Effects of FPL-55712 or indomethacin on leukotriene-induced coronary constriction in the intact pig heart

SK&F S-106203 inhibits leukotriene C4, leukotriene D4 and leukotriene E4 vasopressor responses in the conscious rat

1. The purpose of these experiments was to investigate the effects of the selective peptidoleukotriene receptor antagonist, SK&F S-106203, on leukotriene C4 (LTC4), LTD4 and LTE4 vasopressor responses in the conscious, normotensive rat. SK&F S-106203 was administered as a bolus followed by a continuous infusion in order to provide information on the relationship between antagonism of leukotriene responses and steady-state plasma concentrations. 2. Infusion of SK&F S-106203 at doses of 0.2 mgkg-1 + 1 mgkg-1 h-1, 1 mgkg-1 + 3 mgkg- h-1 or 2 mgkg-1 + 10 mgkg-1 h-1 produced dose-dependent steady-state plasma drug concentrations of 1.0, 3.2 and 23.8 micrograms ml-1, respectively. Plasma SK&F S-106203 concentrations appeared to increase in a linear fashion at doses of 1 and 3 mgkg-1 h-1; at the highest dose the increment in plasma drug concentrations (i.e., 7-8 fold) was greater than the increment in dose (i.e., 3 fold), suggesting saturation of the primary clearance mechanism(s) at this dose. 3. SK&F S-106203 (2 mgkg-1 + 10 mgkg-1 h-1) had no effect on noradrenaline-, vasopressin-, isoprenaline-, or U 46619-induced responses. 4. SK&F S-106203 produced dose-dependent rightward shifts in the LTC4 and LTE4 dose-response curves. Administration of SK&F S-106203 at doses of 0.2mg kg1 + 1 mg kg1 h-, mg kg' + 3mgkg-'h-1, or 2mgkg-' + lOmgkg-1h'- produced dose-ratios of 1.0, 3.1 and 19.9, respectively, against LTC4 responses, and dose-ratios of 1.6, 3.8 and 9.1, respectively, against LTE4 responses. 5. Against LTD4 responses, SK&F S-106203 at doses of 0.2mgkg- + mgkg-1 h-, mg kg' + 3 mg kg- 1h - ', or 2 mg kg- + 10 mg kg- h- produced dose-ratios of 2.5, 2.8, and 11.4, respectively. Administration of D-penicillamine, a non-competitive LTD4 dipeptidase inhibitor, had no effect on LTD4 responses. 6. The similarity in the LTD4 dose-ratios at the two lower infusion rates, despite increases in the plasma drug concentrations, suggests the existence of pharmacologically heterogeneous LTD4 receptors. These results indicate that SK&F S-106203 is a potent, selective and apparently competitive antagonist of LTC4, LTD4 and LTE4 vascular responses in the intact rat.

Ischemia-induced epicardial vasoconstriction. A potential mechanism for distant myocardial ischemia

This study evaluated the effects of transient coronary occlusion on the diameter of a nonischemic vessel or a nonischemic coronary segment proximal to the site of occlusion. Awake mongrel dogs chronically instrumented with dimension crystals, Doppler flow probes, and distal pneumatic occluders on the circumflex coronary arteries were subjected to transient 2-minute circumflex occlusions (n = 9) under constant heart rate (120 beats/min). Left ventricular end-diastolic pressure increased by 60% (from 10 +/- 1 to 16 +/- 2 mm Hg), and dP/dt decreased by 8% (from 2,048 +/- 130 to 1,885 +/- 110 mm Hg/sec); systemic hemodynamics were unaltered. Epicardial coronary diameter proximal to the site of occlusion decreased by 4.37% (from 3.62 +/- 0.25 to 3.46 +/- 0.29 mm, p less than 0.05). Constriction began 15-20 seconds after the onset of ischemia and progressed to maximum in 1-2 minutes. Combined alpha- and beta-receptor blockade (n = 8) with phentolamine (2 mg/kg) and propranolol (1 mg/kg) or cyclooxygenase inhibition (n = 5) with indomethacin (7.5 mg/kg) did not attenuate the ischemia-induced vasoconstriction response. Transient 2-minute occlusion of the left anterior descending coronary artery (n = 6) also elicited significant epicardial vasoconstriction in the circumflex coronary artery in the first minute (from 3.88 +/- 0.31 to 3.81 +/- 0.31 mm, p less than 0.05); the constriction was attenuated subsequently by an increase (25.5%) in circumflex flow. When left anterior descending occlusion was repeated (n = 6) with circumflex flow held constant, the ischemia-induced circumflex constriction was augmented; diameter decreased 3.7% (from 3.83 +/- 0.29 to 3.69 +/- 0.29 mm, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Indomethacin and LY171883 modify porcine cardiopulmonary responses to leukotrienes

We evaluated the effects of leukotriene (LT) C4 (0.8, 1.6, 2.4 nmol/kg), LTD4 (0.2, 1.0, 2.0 nmol/kg), and LTE4 (4.6 nmol/kg) on the cardiopulmonary system in anesthetized pigs. LTC4 and LTD4 increased mean pulmonary arterial (Ppa), mean aortic (Pma), and peak tracheal (Pt) pressures and decreased cardiac index (Cl). After indomethacin (cyclooxygenase blocker) or indomethacin + LY171883 (LTD4/LTE4 receptor antagonist), the highest doses of sulfidopeptide LTs were repeated. Indomethacin attenuated the increased Ppa and Pt, but did not affect the decreased Cl or increased Pma; LY171883 blocked or greatly attenuated the residual responses. LY171883 (without indomethacin) also blocked or greatly attenuated the LT-induced increases in Ppa and Pma and the decrease in Cl. We conclude that sulfidopeptide LTs cause potent systemic and pulmonary vasoconstriction in the anesthetized pig. Moreover, approximately two-thirds of the pulmonary arterial hypertension is indirectly mediated (i.e., cyclooxygenase products), with the residual one-third possibly due to direct LT-receptor stimulation. On the other hand, systemic vasoconstriction and decreased Cl are independent of cyclooxygenase products, and thus are likely to be directly mediated by LTs. The data support an important interaction between LT receptors and release of cyclooxygenase products.

Modulation of arachidonic acid metabolites and vulnerability to ventricular fibrillation during myocardial ischemia in the cat

To determine the relative importance of arachidonic acid pathway products on vulnerability to ventricular fibrillation (VF), we examined the effects of synthesis inhibitors and a receptor blocker acting in the cyclooxygenase (C) and lipoxygenase (L) pathways on VF thresholds in a feline model of coronary occlusion. Thresholds for the induction of VF wer measured before and after a 5-minute coronary occlusion in drug-treated animals and control subjects. Animals were treated with BW755c, a dual L and C inhibitor, CGS-8515, and L inhibitor, FPL-55712, a leukotriene receptor blocker, or sulfinpyrazone, a C inhibitor. BW755c, CGS-8515, and FPL-55712 all prevented an otherwise significant fall in VF threshold during coronary occlusion (p less than 0.01) independent of an effect on effective refractory period, heart rate, or blood pressure. In contrast, sulfinpyrazone, the only compound devoid of an effect on the L pathway, did not protect against an occlusion-related fall in VF threshold. BW755c and CGS-8515 inhibited the synthesis of L and C metabolites coincident with their protection against VF (p less than 0.01). We conclude that agents that antagonize the effects of L products protect against enhanced ventricular vulnerability during acute ischemia, whereas C inhibition alone may not afford this protection.

Effects of a new thromboxane A2-antagonist (ONO-3708) and a new leukotriene-antagonist (ONO-1078) on thromboxane A2 analogue-, leukotriene C4-, and D4-induced regional myocardial blood flow reduction

Effects of the administration of a thromboxane A2 (TXA2) analogue (STA2), a leukotriene C4 (LTC4), and a leukotriene D4 (LTD4) on regional myocardial blood flow (RMBF) and hemodynamics were studied in anesthetized, open-chest dogs. The blocking ability of a recently synthesized TXA2 selective antagonist, ONO-3708, and a peptidoleukotriene-selective antagonist, ONO-1078, was also investigated. RMBF was measured continuously in three areas: the left anterior descending coronary artery (LAD) area, the circumflex artery (Cx) area, and the area between LAD and Cx. STA2, LTC4, and LTD4 caused a significant dose-dependent reduction of the RMBF in the LAD area. The peak percentage decrease in RMBF followed by a 10 micrograms dose of STA2, 1 micrograms dose of LTC4, and 1 micrograms dose of LTD4 is 38.6% +/- 3.0%, 39.0% +/- 3.1%, and 36.2% +/- 2.4%, respectively. ED50 for the action of LTC4, LTD4, and STA2 on RMBF is 3, 3, and 50 micrograms, respectively. Pretreatment with the newly developed TXA2 antagonist, ONO-3708 (1 micrograms/kg/min for 10 min), completely inhibited the RMBF reduction induced by STA2 (10 micrograms). Pretreatment with the peptidoleukotriene antagonist, ONO-1078 (1 mg), inhibited the RMBF reduction induced by LTC4 or LTD4 (0.3-3 micrograms). Following pretreatment with a 1 mg dose of ONO-1078, the peak percentage decrease of RMBF caused by a 1 micrograms dose of LTC4 and LTD4 was reduced to 21.1% +/- 2.3% and 19.8% +/- 3.1%, respectively. However, the LTC4 (1 micrograms)-induced reduction of the RMBF was not affected by pretreatment with a TXA2 antagonist, ONO-3708, or an inhibitor of the endogenous production of TXA2, OKY-046.(ABSTRACT TRUNCATED AT 250 WORDS)

Leukotriene C4- and D4-induced diffuse peripheral constriction of swine coronary artery accompanied by ST elevation on the electrocardiogram: angiographic analysis

Effects of leukotriene (LT) C4 and LTD4 on coronary artery spasm in atherosclerotic miniature pigs were examined angiographically. Endothelial balloon denudation of the left circumflex coronary artery was performed in 15 Göttingen miniature pigs; 11 were fed a 2% cholesterol diet and four were fed a regular diet for 3 months. Three months after this denudation, the area of the coronary artery was reduced by 94 +/- 2% and 43 +/- 5% (p less than .01) in the denuded and nondenuded areas by the intracoronary administration of 10 micrograms/kg histamine after pretreatment with 60 mg/kg iv cimetidine. The effects of LTC4 and LTD4 on coronary diameter and the preventive effects of FPL-55712, a LTC4 and LTD4-receptor blocker, or diphenhydramine, a histamine H1-receptor blocker, on histamine-induced coronary spasm were then examined angiographically. Administration of LTC4 or LTD4 in doses of 1 and 10 micrograms into the left coronary artery, or selectively into the left circumflex and left anterior descending coronary arteries in a dose of 5 micrograms, led to the elevations in the ST segment on the electrocardiogram and there was delayed filling of the contrast medium in the peripheral coronary artery. However, these LTs provoked no augmented constrictions at any site on the epicardial coronary arteries (n = 15). Diphenhydramine, 1 mg/kg (n = 6), abolished the histamine-induced coronary spasm FPL-55712, 0.1 mg/kg, with which the LT-induced myocardial ischemia was abolished, did not prevent the histamine-induced coronary artery spasm.(ABSTRACT TRUNCATED AT 250 WORDS)

Leukotrienes increase levels of prostanoids in cerebrospinal fluid in piglets

We investigated effects of exogenous leukotrienes (C4, D4, or E4) on levels of prostanoids in cerebrospinal fluid in newborn pigs (1-5 days). A "closed" cranial window was placed over the parietal cortex. Pial arterial diameter was measured with a microscope and electronic micrometer system. Levels in cerebrospinal fluid (CSF) of 6-keto-Prostaglandin F1 alpha (6-keto-PGF1 alpha), Thromboxane B2 (TXB2), and Prostaglandin E2 (PGE2) were measured by radioimmunoassay. Topical application of leukotrienes C4, D4, or E4 (5,000 ng/ml) similarly constricted pial arteries by 15 +/- 2% (n = 14) (mean +/- SEM). In addition, leukotrienes increased levels of 6-keto-PGF1 alpha from 806 +/- 136 to 1,612 +/- 304 pg/ml (n = 13), TXB2 from 161 +/- 31 to 392 +/- 81 pg/ml (n = 10), and PGE2 from 2,271 +/- 342 to 4,636 +/- 740 pg/ml (n = 13). Each type of leukotriene had similar effects on prostanoid synthesis. In other experiments (n = 5), we found that 2.0 ng/ml PGE2 in CSF dilated pial arteries by 24 +/- 8% and that 1.0 ng/ml PGI2 dilated pial arteries by 15 +/- 6%. These results indicate that leukotrienes are able to increase levels of prostanoids in cerebral cortex.

Leukotrienes on porcine hemodynamics and prostanoid release

We studied the effect of intracoronary leukotriene B4, C4, D4 and E4 (0.1-3 micrograms) on coronary artery blood flow and resistance in anesthetized pigs. Conventional hemodynamics were measured, and the peripheral electrocardiogram was obtained in lead II. Thromboxane B2 and 6-keto-prostaglandin F1 alpha (as breakdown products of thromboxane and prostacyclin, respectively) were measured during the influence of leukotrienes on the heart. All leukotrienes except B4 reduced coronary flow. Peak reduction was produced by 3 micrograms of each eicosanoid: C4 = 96 +/- 4%+; D4 = 98 +/- 2%+; E4 = 82 +/- 8%+. Coronary resistance increased after the same dose B4 = 65 +/- 18%; C4 = 225 +/- 94% (P less than 0.01); D4 = 442 +/- 118%+; E4 = 110 +/- 43% (+ = P less than 0.001). Increase in filling pressure and heart rate but blood pressure reduction and diminution in left ventricular d P/dtmax were observed with leukotriene C4, D4 and E4. The S-T segments of the electrocardiogram were elevated, thus indicating myocardial ischemia during the blood flow reduction. Indomethacin (5 mg/kg i.v.) had no effects on the leukotriene-induced hemodynamic sequelae. Thromboxane B2 concentration in coronary sinus blood plasma increased by 132-176% (P less than 0.05) at peak leukotriene effects on blood flow. Thus, leukotriene C4, D4, and E4 are vasoconstrictors in the situ porcine heart. Leukotriene B4, however, exerts no hemodynamic effects. The electrocardiographic ischemia and changes in hemodynamics indicate actions on coronary resistance and myocardial depression. These eicosanoids may contribute to cardiac dysfunction and vasospasm in coronary artery disease.

[Eicosanoids and phospholipases]

Prostaglandins, thromboxanes, and leukotrienes have been implicated to play an important role in physiology as well as in a growing list of pathophysiologic conditions. These oxidation products of 8.11.14-eicosatrienoic-, 5.8.11.14.-eicosatetraenoic-, and 5.8.11.14.17.-pentaenoic acids have been collectively designated eicosanoids. Many clinically important diseases are associated with altered eicosanoid biosynthesis. Furthermore, a series of hormones are known to induce acutely formation of eicosanoids, suggesting a crucial role in a multitude of tissue responses including phenomena such as secretion, platelet aggregation, chemotaxis, and smooth muscle contraction. The major precursor for the eicosanoids seems to be 5.8.11.14.-eicosatetraenoic acid or arachidonic acid. Virtually all of arachidonic acid however is present in esterified form in complex glycerolipids. Since cyclooxygenase and the lipoxygenases utilize arachidonic acid in its free form, a set of acylhydrolases is required to liberate arachidonic acid from membrane lipids before eicosanoid formation can occur. It became only recently apparent that a minor acidic phospholipid, phosphatidylinositol, comprising only 5%-10% of the phospholipid mass in mammalian cells, plays an important role in arachidonic acid metabolism. Phosphatidylinositol--after phosphorylation to phosphatidylinositolphosphate and phosphatidylinositolbisphosphate--appears to be hydrolyzed by specific phospholipases C generating 1-stearoyl-2-arachidonoyl-diglyceride. Diglyceride serves as substrate for diglyceride lipase to form monoglyceride and free fatty acid. Alternatively diglyceride is phosphorylated by diglyceride kinase yielding phosphatidic acid, which is believed to be reincorporated into phosphatidylinositol. In addition to phosphatidylinositol phosphatidylcholine, phosphatidylethanolamine and phosphatidic acid may contribute to arachidonic acid release. These phospholipids are substrates for phospholipases A2 generating free arachidonic acid and the respective lysophospholipid. Understanding of the biochemistry of arachidonic acid liberation may be critical in developing strategies of pharmacological intervention in a variety of pathological conditions.

Nifedipine on cardiovascular leukotriene D4 actions in the anaesthetized dog

Open-chest dogs were used to study the effects of intracoronary leukotriene (LTD4; 0.5 microgram/kg) on haemodynamics, coronary blood flow in the left circumflex artery and coronary resistance in the absence or presence of nifedipine (10 micrograms/kg, i.v.). LTD4 increased ventricular filling pressure by 133% (P less than 0.001), the S-T segments and coronary resistance by 490% (P less than 0.001) and abolished coronary flow for 3 min. Nifedipine pretreatment inhibited the cessation of coronary flow. No change in filling pressure and no ischemia signs in the peripheral ECG were noted. However, nifedipine did not inhibit the LTD4-induced decrease in left ventricular dP/dtmax. Haemodynamic LTD4 actions thus could be partially reversed by i.v. nifedipine, suggesting that leukotriene effects on the coronary and peripheral circulation are mediated by calcium release.

Actions of cysteinyl leukotrienes in coronary, femoral and carotid vessels of the pig

Coronary, femoral and carotid vascular beds of anaesthetised pigs were perfused with heparinised arterial blood using an extracorporeal perfusion system. Blood flow was measured in each vascular bed. Leukotriene (LT) D4 caused a dose-related reduction in flow in the left anterior descending (LAD) artery. LTs C4 and D4, angiotensin and noradrenaline caused dose-related reductions in flow in femoral and carotid vascular beds. High doses of LTD4 caused total cessation of blood flow in the LAD and femoral beds. In the femoral and carotid beds LTC4 but not LTD4 caused an initial increase followed by a prolonged reduction in flow. Indomethacin (1.4 X 10(-5) mol kg-1, i.v.) did not affect the vasoconstrictor action of LTs.

C-6-sulfidopeptide leukotrienes are unlikely to be involved in the endothelium dependent relaxation of rabbit aorta by acetylcholine

Acetylcholine (ACh) induced dilation of precontracted strips of rabbit aorta by a mechanism dependent on an intact endothelium, probably by releasing an unknown endothelial relaxing factor (ERF). The relaxation was completely inhibited by the lipoxygenase inhibitor nordihydroguaiaretic acid (10(-5) M) but not by the cyclooxygenase inhibitor indomethacin (10(-5) M). The aortic strips were found to release small amounts of a material with a leukotriene-like activity. Its action on the guinea pig ileum was antagonized by FPL 55712 (10(-6) M). However, FPL 55712 (10(-6) - 10(-4) M) did not alter the response of rabbit aortic strips to ACh. Also when decreasing intracellular concentrations of glutathion (GSH) by incubating the strips with diethylmaleat or 2-cyclohexen-1-one (both 10(-3) M) the vasodilator response could still be elicited. Leukotriene (LT) C4 and LTD4 (10(-9) - 10(-6) M) were found to be ineffective on aortic strips under basal or induced tension. The same held true for LTE4 (10(-9) - 10(-7) M). At 10(-6) M, however, LTE4 induced slight relaxations of the vascular tissues. For reasons discussed this is likely to be a pharmacological action independent of the effects of endogenous ERF (e.g. inhibition of the formation of the LTE4 precursor LTD4 by high extracellular GSH concentrations did not reverse the ACh-induced vasodilation). It is concluded from these data, that C-6-sulfidopeptide leukotrienes, although probably produced by vascular tissue, are unlikely to be involved in the ACh-induced relaxation of rabbit aorta.

Leukotriene D4-induced hypotension is reversed by thyrotropin-releasing hormone

Injection of leukotriene D4 (LTD4, 20 micrograms/kg, i.a.) to conscious spontaneous hypertensive (SHR) rats produces a short-lasting pressor and tachycardic response followed by prolonged hypotension and bradycardia. Plasma norepinephrine and epinephrine were elevated at the peak pressor/tachycardic phase as well as at the hypotensive phase. Injection of thyrotropin-releasing hormone (TRH, 2 or 5 mg/kg) at the peak of the LTD4-induced hypotension resulted in prompt reversal of the hypotension and bradycardia in a dose-related manner. Naloxone (5 mg/kg) had no effect on blood pressure and heart rate of LTD4-treated SHR rats. Pretreatment with TRH (5 mg/kg) did not prevent the depressor effect of LTD4, but attenuated the bradycardic effect of this leukotriene. In addition, TRH had no effect on LTD4-induced hypotension in the pithed SHR rat. These results suggest that TRH might exert beneficial effects in hypotensive states mediated by leukotrienes or other mediators of anaphylactic reactions.