Microglia and Autism Spectrum Disorder: Overview of Current Evidence and Novel Immunomodulatory Treatment Options

Autism spectrum disorder is a rapidly increasing heterogeneous neurodevelopmental syndrome, remarked by persistent deficit in social communication, and restricted, repetitive patterns of behavior and interest. Lately, maternal immune activation and micgroglial dysfunction in the developing brain have been gaining mounting evidence and leading to studies of various novel agents as potential treatment options. A few immunomodulatory treatment options—luteolin, minocycline, suramin, vitamin D, gut microbiota—are discussed in the current article, regarding the current understanding of their mechanisms and evidence for potential clinical use. More studies are warranted to understand their exact mechanisms of action and to verify efficacy and safety in human subjects.

Effects of ATP on Pacemaker Activity of Interstitial Cells of Cajal from the Mouse Small Intestine / 전남의대학술지

Purinergic receptors play an important role in regulating gastrointestinal (GI) motility. Interstitial cells of Cajal (ICCs) are pacemaker cells that regulate GI smooth muscle activity. We studied the functional roles of external adenosine 5′-triphosphate (ATP) on pacemaker activity in cultured ICCs from mouse small intestines by using the whole-cell patch clamp technique and intracellular Ca²⁺ ([Ca²⁺]ᵢ) imaging. External ATP dose-dependently depolarized the resting membrane and produced tonic inward pacemaker currents, and these effects were antagonized by suramin, a purinergic P2 receptor antagonist. ATP-induced effects on pacemaker currents were suppressed by an external Na⁺-free solution and inhibited by the nonselective cation channel blockers, flufenamic acid and niflumic acid. The removal of external Ca²⁺ or treatment with thapsigargin (inhibitor of Ca²⁺ uptake into endoplasmic reticulum) inhibited the ATP-induced effects on pacemaker currents. Spontaneous [Ca²⁺]ᵢ oscillations were enhanced by external ATP. These results suggest that external ATP modulates pacemaker activity by activating nonselective cation channels via external Ca²⁺ influx and [Ca²⁺]ᵢ release from the endoplasmic reticulum. Thus, it seems that activating the purinergic P2 receptor may modulate GI motility by acting on ICCs in the small intestine.

Three Gaseous Neurotransmitters, Nitric oxide, Carbon Monoxide, and Hydrogen Sulfide, Are Involved in the Neurogenic Relaxation Responses of the Porcine Internal Anal Sphincter

BACKGROUND/AIMS: The internal anal sphincter (IAS) plays an important role in maintaining continence and a number of neurotransmitters are known to regulate IAS tone. The aim of this study was to determine the relative importance of the neurotransmitters involved in the relaxant and contractile responses of the porcine IAS. METHODS: Responses of isolated strips of IAS to electrical field stimulation (EFS) were obtained in the absence and presence of inhibitors of neurotransmitter systems. RESULTS: Contractile responses of the sphincter to EFS were unaffected by the muscarinic receptor antagonist, atropine (1 muM), but were almost completely abolished by the adrenergic neuron blocker guanethidine (10 muM). Contractile responses were also reduced (by 45% at 5 Hz, P carbon monoxide > hydrogen sulfide.

Inhibitory effect of suramin on inflammatory response in pulmonary tissue and peripheral blood in LPS-induced septic mice / 浙江大学学报·医学版

<p><b>OBJECTIVE</b>To investigate the effect of suramin on inflammatory response in pulmonary tissue and peripheral blood in septic mice.</p><p><b>METHODS</b>Twenty-four male C57BL/6 mice were randomly divided into two groups, and suramin(5 mg/kg) or normal saline was intravenously injected 30 min before LPS(5 mg/kg)infusion, respectively. The contents of TNF-α and IL-6 in pulmonary tissue and peripheral blood were detected by ELISA. Suramin or saline-pretreated human mononuclear THP-1 cells were treated with 100 ng/mL LPS in vitro. The expression of TNF-α and IL-6 mRNA and the activity of NF-κB were analyzed by quantitative PCR and Western blotting at different time points after LPS treatment, respectively.</p><p><b>RESULTS</b>Compared with the saline group, the TNF-α and IL-6 levels in pulmonary tissue and peripheral blood were significantly reduced in suramin group at 24 h after LPS treatment(all P<0.01); while there was no significant difference at 72 h between two groups(all P>0.05). The expression of TNF-α, IL-6 mRNA and the activity of NF-κB was decreased in suramin group at different time points after LPS treatment.</p><p><b>CONCLUSION</b>Suramin can protect LPS-induced acute lung injury through down-regulation of systemic and pulmonary pro-inflammatory factors, which may be associated with the inhibition of NF-κB activity.</p>

The different contraction between rat gastric longitudinal and circular smooth muscle induced by extracellular nucleotides / 中国应用生理学杂志

<p><b>OBJECTIVE</b>To test the different contrctile responses of extracellular nucleotides, such as ATP, UTP and nucleotide uridine adenosine tetraphosphate (Up4A) in gastric longitudinal muscle (LM) and circular muscle (CM). Examined the effect of P2X and P2Y receptor antagonists (in this study, we used IP5I and suramin) and cyclooxygenase inhibitor (indomethacin) on Up4A induced contractile responses in LM and CM.</p><p><b>METHODS</b>The rats were sacrificed and the stomachs were opened to gain LM and CM. Using organ bath system to assess contrctile responses of smooth muscle.</p><p><b>RESULTS</b>Up4A could induce contractile responses in both CM and LM, which were similar with ATP and UTP. IP5 did not attenuate Up4A could induce contractions in both LM and CM, but suramin and indomethacin significantly inhibited Up4A contraction in CM, but not in LM.</p><p><b>CONCLUSION</b>Our results suggest that extracellular nucleosides and their inhibitors induce different responses between LM and CM.</p>

Reactive Oxygen Species and Nitrogen Species Differentially Regulate Neuronal Excitability in Rat Spinal Substantia Gelatinosa Neurons

Reactive oxygen species (ROS) and nitrogen species (RNS) are implicated in cellular signaling processes and as a cause of oxidative stress. Recent studies indicate that ROS and RNS are important signaling molecules involved in nociceptive transmission. Xanthine oxidase (XO) system is a well-known system for superoxide anions (O2(.-)) generation, and sodium nitroprusside (SNP) is a representative nitric oxide (NO) donor. Patch clamp recording in spinal slices was used to investigate the role of O2(.-) and NO on substantia gelatinosa (SG) neuronal excitability. Application of xanthine and xanthine oxidase (X/XO) compound induced membrane depolarization. Low concentration SNP (10 microM) induced depolarization of the membrane, whereas high concentration SNP (1 mM) evoked membrane hyperpolarization. These responses were significantly decreased by pretreatment with phenyl N-tert-butylnitrone (PBN; nonspecific ROS and RNS scavenger). Addition of thapsigargin to an external calcium free solution for blocking synaptic transmission, led to significantly decreased X/XO-induced responses. Additionally, X/XO and SNP-induced responses were unchanged in the presence of intracellular applied PBN, indicative of the involvement of presynaptic action. Inclusion of GDP-beta-S or suramin (G protein inhibitors) in the patch pipette decreased SNP-induced responses, whereas it failed to decrease X/XO-induced responses. Pretreatment with n-ethylmaleimide (NEM; thiol-alkylating agent) decreased the effects of SNP, suggesting that these responses were mediated by direct oxidation of channel protein, whereas X/XO-induced responses were unchanged. These data suggested that ROS and RNS play distinct roles in the regulation of the membrane excitability of SG neurons related to the pain transmission.

Extracellular Nucleotides Can Induce Chemokine (C-C motif) Ligand 2 Expression in Human Vascular Smooth Muscle Cells

To understand the roles of purinergic receptors and cellular molecules below the receptors in the vascular inflammatory response, we determined if extracellular nucleotides up-regulated chemokine expression in vascular smooth muscle cells (VSMCs). Human aortic smooth muscle cells (AoSMCs) abundantly express P2Y1, P2Y6, and P2Y11 receptors, which all respond to extracellular nucleotides. Exposure of human AoSMCs to NAD+ , an agonist of the human P2Y11 receptor, and NADP+ as well as ATP, an agonist for P2Y1 and P2Y11 receptors, caused increase in chemokine (C-C motif) ligand 2 gene (CCL2) transcript and CCL2 release; however, UPT did not affect CCL2 expression. CCL2 release by NAD+ and NADP+ was inhibited by a concentration dependent manner by suramin, an antagonist of P2-purinergic receptors. NAD+ and NADP+ activated protein kinase C and enhanced phosphorylation of mitogen-activated protein kinases and Akt. NAD(+)- and NADP(+)-mediated CCL2 release was significantly attenuated by SP6001250, U0126, LY294002, Akt inhibitor IV, RO318220, GF109203X, and diphenyleneiodium chloride. These results indicate that extracellular nucleotides can promote the proinflammatory VSMC phenotype by up-regulating CCL2 expression, and that multiple cellular elements, including phosphatidylinositol 3-kinase, Akt, protein kinase C, and mitogen-activated protein kinases, are involved in that process.

Evaluation of anti-allergic activity of gossypin and suramin in mast cell-mediated allergy model.

The mast cell-mediated allergic reactions are involved in many allergic diseases, such as asthma, allergic rhinitis and sinusitis. Stimulation of mast cells initiates the process of degranulation, resulting in the release of mediators such as histamine and an array of inflammatory cytokines. In this report, we investigated the effect of gossypin (a biflavonoid) and suramin (a synthetic polysulphonated naphtylurea) on the mast cell-mediated allergy model, and studied the possible mechanism of their action. Both gossypin and suramin inhibited (P<0.001) compound 48/80-induced systemic anaphylaxis reactions, antiprurities (P<0.001) and reduced the histamine release in rats. Further, both showed significant (P<0.001) protection against rat peritoneal mast cells activated by compound 48/80. Thus, our findings provide evidence that gossypin and suramin inhibit mast cell-derived allergic reactions.

P2X and P2Y Receptors Mediate Contraction Induced by Electrical Field Stimulation in Feline Esophageal Smooth Muscle

It is well-known that electrical field stimulation (EFS)-induced contraction is mediated by a cholinergic mechanism and other neurotransmitters. NO, ATP, calcitonin gene-related peptide (CGRP), and substance P are released by EFS. To investigate the purinergic mechanism involved in the EFS-induced contraction, purinegic receptors antagonists were used. Suramine, a non-selective P2 receptor antagonist, reduced the contraction induced by EFS. NF023 (10(-7)~10(-4) M), a selective P2X antagonist, inhibited the contraction evoked by EFS. Reactive blue (10(-6)~10(-4) M), selective P2Y antagonist, also blocked the contraction in a dose-dependent manner. In addition, P2X agonist alpha,beta-methylene 5'-adenosine triphosphate (alphabetaMeATP, 10(-7)~10(-5) M) potentiated EFS-induced contraction in a dose-dependent manner. P2Y agonist adenosine 5'-[beta-thio]diphosphate trilithium salt (ADPbetaS, 10(-7)~10(-5) M) also potentiated EFS-induced contractions in a dose-dependent manner. Ecto-ATPase activator apyrase (5 and 10 U/ml) reduced EFS-induced contractions. Inversely, 6-N,N-diethyl-D-beta,gamma-dibromomethylene 5'-triphosphate triammonium (ARL 67156, 10(-4) M) increased EFS-induced contraction. These data suggest that endogenous ATP plays a role in EFS-induced contractions which are mediated through both P2X-receptors and P2Y-receptors stimulation in cat esophageal smooth muscle.

Effects of ATP and LTC4 on hypoxic pulmonary vasoconstriction in isolated rat lungs / 대한마취과학회지

BACKGROUND: Hypoxic pulmonary vasoconstriction (HPV) is unique to pulmonary circulation but the mechanism remains elusive. Red blood cells (RBCs) are known to augment HPV and to release more ATP as oxygen content falls. Leukotrienes constrict smooth muscle and could be important for the regulation of the pulmonary circulation. Hence we hypothesized that ATP and leukotrienes are mediators of HPV produced during acute alveolar hypoxia. METHODS: In forty Sprague-Dawley rats, lungs were isolated and perfused. We administered ATP (10 micrometer) to the ATP group (n = 8), the ATP antagonist, suramin (100 micrometer) to the suramin group (n = 8), leukotriene C4 (LTC4, 5 microgram) to the LTC4 group (n = 8), the LTC4 antagonist, LY171883 (20 micrometer) to the LY171883 group (n = 8), and LTC4 (5 microgram) + ATP (10 micrometer) to the LTC4 + ATP group (n = 8) during normoxic ventilation. HPV responses were induced by three hypoxic challenges for 5 minutes separated by 5 minutes of ventilation with a normoxic gas mixture. Baseline pulmonary artery pressure change after exposure to each drug and hypoxic pressor response between a period 21% normoxic gas ventilation and that of 3% hypoxic gas ventilation were measured. RESULTS: ATP and LTC4 + ATP increased baseline pulmonary artery pressures but LTC4 did not alter it. ATP did not affect hypoxic pressor response. Suramin, LY171883 and LTC4 + ATP inhibited the pressor response to hypoxia. LTC4 increased hypoxic pressor response. CONCLUSIONS: In isolated rat lungs, HPV may be mediated by ATP and LTC4 appears more likely to be a modulator than a mediator of HPV.

A rare case of human trypanosomiasis caused by Trypanosoma evansi.

Human trypanosoma infections like the ones seen in Africa and South America are unknown in India. The only exception in literature is of two documented cases of a self-limiting febrile illness, being attributed to Trypanosoma lewisi like parasites. We are reporting an unusual case of trypanosomiasis from the rural parts of Chandrapur district in Maharashtra. An adult male farmhand who used to practice veterinary medicine also, presented with history of febrile episodes on and off since five months and drowsiness before admission to this Institute. Though routine blood and other investigations were within normal limits, the peripheral smear showed a large number of trypanosomes which morphologically resembled the species Trypanosoma evansi, the aetiological agent of surra - a form of animal trypanosomiasis. A battery of assays covering the spectrum of parasitology, serology, and molecular biology confirmed the infecting parasite to be T. evansi. Failure to demonstrate the central nervous system (CNS) involvement, as evidenced by the absence of parasite in cerebrospinal fluid (CSF) advocated the use of suramin - the drug of choice in early stage African trypanosomiasis without any CNS involvement. Suramin achieved cure in our patient. The case is being reported because of its unique nature as the patient was not immunocompromised and showed infestation with a parasite which normally does not affect human beings.

Inhibition of proteinase 3 [PR3] by suramin and fetal calf serum [FCS]: effect of PR3 and suramin on Chinese hamster ovary cells [CHO-Cells]

Proteinase 3 [PR3] is a lysosomal protease that is stored in azurophilic granules neutrophilic granulocytes and monocytes. A number of inhibitors for this proteinase are reported. Comprehensive studies on the inhibitory effect of suramin and heat treated fetal calf serum [pound GFCS] on PR3 have not been reported. It has been reported that PR3 is able to destroy the cytoskeletal integral proteins, but we have not find any reports which showed the effect of this protease on Chinese hamster ovary cells [CHO-cells] in culture medium. Suramin has proven to be useful as an antitumor drug, but there was not any report on the effect of suramin on CHO-cells. The effects of various concentrations of pound GFCS [from 0.5% up to 10%] and suramin [from 0.8 pound gM up to 100 pound gM] on PR3 and different concentrations of suramin [from 0.8 pound gM up to 1000 pound gM] on CHO-cells were investigated. Data analysis were performed by, Kolmogorov-Smirnov test, ANOVA test and Tukey HSD post tests. Results showed that pound GFCS and suramin have an inhibitory effect on PR3 and these effects increased with increasing the concentration significantly [p < 0.01]. PR3 with the concentration of 2.2 Unit/ml has no effect on CHO-cells. Although suramin with the concentration of less than 125 poundgM cell growth retarded for only a few hours, but with the concentration of 125 to 250 pound gM inhibit the cell growth for a week, and after that cells gain normal growth gradually. Suramin with concentration of more than 500 pound gM inhibited the cell growth completely. Although suramin reversibly inhibit the PR3 activity but in concentration of less than 250 pound gM it had no long-term effect on CHO-cells. Therefore it can be used in the investigation of proteases. There were unknown components in pound GFCS, which cause the inhibition of PR3 activity. This finding is very important in PR3 production in culture medium. However CHO-cells are resistant to PR3 and suramin in low concentration

The Effects of Neurotransmitters on the Ion Channels in the Isolated Deiters'Cells of Guinea Pig Cochlea / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: The supporting cells in the organ of Corti help to maintain the structural integrity of the organ, but it has been suggested that they also actively participate in regulating sound transduction. The existence of neural control was implied by the finding of efferent synapses in Deiters' cells, and the fact that the intracellular Ca2+ concentration was increased by the application of neurotransmitters, such as ATP (adenosine triphosphate) and Ach (acetylcholine), resulting in movement of the phalangeal processes of the Deiters' cells. This study investigated the effects of neurotransmitters on the ion channels in Deiters' cells. MATERIALS AND METHOD: Deiters' cells were isolated from guinea pig organs of Corti using collagenase and pipettes. Whole-cell patch clamps were performed under an inverted microscope and the current was measured with pClamp 8.0.2 software. RESULTS: The resting membrane potential was -21.1+/-3.5 mV. ATP (100 microM) treatment depolarized the potential to -3.1+/-1.1 mV, while the same concentration of Ach had no effect on the resting potential. In the voltage-clamping condition, the holding potential was 0 mV, and then a -80 mV pre-pulse was applied for 500 ms, followed by step pulses from -140 to +10 mV. Under these conditions, 10 microM ATP increased the inward current from -14.9+/-1.9 to -163.5+/-14.9 pA/pF at the maximal stimulus of -140 mV (n=4). In the current-voltage curve, the reversal potential was around -20 mV. Neither Ach nor carbachol induced current responses. The co-application of suramin (30 microM) and ATP (10 microM) suppressed the ATP-induced currents by 50%, and 30 microM of PPADS (pyridoxal-phosphate- 6-azophenyl-2, 4-disulphonic acid) inhibited the current almost to the level of the control. The purinoceptor-agonist, alpha, beta-meATP (alpha, beta-methylene adenosine triphosphate), 30 microM increased the inward current from -16.2+/-2.9 to -27.7+/-3.8 pA/pF, which was much smaller than the ATP-induced change. CONCLUSION: ATP-gated purinergic receptors may play an important role in regulating sound transduction by inducing an inward current and depolarizing the Deiters' cell membrane.

Suramin inhibits the in vitro expression of encephalitis B virus proteins NS3 and E / 华中科技大学学报（医学）（英德文版）

In this study, the mechanism by which Suramin inhibits the replication of epidemic encephalitis B virus was explored to provide a theoretical basis for its further application in clinical practice. After viral infection of HepG2 and IMR-32 cells, different concentrations of Suramin were added to the culture media, and then the cultural supernatants and infected cells were collected 48 h later. For the evaluation of the curative effect, cytopathic effect (CPE), virus titers, the expression of viral protein and viral RNA were determined by Western blot, RT-PCR and in vitro RNA synthesis, respectively. At the concentration of 50 microg/ml of Suramin, HepG2 and IMR-32 infected with epidemic encephalitis B virus decreased by 51.8% and 0.03% respectively, as compared with controls. It was suggested that expression of encephalitis B virus proteins NS3 and E was notably reduced by Suramin. This is especially true of E protein. At RNA level, however, no difference in RNA virus was found between Suramin-treated virus and non-treated cells. Our results suggest that Suramin can inhibit viral replication by blocking the production of viral proteins.

Progress in researches on drugs for prostate cancer / 中华男科学杂志

In the recent years, researches on drugs for prostate cancer have received more attention than ever before. This article reviews the mechanism and efficacy of such prostate cancer drugs as bicalutamide, medroxyprogesterone acetate, megestrol acetate, flutamide and so on, as well as the clinical data and clinical uses of calcitriol analogue EB1089, SR233377, etc.

Naftiluréia polisulfonada (Suramin) na inibição da migração, proliferação e formação de tubo vascular em culturas de células endoteliais coroidianas "in vitro" estimuladas por fatores de crescimento e em membrana coroidiana sub-retiniana experimental / Plysuldonated naphthylurea (Suramin) inhibeted migration, proliferation and the tube formation on coroidal endothelial cell culture

Avaliar o efeito do suramin na migração, proliferação e formação de tubo vascular em células endoteliais coroidianas (CECs) “in vitro” e em neovascularização coroidiana (NC) “in vivo”. Foi avaliada a migração através do experimento de Boyden Chamber. Foi avaliada a proliferação através do experimento MTT. Foi avaliada a formação de tubo vascular através do experimento gel colágeno 3D. As CECs foram estimuladas por fatores de crescimento (FC) e tratadas com suramin.O efeito sistêmico do suramin foi avaliado em NC induzidos por laser em olhos de ratos. O suramin inibiu a migração, proliferação e formação de tubo vascular estimulada por FC de forma dose dependente / This study evaluated the effects of suramin on choroidal endothelial cell (CEC) migration, proliferation and tube formation “in vitro” and choroidal neovascularization (CNV) “in vivo”. Migration was evaluated using Boyden chamber assay. Proliferation was evaluated by an MTT assay. Tube formation was evaluated using a 3D-tube formation assay. CECs were stimulated by growth factor (GF) treated with suramin. The effect of systemic administration of Suramin was evaluated on laser induced CNV in rats eyes. Suramin inhibited CEC migration, proliferation, and tube formation induced by GF in a dose dependent manner. CNV in rats was inhibited by systemic administration of Suramin 30mg/Kg. These studies indicate that suramin inhibits Angiogenesis “in vitro” and “in vivo”...

Influence of suramin on the proliferation of prostatic carcinoma cells PC-3M / 中华男科学杂志

<p><b>OBJECTIVES</b>To examine the effects of suramin on the growth, cell cycle and apoptosis of a hormone refractory prostate cancer cell line PC-3M, and to explore the possible mechanisms.</p><p><b>METHODS</b>The roles of diverse concentrations (10, 50, 100 and 200 mumol/L) of suramin on PC-3M cell proliferation at different ratios of fetal calf serum (FCS) (2%, 5%, 10%) were assayed respectively by trypan blue exclusion and tetrazolium (MTT) assay. The effect of suramin on cell cycle distribution and apoptosis induction of PC-3M cells was evaluated with flow cytometry (FCM).</p><p><b>RESULTS</b>A higher dosage of suramin (200 mumol/L) had a cytotoxic effect on PC-3M cells, while lower dosages from 10 to 100 mumol/L produced a predominant inhibiting effect. Suramin could also play a growth suppressive role in the culture media containing 10% FCS, but to a much less extent than in the media containing lower concentrations(5%, 2%) of FCS. FCM analysis exhibited that suramin at a high dosage of 200 mumol/L could induce apoptosis, and at the other concentrations, G0/G1 cell cycle arrest.</p><p><b>CONCLUSION</b>Suramin's proliferative suppression on PC-3M cells might result from several mechanisms including antagonistic action on growth stimulation via growth factor, arrest of cell cycle and induction of apoptosis.</p>

Effect of suramin on myotoxicity of some crotalid snake venoms

We investigated the protective effect of suramin, an enzyme inhibitor and an uncoupler of G protein from receptors, on the myotoxic activity in mice of different crotalid snake venoms (A.c. laticinctus, C.v. viridis, C.d. terrificus, B. jararacussu, B. moojeni, B. alternatus, B. jararaca, L. muta). Myotoxicity was evaluated in vivo by injecting im the venoms (0.5 or 1.0 mg/kg) dissolved in physiological saline solution (0.1 ml) and measuring plasma creatine kinase (CK) activity. Two experimental approaches were used in mice (N = 5 for each group). In protocol A, 1 mg of each venom was incubated with 1.0 mg suramin (15 min, 37ºC, in vitro), and then injected im into the mice at a dose of 1.0 mg/kg (in vivo). In protocol B, venoms, 1.0 mg/kg, were injected im 15 min prior to suramin (1.0 mg/kg, iv). Before and 2 h after the im injection blood was collected by orbital puncture. Plasma was separated and stored at 4ºC for determination of CK activity using a diagnostic kit from Sigma. Preincubation of some venoms (C.v. viridis, A.c. laticinctus, C.d. terrificus and B. jararacussu) with suramin reduced (37-76 percent) the increase in plasma CK, except for B. alternatus, B. jararaca or L. muta venoms. Injection of suramin after the venom partially protected (34-51 percent) against the myotoxicity of B. jararacussu, A.c. laticinctus and C.d. terrificus venom, and did not protect against C.v. viridis, L. muta, B. moojeni, B. alternatus or B. jararaca venoms. These results show that suramin has an antimyotoxic effect against some, but not all the North and South American crotalid snake venoms studied here

Vascular Reactivity by Purinoceptor Activation in Rat Inferior Vena Cava

BACKGROUND: Extracellular ATP, released from platelets and nerve endings, plays significant roles in the regulation of circulation. The effects of ATP depend on the location of the vessels and the species of experimental animals. Until now, studies were limited to arteries, so we compared the effects of ATP in rat vena cava with those in the aorta and attempted to identify the characteristics of their receptors. METHODS: Vascular rings were isolated from the rat inferior vena cava and descending thoracic aorta. Endothelial cells were preserved or removed by gentle rubbing. The isometric contractions were recorded on polygraph using a force transducer. RESULTS: In the vena cava ring precontracted by 100 nM norepinephrine (NE), ATP elicited relaxations in a dose-dependent manner. These effects were abolished by removal of the endothelium or pretreatment with a nitric oxide synthase inhibitor. Relaxations to ATP in the vena cava (EC50 :9.9 microM) were less potent than those in the aorta (1.7 microM). The relative order of potencies was ADP>ATP>AMP>adenosine, but the maximal relaxation to ADP was smaller than to ATP. ATP-induced vasorelaxation was blocked by suramin, a nonselective antagonist for P2 purinoceptor and reactive blue-2, a P2Y blocker. At basal tension, ATP contracted the vena cava dose-dependently and these effects were potentiated by endothelium-removal. Contractions in the vena cava were also less potent than in the aorta, and the order of potencies was alpha, beta-MeATP>UTP>ATP>ADP>AMP=adenosine. ATP-induced vasoconstriction was blocked by suramin and alpha, beta-MeATP, a desensitizing antagonist of P2X purinoceptor, and potentiated by pretreatment with UTP. CONCLUSION: These results suggest that ADP and ATP acts on P2Y1- and P2Y2-purinoceptor in the endothelium, respectively and induces vasorelaxation of the vena cava, which is mediated by nitric oxide. Since ATP and UTP induced vasoconstriction in endothelium-denuded condition, it may be mediated by the activation of the P2X and P2Y4, 6 purinoceptor on smooth muscles, respectively.