3. In light of the biological effects of ET, the data suggest that these peptides might be of pathophysiological significance in this model of adult respiratory distress syndrome.

Effect of 3-morpholinosydnonimine (SIN-1), NG-nitro-L-arginine (NNA) and NG-monomethyl-L-arginine (NMMA) on isolated anaphylactic guinea-pig hearts

In isolated perfused ovalbumin-sensitized guinea-pig hearts modulating effects of nitric oxide (NO) on cardiac function and eicosanoid release were investigated. While the NO-donor SIN-1 exhibited a protective effect during cardiac anaphylaxis, inhibition of NO biosynthesis by NNA or NMMA aggravated anaphylactic changes of cardiac functions. Exogenous and endogenous NO seems to functionally antagonize the effects of vasoconstrictor mediators released during the anaphylactic reaction. In addition, inhibition of cysteinyl-leukotriene (cys-LT) release could contribute to the protective effect of SIN-1 observed.

Release of eicosanoids and endothelin in an experimental model of adult respiratory distress syndrome

In an experimental model of adult respiratory distress syndrome (ARDS) we have investigated the release of several vasoactive mediators since the rapid and severe increase in pulmonary arterial pressure is known to be a key feature in this condition. Intravenous injection of oleic acid (OA) into rats resulted in the development of a syndrome similar to ARDS characterized by severe hypoxia. As early as 15 min after OA injection elevated levels of 11-deoxy-15-keto-13,14-dihydro-11,16-cyclo-prostaglandin (PG) E2 (DKH2-cyclo-PGE2) as an indicator of endogenous PGE2 formation could be observed. Similarly, elevated levels of cysteinyl-leukotrienes (LT), determined as immunoreactive (ir) LTE4, and ir-endothelin (ET) could be detected. These mediators were found to be elevated in plasma samples for at least 3 h. In addition, rather large amounts of ir-ET could be detected in bronchoalveolar lavage (BAL) fluid samples between 1 h and 3 h. Thus, it seems possible that cysteinyl-LT and peptides of the ET family, both known for their vasoactivity, might be involved in the pathophysiological process of ARDS.

Effect of 3-morpholinosydnonimine (SIN-1) and NG-nitro-L-arginine (NNA) on isolated perfused anaphylactic guinea-pig hearts

The modulating effects of exogenous and endogenous nitric oxide (NO) on the cardiac anaphylactic reaction and eicosanoid release were investigated in isolated perfused sensitized guinea-pig hearts using 3-morpholinosydnonimine (SIN-1), the active metabolite of molsidomine, as NO-donor and NG-nitro-L-arginine (NNA) as an inhibitor of NO biosynthesis. Infusion of SIN-1 (final concentrations in the perfusates 0.3 or 1.0 mmol/l) elevated coronary flow under basal conditions as well as during cardiac anaphylaxis, while NNA (0.1 mmol/l) decreased basal coronary flow and aggravated the anaphylactic coronary constriction. Both drugs did not modify the characteristic biphasic profile of the coronary constriction after antigen challenge with an initial more severe phase followed by a less pronounced long-lasting flow reduction. Neither SIN-1 nor NNA affected spontaneous heart rate. However, while NNA tended to prolong the duration of antigen-induced arrhythmias, SIN-1 (1 mmol/l) had an inhibitory effect. This protection might be related to the increased coronary flow in the presence of SIN-1. SIN-1 inhibited anaphylactic release of cysteinyl-leukotrienes (LT) and 6-keto-prostaglandin (PG) F1 alpha, but did not influence thromboxane (TX) B2 release. On the other hand, NNA (0.1 mmol/l) inhibited anaphylactic release of TXB2, but had only marginal effects on the release of cysteinyl-LT and 6-keto-PGF1 alpha. The results suggest that exogenous and endogenous NO functionally antagonize the effects of vasoconstrictor mediators released after antigen challenge. Additional effects of high concentrations of SIN-1 and NNA on antigen-induced eicosanoid release could modulate the vascular actions of these drugs during cardiac anaphylaxis.