Low-dose aspirin inhibits platelet-induced contraction of the human isolated coronary artery. A role for additional 5-hydroxytryptamine receptor antagonism against coronary vasospasm?

Aspirate from human stented saphenous vein grafts induces epicardial coronary vasoconstriction and impairs perfusion and left ventricular function in rat bioassay hearts with pharmacologically induced endothelial dysfunction

Stent implantation into aortocoronary saphenous vein grafts (SVG) releases particulate debris and soluble vasoactive mediators, for example, serotonin. We now analyzed effects of the soluble mediators released into the coronary arterial blood during stent implantation on vasomotion of isolated rat epicardial coronary artery segments and on coronary flow and left ventricular developed pressure in isolated perfused rat hearts. Coronary blood was retrieved during percutaneous SVG intervention using a distal occlusion/aspiration protection device in nine symptomatic patients with stable angina pectoris and a flow‐limiting SVG stenosis. The blood was separated into particulate debris and plasma. Responses to coronary plasma were determined in isolated rat epicardial coronary arteries and in isolated, constant pressure‐perfused rat hearts (±nitric oxide synthase [NOS] inhibition and ±serotonin receptor blockade, respectively). Coronary aspirate plasma taken after stent implantation induced a stronger vasoconstriction of rat epicardial coronary arteries (52 ± 8% of maximal potassium chloride induced vasoconstriction [% KCl_max = 100%]) than plasma taken before stent implantation (12 ± 8% of KCl_max); NOS inhibition augmented this vasoconstrictor response (to 110 ± 15% and 24 ± 9% of KCl_max). Coronary aspirate plasma taken after stent implantation reduced in isolated perfused rat hearts only under NOS inhibition coronary flow by 17 ± 3% and left ventricular developed pressure by 25 ± 4%. Blockade of serotonin receptors abrogated these effects. Coronary aspirate plasma taken after stent implantation induces vasoconstriction in isolated rat epicardial coronary arteries and reduces coronary flow and left ventricular developed pressure in isolated perfused rat hearts with pharmacologically induced endothelial dysfunction.

Aspirate from human stented native coronary arteries vs. saphenous vein grafts: more endothelin but less particulate debris

Stent implantation into atherosclerotic coronary arteries releases particulate debris and soluble substances that contribute to impaired microvascular perfusion. Here we addressed the potential for microvascular obstruction in patients with stenotic native right coronary arteries (nRCA) compared with saphenous vein grafts on right coronary arteries (SVG-RCA). We enrolled symptomatic, male patients with stable angina pectoris and a flow-limiting stenosis in their nRCA or SVG-RCA ( n = 18/18). Plaque volume and composition were analyzed using intravascular ultrasound before stent implantation. Coronary aspirate was retrieved during stent implantation under protection with a distal occlusion/aspiration device and divided into particulate debris and plasma. The release of catecholamines, endothelin, serotonin, thromboxane B2, and tumor necrosis factor-α was measured. The response of rat mesenteric arteries with intact (+E) and denuded (−E) endothelium to aspirate plasma (without and with selective endothelin receptor blockade) was normalized to that by potassium chloride (KClmax = 100%). Plaque volume and composition were not different between nRCA and SVG-RCA. There was less particulate debris (65 ± 8 vs. 146 ± 23 mg; P < 0.05) and more endothelin release (5.8 ± 0.8 vs. 1.3 ± 0.7 pg/ml; P < 0.05) in nRCA than in SVG-RCA, whereas the release of the other mediators was not different. Aspirate from nRCA induced stronger vasoconstriction than that from SVG-RCA [nRCA, 78 ± 6% (+E)/84 ± 5% (−E); SVG-RCA, 59 ± 6% (+E)/68 ± 3% (−E); P < 0.05 nRCA vs. SVG-RCA], which was attenuated by a nonspecific endothelin and a specific endothelin receptor A antagonist. Thus coronary aspirate from stented nRCA is characterized by less debris but more endothelin and stronger vasoconstrictor response than that from SVG-RCA.

Recurrent transient monocular blindness from stenotic central retinal artery

Transient monocular blindness (TMB) is caused by a temporary reduction of blood flow to the retina or optic nerve. Even though embolism from the ipsilateral carotid artery has been considered the main mechanism of TMB, the vascular pathology remains unknown in many patients. A 42-year-old man presented with recurrent transient visual loss in the left eye for 2 months. The attacks tended to develop more frequently when his head was bent down. Fluorescence angiography during an attack revealed hypoperfusion of the left central retinal artery (CRA) and cerebral angiography documented a focal isolated stenosis of the CRA at the origin. Aspirin and nimodipine reduced the attacks markedly. Stenosis of the CRA may be a cause of TMB. Intermittent vasospasm in addition to static hypoperfusion may have caused TMB in our patient with isolated CRA stenosis.

Coronary aspirate TNFα reflects saphenous vein bypass graft restenosis risk in diabetic patients

BACKGROUND

Patients with diabetes mellitus (DM) have an increased risk for periprocedural complications and adverse cardiac events after percutaneous coronary intervention. We addressed the potential for coronary microvascular obstruction and restenosis in patients with and without DM undergoing stenting for saphenous vein bypass graft (SVG) stenosis under protection with a distal occlusion/aspiration device.

METHODS

SVG plaque volume and composition were analyzed using intravascular ultrasound before stent implantation. Percent diameter stenosis was determined from quantitative coronary angiography before, immediately after and 6 months after stent implantation. Coronary aspirate was retrieved during stent implantation and divided into particulate debris and plasma. Total calcium, several vasoconstrictors, and tumor necrosis factor (TNF)α in particulate debris and coronary aspirate plasma were determined.

RESULTS

Patients with and without DM had similar plaque volume, but larger necrotic core and greater particulate debris release in patients with than without DM (20.3±2.7 vs. 12.7±2.6% and 143.9±19.3 vs. 75.1±10.4 mg, P<0.05). The TNFα concentration in particulate debris and coronary aspirate plasma was higher in patients with than without DM (15.9±6.6 vs. 5.1±2.4 pmol/mg and 2.2±0.7 vs. 1.1±0.2 pmol/L, P<0.05), whereas total calcium and vasoconstrictors were not different. Patients with DM had a greater percent diameter stenosis 6 months after stent implantation than those without DM (22.17±5.22 vs. 6.34±1.11%, P<0.05). The increase in TNFα immediately after stent implantation correlated with restenosis 6 months later (r=0.69, P<0.05).

CONCLUSION

In diabetics, particulate debris and coronary aspirate plasma contained more TNFα, which might reflect the activity of the underlying atherosclerotic process.

TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov/ct2/results?term=NCT01430884; unique identifier: NCT01430884.

Saphenous vein aorto-coronary graft atherosclerosis in patients with chronic kidney disease: more plaque calcification and necrosis, but less vasoconstrictor potential

Atherosclerotic coronary arteries are more calcified in patients with than without chronic kidney disease (CKD). We addressed the potential for coronary microvascular obstruction in patients with and without CKD during stenting for saphenous vein aorto-coronary graft (SVG) stenosis under protection with a distal occlusion/aspiration device. In patients with and without CKD (n = 20/20), SVG plaque composition was analyzed from virtual histology using intravascular ultrasound analysis before stent implantation. There was more dense calcium and more necrotic core in patients with than without CKD (14 ± 3 vs. 3 ± 1 % and 21 ± 3 vs. 12 ± 2 % of plaque volume, respectively). Coronary aspirate was retrieved during stent implantation and divided into particulate debris and plasma. Patients with CKD had more particulate debris and calcium release than patients without CKD. In contrast, the release of serotonin was less in patients with than without CKD (0.4 ± 0.1 vs. 1.2 ± 0.3 μmol/L), whereas that of catecholamines, endothelin, tissue factor, thromboxane, tumor necrosis factor α, and C reactive protein was not significantly different. Confirming the biochemical results, aspirate plasma from patients with CKD induced less vasoconstriction of rat mesenteric arteries than that from patients without CKD (with endothelium (+E), 26 ± 7 %; without endothelium (-E): 28 ± 7 % vs. +E, 68 ± 12 %; -E: 95 ± 16 % of maximum KCl-induced vasoconstriction). Graft atherosclerosis of patients with CKD is more degenerated and releases more particulate debris and calcium, but the aspirate has surprisingly less serotonin and vasoconstrictor potential.

Lessons from human coronary aspirate

The interventional implantation of a stent into an atherosclerotic coronary artery is a unique and paradigmatic scenario of plaque rupture in humans. The use of protection devices not only prevents the released plaque particles and the superimposed thrombotic material from being washed and embolized into the coronary microcirculation of the individual patient, but permits also the retrieval and ex vivo analysis of particulate plaque debris and soluble substances. The particulate debris comprises typical cholesterol crystals, foam cells, hyalin material and calcium deposits from the atheroma as well as platelets and coagulation material; soluble substances include vasoconstrictors, such as serotonin and thromboxane, as well as inflammatory mediators, such as TNFα which amplifies vasoconstriction by inducing endothelial dysfunction. The vasoconstriction observed in a bioassay ex vivo correlates to clinical symptoms, angiographic stenosis and plaque burden, as assessed by intravascular ultrasound. The release of TNFα into the aspirate correlates to restenosis. Detailed analysis of the human coronary aspirate may promote a better understanding of the pathophysiology of the vulnerable atherosclerotic plaque and help to better antagonize the microvascular consequences of coronary microembolization, including the no reflow phenomenon. This article is part of a Special Issue entitled "Coronary Blood Flow."

Increased plasma serotonin in complex regional pain syndrome type 1

BACKGROUND

In patients with complex regional pain syndrome type 1 (CRPS1), some improvement can be achieved by the administration of ketanserin, a 5-HT(2A) receptor antagonist. We measured plasma levels of serotonin (5-HT) during CRPS1 and correlated these levels with disease characteristics.

METHODS

Plasma 5-HT was measured in 35 patients who had CRPS1 for 3 yr and compared with 35 age-matched healthy controls.

RESULTS

The plasma 5-HT levels were 411 +/- 263 nmol/L and 29 +/- 18 nmol/L, respectively (P < 0.001). No correlations with disease characteristics were observed.

CONCLUSIONS

The markedly elevated levels of plasma 5-HT in CRPS1 patients suggest a role for 5-HT during the course of this disease. However, because of the lack of correlations with distinct disease characteristics, 5-HT is probably one of a number of mediators in CRPS1.

Platelets and prostacyclin in arterial bypasses: implications for coronary artery surgery

BACKGROUND

We investigated effects of platelets and prostacyclin formation in human internal mammary (IMA) and radial (RA) arteries.

METHODS

IMA and RA segments were suspended in organ bath with increasing concentrations of platelets. Experiments were applied with and without ketanserin, a 5HT2 receptor antagonist, or U3405, a TXA2 receptor antagonist. The release of prostacyclin (PGI2) was assessed by enzyme immunoassay in vessels without endothelium, before and after contraction with angiotensin (AT) I-II.

RESULTS

In IMA and RA with endothelium, platelets caused contractions, significantly enhanced in arteries without endothelium. Contractions to platelets were higher in RA than in IMA. U3405 reduced the platelet induced contractions in RA but not in IMA. Ketanserin inhibited the platelet induced contractions in IMA and RA. The basal release of PGI2 was more important in IMA than in RA. Addition of AT/I-II significantly reduced the release of PGI2 in IMA but not in RA.

CONCLUSIONS

The RA responds more powerfully to platelets than IMA. Protective system with PGI2 seems to be more powerless in RA than in IMA. This accentuates the importance of antispastic and antiplatelet drugs when arteries are used for coronary artery bypass surgery.

Serotoninergic status in patients with hereditary vascular retinopathy syndrome

AIM/BACKGROUND

In a new autosomal dominant syndrome (which the authors called hereditary vascular retinopathy (HVR)) cerebral ischaemia, Raynaud's phenomenon, and migraine are the most striking features. As serotonin (5-HT) is known to play a role in vasospastic processes, Raynaud's phenomenon, and migraine they wondered whether the serotoninergic status in patients with HVR is different. Therefore, it was decided to investigate some serotoninergic variables in these patients.

METHODS

The study was conducted in 12 patients with HVR, 10 relatives, and 19 healthy controls. The levels of intraplatelet and plasma 5-HT were measured, as well as the plasma levels of its precursor amino acid tryptophan and the ratio of tryptophan to the large neutral amino acids, which compete with the transport of tryptophan through the blood-brain barrier.

RESULTS

In both the patients with HVR and in nine relative the concentrations of 5-HT in plasma and platelets were significantly lower than in controls. The plasma levels of tryptophan and the tryptophan ratio were also found to be lower in the patient group compared with the control group, but not in the relatives.

CONCLUSION

The observed alterations in 5-HT and its precursor tryptophan strongly suggest the existence of a malfunctioning of the serotoninergic system in the HVR syndrome.

Chemically induced platelet lysis causes vasoconstriction by release of serotonin

Our previous studies have shown that menadione is cytotoxic to platelets, leading to substantial release of vasoactive substances. To test whether platelet lysis induced by menadione could cause vasoconstriction, we investigated the effect of platelet lysate induced by menadione on rat aorta in organ bath system. We showed that menadione-induced platelet lysate caused vasoconstriction in a dose- and time-dependent manner. These effects were seen in aortic rings both with and without endothelium, but it was much greater in rings without intact endothelium. The time course of vasoconstriction was well correlated with the time courses of platelet lysis (assessed by lactate dehydrogenase release) as well as serotonin release. The vasoconstriction by platelet lysate was blocked by serotonin antagonists, ketanserin, and LY53,857, but not by thromboxane A2 (TXA2) receptor antagonist, SQ29,548, suggesting that vasoconstriction mainly occurred secondary to the release of serotonin in our in vitro system. However, potentiation of vasoconstriction by combined treatment of serotonin and a stable TXA2 mimic, U46619, suggests the possibility of the increased risk for vasoconstriction in vivo. In addition, the serotonin-induced vasoconstriction was potentiated by residual menadione present in the organ bath. These results suggest that chemically induced platelet cytotoxicity can provoke alteration in vasomotor tone by release of serotonin.

Diminished nitroprusside-induced relaxation of inflamed colonic smooth muscle in mice

The dextran sodium sulphate (DSS) induced colitis in mice was used as a experimental model to study the contractility of murine longitudinal colonic smooth muscle during inflammation. Smooth muscle segments of proximal, middle and distal colon were mounted in organ baths. Smooth muscle contraction was induced by carbachol showing an aboral increase in activity, whereas in the inflamed middle colonic segment a marked decrease in activity was observed. The dilatative effect of sodium-nitroprusside (SNP) as a nitric oxide donor was investigated after precontraction by carbachol. Both in normal and DSS segments administration of SNP to isolated mouse colonic smooth muscle preparations caused regional differences in relaxation, the highest relaxation seen in normal proximal colonic tissue. However, this relaxation was markedly reduced in inflamed proximal preparations, associated with a diminished cGMP contents.

Effects of clomipramine on plasma amino acids and serotonergic parameters in panic disorder and depression

We examined the effects of long-term (six months) treatment with the serotonin potentiating tricyclic antidepressant clomipramine on several serotonergic parameters in panic disorder and depressive patients. Serotonin (5-HT) levels in blood, platelets and plasma were significantly reduced to 4%, 3% and 28% of their respective baseline values. In addition, the plasma level of tryptophan was also significantly reduced, although the decrease was only 16%. Three months after discontinuation of clomipramine treatment, 5-HT in blood and platelets reached baseline values again, while the plasma 5-HT level was still reduced to 68% of pretreatment values. Unexpectedly, the plasma tryptophan concentration was even lower at this time-point than after six months of treatment. These results show that clomipramine not only has an effect on 5-HT levels in blood, platelets and plasma, but also on plasma tryptophan concentration. We speculate that low plasma tryptophan after treatment may constitute a risk for the recurrence of psychopathology.

Combined administration of 5-HT2 and thromboxane A2 antagonists: effects on platelet aggregation and isolated cardiac muscle

1. To investigate possible mechanisms underlying the ability of combined administration of a 5-hydroxytryptamine2 (5-HT2) antagonist and a thromboxane A2 antagonist to reduce reperfusion-induced arrhythmias, the effects of these drugs alone and in combination on platelet aggregation and on cardiac muscle were determined. 2. Platelet aggregation was measured in whole blood obtained from anaesthetized rats. Concentrations of 5-HT (10 microM) and the thromboxane A2 mimetic U46619 (1 microM) which did not cause aggregation themselves, enhanced the responses to ADP (0.1 microM) and to collagen (1 microgram ml-1). For example, the response of 1.0 +/- 0.5 omega to ADP alone was increased significantly to 6.4 +/- 1.0 omega by 5-HT, 15.5 +/- 2.8 omega by U46619, and 17.3 +/- 1.3 omega when U46619, 5-HT and ADP were added together. 3. In further experiments blood was obtained from rats which had received either the 5-HT2 antagonist, ICI 170,809 (1 mg kg-1), or the thromboxane A2 antagonist. ICI 192,605 (1 mg kg-1 min-1), or both in combination. When ADP was used as the primary aggregating agent, the ability of U46619 alone, or together with 5-HT, to enhance responses was reduced significantly by ICI 192,605 alone and in combination with ICI 170,809. Similar results were obtained with lower doses of ICI 170,809 (0.3 mg kg-1) and ICI 192,605 (0.3 mg kg-1 min-1). 4. When collagen was used as the primary aggregating agent ICI 170,809 (1 mg kg-1) reduced the response to 5-HT (5.0 +/- 0.8 omega versus 10.9 +/- 1.2 omega in controls), and ICI 192,605 (1 mg kg-1 min-1) reduced the response to U46619 (6.8 +/- 2.5 omega versus 11.2 +/- 2.2 omega in control). The greatest reduction of platelet aggregation was seen in blood from rats which had received both antagonists, with the response to U46619 plus 5-HT plus collagen being 2.7 +/- 0.6 omega compared to 14.2 +/- 1.7 omega in controls. In contrast, there was no significant attenuation of platelet aggregation in blood from rats which had received the lower doses of each antagonist alone. Only the combination of ICI 170,809 (0.3 mg kg-1) and ICI 192,605 (0.3 mg kg-1 min-1) reduced the response to U46619 plus 5-HT plus collagen (7.6 +/- 1.4 omega versus 15.0 +/- 0.5 omega in controls). 5. In rat isolated ventricular muscle preparations, ICI 170,809 increased the effective refractory period; e.g. from 39 +/- 4 to 86 +/- 18 ms, 10 min after adding 30 microM to left papillary muscles. ICI 192,605 did not increase the effective refractory period itself and did not alter the ability of ICI 170,809 to prolong the effective refractory period. In the presence of 100 microM ICI 192,605, ICI 170,809 (30 microM) increased the effective refractory period from 38 +/- 7 to 100 +/- 30 ms. 6. These results indicate that the previously observed antiarrhythmic activity of combined administration of the higher doses of ICI 170,809 and ICI 192,605 is unlikely to be due to direct effects on cardiac muscle but could be a consequence of reduced platelet aggregation.

Augmented contraction of the human isolated coronary artery by sumatriptan: a possible role for endogenous thromboxane

1. The antimigraine drug, sumatriptan, contracts the human coronary artery and, in some patients, elicits chest symptoms (e.g. pressure and pain), particularly after subcutaneous administration. We studied the effects of the thromboxane A2 (TxA2) analogue, U46619 and endothelin-1 on contractile responses to sumatriptan in the human isolated coronary artery as well as the role of endogenously produced TxA2 and endothelin-1 in contractions evoked by sumatriptan. 2. In the presence of U46619 (1 and 3 nM), mean concentration-response curves to sumatriptan in the human coronary artery were shifted vertically due to the initial contraction by U46619, but when this initial contraction was subtracted from the response to sumatriptan, no significant augmentation was observed. However, analysis of the degree of augmentation in individual arterial segments revealed that the augmentation was variable and related inversely to the Emax of sumatriptan in the absence of U46619 (r = 0.78 and 0.81 for 1 and 3 nM, respectively; P < 0.05). 3. Treatment with the TxA2 receptor antagonist, SQ30741 (100 nM), or incubation of vessel segments with aspirin (10 microM), significantly reduced responses to sumatriptan; in aspirin-treated vessel segments, SQ30741 failed to decrease further the contractions to sumatriptan. The decrease in Emax of sumatriptan by both SQ30741 and aspirin correlated significantly with the Emax of sumatriptan without SQ30741 (r = 0.74; P < 0.01) or aspirin (r = 0.94; P < 0.01). In aspirin-treated vessel segments, responses to sumatriptan were significantly augmented in the presence of U46619 (3 nM; P < 0.05). 4. The specificity of SQ30741 was demonstrated by its ability to antagonize coronary artery contractions to U46619 (pA2: 7.54 +/- 0.30), but not endothelin-1. Similarly, incubation with aspirin (10 microM) did not affect contractile responses to endothelin-1, but significantly reduced TxA2 production in coronary artery segments as judged by a decrease in thromboxane B2 (TxB2) from 4.77 +/- 0.98 to 1.38 +/- 0.36 ng g-1 2 h-1. 5. Endothelin-1 (1 nM) did not significantly augment contractions to sumatriptan; there was also no relationship between the degree of augmentation and the control Emax of sumatriptan in the absence of endothelin-1. Furthermore, unlike SQ30741 or aspirin, a high concentration (100 nM) of the non-selective ETA/ETB receptor antagonist, SB 209670, failed to affect contractile responses to sumatriptan. However, SB 209670 potently antagonized coronary artery contractions induced by endothelin-1 with a pA2 of 8.84 +/- 0.32. 6. Compared to control vascular segments, endothelial denudation did not reduce TxA2 production (with endothelium = 2.56 +/- 1.38 vs. without endothelium = 12.32 +/- 4.94 ng TxB2 g-1 2 h-1), suggesting that the production of TxA2 is not confined to the endothelium. The sumatriptan-induced contractions were also unaffected by endothelial denudation. 7. The results of the present study suggest that endogenously produced TxA2 enhances contractions to sumatriptan in the human isolated coronary artery. Such a mechanism may play a role in causing chest symptoms after sumatriptan by potentiating coronary vascular contraction by sumatriptan in vivo.

Serotonin receptors: subtypes, functional responses and therapeutic relevance

Recent, rapid progress in the molecular biology of serotonin (5-HT) receptors requires conceptual re-thinking with respect to receptor classification. Thus, based on operational criteria (agonist and antagonist rank order), as well as transduction mechanisms involved and the structure of the receptor protein, the Nomenclature Committee of the Serotonin Club has proposed the following classification and nomenclature: the main receptor types 5-HT1 to 5-HT4, recombinant receptors (e.g. 5-ht5 to 5-ht7) and 'orphan' receptors. The aim of the present review is to discuss the events leading to this classification, the criteria for and functional responses mediated by various 5-HT receptors, as well as the therapeutic possibilities with 5-HT ligands.