Pharmacological actions of Y-24180: I. A potent and specific antagonist of platelet-activating factor

The ability of Y-24180, 4-(2-chlorophenyl)-2-[2-(4-isobutylphenyl)ethyl]-6,9-dimethyl-6H-thieno[3,2-f][1,2,4]triazolo[4,3-a] [1,4]diazepine to inhibit platelet-activating factor (PAF)-induced reactions was investigated. Y-24180 (0.0003–0.003 mg/kg, i.v.) dose-dependently inhibited PAF-induced bronchoconstriction in guinea pigs, but even at a high dose of 10 mg/kg, i.v., it was either inactive or weakly active against the bronchoconstriction induced by histamine, serotonin, acetylcholine, arachidonic acid, bradykinin, or leukotriene D₄. Oral doses (0.003–0.1 mg/kg) of Y-24180 also prevented hemoconcentration due to PAF in a dosedependent manner and produced a parallel shift of the PAF dose-response curve. Y-24180 (0.0003–0.1 mg/kg, i.v.) and WEB 2086 (0.03–1 mg/kg, i.v.) dose-dependently reversed PAF-induced hypotension in anesthetized rats. In mice, PAF-induced lethality was inhibited by Y-24180 and WEB 2086 with ED₅₀ values of 0.022 and 1.42 mg/kg, p.o., and 0.023 and 0.12 mg/kg, i.v., respectively. This protective effect of Y-24180 given p.o. persisted for at least 6 hr. In actively sensitized mice lethal anaphylactic shock was prevented by oral doses of Y-24180 and WEB 2086 with ED₅₀ values of 0.095 and 0.69 mg/kg, respectively. These results suggested that Y-24180 is an extremely potent and specific PAF antagonist with a good duration of action.     

Endothelin-induced mobilization of Ca2+ and the possible involvement of platelet activating factor and thromboxane A2

Endothelin (ET) caused transient and sustained elevations of cytosolic free Ca2+ concentrations ([Ca2+]i) in cultured rat and rabbit vascular smooth muscle cells (VSMC). Specific platelet activating factor (PAF) antagonists (CV-6209 and WEB-2086) and arachidonic acid (AA) cascade blockers (chlorpromazine, indomethacin, CV-4151 and AA-2414) potently inhibited the ET-induced increase in [Ca2+]i. Additionally, these compounds inhibited the PAF-induced increase in [Ca2+]i. These results suggest that PAF and thromboxane A2 (TXA2) may be involved in the mechanism of ET-induced mobilization of Ca2+ in cultured rat and rabbit VSMC.     

CV-3988 - a specific antagonist of platelet activating factor (PAF)

CV-3988, rac-3-(N-n-octadecylcarbamoyloxy)-2-methoxypropyl 2-thiazolioethyl phosphate was shown to be a specific inhibitor of platelet activating factor (PAF). This compound in concentrations of 3 x 10(-6) to 3 x 10(-5)M inhibited aggregation of rabbit platelets induced by PAF (3 x 10(-8)M), while it had no effect on the aggregation induced by arachidonic acid, ADP, collagen or A-23187. CV-3988 alone even at a concentration of 10(-3)M had no effect on platelet aggregation. The inhibitory action of CV-3988 on the PAF-induced aggregation was independent of the formation of micelles. The PAF (0.1 to 1.0 micrograms/kg, i.v.)-induced hypotension in anesthetized rats was also inhibited dose-dependently by the i.v. administration of CV-3988 (1 and 10 mg/kg), while the hypotensive actions induced by the i.v. administration of acetylcholine (1 micrograms/kg), arachidonic acid (1 mg/kg), bradykinin (10 micrograms/kg), isoproterenol (1 microgram/kg) and histamine (100 micrograms/kg) were not altered by CV-3988 (10 mg/kg, i.v.). All these findings indicate that CV-3988 specifically inhibits the action of PAF in vitro and in vivo. This is the first report of a PAF antagonist which can specifically inhibit the PAF-induced hypotension as well as the PAF-induced platelet aggregation.     

Pharmacological actions of Y-24180, a new specific antagonist of Platelet Activating Factor (PAF): II. Interactions with PAF and benzodiazepine receptors

The inhibitory effect of Y-24180, 4-(2-chlorophenyl)-2-[2-(4-isobutylphenyl)ethyl]-6,9-dimethyl-6H-thieno[3,2-f][1,2,4]triazolo[4,3-a][1,4]diazepine, on platelet activating factor (PAF)-induced platelet aggregation and the specific binding of ³H-PAF to platelets was compared with other thienodiazepine derivatives, WEB 2086 and etizolam. Y-24180 inhibited PAF-induced rabbit platelet aggregation in vitro (IC₅₀ 3.84 nM), but had little effect on adenosine diphosphate- or arachidonic acid-induced aggregation. WEB 2086 and etizolam also showed an inhibitory effect of PAF-induced aggregation (IC₅₀ values are 456 and 6730 nM, respectively). In PAF-induced human platelet aggregation, Y-24180 (IC₅₀ 0.84 nM) was more potent than WEB 2086 (IC₅₀ 4.21 nM) and etizolam (IC₅₀ 998 nM). Y-24180, WEB 2086 and etizolam displaced ³H-PAF binding from the washed-platelets of rabbits with an IC₅₀ value of 3.50, 9.35 and 29.5 nM, respective- ly. In rabbits, pretreatment with Y-24180 and WEB 2086 antagonized PAF-induced platelet aggregation dose-dependently. The significant inhibitory effect of Y-24180(1 mg/kg, p.o.) lasted 72 hr after a single dose oral administration. WEB 2086 (10 mg/kg, p.o.) also antagonized the ex vivo response induced by PAF 1 hr after administration, but no significant effect was observed 3 hr after administration. Y-24180 displaced ³H-diazepam binding from the synaptosomal membranes of rat cerebral cortex with a Ki value of 3.68 μ M. The affinity of Y-24180 for benzodiazepine(BZP) receptors was lower than those of WEB 2086 and etizolam and was about 1000 times lower than that for PAF receptors in platelets.     

Pharmacological actions of Y-24180, a new specific antagonist of platelet activating factor (PAF): II. Interactions with PAF and benzodiazepine receptors

The inhibitory effect of Y-24180, 4-(2-chlorophenyl)-2-[2-(4-isobutylphenyl)ethyl]-6,9-dimethyl-6H-t hieno [3,2-f][1,2,4]triazolo [4,3-a][1,4]diazepine, on platelet activating factor (PAF)-induced platelet aggregation and the specific binding of 3H-PAF to platelets was compared with other thienodiazepine derivatives, WEB 2086 and etizolam. Y-24180 inhibited PAF-induced rabbit platelet aggregation in vitro (IC50 3.84 nM), but had little effect on adenosine diphosphate- or arachidonic acid-induced aggregation. WEB 2086 and etizolam also showed an inhibitory effect of PAF-induced aggregation (IC50 values are 456 and 6730 nM, respectively). In PAF-induced human platelet aggregation, Y-24180 (IC50 0.84 nM) was more potent than WEB 2086 (IC50 4.21 nM) and etizolam (IC50 998 nM). Y-24180, WEB 2086 and etizolam displaced 3H-PAF binding from the washed-platelets of rabbits with an IC50 value of 3.50, 9.35 and 29.5 nM, respectively. In rabbits, pretreatment with Y-24180 and WEB 2086 antagonized PAF-induced platelet aggregation dose-dependently. The significant inhibitory effect of Y-24180 (1 mg/kg, p.o.) lasted 72 hr after a single dose oral administration. WEB 2086 (10 mg/kg, p.o.) also antagonized the ex vivo response induced by PAF 1 hr after administration, but no significant effect was observed 3 hr after administration. Y-24180 displaced 3H-diazepam binding from the synaptosomal membranes of rat cerebral cortex with a Ki value of 3.68 microM. The affinity of Y-24180 for benzodiazepine(BZP) receptors was lower than those of WEB 2086 and etizolam and was about 1000 times lower than that for PAF receptors in platelets.     

Endothelin, PAF and thromboxane A2 in allergic pulmonary hyperreactivity in mice

The role of endothelin, PAF and thromboxane A2 in airway hyperreactivity (AHR) to carbachol induced by ovalbumin sensitization and challenge in Balb/c mice was investigated. Ovalbumin sensitization and challenge induced significant AHR to carbachol in actively sensitized and challenged mice. Treatment of these mice with the PAF antagonist CV-3988 (10 microg kg(-1), i.v.) completely abolished OVA-induced AHR to carbachol. Treatment of sensitized mice with the TxA2 antagonist L-654,664 (1 mg kg(-1), i.v.) partially blocked the induction of AHR in OVA-challenged mice. The intranasal administration of 50 pmol of the ET(A) receptor antagonist BQ-123 had no effect on the PIP but produced a significant reduction at the dose of 100 pmol. The intravenous administration of BQ-123 (100 pmol) reduced the PIP only at the highest doses of carbachol. The ET(B) receptor antagonist BQ-788 administered either via the intranasal or intravenous route had no effect on the PIP at the dose of 100 pmol. Na?ve mice treated with either U-44069 (25 or 100 microg kg(-1), i.v.), endothelin-1 (100 pmol, intranasally) or the ET(B) receptor agonist IRL-1620 (100 pmol, intranasally) showed a marked increase in airway reactivity to carbachol. These results suggest an important role for endothelin, PAF and thromboxane A2 in AHR in mice actively sensitized and challenged with ovalbumin.     

Effect of a platelet activating factor antagonist (CV6209) on shock caused by temporary hepatic inflow occlusion

Platelet activating factor (PAF) is a newly discovered inflammatory chemical mediator, which was reported to play a pivotal role in various types of shock. There is also a great possibility that PAF plays an important role in the shock caused by hepatic inflow occlusion. In the present study, the effect of CV6209, a PAF antagonist, on the shock caused by the occlusion was investigated. Intravenous 3 micrograms/kg of PAF caused hypotension in Wistar rats (n=6), and pretreatment with intravenous 3 mg/kg of CV6209 significantly (p less than 0.01) prevented the hypotension (n=6). Forty-five minutes of hepatic inflow occlusion caused hypotension in rats during the occlusion period, and the hypotension continued even after restoration of blood flow in control group (pretreated with saline i.v. only, n=5). In contrast, this hypotension was significantly (p less than 0.01) reversed in PAF antagonist group (pretreated with 3 mg/kg of CV6209 i.v., n=5). In sham-operated rats (n=6), arterial pressure remained unchanged and not hypotensive during the monitoring period. The survival rate of rats 90 minutes after declamp was 30% in control group (n=20), and that was significantly (p less than 0.05) improved to be 65% in PAF antagonist group (n=20). In conclusion, PAF plays an important role in the shock and death caused by temporary hepatic inflow occlusion, and a PAF antagonist could be a therapeutic drug against temporary hepatic inflow occlusion.     

Priming interactions between platelet activating factor and histamine in the in vivo microcirculation.

To elucidate whether priming exists between platelet-activating factor (PAF) and histamine in the microcirculation, we measured the clearance of FITC-dextran 150 in response to the topical applications of substimulatory concentrations of PAF and histamine. Maximal priming by PAF was observed when a 5-min interval separated the applications of 10(-9) M PAF and 10(-6) M histamine. The mean (+/- SEM) clearance resulting from this sequence of agonist administration was 7529 +/- 659 nl.2 h-1.g-1, representing a 4.5-fold enhancement in FITC-dextran 150 clearance compared with that evoked by 10(-6) M histamine alone (1664 +/- 397 nl.2 h-1.g-1). Lowering the PAF priming dose to 10(-11) M, or reversing the order of agonist addition to the microcirculation, resulted in diminished but significant responses of 3545 +/- 1143 and 4467 +/- 1170 nl.2 hr-1.g-1, respectively. Coapplication of PAF and histamine or increasing the time interval between the agonists to 15 min greatly reduced the responses to 1906 +/- 678 and 2770 +/- 837, respectively. The PAF receptor antagonist WEB 2086 (2 mg/kg i.v.), the H1 blocker pyrilamine (10 mg/kg i.v.), and leukocyte depletion with cyclophosphamide (150 mg/kg i.p.) completely abolished the PAF priming effect. In addition, the 5-lipoxygenase inhibitor RG 5901 (1 or 10 mg/kg i.v.) produced a two-thirds attenuation in PAF priming. We conclude that 1) PAF has the ability to prime the in vivo microvascular actions of histamine in both a concentration and time-dependent fashion; 2) this primed response is receptor mediated; and 3) histamine can prime the microcirculation for enhanced responses to PAF. Our data also demonstrate that leukocytes and the release of leukotrienes participate in PAF priming.     

Pharmacological modulation of the bronchopulmonary action of the vasoactive peptide, endothelin, administered by aerosol in the guinea-pig

Administration by aerosol for 1 min of solutions of endothelin (ENDO; 1, 5 or 10 micrograms/ml) to anaesthetized and ventilated guinea-pigs induced a dose-dependent bronchopulmonary response (BR) which was maximal within 4 to 5 min. In contrast, no significant change of the mean arterial blood pressure was observed. Pretreatment of guinea-pigs with propranolol (1 mg/kg, i.v.), mepyramine (1 mg/kg, i.v.), nifedipine (50 mg/kg, i.p.) or verapamil (0.3 mg/kg, i.v.) did not significantly affect the BR induced by an aerosol of a solution of 10 micrograms/ml ENDO. In contrast, BR was significantly reduced when the animals were pretreated with the cyclooxygenase inhibitor, indomethacin (10 mg/kg, i.v.) or the platelet-activating factor (PAF) receptor antagonist, BN 52021 (10 mg/kg, i.v.). These results indicate that aerosolized ENDO induces a BR via the generation of secondary mediators such as cyclooxygenase products and PAF in a process which is unaffected by the blockers of the voltage-dependent calcium channels.     

Possible role of platelet activating factor (PAF) in disseminated intravascular coagulation (DIC), evidenced by use of a PAF antagonist, CV-3988

The i.v. infusion of endotoxin (ET) (0.25 mg/kg/hr for 4 hr) induced disseminated intravascular coagulation (DIC) in rats; thrombocytopenia, prolongation of prothrombin time (PT) and partial thromboplastin time (PTT), hypofibrinogenemia and elevated levels of fibrinogen/fibrin degradation products (FDP) were observed. Platelet activating factor (PAF) (8 micrograms/kg/hr for 4 hr) also induced DIC-like changes, except in platelets. A specific PAF antagonist, CV-3988 (2 mg/kg bolus 5 min before ET + 1 or 2 mg/kg/hr for 4 hr of ET infusion) improved all the parameters that had been altered by both ET and PAF. CV-3988 (2 mg/kg bolus 2 hr after ET + 2 mg/kg/hr for 2 hr of ET infusion) also had beneficial effects on DIC. CV-3988 itself had no effects on the parameters of DIC. These results strongly suggest that PAF may play a role in the pathogenesis of DIC and CV-3988 may prove to be useful for the treatment of DIC.     

Effects of the PAF-analog and -antagonist CV-6209 on cultured human glioma cell lines

Cell lines of human glioma (U-343 MGa and U-251 MG) and human glia (U-533 CG) origin were cultured as monolayers and exposed to CV-6209, an alkyl-phospholipid analog and antagonist of platelet activating factor. This drug had very potent antiproliferative effects on the studied human glioma cell lines; IC50 was 0.9 microM after 48 h treatment and 0.2 microM after 2 weeks treatment. At these doses no growth inhibitory effect was noted on the normal glia cells. The effects on the glioma cells were reversible in the dose intervals, where cell proliferation, 3H-thymidine and 14C-methionine uptakes were greatly inhibited. The simultaneous administration of platelet activating factor [(R)PAF] did not influence the antiproliferative effects of CV-6209 on the cells cultured as monolayers. The structurally similar analog CV-3988 also had antiproliferative effects, although at 10 times higher concentration than CV-6209. Two other, structurally unrelated, PAF-antagonists (WEB-2086 and TCV-309) gave effects only at very high concentrations. The U-343 MGa cell line was also exposed to CV-6209 when growing as multicellular spheroids. The studies on the spheroid cultures also demonstrated good antitumoral effects with decreases of both the volume growth and the thymidine uptake. The simultaneous administration of (R)PAF reversed the inhibitory effect of CV-6209 on thymidine incorporation. This study demonstrates a strong antitumoral effect at low concentrations of CV-6209. The antiproliferative effects were probably primarily related to the ether-lipid structure and not to the PAF-antagonistic properties. The good antitumoral effect of CV-6209 on both monolayer and spheroid cultures and the possible PAF-antagonistic properties are discussed.     

A PAF antagonist blocks antigen-induced airway hyperresponsiveness and inflammation in sheep

We studied the effects of WEB-2086, a specific antagonist of platelet-activating factor (PAF), on the development of antigen-induced airway hyperresponsiveness and inflammation in sheep (n = 8). For these studies, airway responsiveness was determined from slopes of carbachol dose-response curves (DRC) performed at base line (prechallenge) and 2 h after Ascaris suum antigen challenges in the following three protocols: 1) antigen challenge alone (control trial), 2) WEB-2086 (1 mg/kg iv) given 30 min before antigen challenge (WEB pretreatment), and 3) WEB-2086 given 2 h after antigen challenge, immediately before the postchallenge DRC (WEB posttreatment). Airway inflammation was assessed by bronchoalveolar lavage (BAL) before antigen challenge and after the postchallenge DRC for each trial. A. suum challenge resulted in acute increases in specific lung resistance that were not different among the three trials. Antigen challenge (control trial) caused a 93% increase (P less than 0.05) in the slope of the carbachol DRC when compared with the prechallenge value. WEB pretreatment (1 mg/kg) reduced (P less than 0.05) this antigen-induced hyperresponsiveness, whereas pretreatment with a 3-mg/kg dose completely prevented it. WEB posttreatment was ineffective in blocking this hyperresponsiveness. BAL neutrophils increased after antigen challenge in the control trial and when WEB-2086 was given after antigen challenge (P less than 0.05). Pretreatment with WEB-2086 (1 or 3 mg/kg) prevented this neutrophilia. This study provides indirect evidence for antigen-induced PAF release in vivo and for a role of endogenous PAF in the modulation of airway responsiveness and airway inflammation after antigen-induced bronchoconstriction in sheep.     

Protective effect of a calcium antagonist against renal vasoconstriction induced by endothelin in the normotensive rat

We studied the effect of nifedipine, a dihydropyridine calcium antagonist, on the hemodynamic changes induced by endothelin, in awake normotensive rats. Endothelin (0.07-1.40 nmol/kg, e.v.) caused an initial hypotensive effect, followed by long lasting hypertension. Renal blood flow was reduced immediately and still remained below basal levels, at 30 minutes after endothelin injection. Nifedipine (1 mg/kg, i.p.) significantly prevented the effect of endothelin on mean blood pressure and induced a right-ward shift in the dose response curve of renal hemodynamic changes induced by endothelin. We conclude that treatment with calcium antagonist could be very useful in all those conditions in which systemic and regional vasocostriction is provoked by endothelin.     

Failure of platelet-activating factor (PAF-acether) to induce decidualization in mice and failure of antagonists of PAF to inhibit implantation

The possible role of platelet-activating factor (PAF) in the uterine responses associated with implantation was investigated. Attempts to trigger a decidual cell response in the uteri of hormonally sensitized, ovariectomized mice by instilling PAF-acether (1-1000 ng) intraluminally were unsuccessful. The effect of PAF antagonists on implantation was investigated in females ovariectomized on Day 3 of pregnancy and treated with progesterone. Implantation was induced in these females by injection of 10 ng oestradiol-17 beta on Day 8. Hourly intraperitoneal injections of three PAF antagonists (WEB 2086, CV 3988 and BN 52021 at doses of 1.2-1.4 mg/kg) given over a 24-h period starting 1 h before the injection of oestradiol-17 beta had no significant effect on the occurrence of implantation sites. Intraluminal injection of WEB 2086 (15 micrograms) or BN 52021 (5 micrograms) either 3 h before or 6 h after the nidatory oestradiol also had no significant inhibitory effect on implantation. SRI 63-441 given once daily over the first 4 days of pregnancy at a dose of 40 micrograms/30 g body weight had no inhibitory effect on the establishment of pregnancy. These results are not consistent with a critical role for PAF in implantation in mice.     

Inhibition of immune complex-induced enteropathy by three different platelet-activating factor receptor antagonists.

We previously showed that intravenous injection of rat anti-BSA-BSA complexes (IC) prepared in 5x antigen excess rapidly induced a striate pattern of serosal (to mucosal) hemorrhage and vascular congestion throughout the small intestine of the Sprague-Dawley rat. In this study, we tested the effect of three different platelet-activating factor (PAF) receptor antagonists on the development of lesions. L-652,731, a synthetic derivative of kadsurenone (at doses of 1.3-2.7 mg/kg), SRI 63-675, a substituted quinolinium compound (6.7-15 mg/kg), and WEB 2086, a thienotriazolodiazepine (5-25 mg/kg) were each capable of completely or partially inhibiting IC-induced enteropathy in the majority of animals tested. Pretreatment with WEB 2086 prevented IC-induced hemoconcentration but not neutropenia. The antagonists did not lower the level of blood complement nor interfere with the fall in complement induced by administration of IC. The ability of PAF receptor antagonists to completely or partially inhibit IC-induced small intestinal lesions suggests that endogenous PAF is a major mediator of IC-induced enteropathy.     

Influence of honey on orally and intravenously administered diltiazem kinetics in rabbits

Effect of honey on plasma concentration of diltiazem after oral and intravenous administration in rabbits, has been studied. For oral study, single dose of diltiazem (5 mg/kg, p.o.) along with saline was administered to New Zealand white rabbits (n=8). Blood samples were collected at 0, 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, 6 and 8 hr after drug administration from marginal ear vein. After a washout period of one week, diltiazem was administered with honey (2.34 ml/kg; p.o.) and the blood samples were collected as above. To the same animals honey (2.34 ml/kg; p.o.) was continued once daily for 7 days. On 8th day, honey and diltiazem were administered simultaneously and blood samples were collected at similar time intervals as mentioned above. For intravenous study the pharmacokinetic was done in each animal on two occasions. The first study was done after single dose administration of diltiazem (5 mg/kg; i.v.) along with saline (2.34 ml/kg; p.o.). Blood samples were collected at 0, 0.083, 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4 and 6 hr after i.v. diltiazem administration. The same animals were treated with honey (2.34 ml/kg; p.o.) for seven days. On day 8, the second study was carried out with single dose i.v. administration of diltiazem along with honey (2.34 ml/kg; p.o.) and blood samples were collected. In the oral study, single dose administration of honey decreased the AUC and Cmax of diltiazem associated with significant increase in clearance and volume of distribution when compared to saline treated group. After one week administration of honey, diltiazem kinetic data showed further reduction in AUC and Cmax and increase in clearance and volume of distribution. In the i.v. study also, multiple dose administration of honey significantly reduced the AUC and increased the clearance value of diltiazem. The results suggest that honey may decrease the plasma concentration of diltiazem after its oral or i.v. administration in rabbits.     

Inhibition of immune complex-induced enteropathy by three different platelet-activating factor receptor antagonists

We previously showed that intravenous injection of rat anti-BSA-BSA complexes (IC) prepared in 5x antigen excess rapidly induced a striate pattern of serosal (to mucosal) hemorrhage and vascular congestion throughout the small intestine of the Sprague-Dawley rat. In this study, we tested the effect of three different platelet-activating factor (PAF) receptor antagonists on the development of lesions. L-652, 731, a synthetic derivative of kadsurenone (at doses of 1.3–2.7 mg/kg), SRI 63–675, a substituted quinolinium compound (6.7–15 mg/kg), and WEB 2086, a thienotriazolodiazepine (5–25 mg/kg) were each capable of completely or partially inhibiting IC-induced enteropathy in the majority of animals tested. Pretreatment with WEB 2086 prevented IC-induced hemoconcentration but not neutropenia. The antagonists did not lower the level of blood complement nor interfere with the fall in complement induced by administration of IC. The ability of PAF receptor antagonists to completely or partially inhibit IC-induced small intestinal lesions suggests that endogenous PAF is a major mediator of IC-induced enteropathy.     

WEB 2086, a platelet-activating factor antagonist, inhibits prophenoloxidase-activating system and hemocyte microaggregation reactions induced by Trypanosoma rangeli infection in Rhodnius prolixus hemolymph

The effects of the triazolodiazepine WEB 2086, a platelet-activating factor (PAF) antagonist, on hemocyte microaggregation and prophenoloxidase (proPO)-activating system in the hemolymph, hemocoelic infection and mortality in fifth-instar larvae of Rhodnius prolixus inoculated with Trypanosoma rangeli were investigated. Hemocoelic injection of short T. rangeli epimastigotes (1x10(4) parasites/insect) in R. prolixus that were previously fed with blood containing 1muM of WEB 2086 resulted in (i) reduced hemocyte microaggregations as well as an attenuated proPO system in the hemolymph and (ii) greater parasitemia and mortality among the insects. In vitro assays using hemolymph from insects previously fed with blood containing WEB 2086 exhibited attenuated hemocyte microaggregations when T. rangeli was employed as the inducer of the reaction, and this effect was not counteracted by PAF treatment. In vitro assays using hemolymph from insects previously fed with blood, regardless of WEB 2086 presence increased the PO activity when incubated with the parasites. However, the PO activity was drastically inhibited when hemolymph from insects fed with blood, whether or not it contained WEB 2086, was incubated with fat body homogenates from insects fed with blood containing WEB 2086. The addition of PAF did not enhance the PO activity. These analyses did not reveal any PAF influence on WEB 2086 effects in the two defense reactions.     

Attenuation of amiodarone induced lung fibrosis and phospholipidosis in hamsters, by treatment with the platelet activating factor receptor antagonist, WEB 2086

Therapeutic use of amiodarone (AMD), a Class III antiarrhythmic drug is complicated by the development of lung fibrosis (LF) and phospholipidosis (PL). In the present study, the effectiveness of a PAF antagonist, WEB 2086, against AMD induced LF and PL has been tested in hamsters. The animals were randomly divided into four groups: (1) saline + H(2)O; (2) WEB + H(2)O; (3) saline + AMD; and (4) WEB + AMD. Saline or WEB (10 mg/kg i.p.) was given 2 days prior to intratracheal instillation of water or AMD (1.5 mumol/0.25 ml/100 g BW) and thereafter daily throughout the study. Twenty-eight days after intratracheal instillation, the animals were killed and the lungs processed for various assays. The amount of lung hydroxyproline, an index of LF, in saline + H(2)O, WEB + H(2)O, saline + AMD, and WEB + AMD groups were 959 +/- 46, 1035 +/- 51, 1605 +/- 85 and 1374 +/- 69 mug/lung, respectively. Total lung PL, an index of phospholipidosis, in the corresponding groups were 8.4 +/- 0.4, 8.3 +/- 0.3, 11.7 +/- 0.3 and 9.9 mug/lung. Lung malondialdehyde, an index of lipid peroxidation and superoxide dismutase activity in saline + H(2)O WEB + H(2)O, saline + AMD, and WEB + AMD were 93.0 +/- 4.3, 93.0 +/- 2.7, 138.9 +/- 6.0 and 109.0 +/- 3.8 nmol/lung and 359.7 +/- 13.9, 394.0 +/- 22.8, 497.5 +/- 19.7 and 425.5 +/- 4.9 units/lung, respectively. Administration of AMD alone caused significant increases in all the above indexes of lung toxicity, and treatment with WEB 2086 minimized the AMD induced toxicity as reflected by significant decreases in these indexes. Histopathological studies revealed a marked reduction in the extent and severity of lung lesions in the WEB + AMD group compared with the saline + AMD group. Treatment with WEB 2086 also reduced the acute mortality from 35% in saline + AMD group to 22% in WEB + AMD group. It was concluded that PAF is involved in the AMD induced lung fibrosis and phospholipidosis and that the PAF receptor antagonist may, therefore, be potentially useful in reducing AMD induced lung toxicity.     

Acute toxicities of 2-dialkylaminoalkyl-(dialkylamido)-fluoro-phosphates.

Toxicities expressed as LD50 values of 2-dialkylaminoalkyl-(dialkylamido)-fluorophosphates for rats and mice (i.m. administration) were determined. Rats were more sensitive to these compounds than mice: LD50 values varied from 17 (rats) to 1222 (mice) micrograms/kg. LD50 values at different routes of administration (i.v., i.m., s.c., p.o. and p.c.) for one derivative of this group, 2-dimethylaminoethyl-(dimethylamido)-fluorophosphate, were determined. Depending on the route of administration, LD50 values varied from 11 (i.v.) to 190 (p.o.) micrograms/kg for rats and from 27.6 (i.v.) to 222 (p.o.) micrograms/kg for mice, respectively. Percutaneous toxicity in rats only (LD50 = 1366 micrograms/kg) was determined.