GR 32191B Research Articles

Maturation reveals a decrease in endothelium-dependent contraction induced by depolarization in the aorta of spontaneously hypertensive rats

The influence of the endothelium on aortic contractility to KCl 100 mM was studied during maturation and aging in normotensive Wistar and spontaneously hypertensive rats (SHR). In Wistar rats, there was no significant difference in maximal responses in the course of aging whether the endothelium was present (E+) or not (E−). A similar result was obtained in SHR E− rings. However, contraction was significantly higher in E+ rings of young (9 weeks) compared to adult and old SHR (18, 25, 36 and 72 weeks) (in mN/mm 2: 34.8 ± 3.1 versus 24.8 ± 1.8, 16.0 ± 2.5, 17.4 ± 2.0 and 12.9 ± 1.8, p<0.01). This increase remained significant in 18- compared to that of 25-, 36- and 72-week-old rats (p<0.01). No change appeared with age in noradrenaline-induced contractions of E+ rings neither in Wistar nor in SHR. A dose-dependent decrease in response to KCl was observed after an in vivo pre-treatment of the young SHR with acetylsalicylic acid. Finally, blocking the TXA 2/ PGH 2 receptor by addition of GR 32191B or ONO-3708 led to a decrease in the response of young SHR aortic rings to KCl. This study points out a decrease in the response of SHR aortic rings to a depolarizing agent during maturation. The enhanced contraction observed in young SHR seems to be the result of an increased participation of an endothelium-derived, cyclooxygenase-dependent contracting factor(s), most likely either TXA 2 or PGH 2. This factor might play a key role in the onset of hypertension in the spontaneously hypertensive strain.

Characterization of endothelial factors involved in the vasodilatory effect of simvastatin in aorta and small mesenteric artery of the rat.

1. Vascular effects of the 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitor, simvastatin, were studied in conductance (aorta) and resistance vessels (branch II or III of superior mesenteric artery, SMA) of the rat (12 - 14 weeks old). 2. Simvastatin produced relaxation of both aorta and SMA, with and without functional endothelium. These responses were inhibited by the product of HMG-CoA reductase, mevalonate (1 mmol l(-1)). 3. In vessels with functional endothelium, the NO-synthase inhibitor, L-N(G)-nitroarginine (L-NOARG, 30 micromol l(-1)), inhibited simvastatin-induced relaxation. In the presence of L-NOARG, relaxation to simvastatin was lower in vessels with endothelium than in endothelium-denuded arteries without L-NOARG. 4. The cyclo-oxygenase inhibitor, indomethacin (10 micromol l(-1)), abolished endothelium-dependent component of the response to simvastatin in both arteries. The combination of L-NOARG plus indomethacin did not produce further inhibition. The T(p) receptor antagonist, GR 32191B (3 micromol l(-1)), did not affect relaxation in aorta but it reduced response to low concentrations of simvastatin in SMA. However, the inhibitory effect of L-NOARG was less marked in the presence of GR 32191B in aorta but not in SMA. 5. The endothelium-dependent relaxation to simvastatin was inhibited by the superoxide dismutase (SOD, 100 u ml(-1)) or by the tyrosine kinase inhibitor, genistein (30 micromol l(-1)) in the two arteries. 6. The present study shows that simvastatin produces relaxation of conductance and small arteries through mevalonate-sensitive pathway. The endothelium-dependent relaxation to simvastatin involves both NO and vasodilator eicosanoids by a mechanism sensitive to SOD, and to genistein. Also, the results highlighted participation in the aorta of endothelial vasoconstrictor eicosanoids acting on the T(p) receptor after blockage of NO synthase only.

Vascular bed heterogeneity in age-related endothelial dysfunction with respect to NO and eicosanoids.

1. Endothelial dysfunction has been described with ageing but the mechanisms responsible have not been clearly elucidated and might be different from one vessel to the other. This study assesses the relative contribution of endothelial nitric oxide (NO) and cyclo-oxygenase (COX) metabolites in relaxation to acetylcholine with ageing in the aorta and the small mesenteric artery of the rat. 2. In the aorta and branch II or III of superior mesenteric artery (SMA), endothelium-dependent relaxation to acetylcholine was not different between 12 - 14 (adult) and 32-week-old rats whereas it was reduced at 70 - 100 (old) weeks of age. 3. Despite an increased endothelial NO-synthase protein expression, the NO-synthase inhibitor, N(G)-nitro-L-arginine-sensitive component of relaxation decreased with ageing. 4. In old rats, exposure to the COX inhibitor, indomethacin, but not the selective COX-2 inhibitor, NS-398, potentiated response to acetylcholine. The thromboxane A(2)/prostaglandin H(2) receptor antagonist, GR 32191B enhanced relaxation to acetylcholine in aorta but it had no effect in SMA. Furthermore, acetylcholine increased thromboxane B(2) production (enzymeimmunoassay) in aorta but not in SMA. Finally, Western blot analysis showed enhanced expression of COX-1 and 2 in the two arteries with ageing. 5. These results suggest that the decrease in acetylcholine-induced relaxation with ageing involves reduced NO-mediated dilatation and increased generation of vasoconstrictor prostanoids most likely from COX-1. They also point out vascular bed heterogeneity related to the nature of prostanoids involved between the aorta (i.e., thromboxane A(2)) and the SMA (unidentified) arteries even though increased expression of COX occurs in both vessels.

20-Hydroxyeicosatetraenoic acid and renal function in Lyon hypertensive rats

To evaluate the contribution of cytochrome P450 (CYP450) metabolites of arachidonic acid in the increased renal vascular resistance and blunted pressure–natriuresis response exhibited by Lyon hypertensive (LH) rats, the effects of an intrarenal infusion of 17-octadecynoic acid (3 μM), an inhibitor of the formation of epoxyeicosatrienoic and 20-hydroxyeicosatetraenoic acids, were compared in 8-week-old LH and low blood pressure (LL) control rats. 17-Octadecynoic acid failed to affect renal function in LL rats. In contrast, it reduced renal vascular resistance and shifted the pressure–natriuresis relationship to lower pressures in LH rats. Blockade of thromboxane–endoperoxide (TP) receptors with GR 32191B prevented the renal vasodilator response to 17-octadecynoic acid but not its natriuretic action. Miconazole (1 μM), an inhibitor of epoxygenase activity, had no effect on renal function in LH rats. These results indicate that CYP450 metabolites of arachidonic acid, likely 20-hydroxyeicosatetraenoic acid, contribute to the resetting of the pressure–natriuresis relation in LH rats and that the renal vasoconstrictor effects of 20-hydroxyeicosatetraenoic acid in LH rats may be related to activation of TP receptors.

Cytochrome P-450 arachidonate metabolite inhibition improves renal function in Lyon hypertensive rats

The present study evaluated the effects of miconazole, a selective inhibitor of epoxygenase activity, on renal hemodynamics and the pressure-natriuresis response of saline-drinking, uninephrectomized Lyon hypertensive (LH) and Lyon low blood pressure (LL) rats. Infusion of miconazole (final concentration, 1 μmol/L) into the renal artery had no effect on the renal function of LL rats over a range of renal perfusion pressures (RPP) from 100 to 140 mm Hg. In contrast, miconazole lowered renal vascular resistance (RVR, 17.9 ± 1.1 v 26.3 ± 1.5 mm Hg/mL/min/g, P < .01) and increased urinary sodium excretion (6.4 ± 1.2 v 4.2 ± 0.8 μmol /min/g, P < .05) in LH rats at a RPP of 140 mm Hg. To determine whether the effects of epoxyeicosatrienoic acids were dependent on activation of the thromboxane A2-prostaglandin H2 (TP) receptor, we studied the effects of a TP receptor antagonist, GR 32191B (0.1 mg/kg/min), on the renal response to an infusion of miconazole into the renal artery in LH rats. GR 32191B decreased basal RVR and prevented the dilation induced by miconazole. It did not, however, alter its natriuretic effect. The renal metabolism of arachidonic acid was also compared in LH and LL rats. The production of epoxygenase metabolites was 25% lower in microsomes prepared from the renal cortex of LH versus LL rats. Miconazole (1 μmol /L) reduced epoxygenase activity similarly, by approximately 60%, in both strains. These results suggest that endogenously formed P450 metabolites of arachidonic acid may serve as a substrate for the formation of vasoconstrictor endoperoxides that interact with TP receptors in LH rats and contribute to the enhanced renal vascular tone but not the blunted pressure-natriuresis response.

Cytochrome P-450 arachidonate metabolite inhibition improves renal function in lyon hypertensive rats

The present study evaluated the effects of miconazole, a selective inhibitor of epoxygenase activity, on renal hemodynamics and the pressure-natriuresis response of saline-drinking, uninephrectomized Lyon hypertensive (LH) and Lyon low blood pressure (LL) rats. Infusion of miconazole (final concentration, 1 μmol/L) into the renal artery had no effect on the renal function of LL rats over a range of renal perfusion pressures (RPP) from 100 to 140 mm Hg. In contrast, miconazole lowered renal vascular resistance (RVR, 17.9 ± 1.1 v 26.3 ± 1.5 mm Hg/mL/min/g, P < .01) and increased urinary sodium excretion (6.4 ± 1.2 v 4.2 ± 0.8 μmol /min/g, P < .05) in LH rats at a RPP of 140 mm Hg. To determine whether the effects of epoxyeicosatrienoic acids were dependent on activation of the thromboxane A2- prostaglandin H2 (TP) receptor, we studied the effects of a TP receptor antagonist, GR 32191B (0.1 mg/kg/min), on the renal response to an infusion of miconazole into the renal artery in LH rats. GR 32191B decreased basal RVR and prevented the dilation induced by miconazole. It did not, however, alter its natriuretic effect. The renal metabolism of arachidonic acid was also compared in LH and LL rats. The production of epoxygenase metabolites was 25% lower in microsomes prepared from the renal cortex of LH versus LL rats. Miconazole (1 μmol /L) reduced epoxygenase activity similarly, by approximately 60%, in both strains. These results suggest that endogenously formed P450 metabolites of arachidonic acid may serve as a substrate for the formation of vasoconstrictor endoperoxides that interact with TP receptors in LH rats and contribute to the enhanced renal vascular tone but not the blunted pressure-natriuresis response. Am J Hypertens 1999;12:398–404 © 1999 American Journal of Hypertension, Ltd.

Pharmacological characterization of thromboxane and prostanoid receptors in human isolated urinary bladder.

1. Cumulative concentration-response curves (CRC) to prostaglandin E1 (PGE1), PGE2, PGD2 and PGF2alpha (0.01-30 microM) and to the thromboxane A2 (TXA2) receptor agonist U-46619 (0.01-30 microM) were constructed in human isolated detrusor muscle strips both in basal conditions and during electrical field stimulation. 2. All the agonists tested contracted the detrusor muscle. The rank order of agonist potency was: PGF2alpha > U-46619 > PGE2 whereas weak contractile responses were obtained with PGD2 and PGE1. Any of the agonists tested was able to induce a clear plateau of response even at 30 microM. 3. The selective TXA2 antagonist, GR 32191B (vapiprost), antagonized U-46619-induced contractions with an apparent pK(B) value of 8.27+/-0.12 (n = 4 for each antagonist concentration). GR 32191B (0.3 microM) did not antagonize the contractile responses to PGF2alpha and it was a non-surmountable antagonist of PGE2 (apparent pK(B) of 7.09+/-0.04; n = 5). The EP receptor antagonist AH 6809 at 10 microM shifted to the right the CRC to U-46619 (apparent pK(B) value of 5.88+/-0.04; n = 4). 4. Electrical field stimulation (20 Hz, 70 V, pulse width 0.1 ms, trains of 5 s every 60 s) elicited contractions fully sensitive to TTX (0.3 microM) and atropine (1 microM). U-46619 (0.01-3 microM) potentiated the twitch contraction in a dose-dependent manner and this effect was competitively antagonized by GR 32191B with an estimated pK(B) of 8.54+/-0.14 (n = 4 for each antagonist concentration). PGF2alpha in the range 0.01-10 microM (n = 7), but not PGE2 and PGE1 (n = 3 for each), also potentiated the twitch contraction of detrusor muscle strips (23.5+/-0.3% of KCl 100 mM-induced contraction) but this potentiation was unaffected by 0.3 microM GR 32191B (n = 5). 5. Cumulative additions of U-46619 (0.01-30 microM) were without effect on contractions induced by direct smooth muscle excitation (20 Hz, 40 V, 6 ms pulse width, trains of 2 s every 60 s, in the presence of TTX 1 microM; n = 3). Moreover, pretreatment of the tissue with 0.3 microM U-46619 did not potentiate the smooth muscle response to 7 microM bethanecol (n = 2). 6. We concluded that TXA2 can induce direct contraction of human isolated urinary bladder through the classical TXA2 receptor. Prostanoid receptors, fully activated by PGE2 and PGF2alpha are also present. All these receptors are probably located post-junctionally. The rank order of agonist potency and the fact that GR 32191B, but not AH6809, antagonized responses to PGE2 seem to indicate the presence of a new EP receptor subtype. Moreover, we suggest the presence of prejunctional TXA2 and FP receptors, potentiating acetylcholine release from cholinergic nerve terminals.

Effects of prostaglandin E2, F2alpha, and latanoprost acid on isolated ocular blood vessels in vitro.

The vascular effects of PGE2, PGF2alpha and latanoprost acid on isolated bovine long posterior ciliary arteries and episcleral veins have been investigated using a small vessel myograph. PGE2 caused vasorelaxation both in the ciliary artery and episcleral vein (EC50: 7.9x10(-9) M and 2.1x10(-8) M respectively). Blockade of thromboxane receptors with GR 32191B, a TP receptor antagonist, shifted the concentration-response curves to the left in both preparations, probably indicating a slight co-stimulation of TP receptors in these vessels. Blockade of tachykinin NK-1 receptors had no effect on the PGE2 concentration-response curve. PGF2alpha caused a concentration dependent contraction in half of the ciliary arteries examined and relaxation in the other half. In the presence of the thromboxane receptor antagonist (GR 3211B) PGF2alpha always induced relaxation of the ciliary artery (EC50:1.3x10[-5] M). At higher concentrations PGF2alpha tended to slightly constrict the episcleral veins, but in the presence of the TP receptor antagonist (GR 32191B) only relaxation was observed. Latanoprost acid contracted the ciliary artery at concentrations above 10(-6) M. This effect was completely abolished by the TP receptor antagonist (GR 32191B). In the episcleral vein latanoprost acid induced a slight relaxation but in the presence of the TP receptor antagonist (GR 32191B) no effect was observed. These results indicate that PGE2 invariably induces vasorelaxation of bovine ciliary arteries and episcleral veins, whereas both PGF2alpha and latanoprost acid at high concentrations can cause vasoconstriction probably by stimulating TP receptors. PGF2alpha causes marked relaxation of both ciliary arteries and episcleral veins in the presence of the TP blocker which seems unlikely to be mediated by FP receptors.

Expression of Acute Otitis Media after Receptor Blockade of Platelet Activating Factor, Thromboxane, and Leukotrienes in the Chinchilla

To determine the role of inflammatory products of phospholipid metabolism in acute otitis media (AOM), we infected 128 chinchillas with Streptococcus pneumoniae and randomly assigned them to one of four equal-sized treatment groups receiving intramuscular ampicillin sodium (control) or intramuscular ampicillin plus receptor blockers of platelet activating factor (WEB 2086, 5 mg/d orally), of leukotriene (MK 571, 0.5 mg/d orally), or of thromboxaneA2 (GR 32191B, 5 mg/d orally). All treatments were begun on day 2 postinoculation and continued for 10 days. On days 3, 6, 9, and 12, 8 animals from each group were sacrificed. Effusions were recovered for biochemical assay, and the right middle ears were prepared for histologic study. Differences among groups in the number of ears with effusion or in effusion volume were not statistically significant. In comparison to the control group, mucosal thickness and the number of ears with histopathologic signs of inflammation were significantly less in the GR and WEB treatment groups, but not the MK group. Also, effusion concentrations of free fatty acids, protease, and hydrolytic enzymes were significantly less in those groups. These results show that the addition of a receptor blocker for either platelet activating factor and/or thromboxane to ampicillin in the treatment of AOM reduces mucosal inflammation and decreases the production of other inflammatory chemicals. The failure of a receptor blocker of leukotrienes to moderate disease expression suggests either a less important role for these chemicals in AOM or an insufficient bioavailability of the specific MK 571 inhibitor. These results confirm that platelet activating factor and thromboxane are active mediators of inflammation in AOM.

Mechanism of prostaglandin E 2-, F 2α- and latanoprost acid-induced relaxation of submental veins

The mechanism of prostaglandin E 2-, prostaglandin F 2α- and latanoprost acid (13,14-dihydro-17-phenyl-18,19,20-trinor-prostaglandin F 2α)-induced relaxation of the rabbit submental vein was studied. Prostaglandin E 2 caused maximum relaxation of endothelin-1 precontracted vessels (EC 50: 1.8×10 −8 M). Much of the relaxation could be abolished by denuding the endothelium with the nitric oxide synthase inhibitor, l-NAME ( N G-Nitro- l-arginine methylester). CGRP-(8–37) (calcitonin gene-related peptide fragment (8–37)), a calcitonin gene-related peptide receptor antagonist, exhibited a partial blocking effect, whereas the tachykinin NK 1 receptor blocker, GR 82334 ([ d-Pro 9[Spiro- γ-Lactam]Leu 10,Trp 11]physalaemin (1–11)), markedly attenuated the response. Both prostaglandin F 2α and the relatively selective FP receptor agonist, latanoprost acid, caused relaxation of the veins to about 50% of the precontracted state in the presence of GR 32191B ([1 R-[1α( Z),2 β,3 β,5α]]-(+)-7-[5-([1,1′-biphenyl]-4-ylmethoxy)-3-hydroxy-2-(1-piperidinyl)cyclopentyl]-4-heptenoic acid), a thromboxane receptor antagonist (EC 50: for prostaglandin F 2α 7.9×10 −9 M, and for latanoprost acid 4.9×10 −9 M). l-NAME, as well as denuding the endothelium, completely abolished the effect. In addition, most or at least a large part of the relaxation was also blocked by CGRP-(8–37) as well as GR 82334. These results indicate that the FP receptor-mediated relaxation of veins is based on release of nitric oxide in addition to involvement of calcitonin gene-related peptide and substance P, or some other tachykinin, probably released from perivascular sensory nerves. The more pronounced relaxation induced by prostaglandin E 2 could be due to vasodilator EP receptors in the smooth muscle layer of the veins.

Myocardial ischaemia induces platelet activation with adverse electrophysiological and arrhythmogenic effects.

The aim was to investigate how platelet activation during myocardial ischaemia can induce electrophysiological and arrhythmogenic effects, and examine the involvement of different platelet membrane receptors in producing these effects. Transmembrane action potentials and electrograms were recorded from isolated, Langendorff perfused guinea pig hearts during normal perfusion, global myocardial ischaemia, and reperfusion during infusion of human platelets. Platelet reactivity was altered by treating platelets with forskolin, aspirin, the platelet activating factor (PAF) receptor antagonist BN 52021, the thromboxane A2 (TP) receptor antagonist GR 32191B, and the alpha 2 adrenoceptor antagonist yohimbine. Myocardial catecholamine depletion was induced by treatment with 6-hydroxydopamine. Platelet infusion had no electrophysiological effects during normal perfusion, but during ischaemia it enhanced the reduction in action potential duration at 95% repolarisation [APD95, 110(SEM 3) ms v 121(5) ms, p < 0.05, at 15 min] and increased the incidence of ventricular arrhythmias (from 56% to 94%, p = 0.04) compared to hearts receiving buffer but no platelets. The reductions in APD95 and the arrhythmogenic effects were attenuated when forskolin treated, aspirin treated or GR 32191B treated platelets were infused (VF: 50% v 94%, p = 0.03; 50% v 94%, p = 0.02; 22% v 94%, p < 0.001, respectively). Similar results were obtained when normal platelets were infused into catecholamine depleted hearts (VF: 60% v 94%, p = 0.0549). These differences were associated with inhibited aggregatory responses to thrombin (for forskolin treated platelets) and the thromboxane mimetic U44069 (for GR 32191B treated platelets). Yohimbine was antiarrhythmic in the presence and absence of platelets, suggesting direct myocardial effects, but BN 52021 had no antiarrhythmic effects. Myocardial ischaemia causes platelet activation resulting in electrophysiological and arrhythmogenic effects. PAF receptor antagonism does not prevent these effects, but inhibition of platelet reactivity, platelet thromboxane receptor antagonism, and myocardial catecholamine depletion are effective. These findings suggest that the arrhythmogenic effects of platelet activation during myocardial ischaemia are principally mediated by a thromboxane dependent mechanism, while catecholamine release has a contributory role.

Thromboxane A2 mediates pulmonary hypertension after cardiopulmonary bypass in the rabbit

Clinically, it is well established that cardiopulmonary bypass results in pulmonary dysfunction. Using a recently developed preparation for cardiopulmonary bypass in the rabbit, we have been able to mimic a similar, but more severe, condition. We found that, despite normal histologic structure of the myocardium, hearts could not be weaned from bypass because of a serious increase in pulmonary vascular resistance. Histologic studies of the lungs showed severe intravascular neutrophil aggregation and marked vasoconstriction. To identify the nature and origin of the mediator responsible for the changes in the pulmonary vasculature, we subjected groups of rabbits (n = 4 per group) to bypass with cooling to 18 degrees C, circulatory arrest for 1 hour, and rewarming on bypass to 33 degrees C. Pulmonary vascular resistance was measured at the same temperature before and after bypass. Four groups were studied: group I were untreated controls; group II received the cyclooxygenase inhibitor, indomethacin (0.2 mg/kg intravenously), before operation; group III received the thromboxane A2 synthetase inhibitor, Dazmegral (5 mg/kg intravenously), before operation together with the thromboxane A2 receptor blocker GR 32191B (2 mg/kg per 30 minutes intravenously); and group IV were treated with mustine hydrochloride (1.75 mg/kg intravenously) 3 days before the experiment to deplete the neutrophils by 90%. During circulatory arrest, the heart was protected with an initial infusion (10 ml at 4 degrees C over 1 minute) of St. Thomas' Hospital cardioplegic solution. At the end of the experiment, the heart and lungs were histologically examined. In the control group, a significant increase (+395% when compared with the value recorded before bypass) in pulmonary vascular resistance was observed after bypass. However, in none of the treated groups did pulmonary vascular resistance increase significantly (percentage changes in groups II, III, and IV were -24%, 0%, and +33%, respectively). Pulmonary histologic characteristics were normal in all treated groups, and all animals were successfully weaned from bypass. These results indicate that the increase in pulmonary vascular resistance that arises as a consequence of bypass in rabbits is primarily a result of the production of thromboxane A2, a process in which the neutrophil plays a pivotal role.

Eicosanoid‐dependence of responses of pre‐ but not postglomerular vessels to noradrenaline in rat isolated kidneys

1. We investigated the role of nitric oxide (NO) and of vasoactive eicosanoids in the control of renal vascular resistance (RVR) and glomerular filtration rate (GFR) and of their responses to noradrenaline (NA). This study was conducted in single-pass perfused, isolated kidney preparations of the rat. 2. NA (63, 110 and 160 nM) dose-dependently increased RVR and to a lesser degree GFR. 3. In baseline conditions, N omega-nitro-L-arginine methylester (L-NAME, 100 microM) increased GFR more than RVR, thus demonstrating a basal release of NO which predominates in postglomerular vessels. 4. In kidneys stimulated with NA, L-NAME potentiated the increases in RVR but not in GFR. Indomethacin (1.5, 150 nM and 15 microM) did not alter GFR but markedly and dose-dependently reduced the NA-induced increase in RVR. Similar results were obtained with GR 32191B (10 and 100 microM), a prostaglandin H2/thromboxane A2 (PGH2/TxA2) receptor antagonist. 5. Indomethacin (15 microM) suppressed the enhancing effects of L-NAME on RVR responses to NA but did not affect those on GFR. 6. It is concluded that the mechanisms of the response to NA differ among pre- and postglomerular vessels. In preglomerular vessels the vasoconstrictor action and the NO release depend upon the activation of PGH2/TxA2 receptors, while both are eicosanoid-independent in the postglomerular vessels.

Leukotriene D4 participates in colonic transit disturbances induced by intracolonic administration of trinitrobenzene sulfonic acid in rats

The effects of colonic inflammation induced by trinitrobenzene sulfonic acid and influence of previous treatment with specific antagonists of inflammatory mediators (platelet-activating factor, leukotrienes, prostaglandins, and thromboxanes) on colonic transit were examined in conscious rats which were permanently fitted with an intracolonic catheter inserted into the proximal colon. Colonic inflammation was induced by intracolonic administration of trinitrobenzene acid (80 mg/kg) in 50% ethanol. Colonic transit time was evaluated by intracolonic administration of a radiolabeled marker ([51Cr]sodium chromate) and collection of the feces per hour on a conveyor belt. Excretion of the marker was then plotted vs. time, permitting calculations of the times elapsed to recover 25%, 50% and 75% of the marker injected (T25, T50 and T75, respectively). In control (saline) animals, excretion of the marker described a regular sigmoid curve with 50% of the marker recovered at 6.92 ± 0.40 hours after intracolonic administration (T25 = 6.4 ± 0.43 hours; T75 = 7.49 ± 0.39 hours). Ethanol (vehicle), 50%, did not modify the profile of marker recovery. On the contrary, single intracolonic administration of trinitrobenzene sulfonic acid/ethanol induced a biphasic response consisting of an early pool of radiolabeled feces (T25 = 4.03 ± 0.55 hours) with a delayed total one (T50 = 11.74 ± 0.83 hours; T75 = 13.70 ± 0.49 hours). Antagonists of the leukotriene pathway, i.e., MK = 886, a lipoxygenase inhibitor, and SKF 104,353 and SR 2640, two different leukotriene D4 receptor antagonists, blocked the effects of trinitrobenzene sulfonic acid on colonic transit time and restored a control profile of radiolabeled marker excretion. In contrast, indomethacin, a cyclooxygenase inhibitor, and SC 19220, a specific prostaglandin E2 receptor antagonist, were inefficient in blocking the effects of trinitrobenzene sulfonic acid on colonic transit time. Specific thromboxane A2 receptor antagonists, KT1-32 and GR 32191B, did not show any improvement in colonic transit after trinitrobenzene sulfonic acid administration. Previous injection of the specific platelet-activating factor receptor antagonists, BN 52021 or BN 50730, was also unable to restore a normal marker excretion profile after administration of trinitrobenzene sulfonic acid. It is concluded that the alterations of colonic transit immediately observed after intracolonic trinitrobenzene sulfonic acid administration are mediated through the release of leukotriene D4. In contrast, platelet-activating factor, prostaglandins, and thromboxanes are not involved in the mediation of these transit disturbances.