Serotonin-induced Contractions Research Articles

Methodological challenges in using human umbilical artery as a model for in vitro studies.

What is the central question of this study? What are the biggest challenges in performing in vitro studies on isolated human umbilical arteries? What is the main finding and its importance? The protocols presented in this study indicate some potential outcomes important for interpretation of the vascular responsivities of human umbilical arteries and could be useful for planning future in vitro studies with human umbilical arteries. Human umbilical artery (HUA) preparations are of particular importance for in vitro studies on isolated blood vessels because their sampling is not risky for the patient, and they can provide the closest possible impression of changes related to the uteroplacental circulation during pre-eclampsia. Using organ bath techniques, useful experimental protocols are provided for measuring some pathophysiological phenomena in the vascular responses of HUAs. Several vasoconstrictors (serotonin, prostaglandin F and phenylephrine) and vasodilators (acetylcholine and minoxidil) were seleted for determination of their vasoactivity in HUAs. The role of L-type voltage-operated calcium channels and different types of potassium channels (KATP , BKCa and KV ) were assessed, as was the impact of homocysteine. Serotonin was confirmed to be the most potent vasoconstrictor, while acetylcholine and phenylephrine caused variability in the relaxation and contraction response of HUA, respectively. The observed increase in serotonin-induced contraction and a decrease in minoxidil-induced relaxation in the presence of homocysteine suggested its procontractile effect on HUA preparations. Using selective blockers, it was determined that KATP and KV channels participate in the minoxidil-induced relaxation, while L-type voltage-dependent Ca2+ channels play an important role in the serotonin-induced contraction. The presented protocols reveal some of the methodological challenges related to HUA preparations and indicate potential outcomes in interpreting the vascular effects of the investigated substances, both in physiological conditions and in the homocysteine-induced pre-eclampsia model.

IN VITRO ANTI-EMETIC EFFECT OF METHANOL ROOT EXTRACT OF TERMINALIA AVICENNIOIDES GUILL. & PERR. ON ISOLATED RABBIT ILEUM

Abstract Background: Terminalia avicennioides is a medicinal plant used traditionally in Nigeria to treat numerous ailments and disorders which include coughs, purgative and emetic. Objective: This study scientifically evaluated the probable mechanism of the anti-emetic activity of methanol root extract of Terminalia avicennioides Guill. & Perr. on histaminergic and serotonergic receptors of isolated rabbit ileum. Methodology: Fresh root bark was extracted using methanol and the antiemetic effect was evaluated by experimenting on a small segment (3 cm) of isolated rabbit ileum, using the data capsule (Ugo Basile) and single chamber isolated tissue apparatus. Varying concentrations of histamine and serotonin (0.05, 0.1, 0.2, and 0.4 mg/ml) were used to obtain contractions as they act on histamine and serotonergic receptors respectively. Results: META (0.05 mg/ml, 0.1 mg/ml, 0.2 mg/ml, and 0.4 mg/ml) exhibited a significant concentration-dependent decrease at p<0.05 in histamine-induced and serotonin-induced contractions on isolated rabbit ileum from the data capsule reading with percentage inhibition of 43.22, 53.96, 75.35, 85.58 % and 21.62, 49.50, 78.67 and 86.96 % respectively for the different concentrations. Conclusion: The study showed that methanol root extract of Terminalia avicennioides acts on cholinergic (muscarinic), histaminergic, and serotonergic receptors of isolated rabbit ileum by inhibitory spasmolytic action against smooth muscle contractility, hence its ability to possess anti-emetic effect to relieve vomiting.

Chronic Effects of Atypic Antipsychotics on Mice Isolated Vas Deferens Contractility: An In vitro Study

Aims: Antipsychotic drugs are known to be commonly associated with sexual dysfunction. The aim of this study to investigate the effects of sertindole, asenapine and ziprasidone on serotonin (5-HT), noradrenaline (NA), adenosine triphosphate (ATP) and potassium chloride (KCl)-induced contractions of the isolated vas deferens in mice.
 Study design: All the drugs were administered intraperitoneally (i.p.) in a volume of 0.1 ml per 10 g body weight of mice.
 Place and Duration of Study: Department of Pharmacology, Kocaeli University, Animal Research Center, between May 2018 and August 2019.
 Methodology: The mice were randomly divided into groups (n=7) as follows: saline; sertindole 1.3 mg/kg; sertindole 2.5 mg/kg; asenapine 0.05 mg/kg; asenapine 0.075 mg/kg; ziprasidone 1 mg/kg; ziprasidone 2 mg/kg once daily for 21 days. Mice receiving only the vehicle (0.9% saline, i.p.) served as control group. After 21 days of treatment, the effects of drugs were investigated on 5-HT, NA, ATP and KCl-induced contractions of isolated vas deferens.
 Results: The results showed that serotonin-induced contractions of vas deferens were affected by the chronic treatments of sertindole, asenapine and ziprasidone, however these drugs had no significant effect on NA, ATP, and KCl-induced contractions of mice vas deferens.
 Conclusion: Serotonergic receptors may contribute to changes in vas deferens contractions in mice with chronic treatment of sertindole, asenapine and ziprasidone. Thus, our results may explain one of the causes of sexual dysfunction of sertindole, asenapine and ziprasidone.

Modulation of vascular contraction via soluble guanylate cyclase signaling in a novel ex vivo method using rat precision-cut liver slices.

Fibrotic processes in the liver of non‐alcoholic steatohepatitis (NASH) patients cause microcirculatory dysfunction in the organ which increases blood vessel resistance and causes portal hypertension. Assessing blood vessel function in the liver is challenging, necessitating the development of novel methods in normal and fibrotic tissue that allow for drug screening and translation toward pre‐clinical settings. Cultures of precision cut liver slices (PCLS) from normal and fibrotic rat livers were used for blood vessel function analysis. Live recording of vessel diameter was used to assess the response to endothelin‐1, serotonin and soluble guanylate cyclase (sGC) activation. A cascade of contraction and relaxation events in response to serotonin, endothelin‐1, Ketanserin and sGC activity could be established using vessel diameter analysis of rat PCLS. Both the sGC activator BI 703704 and the sGC stimulator Riociguat prevented serotonin‐induced contraction in PCLS from naive rats. By contrast, PCLS cultures from the rat CCl4 NASH model were only responsive to the sGC activator, thus establishing that the sGC enzyme is rendered non‐responsive to nitric oxide under oxidative stress found in fibrotic livers. The role of the sGC pathway for vessel relaxation of fibrotic liver tissue was identified in our model. The obtained data shows that the inhibitory capacities on vessel contraction of sGC compounds can be translated to published preclinical data. Altogether, this novel ex vivo PCLS method allows for the differentiation of drug candidates and the translation of therapeutic approaches towards the clinical use.

Picotamide inhibits a wide spectrum of agonist‐induced smooth muscle contractions in porcine renal interlobar and coronary arteries

Picotamide is a thromboxane A2 (TXA2) receptor antagonist and TXA2 synthase inhibitor. In clinical studies, it has been considered as a platelet aggregation inhibitor and improved renal function. In vitro studies suggested inhibition of smooth muscle contraction by picotamide, which is poorly understood. Here, we examined effects of picotamide on contractions of renal interlobar and coronary porcine arteries, induced by different vasoconstrictors. Contractions were induced in an organ bath by agonists or electric field stimulation (EFS). Picotamide inhibited EFS‐induced contractions of interlobar arteries around 50% using concentrations of 100 and 300 µM. In interlobar arteries, concentration response curves for contractions induced by three different α1‐adrenoceptor agonists were shifted to the right by picotamide (2–10‐fold increases in EC50). In coronary arteries, α1‐adrenergic contractions were inhibited without right shift (approx. 50%). Contractions induced by two different cholinergic agonists in coronary arteries were inhibited by picotamide (≥50%) withouth right shift. Inhibition of serotonin‐induced contractions by picotamide showed features of a right shift, whereas contractions induced by the TXA2 analog U46619, angiotensin‐II, and endothelin‐1 were inhibited by picotamide in interlobar and coronary arteries without right shifts and to different degree. Picotamide inhibits a wide spectrum of vasoconstrictor‐induced contractions in porcine interlobar and coronary arteries. Inhibition of vasocontraction may contribute to beneficial effects of picotamide in the cardiovascular system and kidney.

Neuropharmacological Exploration of Standardized Extract of Annona squamosa (L.) Fruit Pulp in Experimental Animals

Aims: The present study aimed to investigate the neuroprotective potential of standardized Annona squamosa Linn fruit pulp extract using various in-vitro and in-vivo models. Methodology: Neuroprotective potential of standardized extract was screened against dopamine-induced contraction of isolated rat vas deferens, serotonin-induced contractions of isolated rat fundus, acetylcholine-induced contractions of isolated goat tracheal chain. In-vivo models such as elevated plus maze, light and dark model, force swim test, tail suspension test, lithium-induced head twitches, haloperidol-induced catalepsy, PTZ induced seizure and foot shock-induced aggression were implemented to screen various doses intervals (50-200mg/kg) of extracts in experimental animals. Results: Standardization of extract showed content of polyphenols 65.37 mg/g of GAE, total flavonoid 5.33 mg/g of RE and HPLC fingerprinting of ASP-ME showed identical retention time as that of standard gallic acid, quercetine and rutin, viz 3.830, 5.765 and 3.830 respectively. Inhibition of DPPH radical reflected as 91.32±0.19 % while percent inhibition of RRI of DPPH was observed as 95.99±0.47 at 150 min. ASP-ME significantly inhibited dopamine and serotonin induced contraction on isolated rat vas deferens and rat fundus respectively at log dose (1.3, 2.5) for dopamine and log dose (2.2, 2.5) for serotonin. ASP-ME potentiated ach-induced contractions on goat tracheal chain preparation. Ach alone produces 106.90±4.6 % response, while ASP-ME in presence of Ach potentiates response and produces 141.80±10 % response. The extract demonstrated anxiolytic activity by increasing the time spent in open arms and light zone in elevated plus maze and light dark test respectively. The duration of immobility was significantly decreased in force swim & tail suspension test respectively demonstrating antidepressant activity. Administration of ASP-ME shown antipsychotic effect in dose dependent manner by minimising aggression induced by foot shock (reduced number of flights), while potentiation of catalepsy induced by haloperidol. The extract also exhibited serotonergic system inhibitory effect by significantly reducing head twitches imparted by lithium. The ASP-ME significantly delayed the onset of first myoclonic and clonic spasms induced by PTZ indicating anticonvulsant effects. Extract also shown ability to decrease the behavior facilitated by the serotonergic and dopaminergic coordination, while potentiated the actions produced by GABA. Conclusion: Finding of the study suggests anxiolytic, antidepressant, antipsychotic effects of ASP-ME probably mediated through dopamine D2 and 5-HT receptors, with neuroprotective activity.

Increased coronary arteriolar contraction to serotonin in juvenile pigs with metabolic syndrome

Metabolic syndrome (MetS) is associated with alterations in coronary vascular smooth muscle and endothelial function. The current study examined the contractile response of the isolated coronary arterioles to serotonin in pigs with and without MetS and investigated the signaling pathways responsible for serotonin-induced vasomotor tone. The MetS pigs (8-weeks old) were fed with a hyper-caloric, fat/cholesterol diet and the control animals (lean) were fed with a regular diet for 12 weeks (n = 6/group). The coronary arterioles (90–180 μm in diameter) were dissected from the harvested pig myocardial tissues and the in vitro coronary arteriolar response to serotonin was measured in the presence of pharmacological inhibitors. The protein expressions of phospholipase A2 (PLA2), TXA2 synthase, and the thromboxane-prostanoid (TP) receptor in the pigs’ left ventricular tissue samples were measured using Western blotting. Serotonin (10−9–10−5 M) induced dose-dependent contractions of coronary-resistant arterioles in both non-MetS control (lean) and MetS pigs. This effect was more pronounced in the MetS vessels compared with those of non-MetS controls (lean, P < 0.05]. Serotonin-induced contraction of the MetS vessels was significantly inhibited in the presence of the selective PLA2 inhibitor quinacrine (10−6 M), the COX inhibitor indomethacin (10−5 M), and the TP receptor antagonist SQ29548 (10−6 M), respectively (P < 0.05). MetS exhibited significant increases in tissue levels of TXA2 synthase and TP receptors (P < 0.05 vs. lean), respectively. MetS is associated with increased contractile response of porcine coronary arterioles to serotonin, which is in part via upregulation/activation of PLA2, COX, and subsequent TXA2, suggesting that alteration of vasomotor function may occur at an early stage of MetS and juvenile obesity.

Abstract WP154: Estrogen Modulates Serotonin-induced Vasoconstriction Through Tyrisine Kinase Inhibition

Earlier onset of menopause may influence the risk of stroke. However, hormone therapy, estrogen, alone or with a progestogen, increases stroke risk. Thus, it is needed to clarify whether estrogens prevent or promote vasomotor symptoms, as well as the mechanism(s) involved. Recent study showed that serotonin enhancing drugs, including antidepressants, migraine therapies and diet pills, can trigger a stroke via vasoconstriction. In this study, we examined the modulatory mechanisms of estrogen in serotonin -induced vasoconstriction by using a combinatory approach of isometric tension measurements, molecular biology, and patch-clamp techniques. 17β-estradiol (E2) elicited a significant and concentration-dependent relaxation of serotonin-induced contraction in deendothelialized aorta strips isolated from male rats. E2 triggered a relaxation of serotonin-induced contraction even in the presence of tamoxifen, an estrogen receptor antagonist, suggesting that E2-induced changes were not mediated by estrogen receptor. Patch clamp studies in rat arterial myocytes showed that E2 prevented Kv channel inhibition induced by serotonin. Serotonin increased Src activation in arterial smooth muscle required for contraction, which is significantly inhibited by E2. The estrogen receptor-independent inhibition of Src by E2 was confirmed in HEK239T cells that do not express estrogen receptor. Taken together, these results suggest that estrogen exerted vasodilatory effects on serotonin-precontracted artery via Src, implying a critical role of estrogen in prevention of vascular hyperreactivity to serotonin.

Estrogen modulates serotonin effects on vasoconstriction through Src inhibition

Estrogen has diverse effects on cardiovascular function, including regulation of the contractile response to vasoactive substances such as serotonin. The serotonin system recently emerged as an important player in the regulation of vascular tone in humans. However, hyperreactivity to serotonin appears to be a critical factor for the pathophysiology of hypertension. In this study, we examined the modulatory mechanisms of estrogen in serotonin-induced vasoconstriction by using a combinatory approach of isometric tension measurements, molecular biology, and patch-clamp techniques. 17β-Estradiol (E2) elicited a significant and concentration-dependent relaxation of serotonin-induced contraction in deendothelialized aortic strips isolated from male rats. E2 triggered a relaxation of serotonin-induced contraction even in the presence of tamoxifen, an estrogen receptor antagonist, suggesting that E2-induced changes are not mediated by estrogen receptor. Patch-clamp studies in rat arterial myocytes showed that E2 prevented Kv channel inhibition induced by serotonin. Serotonin increased Src activation in arterial smooth muscle required for contraction, which was significantly inhibited by E2. The estrogen receptor-independent inhibition of Src by E2 was confirmed in HEK293T cells that do not express estrogen receptor. Taken together, these results suggest that estrogen exerts vasodilatory effects on serotonin-precontracted arteries via Src, implying a critical role for estrogen in the prevention of vascular hyperreactivity to serotonin.

Ergothioneine prevents endothelial dysfunction induced by mercury chloride.

Exposure to mercury has detrimental effects on the cardiovascular system, particularly the vascular endothelium. The present study aimed to investigate the effects of ergothioneine (EGT) on endothelial dysfunction induced by low-dose mercury chloride (HgCl2). Agonist-induced contractions and relaxations were evaluated in isolated aortic rings from 3-month-old male Wistar rats treated by intra-muscular injection to caudal hind leg muscle with HgCl2 (first dose, 4.6 µg/kg; subsequent doses, 0.07 µg/kg/day for 15 days) and optionally with EGT (2 µg/kg for 30 days). Reactive oxygen species (ROS) in aortic rings were measured by means of lucigenin- and luminol-enhanced chemiluminescence. The protein level of endothelial nitric oxide synthase was evaluated by ELISA. Blood glutathione (GSH) and catalase levels, lipid peroxidation and total nitrite were measured spectrophotometrically. The results indicated that low-dose HgCl2 administration impaired acetylcholine (ACh)-induced relaxation and potentiated phenylephrine- and serotonin-induced contractions in rat aortas. In addition, HgCl2 significantly increased the levels of ROS in the aortic tissue. EGT prevented the loss of ACh-induced relaxations and the increase in contractile responses. These effects were accompanied by a significant decrease in ROS levels. EGT also improved the ratio of reduced GSH to oxidized GSH and catalase levels with a concomitant decrease in lipid peroxidation. In conclusion, to the best of our knowledge, the present study was the first to report that EGT prevents endothelial dysfunction induced by low-dose HgCl2 administration. EGT may serve as a therapeutic tool to reduce mercury-associated cardiovascular complications via improving the antioxidant status.

The enhancement of serotonin-induced contraction of rat femoral artery is mediated by angiotensin II release from intact endothelium

We have performed an in vitro study on isolated intact or denuded femoral artery (FA) of healthy, diabetic, and/or rats submitted to the FA occlusion. The aim was to determine the contribution of endothelium and endothelial dysfunction (ED) on serotonin-induced action in FA. Further, the contribution of angiotensin II and cyclooxygenase products of arachidonic acid was investigated. A marker of ED, vWF was measured in animal serum. Serotonin induced contraction-dependent contraction of isolated FA, which was increased in preparations with endothelium. Pathological conditions such as endothelial denudation, nicotine-induced ED, diabetes or occlusion of FA reduced serotonin-induced contraction. Comparable reduction of serotonin-induced contraction was achieved after inhibition of AT1 receptors with losartan in isolated FA with intact endothelium. Our results demonstrate that angiotensin II contributes to the enhancement of serotonin-induced contraction of femoral arteries with intact endothelium. This increase is attenuated by endothelium removal, nicotine treatment, vascular occlusion, and/or hyperglycemia.

Pharmacology of Serotonin Receptors Causing Contraction of Isolated Bovine Posterior Ciliary Arteries: Role in Ocular Blood Flow.

To determine the serotonergic (5HT) receptor subtype mediating the contraction of bovine posterior ciliary arteries (BPCAs) in vitro. Longitudinal isometric tension was measured in BPCA strips (4-5 mm) mounted in 25 mL organ baths containing oxygenated Krebs solution at 37°C. Cumulative contractile concentration-response (C-R) curves were generated for various 5-HT agonists to assess their potencies and maximal degrees of contraction. Multiple agonist C-R curves were also constructed in the presence and absence of receptor-selective antagonists to determine antagonist potencies using Schild plots. Selective and nonselective agonists for 5-HT receptors elicited concentration-dependent contractile responses in BPCAs with the following rank order of potency: MK-212 > BW723C86 > α-methyl-5-HT >5-methoxy-α-5-methyl-5-HT >> R-DO1 > >5-HT >> cabergoline >> 5-methoxy-dimethyl-tryptamine >> 2-methyl-5-HT >> tryptamine. Interestingly, both 8-OH-DPAT (5HT1A agonist) and quipazine (5HT3 agonist) did not elicit contractions in BPCAs. The contractions produced by BW723C86 (5-HT2B agonist) were antagonized by 5-HT receptor blockers, RS-127445 (5-HT2B antagonist), and M-100907 (5-HT2A antagonist), yielding antagonist pA2 values of 7.5 ± 0.12 (n = 4) and 6.2 ± 0.17 (n = 4), respectively. Furthermore, contractions elicited by MK-212 (5-HT2C agonist) was blocked by RS-102221 (5-HT2C antagonist), although noncompetitively. On the basis of the pharmacological profile of selective agonists and antagonists, we conclude that serotonin-induced contractions of the BPCA are mediated primarily by a combination of 5HT2C and/or 5HT2B receptors. It appears that 5-HT1A and 5-HT3 receptors are not involved in the contractile action of BPCAs to serotonin.

Relationship between PDK1 and contraction in carotid arteries in Goto-Kakizaki rat, a spontaneous type 2 diabetic animal model.

We studied the relationship between 3-phosphoinositide-dependent protein kinase 1 (PDK1) and contractions induced by serotonin, phenylephrine, and thromboxane A2 mimetic (U46619) in the presence of nitric oxide synthase inhibitor in the carotid arteries of Goto-Kakizaki (GK) rats, a spontaneous type 2 diabetic model, in the chronic stage of disease. Serotonin-induced contraction was greater in the GK rats than in the control Wistar rats. A specific PDK1 inhibitor (GSK2334470) decreased the serotonin-induced contraction in the GK rats but not in the Wistar rats, and the difference in such contraction was abolished with this treatment. In GK rats, phenylephrine-induced contraction exhibited a leftward shift and U46619-induced contraction was greater still. Phenylephrine- and U46619-induced contractions were reduced by GSK2334470 in both groups. These results suggest, for the first time, that the contribution of PDK1 is different among 3 vasoconstrictors and that PDK1 contributed to increased serotonin-induced contraction in the carotid arteries of GK rats.

Pharmacological Effects of Gemfibrozil on Some Isolated Smooth Muscle Preparations of Experimental Animals

Background: Gemfibrozil is a member of fibrates (gemfibrozil, fenofibrate, ceprofibrate, and benzafibrate) which is employed for treatment of dyslipidemia particularly hypertriglyceridemiae through its action on peroxisome proliflator activated receptors (PPAR-α). Objective: The aim of this work was to study the site of action and pharmacololgical effects of different doses of gemfibrozil on some isolated smooth muscles preparations of experimental animals. Materials and Methods: The experiments were conducted on isolated jejunum of rabbits, isolated spiral tracheal and urinary bladder strips of guinea pigs. Results: I- On isolated rabbit jejunum, gemfibrozil produced a dose-dependent reduction on the amplitude of jejunal contractions. The inhibitory effect of gemfibrozil was not abolished after complete blockade of alpha and beta adrenergic receptors, while it was completely abolished after inhibition of nitric oxide synthase by N-methyl L-arginine. On the other hand the stimulatory effects of nicotine small dose, acetylcholine, calcium gluconate, histamine and serotonin were not abolished after administration of gemfibrozil. II- On isolated tracheal spiral strips of ginea pigs, gemfibrozil produced a dose- dependent relaxation on the basal tone and a dose-dependent reduction on the amplitude of acetylcholine-induced tracheal contractions of the tracheal strips. The inhibitory effect of gemfibrozil was completely abolished after inhibition of nitric oxide synthase by N-methyl L-arginine. Gemfibrozil completely abolished also serotonin-induced contraction, while it has no effect on histamine or calcium-induced tracheal contractions. III- On isolated urinary bladder strips of guinea pigs, gemfibrozil produced a dose-dependent reduction on the amplitude of urinary bladder contractions. The inhibitory effect of gemfibrozil was not abolished after complete blockade of beta adrenergic receptors, while it was completely abolished after inhibition of nitric oxide synthase by N-methyl L-arginine. On the other hand the stimulatory effects of acetylcholine and serotonin were not abolished after administration of gemfibrozil. Conclusion: Gemfibrozil (antidyslipidemic, PPAR-α agonist) reduced jejunal and urinary bladder contractions and has a relaxant effect on tracheal basal tone. So it has a beneficial effect in obstructive airway diseases and cases of urgency and frequency of micturation and urinary incontinence. However, it may be used cauciously in cases of ,GIT disturbances as constipation and prostatic hypertrophy.

Serotonin-induced contractile responses of esophageal smooth muscle in the house musk shrew (Suncus murinus).

Serotonin (5-hydroxytryptamine, 5-HT) is a regulatory factor in motility of the gastrointestinal tract including the esophagus. Although we proposed that vagal cholinergic and mast cell-derived non-cholinergic components including serotonin coordinately shorten the esophagus, the precise mechanism of serotonin-induced contractions in the suncus esophagus is still unclear. Therefore, the aims of this study were to determine characteristics of contractile responses induced by serotonin and to identify 5-HT receptor subtypes responsible for regulating motility in the suncus esophagus. An isolated segment of the suncus esophagus was placed in an organ bath, and longitudinal or circular mechanical responses were recorded using a force transducer. Serotonin evoked contractile responses of the suncus esophagus in the longitudinal direction but not in the circular direction. Tetrodotoxin did not affect the serotonin-induced contractions. Pretreatment with a non-selective 5-HT receptor antagonist or double application of 5-HT1 and 5-HT2 receptor antagonists blocked the serotonin-induced contractions. 5-HT1 and 5-HT2 receptor agonists, but not a 5-HT3 receptor agonist, evoked contractile responses in the suncus esophagus. The findings suggest that serotonin induces contractile responses of the longitudinal smooth muscle in the muscularis mucosae of the suncus esophagus that are mediated via 5-HT1 and 5-HT2 receptors on muscle cells. The serotonin-induced contractions might contribute to esophageal peristalsis and emetic response.

Dexmedetomidine inhibits vasoconstriction via activation of endothelial nitric oxide synthase.

Despite the complex vascular effects of dexmedetomidine (DEX), its actions on human pulmonary resistance arteries remain unknown. The present study tested the hypothesis that DEX inhibits vascular tension in human pulmonary arteries through the endothelial nitric oxide synthase (eNOS) mediated production of nitric oxide (NO). Pulmonary artery segments were obtained from 62 patients who underwent lung resection. The direct effects of DEX on human pulmonary artery tension and changes in vascular tension were determined by isometric force measurements recorded on a myograph. Arterial contractions caused by increasing concentrations of serotonin with DEX in the presence or absence of L-NAME (endothelial nitric oxide synthase inhibitor), yohimbine (α2-adrenoceptor antagonist) and indomethacin (cyclooxygenase inhibitor) as antagonists were also measured. DEX had no effect on endothelium-intact pulmonary arteries, whereas at concentrations of 10–8~10–6 mol/L, it elicited contractions in endothelium-denuded pulmonary arteries. DEX (0.3, 1, or 3×10–9 mmol/L) inhibited serotonin-induced contraction in arteries with intact endothelium in a dose-dependent manner. L-NAME and yohimbine abolished DEX-induced inhibition, whereas indomethacin had no effect. No inhibitory effect was observed in endothelium-denuded pulmonary arteries. DEX-induced inhibition of vasoconstriction in human pulmonary arteries is mediated by NO production induced by the activation of endothelial α2-adrenoceptor and nitric oxide synthase.

Facilitation of serotonin-induced contraction of rat mesenteric artery by ketamine.

Ketamine is an anesthetic with hypertensive effects, which make it useful for patients at risk of shock. However, previous ex vivo studies reported vasodilatory actions of ketamine in isolated arteries. In this study, we reexamined the effects of ketamine on arterial tones in the presence and absence of physiological concentrations of 5-hydroxytryptamine (5-HT) and norepinephrine (NE) by measuring the isometric tension of endothelium-denuded rat mesenteric arterial rings. Ketamine little affected the resting tone of control mesenteric arterial rings, but, in the presence of 5-HT (100~200 nM), ketamine (10~100 µM) markedly contracted the arterial rings. Ketamine did not contract arterial rings in the presence of NE (10 nM), indicating that the vasoconstrictive action of ketamine is 5-HT-dependent. The concentration-response curves (CRCs) of 5-HT were clearly shifted to the left in the presence of ketamine (30 µM), whereas the CRCs of NE were little affected by ketamine. The left shift of the 5-HT CRCs caused by ketamine was reversed with ketanserin, a competitive 5-HT2A receptor inhibitor, indicating that ketamine facilitated the activation of 5-HT2A receptors. Anpirtoline and BW723C86, selective agonists of 5-HT1B and 5-HT2B receptors, respectively, did not contract arterial rings in the absence or presence of ketamine. These results indicate that ketamine specifically enhances 5-HT2A receptor-mediated vasoconstriction and that it is vasoconstrictive in a clinical setting. The facilitative action of ketamine on 5-HT2A receptors should be considered in ketamine-induced hypertension as well as in the pathogenesis of diseases such as schizophrenia, wherein experimental animal models are frequently generated using ketamine.

Insulin augments serotonin-induced contraction via activation of the IR/PI3K/PDK1 pathway in the rat carotid artery.

Hyperinsulinemia associated with type 2 diabetes may contribute to the development of vascular diseases. Although we recently reported that enhanced contractile responses to serotonin (5-hydroxytryptamine, 5-HT) are observed in the arteries of type 2 diabetes models, the causative factors and detailed signaling pathways involved remain unclear. The purpose of this study was to investigate whether high insulin would be an amplifier of 5-HT-induced contraction in rat carotid arteries and whether the contraction involves phosphoinositide 3-kinase (PI3K)/3-phosphoinositide-dependent protein kinase 1 (PDK1) signaling, an insulin-mediated signaling pathway. In rat carotid arteries organ-cultured with insulin (for 24 h), (1) the contractile responses to 5-HT were significantly greater (vs. vehicle), (2) the insulin-induced enhancement of 5-HT-induced contractions was largely suppressed by inhibitors of the insulin receptor (IR) (GSK1838705A), PI3K (LY294002), and PDK1 (GSK2334470), and (3) the levels of phosphorylated forms of both PDK1 and myosin phosphatase target subunit 1 (MYPT1) were greater upon 5-HT stimulation. In addition, in rat carotid arteries organ-cultured with an activator of PDK1 (PS48), the 5-HT-induced contraction was greater, and this was suppressed by PDK1 inhibition but not PI3K inhibition. In addition, MYPT1 and PDK1 phosphorylation upon 5-HT stimulation was enhanced (vs. vehicle). These results suggest that high insulin levels amplify 5-HT-induced contraction. Moreover, the present results indicated the direct linkage between IR/PI3K/PDK1 activation and 5-HT-induced contraction in rat carotid arteries for the first time.

Sarpogrelate hydrochloride, a serotonin 5HT2A receptor antagonist, ameliorates the development of chronic hypoxic pulmonary hypertension in rats.

The purpose of the present study was to determine if sarpogrelate hydrochloride (SPG), a serotonin 5HT2A receptor antagonist, prevented the development of chronic hypoxia-induced pulmonary hypertension (PH) and hypertensive pulmonary vascular remodeling. Forty-one male Sprague-Dawley rats were exposed to hypobaric hypoxia (380 mmHg, 10 % oxygen) or room air and administered 50 mg/kg SPG or vehicle by gavage once daily from day -2 to day 14. The mean pulmonary artery pressure (PAP) and right ventricular hypertrophy (RVH) were measured. Hypertensive pulmonary vascular remodelings were assessed morphometrically by light microscopy. Serotonin-induced contraction was determined in isolated pulmonary artery rings from 24 rats. In another set of rats, Western blotting, real-time polymerase chain reaction and immunofluorescent staining (n = 9) for lung tissue were performed. Chronic hypoxia induced a rise in mean PAP and RVH, increased the percentage of muscularized arteries in peripheral pulmonary arteries and medial wall thickness in small muscular arteries, and potentiated serotonin-induced contraction, each of which was significantly (p < 0.05) ameliorated by SPG. Chronic hypoxia significantly increased the expression of endothelial nitric oxide synthase (eNOS) and phosphorylated eNOS (peNOS) protein levels, cyclic guanosine monophosphate, and matrix metalloproteinase-13 (MMP-13) mRNA levels in whole lung tissues. SPG increased peNOS expression in the immunofluorescent staining of peripheral pulmonary arteries from chronic hypoxic rats and decreased the MMP-13 mRNA in lung tissue in chronic hypoxic rats. The administration of SPG ameliorated the development of chronic hypoxic PH and hypertensive pulmonary vascular changes.

Double disruption of α2A- and α2C-adrenoceptors induces endothelial dysfunction in mouse small arteries: role of nitric oxide synthase uncoupling.

Knockout mice lacking both α2A- and α2C-adrenergic receptors (α2A/α2C-ARKO) provide a model for understanding the mechanisms underlying the deleterious effects of sympathetic hyperactivity on the cardiovascular system. Thus, in the present study we investigated the vascular reactivity of large and small arteries of α2A/α2C-ARKO mice. Aorta and mesenteric small arteries (MSAs) from 7-month-old male α2A/α2C-ARKO mice and congenic C57BL6/J mice (wild-type, WT) were studied. In the aorta, noradrenaline- and serotonin-induced contraction was similar between groups, but in MSAs there was an increase in agonist-induced contraction in α2A/α2C-ARKO compared with WT. The l-NAME effect was reduced in MSAs of α2A/α2C-ARKO mice compared with WT mice, as was basal NO evaluated by a 4,5-diaminofluorescein diacetate probe. Increased total endothelial nitric oxide synthase (eNOS) protein expression was observed in MSAs from α2A/α2C-ARKO mice, while the dimer/monomer ratio of eNOS was decreased. Mesenteric small arteries from α2A/α2C-ARKO mice showed an increase in ethidium bromide-positive nuclei, indicating oxidative stress, which was attenuated by incubation with l-NAME. The sympathetic hyperactivity present in α2A/α2C-ARKO mice alters vascular reactivity only in certain types of arteries. Moreover, after chronic sympathetic hyperactivity, uncoupling eNOS may be a significant source of superoxide anion and reduced NO bioavailability in small vessels, increasing the contractile tone.