Alain Grosset

Pharmacological profile of SL 59.1227, a novel inhibitor of the sodium/hydrogen exchanger

The NHE1 isoform of the Na+/H+ exchanger plays an important role in the regulation of intracellular pH and in cardiac cell injury caused by ischaemia and reperfusion. SL 59.1227 is a novel imidazolypiperidine Na+/H+ antiport inhibitor which is structurally unrelated to previously described acylguanidine inhibitors such as cariporide. Recovery of pHi following an intracellular acid load was measured in CCL39‐derived PS120 variant cells, selectively expressing either NHE1 or NHE2 isoforms of the Na+/H+ exchanger. pHi recovery was potently and selectively slowed by SL 59.1227 in NHE1‐expressing cells (IC50 3.3±1.3 nM) versus NHE2‐expressing cells (2.3±1.0 μM). The respective IC50 values for cariporide were 103±28 nM (NHE1) and 73±46 μM (NHE2). In anaesthetized rats following left coronary artery occlusion (7 min) and reperfusion (10 min) SL 59.1227 (10–100 μg kg−1 min−1 i.v.) inhibited ischaemia‐mediated ventricular tachycardia (71–100%) and reperfusion‐induced ventricular fibrillation (75–87%) and prevented mortality. Bolus i.v. administration of SL 59.1227 (1 mg kg−1) produced anti‐arrhythmic effects when administered either before or during ischaemia. Cardiac infarct size was determined in anaesthetized rabbits following left coronary artery occlusion (30 min) and reperfusion (120 min). Infarct size measured as a percentage of the area at risk was 36.2±3.4% (control group) versus 15.3±3.9% (SL 59.1227 0.6 mg kg−1 i.v.). SL 59.1227 is the first example of a potent and NHE1‐selective non‐acylguanidine Na+/H+ exchanger inhibitor. It possesses marked cardioprotective properties.

Action of angiotensin II on teh electrical and mechanical activity of rat uterin smooth muscle

The effects of angiotensin II (A II) were studied on membrane potentials, ionic currents and isometric contractions in uterine smooth muscle strips from pregnant rats. In reference solution, A II in a low concentration (5 x 10(-9) M) exerted no effect on the resting potential or the action potential amplitude but significantly increased the rate of repetitive firing. However, in tetraethylammonium chloride (TEA)-containing solution, an increase in the action potential amplitude was always observed. The inward and outward currents were increased simultaneously, so that it was necessary to block the outward current with TEA ions in order to measure the enhancement of the inward current. The reduction of the deactivation time constants of the outward current as well as the increase in the inward current intensity could account for the acceleration of rhythmic activity in the presence of the peptide. The mechanical response to A II consisted of early tetanus which was followed by increased twitch contractions. The calcium contractures were also increased in depolarized strips. The tetanus could be dependent on the increase in and prolongation of repetitive firing while the enhancement of twitch contractions and calcium contractures could be explained by the increase in inward current intensity.

5-HT4 receptors, present in piglet atria and sensitive to SDZ 205-557, are absent in papillary muscle.

Putative 5-HT4 receptors were investigated in isolated piglet left atria and papillary muscles. In atrial tissues, 5-hydroxytryptamine (5-HT) was a potent positive inotropic agent with a pD2 of 6.7. Its effects were antagonised in a selective and competitive manner by the 5-HT4 receptor antagonist, SDZ 205-557, with a pA2 of 7.3. In contrast to atrial tissues, piglet papillary muscles were virtually unresponsive to 5-HT 10(-8)-10(-3) M, suggesting that functional cardiac 5-HT4 receptors are not present in ventricular tissue.

The pharmacological basis and pathophysiological significance of the heart rate-lowering property of diltiazem

Abstract— The calcium channel blocker diltiazem lowers heart rate in man and this property probably contributes to its clinical effectiveness in ischaemic heart disease and hypertension. This review examines the pharmacological basis of diltiazems heart rate‐lowering activity and considers its pathophysiological significance. The points discussed include the potent direct inhibitory effect of diltiazem on the sinus node and the frequency‐dependence of this action. In addition, the well‐balanced tissue selectivity profile of diltiazem and its ability to modulate cardiac reflex responsiveness contribute by counteracting the potential for reflex tachycardia.

In vivo pharmacological profile of SL 84.0418, a new selective, peripherally active α2-adrenoceptor antagonist

SL 84.0418 is a novel pyrrolo-indole derivative with potent and selective alpha 2-adrenoceptor antagonist activity in vitro and anti-hyperglycemic properties in vivo. In the present study we demonstrated that SL 84.0418 and its active (+) enantiomer, SL 86.0715, show a high degree of selectivity for alpha 2-adrenoceptors in vivo, preferentially blocking alpha 2-adrenoceptors in the periphery. While having no effects on basal blood pressure and heart rate, p.o. (3 and 10 mg/kg) or i.v. (0.3 mg/kg) administered SL 84.0418 or SL 86.0715 antagonized the hypertensive responses mediated by postsynaptic vascular alpha 2-adrenoceptors after the administration of UK 14304 or norepinephrine to pithed rats. The (-) enantiomer of SL 84.0418, SL 86.0714, was devoid of alpha 2-adrenoceptor antagonist properties in vivo, while the (+) enantiomer of SL 84.0418, SL 86.0715, showed alpha 2-adrenoceptor antagonist activity similar to that of the racemate. SL 84.0418 (3 mg/kg p.o.) did not modify the centrally mediated hypotensive and bradycardic effects of i.c.v. administered clonidine. Furthermore, in the mouse, SL 84.0418 potently antagonized the hyperglycemic responses to epinephrine or UK 14304, which are mediated by peripheral alpha 2-adrenoceptors, but failed (in doses up to 30 mg/kg i.p.) to antagonize the clonidine-induced hypolocomotion, which is mediated by central alpha 2-adrenoceptors. These results suggest that SL 84.0418 preferentially antagonizes peripheral alpha 2-adrenoceptors. SL 84.0418 administered to pithed rats (3 mg/kg p.o. or 0.3 mg/kg i.v.) did not modify the vasoconstriction induced by cirazoline (effect mediated by alpha 1-adrenoceptors) nor the tachycardia induced by norepinephrine (effect mediated by beta-adrenoceptors).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular effects of SL65.0472, a 5-HT receptor antagonist.

In this study, we describe the cardiovascular effects of SL65.0472 (7-fluoro-2-oxo-4-[2-[4-(thieno[3,2-c] pyridin-4-yl) piperazin-l-yl] ethyl]-1, 2-dihydroquinoline-1-acetamide), a novel 5-hydroxytryptamine (5-HT) receptor antagonist developed for the treatment of cardiovascular disease, in several in vivo models. The haemodynamic profile of SL65.0472 was evaluated in anaesthetised dogs. Following i.v. bolus doses of 0.03 mg/kg i.v. and 0.3 mg/kg, no significant changes in cardiac output, contractility or rate, systemic and pulmonary pressures, regional blood flows and vascular resistances or electrocardiogram were noted. After 1 mg/kg i.v. SL65.0472 significantly reduced arterial blood pressure. In conscious spontaneously hypertensive rats administration of SL65.0472 0.5 mg/kg p.o. had no effect on mean arterial blood pressure or heart rate. Vasoconstriction produced by 5-HT results primarily from the stimulation of two receptor subtypes, 5-HT(1B) and 5-HT(2A) receptors. In anaesthetised dogs SL65.0472 antagonised sumatriptan-induced decreases in saphenous vein diameter (5-HT(1B)-receptor mediated) with an ID(50) of 10.1 microg/kg i.v. (95% c.l. 8.3-12.4). In anaesthetised pithed rats SL65.0472 inhibited 5-HT pressor responses (5HT(2A)-receptor mediated) with ID(50) values of 1.38 microg/kg i.v. (95% c.l. 1.15-1.64) and 31.1 microg/kg p.o. (95% c.l. 22.6-42.6). The duration of the 5-HT(2A)-receptor antagonist effect of SL65.0472 following oral administration was evaluated in conscious rats. SL65.0472 (0.1 mg/kg p.o.) markedly inhibited 5-HT pressor responses 1 and 6 h after administration. Therefore, in vivo, SL65.0472 potently antagonises vasoconstriction mediated by 5-HT(1B) and 5-HT(2A) receptors but has minimal direct haemodynamic effects.

Antithrombotic actions of the thrombin inhibitor, argatroban, in a canine model of coronary cyclic flow: comparison with heparin.

1 The antithrombotic action of argatroban, a synthetic thrombin inhibitor, was studied in a canine model of coronary cyclic flow having some of the characteristics of acute unstable angina. Heparin was studied as a reference anticoagulant. 2 Localized endothelial damage was induced in the circumflex coronary artery of anaesthetized open‐chest foxhounds and a critical stenosis was applied by use of a Lexan constrictor placed around the artery at the site of endothelial damage. An electro‐magnetic flow probe was placed distal to the lesion, and cyclic flow variations (CFVs) were observed, as thrombi formed at the site of the arterial lesion and were dislodged. Test compounds were administered by i.v. infusion commencing 1 h after the appearance of CFVs, and maintained for 1 h. On termination of the treatments, coronary flow was observed for a further 60 min. A series of blood samples were taken at predetermined times throughout each experiment in order to determine the coagulation parameters, thrombin time (TT) activated partial thromboplastin time (aPTT) and for the determination of fibrinopeptide A (FpA) levels before, during and post‐treatment. 3 Argatroban and heparin showed antithrombotic effects in this model. Argatroban dose‐dependently increased the minimum coronary flow at the nadir of the CFVs from 5.4 ± 1.7 to 9.1 ± 2.1 ml min−1 (30 μg kg−1 min−1, P = 0.041) and from 2.9 ± 0.9 to 16.3 ± 4.5 ml min−1 (100 μg kg−1 min−1, P = 0.023, n = 8 dogs at each dose level). Heparin (5 and 15 iu kg−1 min−1) also increased minimum flow, but the increase was not statistically significant at the 5% level, although the P value in animals treated with 15 iu kg−1 min−1 (P = 0.0521, n = 6 dogs) fell just outside this limit. Although neither compound significantly decreased the overall CFV frequency, argatroban (100 μg kg−1 min−1) significantly (P < 0.01) decreased the number of large amplitude CFVs (minimum coronary flow < 10 ml min−1) by 63%, and heparin (15 iu kg−1 min−1) caused a 50% decrease in this parameter (P < 0.05). 4 The thrombin times were increased by a factor greater than 10 during antithrombotic treatment, irrespective of the compound or doses used. Heparin treatment induced 17 and > 30 fold increases in aPTT at 5 and 15 iu kg−1 min−1 respectively. However, argatroban produced only 2 and 3 fold increases in aPTT at 30 and 100 μg kg−1 min−1, despite significant antithrombotic effects. FpA levels were reduced in the presence of both argatroban and heparin. 5 These data show that, when administered as an intravenous infusion, argatroban is a potent antithrombotic agent in a canine model of coronary cyclic flow.

SL65.0472 blocks 5-hydroxytryptamine-induced vasoconstriction in a dog hindlimb ischemia model

We have studied the ability of SL65.0472 (7-fluoro-2-oxo-4-[2-[4-(thieno[3,2-c]pyridin-4-yl)piperazin-1-yl]ethyl]-1,2-dihydroquinoline-1-acetamide), a 5-hydroxytryptamine (5-HT) 5-HT1B/5-HT2A receptor antagonist, to antagonise the vasoconstrictor effects of 5-HT and sumatriptan in a canine model of hindlimb ischemia. Dogs underwent right external iliac artery ligation and right superficial femoral artery excision, resulting in decreased perfusion (-31%, P<0.05) in the right hindlimb. Following pretreatment with L-NAME, phentolamine and propranolol, intra-aortic injection of 5-HT markedly reduced blood flow to the right ischemic hindlimb (-50 +/- 2%, P<0,05). 5-HT induced vasoconstriction was significantly inhibited (-66%, P<0.05) by SL65.0472 (300 microg/kg i.v.), but unaffected by ketanserin (300 microg/kg i.v.), a 5-HT2A receptor antagonist. SL65.0472 also blocked sumatriptan-induced vasoconstriction in ischemic and normally perfused hindlimbs. Thus, SL65.0472 is an effective antagonist of 5-HT-receptor mediated hindlimb vasoconstriction.

Comparison of the haemodynamic profiles of elgodipine and nicardipine in the anaesthetized dog.

1 The haemodynamic profile of elgodipine (1–30 μg kg−1, i.v.), a new dihydropyridine calcium antagonist, has been compared directly with that of nicardipine (1–30 μg kg−1, i.v.) in chloralose‐anaesthetized dogs. 2 Nicardipine produced dose‐related systemic, pulmonary and coronary vasodilatation accompanied by reflex tachycardia, inotropy and increases in cardiac output and myocardial oxygen consumption (MVO2). Elgodipine had similar vasodilator and hypotensive properties to nicardipine but produced less reflex inotropy, little or no reflex tachycardia and did not increase MVO2. 3 Both calcium antagonists were retested in a separate group of anaesthetized dogs pretreated with propranolol (1 mg kg−1, i.v.) and atropine (0.3 mg kg−1, i.v.) to abolish reflex autonomic tone to the heart and thus reveal the direct cardiac effects of each compound. Under these conditions both elgodipine and nicardipine decreased heart rate and cardiac contractility and slowed atrio‐ventricular conduction. Elgodipine was approximately ten times more potent than nicardipine as a decelerator agent and slightly more potent in depressing cardiac contractility and increasing PR interval duration. Elgodipine, unlike nicardipine, slightly reduced the QTc interval of the electrocardiogram. Therefore, the potent decelerator effect of elgodipine, which was present throughout the dose‐range, appears to be largely responsible for the suppression of reflex tachycardia observed when the baroreflex is functional. 4 Elgodipine is a potent systemic and coronary vasodilator with more marked direct cardiac effects than nicardipine, particularly with respect to slowing of heart rate. The ability of elgodipine to increase coronary blood flow without significant reflex tachycardia or increases in MVO2 suggests that this compound will have a more favourable effect on myocardial oxygen supply/demand balance than nicardipine. The haemodynamic profile of elgodipine may be suitable for the treatment of angina.

Combination of aspirin and metoclopramide produces a synergistic antithrombotic effect in a canine model of coronary artery thrombosis

Summary— We compared the antithrombotic properties of low doses of aspirin (0.03, 0.1 mg kg−1 intravenously [iv]) and metoclopramide (0.1, 0.3 mg kg−1 iv) alone or in combination. The animal model chosen for this study involved the generation of cyclic flow variations (CFV) in the circumflex coronary artery of anaesthetized dogs as a result of a critical coronary stenosis associated with a controlled arterial lesion at the site of stenosis. Subsequent regular CFV represent sequential thrombus formation and embolization in the damaged vessel. Neither aspirin nor metoclopramide alone demonstrated antithrombotic properties at the doses tested. However, the combination of aspirin 0.1 mg kg−1 iv and metoclopramide 0.3 mg kg−1 iv produced a significant antithrombotic effect, reducing the frequency of large CFV from 6.7 ± 0.5 to 0.8 ± 0.4 cycles h−1 (P < 0.01) and increasing minimum mean coronary blood flow from 5.0 ± 1.1 to 23.7 ± 2.6 mL min−1 (P < 0.01). This result apparently reflects an antithrombotic synergism between aspirin and metoclopramide since the effects of the combination were greater than the combined effects of the individual treatments. The antithrombotic influence of metoclopramide could be due to its 5HT2‐antagonist or α2‐antagonist properties, both of which would inhibit platelet aggregation. This demonstration of a synergistic antithrombotic action of the combination of aspirin and metoclopramide is of interest since these two agents are often combined in clinical use. Its therapeutic relevance, however, remains to be established.