Sumatriptan-induced saphenous venoconstriction in the anaesthetized dog through 5-HT1-like receptor activation

A review of methodologies evaluating superficial vein properties in viv: focus on compliance and reactivity

The saphenous vein (SV) is a hindlimb superficial vein which has aroused a considerable interest because of its implication in chronic venous disease and its use in coronary artery or lower limb bypass grafts. The morphology and patency of the SV are commonly assessed for diagnosis and management, but the dynamic properties of the vein - compliance, elasticity and reactivity, less widely studied, are also fundamental issues. The subject of this review is neither to review the pathologies, nor the treatments or surgical procedures. The goal is to gather together all existing types of investigation on the superficial vein and to focus on the dynamic venous properties in vivo. The data collected indicate that plethysmography (PG) and ultrasound (US) are extensively used to evaluate SV patency, reflux and morphology. Their use to evaluate superficial vein compliance is less widespread but highly necessary. The protocols used via venous occlusion are described and the various parameters used to accurately measure compliance and distensibility versus elasticity are presented and discussed. The advantage of US diameter measurement is shown, including additional pulsatile compliance evaluation. The overview of venous reactivity greatly differs, being poorly studied in vivo, mainly by optical methods in humans or US echotracking in animals. Existing methodologies are potent but could be certainly developed and improved further for better characterization of the SV in human and for investigations of new devices, surgical techniques and pharmacological treatment in preclinical animal studies.

Serotonin aggravates exercise-induced cardiac ischemia in the dog: effect of serotonin receptor antagonists

We investigated the effects of serotonin (5-HT), SL65.0472 (7-fluoro-2-oxo-4-[2-[4-thieno[3,2-c]pyridine-4-yl)piperazin-1-yl]ethyl]-1,2-dihydroquinoline-1-acetamide, a 5-HT(1B)/5-HT(2A) receptor antagonist) and ketanserin (a 5-HT(2A) receptor antagonist) during exercise-induced cardiac ischemia in conscious dogs. Dogs were administered a hypercholesterolemic diet and an inhibitor of nitric oxide synthetase to produce chronic endothelial dysfunction. Myocardial ischemia was induced by a treadmill exercise test associated with limitation of left anterior descending coronary blood flow. Infusion of serotonin during exercise produced dose-related cardiovascular changes (after 10 microg/kg/min; heart rate +27+/-6 bpm, systolic blood pressure +18+/-3 mm Hg, left circumflex coronary blood flow +64+/-8 ml/min, myocardial segment length shortening in the ischemic zone -5.9+/-1.9%, P<0.05). SL65.0472 blocked serotonin-induced increases in blood pressure, rate pressure product and circumflex coronary artery flow (100 microg/kg i.v., P<0.05) and reduced serotonin-induced ischemic myocardial segment length shortening (300 microg/kg i.v., P<0.05). Ketanserin (30-300 microg/kg i.v.) had no significant effect on any serotonin-induced changes during exercise. Thus, SL65.0472 opposes serotonin-induced myocardial dysfunction in a dog model of exercise-induced ischemia.

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.

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.

Comparative effects of frovatriptan and sumatriptan on coronary and internal carotid vascular haemodynamics in conscious dogs

The effects of frovatriptan and sumatriptan on internal carotid and coronary vascular haemodynamics were investigated and compared in conscious dogs. Frovatriptan and sumatriptan (0.1 - 100 microg kg(-1)) induced a transient increase in external coronary artery diameter (eCOD) of up to 2.9+/-1.2 and 1.8+/-0.6%, respectively (both P:<0.05). This was followed by a prolonged and dose-dependent decrease in eCOD of up to -5.2+/-1.2 and -5.3+/-0.9% (both P:<0.05), with ED(50) values of 86+/-21 and 489+/-113 micromol kg(-1), respectively. In contrast, only a decrease in the external diameter of the internal carotid artery was observed (-6.0+/-0.6 and -6.2+/-1.4%, both P:<0.05, and ED(50) values of 86+/-41 and 493+/-162 micromol kg(-1), respectively). Frovatriptan was thus 5.7 fold more potent than sumatriptan at the level of both large coronary and internal carotid arteries. After endothelium removal by balloon angioplasty in coronary arteries, the initial dilatation induced by the triptans was abolished and delayed constriction enhanced. The selective antagonist for the 5-HT(1B) receptors SB224289 dose-dependently blocked the effects of sumatriptan on large coronary and internal carotid arteries whereas the selective antagonist for the 5-HT(1D) receptors BRL15572 did not affect any of these effects. In conclusion, frovatriptan and sumatriptan initially dilate and subsequently constrict large coronary arteries in the conscious dog, whereas they directly constrict the internal carotid artery. The vascular endothelium modulates the effects of these triptans on large coronary arteries. Finally, 5-HT(1B) but not 5-HT(1D) receptors are primarily involved in canine coronary and internal carotid vasomotor responses to sumatriptan.

In vivo analysis of adrenergic and serotoninergic constrictions of the rabbit saphenous vein

We aimed to develop a model to study in vivo the rabbit saphenous vein pharmacology and to investigate constrictions mediated by adrenoceptor and 5-HT receptor subtypes. We used the technique of high precision ultrasonic echo-tracking for direct measurement of saphenous vein diameters in pentobarbital anesthetized rabbits. Saphenous vein constrictions induced in rabbits by the alpha(1)-adrenoceptor agonist L-phenylephrine and the 5-HT(1B) receptor agonist sumatriptan were comparable with those induced in dogs but those induced by the 5-HT(1B) and 5-HT(7) receptor agonist 5-carboxamidotryptamine failed to appear in dogs. Dose-related constrictions of rabbit veins were obtained with L-phenylephrine and the alpha(2)-adrenoceptor agonist dexmedetomidine. Frequency-related constrictions of rabbit veins induced by nerve stimulation were partially inhibited by an alpha(1)-adrenoceptor or a postsynaptic alpha(2)-adrenoceptor antagonist (prazosin and SKF 104,078) but not affected by the pre- and post-synaptic alpha(2)-adrenoceptor antagonists BRL 44408 or rauwolscine. Constrictions of rabbit veins to sumatriptan and 5-CT were inhibited by GR 127935 and those induced by quipazine, a 5-HT(2) receptor agonist were prevented by ritanserin. The initial constrictions induced by 5-CT were followed by dilatations which were inhibited by the 5-HT(7) receptor antagonist mesulergine. These data indicate that rabbit saphenous veins, in vivo and at rest, respond to activation of 5-HT(1B) and 5-HT(2) receptors, alpha(1)- and alpha(2)-adrenoceptors and nerve stimulation; the dilator effect mediated by 5-HT(7) receptor activation was also detected. The data validate a new animal model to study superficial vein reactivity and its pharmacological sensitivity.

Effects of the novel antimigraine agent, frovatriptan, on coronary and cardiac function in dogs

The effects of frovatriptan (VML 251/SB-209509) on coronary artery function were investigated in isolated coronary arteries from beagle dogs. Low concentrations of frovatriptan produced contraction with -logEC50 7.55 +/- 0.08 (n = 11). The maximal observed contraction attained was 56 +/- 7% of the control 5-hydroxytryptamine (5-HT; 10 microM) response. At high concentrations of frovatriptan (>6 microM), reversal of sumatriptan (10 microM)-induced contractions was noted. In arteries precontracted with the thromboxane mimetic, U46619, frovatriptan produced a bell-shaped concentration-response relation with a maximal response at 600 nM. Concentrations of frovatriptan >2 microM produced marked reversal of tone, with full relaxation of precontracted tissues at 200 microM. In anesthetized, open-chest mongrel dogs, intravenous (n = 5) or intracoronary (n = 5) artery administration of frovatriptan (0.0001-1 mg/kg) had no consistent effect on left ventricular end-diastolic pressure, left end-systolic pressure, cardiac contractility, aortic blood flow, systemic peripheral resistance, coronary blood flow, coronary vascular resistance, mean arterial blood pressure, or heart rate when compared with vehicle (n = 3). Intravenous sumatriptan produced minor effects on blood pressure and heart rate. Intracoronary artery administration of sumatriptan (0.0003 mg/kg) produced an increase in systemic peripheral resistance to 120.5 +/- 8.2% compared with vehicle (97.8 +/- 5.4%; p < 0.05). This dose of sumatriptan also produced a significant increase in coronary blood flow and decrease in coronary vascular resistance. Intravenous administration of sumatriptan produced a dose-related reduction in left ventricular diastolic pressure with a reduction to 58.3 +/- 8.3% and 41.7 +/- 25% of control values observed at 0.3 and 1 mg/kg, respectively; however, administration of sumatriptan by an intracoronary route had no effect. In a model of myocardial infarction, comparable doses of sumatriptan (1.0 mg/kg) or frovatriptan (0.1 mg/kg), in terms of their effect on carotid vascular resistance, had no significant effect on infarct size. Frovatriptan had no effect on coronary blood flow after reperfusion; however, sumatriptan produced a significant reduction in coronary blood flow for < or =3 h. These studies show that frovatriptan has the capability of relaxing coronary arteries in vitro, has no overall effect on cardiac function at rest with no effect on coronary hemodynamics after myocardial infarction, and has a profile superior to that of sumatriptan.

Influence of vascular tone on vasoconstrictor responses to the 5-HT 1-like receptor agonist sumatriptan in anaesthetised rabbits

The cardiovascular profile of the 5-HT1-like receptor agonist sumatriptan has been studied in anaesthetised rabbits pretreated with chlorisondamine (0.5 mg kg-1 i.v.) and enalapril (0.3 mg kg-1 i.v.) to eliminate autonomic reflexes and minimise endogenous vasoconstrictor tone. Under these conditions sumatriptan (2-100 micrograms kg-1 i.v.) produced modest increases in carotid vascular resistance but had no significant influence on heart rate, blood pressure or mesenteric vascular resistance. In a similarly pretreated group of animals in which vasoconstrictor tone was elevated by infusion of angiotensin (100 ng kg-1 min-1 i.v.) sumatriptan caused moderate increases in blood pressure (55 +/- 5 to 65 +/- 5 mm Hg after 25 micrograms kg-1 i.v.) and mesenteric vascular resistance (1.4 +/- 0.2 to 1.6 +/- 0.2 mm Hg min ml-1 after 25 micrograms kg-1 i.v.) and tended to produce a greater carotid vasoconstriction (3.6 +/- 0.5 to 4.7 +/- 0.7 mm Hg min ml-1 after 25 micrograms kg-1). These effects were antagonised by methiothepin 0.3 mg kg-1 i.v. implying the involvement of 5-HT1-like receptor stimulation. Hence, the presence of angiotensin produces a modest amplification of the vasoconstrictor effects of sumatriptan and, in particular, unmasks a constriction of the mesenteric vascular bed. The degree of synergy observed between these two vasoconstrictors was, however, less marked than might have been expected on the basis of previous isolated tissue studies.