5HT-induced Contractions Research Articles

Ethenzamide Exerts Protective Effects against Ibuprofen-Induced Gastric Mucosal Damage in Rats by Suppressing Gastric Contraction.

Nonsteroidal anti-inflammatory drugs (NSAIDs) are known to cause gastric mucosal damage, in which gastric hypermotility has been reported to play a primary role. The antipyretic analgesic drug ethenzamide (ETZ) is widely used in combination with other NSAIDs and, in a recent study, was found to possess 5-hydroxytriptamine (5HT)2B receptor antagonistic activity. Therefore, the inhibition of gastric contraction via 5HT2B receptor blockade by ETZ might contribute to ETZ's protective effect against NSAIDs-induced gastric mucosal damage. In the present study, we examined the effects of ETZ on gastric contraction and ibuprofen (IBP)-induced gastric mucosal damage in rats. We found that ETZ suppressed both 5HT- and α-methyl-5HT (5HT2 receptor agonist)-induced contractions of rat-isolated gastric fundus in a concentration-dependent manner. This suppressive effect of ETZ was not seen for either high-KCl- or acetylcholine-induced contractions. Furthermore, ETZ was confirmed to decrease ibuprofen-induced gastric mucosal damage in a dose-dependent manner in rats. Similarly, clonidine is known to reduce gastric motility, and methysergide (a 5HT2 receptor antagonist) is known to inhibit 5HT-induced contractions of the gastric fundus, which also decreases IBP-induced gastric mucosal damage, respectively. Although further research on other possible sites or mechanisms of action would be needed, these results suggest that ETZ exerts a protective effect against IBP-induced gastric mucosal damage and that suppressing the gastric contraction may play an important role in the gastroprotective effect of ETZ.

High-fat diet increases O-GlcNAc levels in cerebral arteries: a link to vascular dysfunction associated with hyperlipidaemia/obesity?

Obesity and high fat intake induce alterations in vascular function and structure. Aberrant O-GlcNAcylation (O-GlcNAc) of vascular proteins has been implicated in vascular dysfunction associated with cardiovascular and metabolic diseases. In the present study, we tested the hypothesis that high-fat diet (HFD)-mediated increases in O-GlcNAc-modified proteins contribute to cerebrovascular dysfunction. O-GlcNAc-protein content was increased in arteries from male Wistar rats treated with a HFD (45% fat) for 12weeks compared with arteries from rats on control diet (CD). HFD augmented body weight [(g) 550±10 compared with 502±10 CD], increased plasma triacylglycerols [(mg/dl) 160±20 compared with 95±15 CD] and increased contractile responses of basilar arteries to serotonin [5-hydroxytryptamine (5-HT)] [(pD2) 7.0±0.1 compared with 6.7±0.09 CD] and the thromboxane analogue 9,11-dideoxy-9α,11α-methanoepoxy prostaglandin F2α (U-46619) [(pD2) 7.2±0.1 compared with 6.8±0.09 CD]. Of importance, increased levels of O-GlcNAc [induced by 24 h-incubation of vessels with a potent inhibitor of O-GlcNAcase (OGA), O-(2-acetamido-2-deoxy-D-glucopyranosylidene)amino-N-phenylcarbamate (PugNAc)] increased basilar artery contractions in response to U-46619 [(pD2) 7.4±0.07 compared with 6.8±0.08 CD] and 5-HT [(pD2) 7.5±0.06 compared with 7.1±0.1 CD]. Vessels from rats on the HFD for 12weeks and vessels treated with PugNAc displayed increased phosphorylation of p38 (Thr(180/182)) and extracellular signal-regulated kinase 1/2 (Erk1/2) (Ser(180/221)). Increased 5HT-induced contractions in arteries from rats on the HFD or in arteries incubated with PugNAc were abrogated by mitogen-activated protein kinase (MAPK) inhibitors. Our data show that HFD augments cerebrovascular O-GlcNAc and this modification contributes to increased contractile responses and to the activation of the MAPK pathway in the rat basilar artery.

Hypoxia attenuates the ability of cyclic guanine‐dependent protein kinase (PKG) to increase BK channel activity

OBJECTIVEChronic hypoxia attenuates endothelium‐dependent vasodilatation, more in fetal than adult arteries. Here we examine the hypothesis that these effects involve inhibition of PKG activity and reduced BK channel activity.METHODSPregnant and Non‐Pregnant ewes were held at sea level (normoxic) or at 3820m (hypoxic) for the final 110 days of gestation. Carotid arteries from non‐pregnant adults and term fetal sheep were prepared for 5HT concentration‐response determinations with ±8‐pCPT‐cGMP and ±iberiotoxin. Abundances of α/β isoforms of PKG‐I were determined by Western blot. PKG activity was determined by enzyme assay.RESULTSPKG activation depressed 5HT‐induced contractility in normoxic but not hypoxic arteries. Hypoxia did not alter PKG abundance or specific activity but reduced iberiotoxin's ability to block PKG's effect on 5HT‐induced contractions, more in fetal than adult arteries.CONCLUSIONActivation of BK channels accounts for a significant portion of PKG‐induced vasorelaxation in ovine carotid arteries. Chronic hypoxia attenuates the ability of PKG to activate BK channels without effects on PKG activity or abundance.Supported by PHS Grants P01‐HD31226 and R01‐HL64867.

Potentiation by neuropeptide Y of 5HT 2A receptor-mediated contraction in porcine coronary artery

Potentiation by neuropeptide Y of serotonin (5-HT)-induced vasoconstriction was investigated in porcine coronary artery. 5-HT caused concentration-dependent contraction through 5-HT 2A receptors. Neuropeptide Y (30 nM) significantly increased the 5HT-induced contraction by 16 ± 5% in arteries with intact endothelium. Removal of the endothelium abolished the potentiation. A neuropeptide Y 1 antagonist, BIBP3226, blocked this neuropeptide Y-induced potentiation. In vessels with intact endothelium, the potentiation by neuropeptide Y was inhibited by in the presence of a cyclo-oxygenase inhibitor, indomethacin (30 μM), but not by the presence of ET A or ET B endothelin receptor antagonists or an NO synthase inhibitor, N G-nitro- l-arginine (L-NNA) (1 mM) at all. A thromboxane A 2 (TXA 2) synthase inhibitor, ozagrel, and prostanoid TP receptor antagonists, seratrodast and ONO-3708, also inhibited the neuropeptide Y-induced potentiation. In the endothelium-denuded arteries, a prostanoid TP receptor agonist, U-46619 (0.01–0.1 nM), potentiated 5-HT-induced contraction. These results indicate that neuropeptide Y potentiates the 5-HT-induced contraction, due to release of TXA 2 from the endothelium via neuropeptide Y 1 receptors, in porcine coronary artery.

Hydrogen Sulfide Is Synthesized in the Gills of the ClamMercenaria mercenariaand Acts Seasonally to Modulate Branchial Muscle Contraction

Previously we showed that when the gill muscles of the venerid clam Mercenaria mercenaria are stimulated to contract by 5-hydroxytryptamine (5HT), the contraction is about doubled when another identical dose of 5HT is applied after washout. Furthermore, this "endogenous potentiation" is mimicked by nitric oxide (NO), which is synthesized in the gill. We now report that the isolated gills also synthesize H2S; the basal rate of synthesis was 0.70 micromol.g(-1).h(-1) (se = 0.14; n = 24), but in the presence of 5HT (10(-2) M), the rate increased markedly to 35.82 micromol.g(-1).h(-1) (se = 4.93; n = 4). In addition, dithiothreitol (DTT; 2.2 mM) increased the rate of synthesis significantly to 4.9 micromol.g(-1).h(-1) (se = 0.8; n = 8). Stimulation of H2S synthesis by 5HT (5 x 10(-3) M) was seasonal; that is, the rates measured monthly from December through June are significantly lower than those measured from July through November. We also found that if isolated gills were pretreated with the H2S donor, sodium hydrosulfide (NaHS), their contractions in response to 5HT were potentiated. The threshold of the potentiation was 10(-8) M NaHS, and the largest effect was at 10(-6) M. During August, however, when endogenous and NO-induced potentiations are both absent, 10(-6) M NaHS was also ineffective. Like the effect of NO, that of NaHS (10(-6) M) was blocked by oxadiasoloquinoxalin (ODQ; 5 x 10(-5) M), an inhibitor of soluble guanylate cyclase (sGC). Moreover, Rp-8-CPT-cGMPS (10(-5) M), which inhibits protein kinase-G, also blocked the effect of NaHS (10(-6) M). When isolated gills were treated with 2.2 mM DTT, the endogenous potentiation of a second 5HT-induced contraction more than doubled in comparison to untreated controls. In conclusion, H2S is synthesized in the gill and, along with NO, is a seasonal, endogenous modulator of branchial muscle contraction; its action may be mediated through a sGC/cGMP signaling cascade.

Responses to serotonin (5HT) in isolated corpus cavernosum penis of rabbit.

This study was aimed at determining serotonin (5-hydroxytryptamine: 5HT) receptor subtypes participating in 5HT-induced response in the isolated corpus cavernosum penis (CCP) of rabbits. 5HT contracted the CCP in a concentration-dependent manner. Both WAY100635 (5HT(1A) antagonist) and LY53857 (5HT(2) antagonist) concentration-dependently suppressed the 5HT-induced contraction. The suppression of the 5HT-induced contraction by ketanserin (5HT(2A) antagonist) was weaker than that by LY53857. LY278584 (5HT(3) antagonist) did not affect the 5HT-induced contraction. SDZ205557 (5HT(4) antagonist) showed a tendency to potentiate the 5HT-induced contraction. The above results suggest that 5HT(1A) and 5HT(2) receptor subtypes partially participate in the contractile response to 5HT in rabbit CCP, and the potentiation by SDZ205557 of the 5HT-induced contraction implies the existence of dual contractile and relaxing responses to 5HT via 5HT(1) and 5HT(2), and 5HT(4) receptors, respectively. The relaxing response to 5HT(4) receptor stimulation may be masked by 5HT-induced contraction.

Effects of Maturation on Mechanisms of cGMP-Induced Cerebral Vasodilatation

In light of observations that cerebrovascular levels of cGMP vary during maturation, the present study examines the possibility that the mechanisms mediating cGMP-induced cerebral vasodilatation also change during maturation. Specifically, these experiments explore age-related changes in the ability of cGMP to both: (1) depress cytosolic calcium concentration, and (2) attenuate contractile protein calcium sensitivity in α-toxin and β-escin permeabilized preparations as well as fura-2 loaded arteries. The present data demonstrate that: (1) cGMP attenuates cytosolic calcium concentration at lower concentrations than required to reduce myofilament calcium sensitivity; (2) both potassium-induced and 5HT-induced contractions were more sensitive to cGMP in fetal than adult arteries; (3) all potassium-induced increases in cytosolic calcium were resistant to the effects of cGMP, but those produced by 5HT were sensitive to attenuation by cGMP, and more so in fetal than in adult basilar arteries, and (4) cGMP attenuated both basal and agonist-enhanced myofilament calcium sensitivity. Overall, these data demonstrate that the mechanisms mediating the multiple vasoactive effects of cGMP are more potent in immature than in mature cerebral arteries and are heavily influenced by both the artery type and the method of contraction.

Effect of 5-hydroxytryptamine on gastrointestinal motility in conscious guinea-pigs.

Many studies have suggested that 5-hydroxytryptamine (5HT, serotonin) plays an important role in the control of gastrointestinal motility. However, most of these studies have been carried out on guinea-pig ileum in vitro. Therefore, we investigated the mechanisms of action of 5HT on gastrointestinal motility in conscious guinea-pigs. In order to investigate the effects of 5HT on gastrointestinal motility, extraluminal force transducers were sutured onto the serosal surfaces of the gastric antrum, duodenum and ileum and 5HT was infused intravenously. One of three types of 5HT antagonist or atropine was given before a 5HT infusion of 3.0 micrograms kg-1 min-1 was started. Regular cyclic patterns were observed from the gastric antrum to the ileum in both the fasted and fed states. 5HT increased the contraction amplitudes at all sites. 5HT-induced contractions in the gastric antrum and duodenum were significantly inhibited by methysergide, ondansetron and atropine, but not by ketanserin. In the ileum, only atropine inhibited 5HT-induced contractions. These results suggest that 5HT increases the gastrointestinal contraction amplitude mainly via a cholinergic pathway. 5HT3 receptors and 5HT1-like and/or 5HT2C receptors appear to be responsible for 5HT-induced gastric antral and duodenal contractions, but 5HT receptors other than 5HT1-like, 5HT2A, 5HT2C and 5HT3 receptors induce ileal contractions.

ATP modification of serotonin-induced contraction of the rat pulmonary artery.

Serotonin (5HT) and ATP are simultaneously released from activated platelets at the site of vascular injury and are hypothesized to play a significant role in hemostasis. Our laboratory investigated the modulation of vascular contraction of arterial ring segments by 5HT plus ATP as a model of the potential regulation of localized vascular tone by platelet releasates in regions of arterial damage. This study expands our focus on how these two vasoactive components, released from platelet dense granules, regulate vascular tone. 5HT- and 5HT analog-induced vasoconstrictions were measured in the presence or absence of ATP and ATP analogs with intact or deendothelialized rat pulmonary arterial ring segments suspended in organ baths. The possible presence of 5HT2 and 5HT1A receptor types in the rat pulmonary artery was demonstrated by vasoconstrictions induced by 5HT and (+)-8-hydroxy-2-(di-N-propylamino) tetralin hydrobromide (DPAT). The DPAT response was only 30%-50% of that induced by comparable concentrations of 5HT. The 5HT-induced contraction was inhibited by the 5HT2 antagonist, ketanserin. ATP equally relaxed 5HT and DPAT contracted tissue while the P2X agonist, alphabeta-methylene ATP, increased the contracted state of DPAT-treated arteries to a significantly greater extent than observed with 5HT. The P2y agonist, 3'-O-(4-benzoyl)benzoyl ATP (BzATP), the P2X agonist betagamma-methylene ATP, and ATP all relaxed 5HT-induced contractions to similar levels under a number of physiological conditions. The final level of 5HT-induced tissue contraction was the same whether ATP was added prior to, after, or simultaneously with 5HT. ATP and the phosphodiesterase inhibitor, theophylline, inhibited 5HT-induced vasoconstriction in an additive fashion. The ATP effects were endothelium dependent, while the inhibition by theophylline was not. The distribution of 5HT and ATP receptor types, as indicated by these and numerous other studies, appears to vary within different regions of the cardiovascular system. Extracellular ATP can synergistically enhance or inhibit 5HT-contracted blood vessels differentially at localized regions, which would significantly impact on localized vascular tone, and this in turn may modulate hemostasis and thrombosis.

Spontaneous and 5HT-Induced Cyclic Contractions in Superficial Temporal Arteries from Chronic and Episodic Cluster Headache Patients

Superficial temporal arteries (STAs) are abnormally dilated in the painful side during cluster headache (CH) attacks. We have assessed the possible dysfunction of these arteries by comparing in vitro the reactivity of STAs removed from the painful side of CH patients during a cluster of attacks with that of STAs from patients free of CH. The responses to KCl and norepinephrine (NE) of both types of arteries were similar. Serotonin (5HT) induced a classical dose-dependent constriction in arteries from non-CH patients, but systematically triggered rhythmic contractions in arteries from episodic CH patients. Arteries from chronic CH patients also showed spontaneous rhythmic contractions. In both cases, this activity was stopped by calcitonin gene-related peptide (CGRP) but, even in the presence of CGRP, it could be restored by low concentrations of 5HT. Thus, 5HT, unlike NA, can trigger rythmic activity in STAs of CH patients and may play a major role in CH through abnormal smooth muscle cell reactivity.

Gamma-Aminobutyric Acid-A Receptor-Mediated Suppression of 5-Hydroxytryptamine-Induced Guinea-Pig Basilar Artery Smooth Muscle Contractility

The mechanism of gamma-aminobutyric acid (GABA)-induced suppression of 5-hydroxytryptamine (5HT)-induced contractility of cerebral blood vessels was studied in single smooth muscle cells isolated from the guinea-pig basilar artery. GABA reduced 5HT-induced contraction of single smooth muscle cells, and the effect of GABA was mimicked by muscimol, but not baclofen. The response of muscimol was antagonized by bicuculline, thereby indicating that GABAA receptors exist on the smooth muscle of the basilar artery. Since GABA did not change the contraction induced by the addition of Ca2+ to the Ca2+-free medium in the presence of high K+, it is unlikely that GABA inhibits the influx of extracellular Ca2+. The caffeine-induced contraction in the Ca2+-free medium was reduced by GABA, and the effect of GABA was not obtained by treatment with furosemide and in the Cl- -free medium. These results indicate that GABA acts on the GABAA receptor located on smooth muscle cells and reduces the contractility of the basilar artery by suppression of the mobilization of intracellular Ca2+.

Contraction and Relaxation of Rabbit Basilar Artery by Thiopental

Tension measurements were made on rabbit basilar artery segments to test the direct effect of thiopental on serotonin (5HT)- and norepinephrine (NE)-induced contraction. At concentrations of 3 X 10(-5) M or greater, thiopental caused relaxation of NE-induced tension. Thiopental doses greater than 3 X 10(-4) M had a similar relaxing effect on 5HT-induced contraction. However, thiopental doses below 3 X 10(-4) M demonstrated an unexpected dose-dependent potentiation of the 5HT-induced contraction.

Contraction and relaxation of rabbit basilar artery by thiopental.

Tension measurements were made on rabbit basilar artery segments to test the direct effect of thiopental on serotonin (5HT)- and norepinephrine (NE)-induced contraction. At concentrations of 3 X 10(-5) M or greater, thiopental caused relaxation of NE-induced tension. Thiopental doses greater than 3 X 10(-4) M had a similar relaxing effect on 5HT-induced contraction. However, thiopental doses below 3 X 10(-4) M demonstrated an unexpected dose-dependent potentiation of the 5HT-induced contraction.

Surgical decompression of anterior and posterior malignant epidural tumors compressing the spinal cord

Tension measurements were made on rabbit basilar artery segments to test the direct effect of thiopental on serotonin (5HT)- and norepinephrine (NE)-induced contraction. At concentrations of 3 × 10-5M or greater, thiopental caused relaxation of NE-induced tension. Thiopental doses greater than 3 × 10-4M had a similar relaxing effect on 5HT-induced contraction. However, thiopental doses below 3 × 10-4M demonstrated an unexpected dose-dependent potentiation of the 5HT-induced contraction. (Neurosurgery 17:433-435, 1985)

Interaction of 5-Hydroxytryptamine and Ketanserin in Rat Vas Deferens Subjected to Low Frequency Field Stimulation

The interaction of 5-hydroxytryptamine (5HT) and ketanserin was investigated in isolated rat vas deferens. Ketanserin (10−7 M) almost completely abolished the phasic and the following rhythmic contractions induced by 5HT, whereas the inhibition by prazosin (10−6 M) or methysergide (10−6 M) of 5HT-induced contractions were incomplete. The amplitude of twitch contractions of vas deferens subjected to low frequency (0.1 Hz) field stimulation were substantially unchanged by 5HT (10−7—10−5 M) per se. After pretreatment of the tissue with ketanserin (10−8–10−6 M), 5HT, in a concentration-dependent manner, attenuated the amplitude of twitch contractions. Such attenuation of the amplitude was not observed after pretreatments with methysergide (10−8—10−6 M) or prazosin (10−7–10−5 M). The 5HT-induced inhibition of twitch contractions in the presence of ketanserin was not antagonized by phentolamine, propranolol, methysergide, morphine, promethazine, cimetidine, atropine or indomethacin. It is suggested that 5HT has dual (excitatory and inhibitory) effects upon nerve transmission of rat vas deferens, and only the excitatory effect is suppressed by ketanserin.

2-[125Iodo]LSD, a new ligand for the characterisation and localisation of 5-HT2 receptors.

LSD was iodinated with Na125I and chloramine T, to get the radioligand [125I]LSD ( 125IOL ) and with N-I-succinimide to obtain the nonradioactive compound 2-I-LSD (IOL) for comparative pharmacological studies. The introduction of iodine in position 2 of LSD leads to an increase in selectivity for 5HT2 receptors. In rat cortex membranes, 125IOL possesses a KD = 0.9 +/- 0.1 nmol/l, Bmax = 240 +/- 20 fmoles/mg, and a nonspecific binding of 30-40% in presence of 100 nmol/l ketanserin. In competition experiments, 5HT antagonists showed monophasic displacement curves. Their KI-values correlate well with pD'2-values for inhibition of 5HT-induced contraction of canine basilar artery. It can be concluded that the sites labelled by 125IOL have pharmacological properties in common with central 5HT2 receptors, which are identical with vascular postjunctional 5HT receptors. The high specific radioactivity of 125IOL permits detection of even small 5HT2 receptor densities which exist in the guinea pig ileum. These 125IOL binding sites are pharmacologically different to those found in the brain or on the vessels and might be a special subpopulation of 5HT2 sites. For example, ketanserin has a high affinity to the sites labelled by 125IOL in the brain and a 100 times lower affinity to the sites labelled in the ileum. In a routine binding screen with various ligands, the inhibition constants of IOL for alpha 1, alpha 2, beta, histamine and muscarinic receptors are greater than 100 nmol/l with the exception for dopamine receptors, 40 nmol/l. 125IOL was employed for the autoradiographic localisation of its binding sites after in vitro labelling of microtome rat brain sections. 125IOL labelled 5HT2 sites in the cortex and dopamine receptors in the nucleus caudatus. The exposure times required were very short, compared to those of other 5HT2 ligands available.

Actions of the novel bronchodilator, trimetaquinol, on bovine pulmonary vein

The actions of the beta-sympathomimetic bronchodilator trimetaquinol (TMQ) were examined on bovine pulmonary vein smooth muscle in vitro. TMQ partially and reversibly inhibited 5-hydroxytryptamine (5HT) induced contractions of the vein strips. The relaxant activity was neither blocked by propranolol (10(-7) M) nor enhanced by phentolamine (10(-7) M). Isoproterenol, alone or in the presence of phentolamine (10(-7) M), was much less effective than TMQ in relaxing 5HT-induced contractions. From these results it is suggested that TMQ functions via a "non-beta-adrenergic" mechanism to relax bovine pulmonary vein smooth muscle.

Effects of 5HT uptake inhibitors on the pressor response to 5HT in the pithed rat. The significance of the 5HT blocking property

A study was made of the effects of several serotonin (5HT) uptake inhibitors on 5HT-induced pressor responses in pithed rats, 5HT uptake into rat brain synaptosomes and 5HT-induced contractions of rat ileum in vitro. All drugs except desimipramine were potent uptake inhibitors (IC 50 < 10 −7 M). Femoxetine, chlorimipramine, imipramine and desimipramine all inhibited 5HT-induced contractions of the rat ileum in vitro and the pressor response to 5HT in vivo. FG 7051, FG 7052 and dexchlorpheniramine were weak 5HT antagonists on the rat ileum but potentiated the pressor responses to 5HT; the most potent uptake inhibitor, FG 7051, was the strongest potentiator. These results suggest that uptake inhibition is important for this potentiation. It is concluded that 5HT uptake inhibitors with potent 5HT receptor blocking properties antagonize the pressor response to 5HT and mask the potentiation due to uptake inhibition.