Serotonin Contractions Research Articles

Doxorubicin Impairs Smooth Muscle Cell Contraction: Novel Insights in Vascular Toxicity.

Clinical and animal studies have demonstrated that chemotherapeutic doxorubicin (DOX) increases arterial stiffness, a predictor of cardiovascular risk. Despite consensus about DOX-impaired endothelium-dependent vasodilation as a contributing mechanism, some studies have reported conflicting results on vascular smooth muscle cell (VSMC) function after DOX treatment. The present study aimed to investigate the effects of DOX on VSMC function. To this end, mice received a single injection of 4 mg DOX/kg, or mouse aortic segments were treated ex vivo with 1 μM DOX, followed by vascular reactivity evaluation 16 h later. Phenylephrine (PE)-induced VSMC contraction was decreased after DOX treatment. DOX did not affect the transient PE contraction dependent on Ca2+ release from the sarcoplasmic reticulum (0 mM Ca2+), but it reduced the subsequent tonic phase characterised by Ca2+ influx. These findings were supported by similar angiotensin II and attenuated endothelin-1 contractions. The involvement of voltage-gated Ca2+ channels in DOX-decreased contraction was excluded by using levcromakalim and diltiazem in PE-induced contraction and corroborated by similar K+ and serotonin contractions. Despite the evaluation of multiple blockers of transient receptor potential channels, the exact mechanism for DOX-decreased VSMC contraction remains elusive. Surprisingly, DOX reduced ex vivo but not in vivo arterial stiffness, highlighting the importance of appropriate timing for evaluating arterial stiffness in DOX-treated patients.

Cerebrovascular endothelial dysfunction induced by mercury exposure at low concentrations

Mercury (Hg) has many harmful vascular effects by increasing oxidative stress, inflammation and vascular/endothelial dysfunction, all of which may contribute to cerebrovascular diseases development. We aimed to explore the effects of chronic low-mercury concentration on vascular function in cerebral arteries and the mechanisms involved. Basilar arteries from control (vehicle—saline solution, im) and mercury chloride (HgCl2)-treated rats for 30 days (first dose 4.6μg/kg, subsequent dose 0.07μg/kg/day, im, to cover daily loss) were used. Vascular reactivity, protein expression, nitric oxide (NO) levels and superoxide anion (O2−) production were analyzed. HgCl2 exposure increased serotonin contraction and reduced the endothelium-dependent vasodilatation to bradykinin. After NO synthase inhibition, serotonin responses were enhanced more in control than in mercury-treated rats while bradykinin-induced relaxation was abolished. NO levels were greater in control than Hg-treated rats. Tiron and indomethacin reduced vasoconstriction and increased the bradykinin-induced relaxation only in HgCl2-treated rats. Vascular O2− production was greater in mercury-treated when compared to control rats. Protein expressions of endothelial NO synthase, copper/zinc (Cu/Zn), Manganese (Mn) and extracellular-superoxide dismutases were similar in cerebral arteries from both groups. Results suggest that Hg treatment increases cerebrovascular reactivity by reducing endothelial negative modulation and NO bioavailability; this effect seems to be dependent on increased reactive oxygen species and prostanoids generation. These findings show, for the first time, that brain vasculature are also affected by chronic mercury exposure and offer further evidence that even at small concentration, HgCl2 is hazardous and might be an environmental risk factor accounting for cerebral vasospasm development.

5HT2Aand5HT2BReceptors Contribute to Serotonin-Induced Vascular Dysfunction in Diabetes

Although 5HT2A receptors mediate contractions of normal arteries to serotonin (5HT), in some cardiovascular diseases, other receptor subtypes contribute to the marked increase in serotonin contractions. We hypothesized that enhanced contractions of arteries from diabetics to 5HT are mediated by an increased contribution from multiple 5HT receptor subtypes. We compared responses to selective 5HT receptor agonists and expression of 5HT receptor isoforms (5HT1B, 5HT2A, and 5HT2B) in aorta from nondiabetic (ND) compared to type 2 diabetic mice (DB, BKS.Cg-Dock7 m+/+Leprdb/J). 5HT, 5HT2A (TCB2 and BRL54443), and 5HT2B (norfenfluramine and BW723C86) receptor agonists produced concentration-dependent contractions of ND arteries that were markedly increased in DB arteries. Neither ND nor DB arteries contracted to a 5HT1B receptor agonist. MDL11939, a 5HT2A receptor antagonist, and LY272015, a 5HT2B receptor antagonist, reduced contractions of arteries from DB to 5HT more than ND. Expression of 5HT1B, 5HT2A, and 5HT2B receptor subtypes was similar in ND and DB. Inhibition of rho kinase decreased contractions to 5HT and 5HT2A and 5HT2B receptor agonists in ND and DB. We conclude that in contrast to other cardiovascular diseases, enhanced contraction of arteries from diabetics to 5HT is not due to a change in expression of multiple 5HT receptor subtypes.

Potassium induced dilation in bovine coronary artery involves both inward rectifier potassium channels and Na+/K+ATPase

Increases in extracellular potassium (K+) concentration (up to 20 mM) cause dilation in some blood vessels. This may be particularly important in myocardial ischemia because in this condition K+ is released from ischemic cells. In this study, we investigated mechanisms of effect of increased K+ concentration on the tone of isolated bovine coronary artery. Bovine coronary arteries were isolated and mounted in organ baths for isometric tension recording. After an equilibration period, arteries were contracted with serotonin (1 microM). When serotonin contraction reached a steady-state, K+ concentration of organ baths was increased from physiological levels to 10 mM, 14 mM, 18 mM or 22 mM in four groups of the arteries. After a washout period, this procedure was repeated in presence of ouabain, a blocker of Na+ /K+ ATPase or a K+ channel blocker (tetraethylammonium, 4-aminopyridine, glibenclamide or barium). Increasing K+ concentration of the organ baths to 10 mM, 14 mM and 18 mM caused dilation in the arteries. Ouabain abolished the dilation and barium (a blocker of inward rectifier K + channels) inhibited the dilation significantly.According to our results there is K+ -induced dilation in bovine coronary artery and it involves activation of both Na+ /K+ ATPase and inward rectifier K+ channels.

Characterization of receptors involved in serotonin contractions of isolated human umbilical artery in uncomplicated pregnancy

Background Serotonin (5-HT), is a vasoactive substance involved in physiological functioning of fetoplacental blood flow and continuous modulation of smooth muscle tone in umbilical vein and arteries. Since umbilical blood vessels have been shown to be deficient in autonomic innervation, the action of local autocrine vasoactive substances (including serotonin) is of considerable importance. Although seven main groups of 5-HT receptors (5-HT1-7) have been characterized, it has been established that only several 5-HT receptor subtypes may be involved in vascular effects of this biogenic amine. Therefore, the aim of this study was to characterize receptors involved in serotonin-induced effect on isolated human umbilical artery (HUA) in uncomplicated pregnancy.

The modulatory role of androgens and progestins in the induction of vasorelaxation in human umbilical artery

Sex steroids have been described as protectors of the cardiovascular system and one of their relevant actions is inhibition of vascular tone. However, this information has been derived from animal models. The aim of this study was to investigate the vasorelaxant properties of several progestins and androgens on the vascular tone of human umbilical artery (HUA) to elucidate their potential regulatory role on fetoplacental blood flow. HUA rings, obtained from umbilical cords at vaginal deliveries and cesarean section from term uncomplicated pregnancies, were isometrically recorded and precontracted with either KCl or serotonin. Subsequently, dehydroepiandrosterone, testosterone, progesterone and some of their 5-reduced metabolites were added at different noncumulative concentrations on KCl-induced precontraction. There were significant differences in the vasorelaxing responses to these steroids; excluding 5α-pregnandione, the remaining steroids induced concentration-dependent vasorelaxations. In general, androgens were more potent than progestins, with 5β-dihydrotestosterone being the most potent one. These vasorelaxations remained unaffected by inhibitors of transcription and translation, selective steroid receptor antagonists, a nitric oxide synthase inhibitor or specific blockers of K + channels. Interestingly, the serotonin contraction was significantly less sensitive to steroid-induced vasorelaxation. Moreover, the contraction evoked by Ca 2+ in depolarized tissues (by KCl–Ca 2+ free solution) was prevented by steroids. These data, taken together, suggest that sex steroids (particularly androgens) induce an acute (nongenomically-mediated) vasorelaxing effect on the HUA which may be mediated by: (i) a nitric oxide-independent pathway; and/or (ii) a decrease in external Ca 2+ influx by inactivating Ca 2+ channels, but not by activating K + channels.

Effect of ceramide on the contractility of pregnant rat uterus

Ceramide and other sphingolipid mediators have emerged as a novel class of lipid second messengers in cell signaling. We assessed the effect of C 2-ceramide (a membrane permeable analog of ceramide) on spontaneous and agonist-induced contractile responses of uterus, isolated from 19-day pregnant rats. Ceramide (3, 10 μM) moderately, but significantly inhibited the amplitude of spontaneous rhythmic contractions. However, a variable effect was seen on agonist-induced contractions. While 5-HT-induced contractions were markedly inhibited at 3 and 10 μM ceramide, oxytocin and carboprost (a PGF 2α analogue)-induced contractions were not affected by the sphingolipid. Ceramide (10 μM) also markedly inhibited CaCl 2-induced contractions elicited in K +-depolarized tissues. Further, in rabbit portal vein myocytes, which display robust L-type calcium channel current, ceramide inhibited the I Ba in a dose-dependent manner. Therefore, it is suggested that the inhibitory effect of ceramide on uterine contractility may involve a decrease in the influx of Ca 2+ through voltage-dependent L-type Ca 2+ channels, such that contractile responses that are primarily dependent on extracellular Ca 2+, like rhythmic and serotonin contractions, were inhibited by ceramide. Further study is required to establish the role of endogenous ceramide and other sphingolipids in regulating uterine tone during gestation and at term.

Mechanisms involved in the early increase of serotonin contraction evoked by endotoxin in rat middle cerebral arteries.

The present study investigated the mechanisms involved in the increased 5-hydroxytryptamine (5-HT) vasoconstriction observed in rat middle cerebral arteries exposed in vitro to lipopolysaccharide (LPS, 10 microg x ml-1) for 1-5 h. Functional, immunohistochemical and Western blot analysis and superoxide anion measurements by ethidium fluorescence were performed. LPS exposure increased 5-HT (10 microm) vasoconstriction only during the first 4 h. In contrast to control tissue, indomethacin (10 microm), the COX-2 inhibitor NS 398 (10 microm), the TXA2/PGH2 receptor antagonist SQ 29548 (1 microm) and the TXA2 synthase inhibitor furegrelate (1 microm) reduced 5-HT contraction of LPS-treated arteries from hour one. The iNOS inhibitor aminoguanidine (0.1 mm) increased 5-HT contraction from hour three of LPS incubation. The superoxide anion scavenger superoxide dismutase (SOD, 100 U ml-1) and the H2O2 scavenger catalase (1000 U ml-1), as well as the respective inhibitors of NAD(P)H oxidase and xanthine oxidase, apocynin (0.3 mm) and allopurinol (0.3 mm), reduced 5-HT contraction after LPS incubation. LPS induced an increase in superoxide anion levels that was abolished by PEG-SOD. Subthreshold concentrations of the TXA2 analogue U 46619, xanthine/xanthine oxidase and H2O2 potentiated, whereas those of sodium nitroprusside inhibited, the 5-HT contraction. COX-2 expression was increased at 1 and 5 h of LPS incubation, while that of iNOS, Cu/Zn-SOD and Mn-SOD was only increased after 5 h. All the three vascular layers expressed COX-2 and Cu/Zn-SOD. iNOS expression was detected in the endothelium and adventitia after LPS. In conclusion, increased production of TXA2 from COX-2, superoxide anion and H2O2 enhanced vasoconstriction to 5-HT during the first few hours of LPS exposure; iNOS and SOD expression counteracted that increase at 5 h. These changes can contribute to the disturbance of cerebral blood flow in endotoxic shock.

Arachidonate metabolites and serotonin contraction of femoral arteries from DOCA-salt hypertensive rats.

Serotonin stimulates phospholipase A(2)(PLA(2)) leading to the production of prostaglandin products, several of which are vasoconstrictors. We hypothesised that the elevated vascular responsiveness to serotonin in deoxycorticosterone acetate (DOCA)-hypertensive rats is due in part to augmented production of vasoconstrictor cyclooxygenase products (e.g. PGF(2)alpha). Denuded helical strips of femoral arteries from DOCA-salt hypertensive rats (SBP 183 +/- 7 mmHg) and normotensive control rats (SBP 115 +/- 2) were used in all experiments. EC(50) values for several agonists were significantly reduced in DOCA arteries compared with controls (in mu mol/L, control vs. DOCA): PGF(2)alpha (0.99 vs. 0.23), PGE(2) (0.72 vs. 0.22), arachidonate (1.52 vs. 0.73), serotonin (0.19 vs. 0.07), noradrenaline (0.029 vs. 0.013), KCl (40.1 vs. 27.0 mmol/L) and AlF(4) (2.3 vs. 1.4 mmol/L). Treatment with indomethacin (14 mu mol/L) inhibited the responses to serotonin in DOCA arteries (EC(50) values 0.07 untreated vs. 0.70) and eliminated the responses to arachidonate but did not affect KCl or AlF(4-)contractions. Cyclooxygenase inhibitors shifted concentration response curves to serotonin in sham and DOCA tissues equally. Thus increased sensitivity to serotonin in DOCA arteries persisted following cyclooxygenase blockade. Therefore, although arachidonate products contribute to the serotonergic contraction in femoral arteries, the augmented response in arteries from DOCA hypertensive rats is not due to increased production of or sensitivity to cyclooxygenase products. Furthermore,arachidonate metabolites do not contribute to the contraction induced by either AlF(4-)or KCl in this preparation.

A model of bacterially induced umbilical vein spasm, relevant to fetal hypoperfusion.

From experience with placental pathology and autopsies, we hypothesize that infected amniotic fluid may produce umbilical cord and placental surface vasospasm, reduced fetal perfusion, and perinatal asphyxia, morbidity, and mortality. We tested the hypothesis by a preliminary investigation with group B beta-hemolytic streptococcus, a common cause of perinatal morbidity and mortality. Our methods included suspension of isolated human umbilical vein segments in a 30-mL organ bath with modified Krebs solution, pH 7.3-7.4, under continuous aeration by 95% O2 and 5% CO2 at 37C. The vessels were attached to an isometric transducer which was connected to a polygraph. We tested Krebs solution, sterile culture medium, group B streptococcus spent medium, and washed whole group B streptococcus bacteria. Contractility was compared with results produced by 10(-5) M serotonin. The average contraction produced by 30 microL/mL group B streptococcus spent medium was 40.8% of that produced by serotonin. Whole washed bacteria produced 8.6% of the serotonin contraction. Krebs solution and sterile culture medium did not stimulate vascular contraction. Intraperitoneal injection of group B streptococcus spent medium in mice at four times the maximal experimental dose had little effect. Boiling group B streptococcus spent medium failed to affect its vasoactive stimulatory properties. We conclude that in vitro, group B streptococcus synthesizes a heat-stable, non-protein exotoxin that causes human umbilical vein contraction.

Further evidence that the serotonin receptor in the rat stomach fundus is not 5HT 1A or 5HT 1B

The nature of the receptor mediating serotonin contraction in the rat stomach fundus has not been clearly associated with either 5HT 1 or 5HT 2 receptors. We have explored the possibility that such receptors in the rat fundus may better correlate with 5HT 1A or 5HT 1B receptor subtypes as defined by radiolabeled ligand binding studies with brain cortical membranes. Meta chlorophenylpiperazine (CPP) and meta trifluoromethylphenylpiperazine (TFMPP), selective ligands for the 5HT 1B receptor and LY165163, a selective ligand for the 5HT 1A receptor, have been evaluated for their agonist and antagonist activity at serotonin receptors in the rat stomach fundus. CPP and TFMPP were partial agonists in the rat stomach fundus whereas LY165163 showed no agonist activity in this smooth muscle in concentrations up to 10 −4M. All three phenylpiperazines antagonized serotonin-induced contractions in the rat stomach fundus. The affinity for serotonin receptors in the rat fundus was similar for all three phenylpiperazines in spite of the reported selectivity of MCPP and TFMPP for 5HT 1B and of LY165163 for 5HT 1A receptors. Furthermore, the affinity of these agents for serotonin receptors in the rat stomach fundus did not agree with their reported affinity for either 5HT 1A or 5HT 1B binding sites in rat cortical membranes. Thus, the similarity in affinities of these phenylpiperazine derivatives for serotonin receptors mediating contraction in the rat fundus along with their different affinities for 5HT 1A and 5HT 1B binding sites argues against the possibility that the serotonin receptor in the rat fundus is of the 5HT 1A or 5HT 1B subtype of serotonin receptor.

Mechanism of 5-HT contraction in isolated bovine ventricular coronary arteries. Evidence for transient receptor-operated calcium influx channels.

The effect of serotonin on isometric tension and transmembrane calcium influx was investigated in rings cut from branches of male bovine circumflex and left anterior descending coronary arteries. Responses were compared to those produced by potassium chloride, and to the serotonin contraction produced in rabbit thoracic aorta. Serotonin in bovine ventricular coronary arteries produced a strong, transient contraction, even at a maximum concentration. Contraction did not decline because of serotonin degradation in the bathing medium. The ability of serotonin to contract bovine ventricular coronary arteries was largely preserved when rings were exposed to a calcium-free medium. When calcium was replaced in the medium, both tension (T) and calcium influx (C, 45Ca) were increased above control only transiently by serotonin (3 minutes post-serotonin: T = 49.0 +/- 13.3 mg/mg, C = 27.33 +/- 1.8 mumol/kg, compared with control T = -4.8 +/- 1.5, C = 19.7 +/- 1.4; 30 minutes post-serotonin: T = -17.3 +/- 2.1, C = 19.3 +/- 1.1, compared with control T = -19.6 +/- 4.1, C = 18.1 +/- 1.4). Potassium chloride-stimulated increases in tension and calcium influx in bovine ventricular coronary arteries and a maximum serotonin contraction in rabbit thoracic aorta were not transient, but were sustained 30 minutes via a mechanism that appeared to be dependent on the influx of extracellular calcium. We suggest that the transient nature of the serotonin contraction in bovine ventricular coronary arteries was the result of a time-dependent decline in both calcium release from intracellular stores and calcium influx through serotonin receptor-operated calcium channels.(ABSTRACT TRUNCATED AT 250 WORDS)

Responses of dog large coronary arteries to constrictor and dilator substances: Implications for the cause and treatment of variant angina pectoris

Canine circumflex coronary artery ring segments were mounted in organ baths and contracted by ergonovine (ergometrine), serotonin, phenylephrine, norepinephrine (in the presence of propranolol), potassium (K +) and a thromboxane A 2 mimetic, U46619. Ergometrine was classified as a serotonin agonist since concentration-response curves were competitively inhibited by methysergide but not by alpha-adrenoceptor antagonists. Arteries precontracted to 80% of maximum were relaxed by verapamil, nifedipine and glyceryl trinitrate. However, nifedipine was 100-fold more potent against K + than either serotonin- or phenylephrine-contracted vessels. Verapamil showed some selectivity for K + and serotonin contractions compared with phenylephrine and was almost ineffective against U46619. Glyceryl trinitrate was without selectivity. Electrical field stimulation (2 and 20 Hz, 10-second) caused a weak contraction or relaxation or biphasic response in the isolated coronary ring. Contraction was amplified by propranolol (up to 1 μM) or metoprolol (50 ng/ml) and inhibited by alpha-adrenoceptor antagonists. In a blood-perfused left anterior descending coronary artery preparation, external diameter was measured by sonomicrometry under conditions of controlled flow and resistance. Intraarterial serotonin, U46619 and ergometrine infusions decreased the diameter by up to 18% without causing spasm (0 lumen diameter). Lowering the perfusion pressure from 90 to 60 mm Hg increased the decrease in diameter during serotonin infusions. Verapamil (50 to 150 ng/ml) and nifedipine (15 to 45 ng/ml) inhibited, to a similar degree, the decrease in coronary artery diameter in response to serotonin infusions. However, verapamil was more effective than nifedipine in depressing the sinoatrial node, abolishing reflex tachycardia and lengthening the atrioventricular conduction time. These studies suggest that verapamil and nifedipine are only selective antagonists of constrictor agents in the dog coronary artery, that both low perfusion pressure and beta-adrenoceptor blockade may amplify constrictor responses, and that nifedipine has fewer cardiotoxic effects than verapamil.

Dose responses of cerebral arteries of the dog, rabbit, and man to human hemoglobin in vitro.

Dose responses in vitro of the basilar arteries of the dog, rabbit, and man to human hemoglobin and reported. For each species, the response occurred over a range of 10(-9)M to greater than 10(-5)M hemoglobin. When compared to a maximum serotonin contraction, the relative constriction induced by 10(-5)M hemoglobin was greater in the rabbit than in the dog, which in turn was greater than in man. The comparatively weak response of the human arteries is probably attributable to postmortem changes.

Cerebral Vasospasm

Because previous studies suggest that prostaglandins (PGs) are involved in the contraction of cerebral arteries, the present study was undertaken to assess the direct effects of arachidonic acid, the precursor of PGs, on isolated dog basilar arteries and to ascertain the actions of three prostaglandin synthesis inhibitors, aspirin, indomethacin, and meclofenamate, on contractions induced by agonists of diverse chemical structure. Arachidonic acid induced sustained contractions and in optimal concentrations produced constriction that was 56% as great as that produced by serotonin. These responses were markedly inhibited (95%) by meclofenamate (10(-5) M), but aspirin (10(-3) M) had no such effect. Moreover, this concentration of meclofenamate reduced resting tension and inhibited by 16% the optimal responses caused by PGF2 alpha, while having no significant effect on serotonin contractions. Higher doses of meclofenamate (10(-4) M, 10(-3) M) produced increasing degrees of inhibition of contractions caused by serotonin or PGF2 alpha. Conversely, aspirin had no effect on PGF2 alpha contractions and slightly enhanced serotonin effects. The actions of indomethacin resembled those of meclofenamate. The results show clearly that different prostaglandin synthesis inhibitors have different effects on cerebral vasomotion in vitro. Aspirin, known to inhibit platelet function markedly, seems to have little effect on isolated vascular smooth muscle. On the other hand, the pharmacodynamic effects of meclofenamate and some related drugs may afford a new approach in the treatment of cerebral vasospasm.

Drug interactions in cat isolated tracheal smooth muscle.

1. The interactions between some drugs that contract and relax airways smooth muscle have been investigated in the cat isolated trachea. 2. Isoprenaline and theophylline inhibited serotonin-elicited contractions more than acetylcholine-mediated responses. This was observed both in terms of the degree of inhibition and the concentration of the relaxant drug producing this inhibition. 3. The acetylcholine- and serotonin-induced contractions were inhibited more by theophylline than by isoprenaline displaced acetylcholine and serotonin response curves to the right whereas theophylline caused a flattening of the curves. 4. Isoprenaline was more effective in hibiting serotonin contractions than acetylcholine contractions when the tracheas were bathed in K+ depolarizing solution, suggesting that the difference in the suscepbibility of serotonin and acetylcholine contractions to isoprenaline was not dependent on the electrical membrane potential. 5. Isoprenaline inhibited the tonic component of acetylcholine contractions more than the phasic component. 6. The differences in the pharmacological responses to the contractile and relaxant drugs in cat tracheal preparations provide further examples in smooth muscle of different mechanisms by which acetylcholine and serotonin induce contraction and isoprenaline and theophylline relaxation.

Influence of E. coli endotoxin on serotonin contractions of the rabbit aortic strip.

The mechanisms by which bacterial endo-toxins disrupt peripheral vascular function remain largely conjectural (1). Among the explanations advanced for the shock-like collapse of the individual following endotoxin are a release of mediators such as his-tamine, serotonin, catecholamin.es, etc. (1), a direct biphasic action on vascular smooth muscle(2), an increased responsiveness to catecholamines(3), and a depressing action on myocardial muscle(2). Data based on in vitro experiments to support a direct action of bacterial endotoxins on smooth muscle are for the most part inconclusive (1). The present report describes experiments with isolated strips of aortic smooth muscle which show that bacterial endotoxin under in vitro conditions potentiates the contractile response of smooth muscle to serotonin (5HT).Materials and methods. Batches of E. coli endotoxin obtained commercially (Difco) were tested for biological activity by their ability to elicit a modified Shwartzman reaction in the abdominal skin of rab...