Aqueous extracts of Urtica dioica (stinging nettle) leaf contain a P2-purinoceptor antagonist-Implications for male fertility.

Stinging nettle root and leaf extracts were tested for their effect on prostatic smooth muscle contractility. Root extract did not affect electrical field stimulation induced-nerve mediated contractions of isolated rat prostates. On the other hand, leaf extract attenuated electrical field stimulation-induced contractions at all frequencies. Similarly, contractions elicited by exogenous administration of ATP and αß-methylene ATP were inhibited by leaf extract, whereas contractions elicited by exogenous administration of noradrenaline or acetylcholine were unaffected. The active component was present within the aqueous phase of the leaf extract. In mouse mating studies, stinging nettle leaf extract (50 mg p.o. daily) reduced male fertility by 53% compared to vehicle-treated male mice. Cardiovascular parameters were unaffected by administration of stinging nettle leaf extract (p ≥ 0.057). Treated mice exhibited normal mating behaviour. Bladder and testes weighed less in stinging nettle leaf extract treated mice. All other organs and total body weight were unaffected. It is concluded that stinging nettle leaf extract reduces contractility of genitourinary smooth muscle by acting as an antagonist at postjunctional P2X1-purinoceptors. These data indicates that blocking sperm transport through pharmacological blockade of P2X1-purinoceptors via oral administration is consistent with an effective and convenient biological strategy male contraception.

Targeting P2 receptors in purinergic signaling: a new strategy of active ingredients in traditional Chinese herbals for diseases treatment.

Adenosine triphosphate (ATP) and its metabolites adenosine diphosphate, adenosine monophosphate, and adenosine in purinergic signaling pathway play important roles in many diseases. Activation of P2 receptors (P2R) channels and subsequent membrane depolarization can induce accumulation of extracellular ATP, and furtherly cause kinds of diseases, such as pain- and immune-related diseases, cardiac dysfunction, and tumorigenesis. Active ingredients of traditional Chinese herbals which exhibit superior pharmacological activities on diversified P2R channels have been considered as an alternative strategy of disease treatment. Experimental evidence of potential ingredients in Chinese herbs targeting P2R and their pharmacological activities were outlined in the study.

Plant natural products as source of new P2 receptors ligands.

In recent years, interest in the research of P2 receptor (P2R)-mediated responses has grown significantly due to the recognition of the involvement of these receptors in various physiological and pathological processes. Despite all the progress made in the functional characterization of P2Rs, purinergic signaling research is still limited by the lack of selective or efficient ligands for different receptor subtypes. In this sense, several molecules have been tested towards these receptors as agonists or antagonists. Historically, natural products have always been sources of new bioactive substances for diverse purposes. However, compared to synthetic molecules, the number of natural products assessed for P2R ligands is still low. In this review, we present examples of studies that demonstrated plant natural products acting directly on P2R and modulating their functionality. In some cases, we highlight that the pharmacological activity previously described for the original organism could be correlated to an agonist or antagonist activity of a specific natural product on these receptors. These examples reinforce the need for more studies to investigate the pharmacological potential of new or known natural compounds targeting P2 receptors.

The therapeutic potential of purinergic signalling.

This review is focused on the pathophysiology and therapeutic potential of purinergic signalling. A wide range of diseases are considered, including those of the central nervous system, skin, kidney, musculoskeletal, liver gut, lower urinary tract, cardiovascular, airways and reproductive systems, the special senses, infection, diabetes and obesity. Several purinergic drugs are already on the market, including P2Y12 receptor antagonists for stroke and thrombosis, P2Y2 receptor agonists for dry eye, and A1 receptor agonists for supraventricular tachycardia. Clinical trials are underway for the use of P2X3 receptor antagonists for the treatment of chronic cough, visceral pain and hypertension, and many more compounds are being explored for the treatment of other diseases. Most experiments are 'proof of concept' studies on animal or cellular models, which hopefully will lead to further clinical trials. The review summarises the topic, mostly referring to recent review articles.

Extracellular nucleotides as novel, underappreciated pro-metastatic factors that stimulate purinergic signaling in human lung cancer cells.

BACKGROUND: One of the challenging problems of current radio-chemotherapy is recurrence and metastasis of cancer cells that survive initial treatment. We propose that one of the unwanted effects of radiochemotherapy is the release from damaged ("leaky") cells of nucleotides such as ATP and UTP that exert pro-metastatic functions and can directly stimulate chemotaxis of cancer cells. METHODS: To address this problem in a model of human lung cancer (LC), we employed several complementary in vitro and in vivo approaches to demonstrate the role of extracellular nucleotides (EXNs) in LC cell line metastasis and tumor progression. We measured concentrations of EXNs in several organs before and after radiochemotherapy. The purinergic receptor agonists and antagonists, inhibiting all or selected subtypes of receptors, were employed in in vitro and in vivo pro-metastatic assays. RESULTS: We found that EXNs accumulate in several organs in response to radiochemotherapy, and RT-PCR analysis revealed that most of the P1 and P2 receptor subtypes are expressed in human LC cells. EXNs were found to induce chemotaxis and adhesion of LC cells, and an autocrine loop was identified that promotes the proliferation of LC cells. Most importantly, metastasis of these cells could be inhibited in immunodeficient mice in the presence of specific small molecule inhibitors of purinergic receptors. CONCLUSIONS: Based on this result, EXNs are novel pro-metastatic factors released particularly during radiochemotherapy, and inhibition of their pro-metastatic effects via purinergic signaling could become an important part of anti-metastatic treatment.

The discovery and development of prasugrel.

INTRODUCTION: Prasugrel (CS-747, LY640315) is a third-generation thienopyridine, which gained approval by the FDA in 2009 for its use in patients with acute coronary syndrome undergoing percutaneous coronary intervention. AREAS COVERED: This article focuses on the preclinical profile of prasugrel. Using published preclinical and clinical studies, the authors summarize the pharmacokinetics, pharmacodynamics, and pharmacogenomics of prasugrel and their distinguishing features in efficacy and safety. EXPERT OPINION: Prasugrel has a more rapid, more potent antiplatelet effect with less interindividual response variability when compared to clopidogrel. Those therapeutic advantages are attributed to features of its chemical structure that favor the metabolic conversion of prasugrel to its active metabolite. However, the increased risk of bleeding has been associated with a greater antiplatelet effect and dosing profile; this is especially the case in those patients who are at a higher risk of bleeding complications. It is therefore important for an optimal dosing strategy of prasugrel to be identified to provide a formulation that has the best balance for efficacy and safety.

Discovery of novel P2Y14 agonist and antagonist using conventional and nonconventional methods.

P2Y14 is a member of the pyrimidinergic GPCR family. UDP-Glc has been previously shown to activate human P2Y14, whereas UDP was unable to activate the receptor. In this study, the authors used conventional and nonconventional methods to further characterize P2Y14 and its ligands. Conventional calcium mobilization and nonconventional cellular impedance functional assays revealed that UMP and UDP selectively activated HEK cells coexpressing P2Y14 and Gα(qi5). In the impedance assays, the presence of exogenous Gα(qi5) resulted in agonist-induced Gq signaling, whereas in the absence of exogenous Gα(qi5), the signal was indicative of Gi. The authors established the first P2Y14 membrane filtration binding assay using a novel optimized expression vector and [(3)H]UDP as radioligand. UDP-Glc, UMP, and UDP dose dependently inhibited [(3)H]UDP binding in the binding assay, and saturation analysis revealed that UDP bound P2Y14 with a K(D) = 10 nM and a B(max) = 110 pmol/mg. The authors screened a phosphonate library and identified compound A, which inhibited UDP-Glc-mediated calcium signaling in the fluorometric imaging plate reader assay (IC(50) = 2.3 µM) and competed for [(3)H]UDP binding in the novel binding assay with a K(i) = 1280 nM.

Intrinsic platelet reactivity before P2Y12 blockade contributes to residual platelet reactivity despite high-level P2Y12 blockade by prasugrel or high-dose clopidogrel. Results from PRINCIPLE-TIMI 44.

It was the objective of this study to determine whether the intrinsic platelet response to adenosine diphosphate (ADP) before thienopyridine exposure contributes to residual platelet reactivity to ADP despite high level P2Y12 blockade by prasugrel (60 mg loading dose [LD]), 10 mg daily maintenance dose [MD]) or high-dose clopidogrel (600 mg LD, 150 mg daily MD). High residual platelet function during clopidogrel therapy is associated with poor clinical outcomes. It remains unknown whether the relationship between platelet reactivity prior to treatment with clopidogrel (300 mg LD, 75 mg daily MD) and residual on-treatment platelet reactivity is maintained after more potent P2Y12 inhibition. PRINCIPLE-TIMI 44 was a randomised, double-blind, two-phase crossover study of prasugrel compared with high-dose clopidogrel in 201 patients undergoing cardiac catheterisation for planned percutaneous coronary intervention. ADP-stimulated platelet-monocyte aggregates, platelet surface P-selectin and platelet aggregation were measured pre-treatment, during LD (6 h and 18-24 h) and MD (15 d). Correlations of pre-treatment to on-treatment values were determined by Spearman rank order. Prasugrel resulted in greater platelet inhibition than high-dose clopidogrel for each measure. However, for both drugs, pre-treatment reactivity to ADP predicted 6 h, 18-24 h and 15 day reactivity to ADP (correlations 0.24-0.62 for platelet-monocyte aggregates and P-selectin). In conclusion, a patient's intrinsic platelet response to ADP before exposure to thienopyridines contributes to residual platelet reactivity to ADP despite high level P2Y12 blockade with high-dose clopidogrel or even higher level P2Y12 blockade with prasugrel. Patients who are hyper-responsive to ADP pre-treatment are more likely to be hyper-responsive to ADP on-treatment, which may be relevant to therapeutic strategies.

Selective blockade of P2Y12 receptors by prasugrel inhibits myocardial infarction induced by thrombotic coronary artery occlusion in rats.

We evaluated the effects of prasugrel, a third-generation thienopyridyl prodrug, on P2Y12 receptors, adenosine 5'-diphosphate (ADP)-induced platelet aggregation, and myocardial infarction (MI) in rats. Oral administration of prasugrel (0.3-3 mg/kg) resulted in the dose-related inhibition of washed platelet aggregation induced by ADP (1-10 µM). Ex vivo [H]-2-MeS-ADP binding to platelet P2Y12 receptors was also inhibited by prasugrel in a similar dose range. The antiaggregatory effects of prasugrel correlated strongly with P2Y12 blockade with correlation coefficients of 0.85-0.92, suggesting that the antiaggregatory activity of prasugrel largely reflected P2Y12 blockade achieved in vivo. We further examined the effects of the in vivo P2Y12 inhibition by prasugrel (1-10 mg/kg, po) on MI induced by thrombotic coronary artery occlusion in rats. In surviving rats, infarct size at 24 hours after photoirradiation was evaluated. In the vehicle group, necrosis area/total left ventricular area was 37.9% ± 6.8% (mean ± SE, n = 7). At all prasugrel doses tested (n = 7 for each dose), necrosis area/total left ventricular area was significantly smaller than that in the vehicle group: 14.4% ± 4.0% for 1 mg/kg (P < 0.01), 19.8% ± 4.5% for 3 mg/kg (P < 0.05), and 14.8% ± 3.6% for 10 mg/kg (P < 0.01). At the highest administered dose of prasugrel (10 mg/kg), blood pressure and heart rate were unchanged. Arrhythmia was observed in 5 of 7 animals in the vehicle group at 24 hours after irradiation; in contrast, no arrhythmia was found in the group treated with prasugrel (10 mg/kg). Taken together, these results demonstrate that prasugrel is a selective P2Y12 inhibitor in vivo, providing effective inhibition of platelet aggregation and MI in rats.

Ivermectin antagonizes ethanol inhibition in purinergic P2X4 receptors.

ATP-gated purinergic P2X4 receptors (P2X4Rs) are expressed in the central nervous system and are sensitive to ethanol at intoxicating concentrations. P2XRs are trimeric; each subunit consists of two transmembrane (TM) alpha-helical segments, a large extracellular domain, and intracellular amino and carboxyl terminals. Recent work indicates that position 336 (Met336) in the TM2 segment is critical for ethanol modulation of P2X4Rs. The anthelmintic medication ivermectin (IVM) positively modulates P2X4Rs and is believed to act in the same region as ethanol. The present study tested the hypothesis that IVM can antagonize ethanol action. We investigated IVM and ethanol effects in wild-type and mutant P2X4Rs expressed in Xenopus oocytes by using a two-electrode voltage clamp. IVM antagonized ethanol-induced inhibition of P2X4Rs in a concentration-dependent manner. The size and charge of substitutions at position 336 affected P2X4R sensitivity to both ethanol and IVM. The first molecular model of the rat P2X4R, built onto the X-ray crystal structure of zebrafish P2X4R, revealed a pocket formed by Asp331, Met336, Trp46, and Trp50 that may play a role in the actions of ethanol and IVM. These findings provide the first evidence for IVM antagonism of ethanol effects in P2X4Rs and suggest that the antagonism results from the ability of IVM to interfere with ethanol action on the putative pocket at or near position 336. Taken with the building evidence supporting a role for P2X4Rs in ethanol intake, the present findings suggest that the newly identified alcohol pocket is a potential site for development of medication for alcohol use disorders.

P2X and NMDA receptor involvement in temporomandibular joint-evoked reflex activity in rat jaw muscles.

We have previously shown that injection of the excitatory amino glutamate into the rat temporomandibular joint (TMJ) evokes reflex activity in both anterior digastric (DIG) and masseter (MASS) muscles that can be attenuated by prior TMJ injection of an N-methyl-d-aspartate (NMDA) receptor antagonist. The aim of the present study was to test if jaw muscle activity could also be evoked by P2X receptor agonist injection into the rat TMJ region and if the reflex activity could be modulated by TMJ injection of P2X receptor antagonist or NMDA receptor antagonist. The selective P2X subtype agonist alpha,beta-methylene adenosine 5'-triphosphate (alpha,beta-me ATP) and vehicle (phosphate-buffered saline) or the selective P2X antagonist, 2'-(or-3')-O-(2,4,6-trinitrophenyl) adenosine 5'-triphosphate (TNP-ATP) or the selective NMDA antagonist (+/-)-d-2-amino-5-phosphonovalerate(APV) were injected into the rat TMJ region. Electromyographic (EMG) reflex activity was recorded in both DIG and MASS muscles. Compared with the baseline EMG activity, alpha,beta-me-ATP injection into the TMJ (but not its systemic administration) following pre-injection of the vehicle significantly increased the magnitude and the duration of ipsilateral DIG and MASS EMG activity in a dose-dependent manner. The alpha,beta-me-ATP-evoked responses could be antagonized by pre-injection of TNP-ATP into the same TMJ site but contralateral TMJ injection of TNP-ATP proved ineffective. Furthermore, the alpha,beta-me-ATP-evoked responses could also be antagonized by APV injected into the same TMJ site but not by its systemic injection. These results indicate the interaction of peripheral purinergic as well as glutamatergic receptor mechanisms in the processing of TMJ nociceptive afferent inputs that evoke reflex activity in jaw muscles.

Purinergic and nitrergic neuromuscular transmission mediates spontaneous neuronal activity in the rat colon.

Nitric oxide (NO) and ATP mediate smooth muscle relaxation in the gastrointestinal tract. However, the involvement of these neurotransmitters in spontaneous neuronal activity is unknown. The aim of the present work was to study spontaneous neuromuscular transmission in the rat midcolon. Microelectrode experiments were performed under constant stretch both in circular and longitudinal directions. Spontaneous inhibitory junction potentials (sIJP) were recorded. Tetrodotoxin (1 microM) and apamin (1 microM) depolarized smooth muscle cells and inhibited sIJP. N(omega)-nitro-l-arginine (l-NNA, 1 mM) depolarized smooth muscle cells but did not modify sIJP. In contrast, the P2Y(1) antagonist MRS-2500 (1 microM) did not modify the resting membrane potential (RMP) but reduced sIJP (IC(50) = 3.1 nM). Hexamethonium (200 microM), NF-023 (10 microM), and ondansetron (1 microM) did not modify RMP and sIJP. These results correlate with in vitro (muscle bath) and in vivo (strain gauges) data where l-NNA but not MRS-2500 induced a sustained increase of spontaneous motility. We concluded that, in the rat colon, inhibitory neurons regulate smooth muscle RMP and cause sIJP. In vitro, the release of inhibitory neurotransmitters is independent of nicotinic, P2X, and 5-hydroxytryptamine type 3 receptors. Neuronal NO causes a sustained smooth muscle hyperpolarization that is responsible for a constant inhibition of spontaneous motility. In contrast, ATP acting on P2Y(1) receptors is responsible for sIJP but does not mediate inhibitory neural tone. ATP and NO have complementary physiological functions in the regulation of gastrointestinal motility.

Antiplatelet therapy prasugrel: a novel platelet ADP P2Y12 receptor antagonist.

Novel adenosine diphosphate (ADP) P2Y(12) antagonists, including prasugrel, ticagrelor, cangrelor and elinogrel, are in various phases of clinical development. These ADP P2Y(12) antagonists have advantages over clopidogrel ranging from faster onset to greater and less variable inhibition of platelet function. Novel ADP P2Y(12) antagonists are under investigation to determine whether their use can result in improved antiplatelet activity, faster onset of action, and/or greater antithrombotic effects than clopidogrel, without an unacceptable increase in hemorrhagic or other side effects. Prasugrel (CS-747; LY-640315), a novel third-generation oral thienopyridine, is a specific, irreversible antagonist of the platelet ADP P2Y(12) receptor. Preclinical and early phase clinical studies have shown prasugrel to be characterized by more potent antiplatelet effects, lower interindividual variability in platelet response, and faster onset of activity compared to clopidogrel. Recent findings from large-scale phase III testing showed prasugrel to be more efficacious in preventing ischemic events in patients with acute coronary syndrome (ACS) undergoing percutaneous coronary intervention (PCI); however, this is achieved at the expense of an increased risk of bleeding. Prasugrel provides more rapid and consistent platelet inhibition than clopidogrel.

What is the risk of intensifying platelet inhibition beyond clopidogrel? A systematic review and a critical appraisal of the role of prasugrel.

Thienopyridines are a class of drug targeting the platelet adenosine diphosphate 2 receptor. They have been shown to significantly reduce platelet activity exerting an important role in those clinical settings in which such an effect is beneficial. Ticlopidine was first to be introduced several years ago but it was quickly replaced by clopidogrel as it had a better risk/benefit profile. Recently, prasugrel has been developed and tested in several ex vivo studies and clinical trials showing able to provide a more powerful antiplatelet effect at the expense of a higher risk of bleeding complications. Great debate rose around its recent approval in the US as well as in Europe. This review aims at exploring the development and available clinical data of this third-generation thienopyridine while discussing its practical implementation in routine practice.

Selective potentiation of homomeric P2X2 ionotropic ATP receptors by a fast non-genomic action of progesterone.

P2X receptors are ligand-gated ion channels activated by ATP that are widely expressed in the organism and regulate many physiological functions. We have studied the effect of progesterone (PROG) on native P2X receptors present in rat dorsal root ganglion (DRG) neurons and on recombinant P2X receptors expressed in HEK293 cells or Xenopus laevis oocytes. The effects of PROG were observed and already maximal during the first coapplication with ATP and did not need any preincubation of the cells with PROG, indicating a fast mechanism of action. In DRG neurons, PROG rapidly and reversibly potentiated submaximal but not saturating plateau-like currents evoked by ATP, but had no effect on the currents activated by alpha,beta-methylene ATP, an agonist of homomeric or heteromeric receptors containing P2X1 or P2X3 subunits. In cells expressing homomeric P2X2 receptors, responses to submaximal ATP, were systematically potentiated by PROG in a dose-dependent manner with a threshold between 1 and 10 nM. PROG had no effect on ATP currents carried by homomeric P2X1, P2X3, and P2X4 receptors or by heteromeric P2X1/5 and P2X2/3 receptors. We conclude that PROG selectively potentiates homomeric P2X2 receptors and, in contrast with dehydroepiandrosterone (DHEA), discriminates between homomeric and heteromeric P2X2-containing receptors. This might have important physiological implications since the P2X2 subunit is the most widely distributed P2X subunit in the organism. Moreover, DHEA and PROG might be useful tools to clarify the distribution and the role of native homo- and heteromeric P2X2 receptors.

Cangrelor: a novel P2Y12 receptor antagonist.

Antiplatelet therapy is critical in the prevention of thrombotic complications of acute coronary syndrome and percutaneous coronary interventions. Current antiplatelet agents (aspirin, clopidogrel and glycoprotein IIb/IIIa antagonists) have demonstrated the capacity to reduce major adverse cardiac events. However, these agents have limitations that compromise their clinical utility. The platelet P2Y12 receptor plays a central role in platelet function and is a focus in the development of antiplatelet therapies. Cangrelor is a potent, competitive inhibitor of the P2Y12 receptor that is administered by intravenous infusion and rapidly achieves near complete inhibition of ADP-induced platelet aggregation. This investigational drug has been studied for use during coronary procedures and the management of patients experiencing acute coronary syndrome and is undergoing evaluation for use in the prevention of perioperative stent thrombosis.

Purinergic P2X(7) receptor antagonists: Chemistry and fundamentals of biological screening.

The purinergic P2X(7) receptor is a unique member of the ATP-gated P2X family. This receptor has been implicated in numerous diseases and many structurally diverse ligands have been discovered via high throughput screening. This perspective will attempt to highlight some of the most recent key findings in both the biology and chemistry.

The antihyperalgesic activity of a selective P2X7 receptor antagonist, A-839977, is lost in IL-1alphabeta knockout mice.

The pro-inflammatory cytokine interleukin-1beta (IL-1beta) has been implicated in both inflammatory processes and nociceptive neurotransmission. Activation of P2X7 receptors is the mechanism by which ATP stimulates the rapid maturation and release of IL-1beta from macrophages and microglial cells. Recently, selective P2X7 receptor antagonists have been shown to reduce inflammatory and neuropathic pain in animal models. However, the mechanisms underlying these analgesic effects are unknown. The present studies characterize the pharmacology and antinociceptive effects of a structurally novel P2X7 antagonist. A-839977 potently (IC50=20-150 nM) blocked BzATP-evoked calcium influx at recombinant human, rat and mouse P2X7 receptors. A-839977 also potently blocked agonist-evoked YO-PRO uptake and IL-1beta release from differentiated human THP-1 cells. Systemic administration of A-839977 dose-dependently reduced thermal hyperalgesia produced by intraplantar administration of complete Freund's adjuvant (CFA) (ED50=100 micromol/kg, i.p.) in rats. A-839977 also produced robust antihyperalgesia in the CFA model of inflammatory pain in wild-type mice (ED50=40 micromol/kg, i.p.), but the antihyperalgesic effects of A-839977 were completely absent in IL-1alphabeta knockout mice. These data demonstrate that selective blockade of P2X7 receptors in vivo produces significant antinociception in animal models of inflammatory pain and suggest that the antihyperalgesic effects of P2X7 receptor blockade in an inflammatory pain model in mice are mediated by blocking the release of IL-1beta.

Adenine nucleotide effect on intraocular pressure: Involvement of the parasympathetic nervous system.

Nucleotides are present in the aqueous humor possibly exerting physiological effects on intraocular pressure (IOP). To determine the effect of nucleotides such as ATP and its related derivatives on IOP, New Zealand white rabbits were used. IOP was measured in rabbits treated topically either with saline (control) or with a single dose (10 microg/microL) of adenine nucleotides (ATP, 2-meS-ATP, ATP-gamma-S, alpha,beta-meADP, alpha,beta-meATP and beta,gamma-meATP). Those nucleotides reducing IOP (alpha,beta-meATP and beta,gamma-meATP) were then tested in concentrations ranging from 1 to 100 microg/microL to obtain the IC(50) value. Several antagonists for the P2 and adenosine A1 receptors (all at 10 microg/microL) were assayed 30 min before the application of the hypotensive nucleotide beta,gamma-meATP. To see whether the nucleotide was acting directly on the structures involved in aqueous humor dynamics or on the autonomic nerves controlling IOP, animal denervation and sympathetic (yohimbine and ICI-118,551 at 10 microg/microL) and parasympathetic (atropine and hexametonium at 10 microg/microL) receptors' antagonists were used 30 min before the instillation of beta,gamma-meATP. alpha,beta-meATP and beta,gamma-meATP decreased IOP to 60% of control value (basal IOP=23.2+/-1.3 mmHg), with IC(50) of 1.59+/-0.21 microg/microLand 0.56+/-0.62 microg/microL, which corresponds to 3mM and 1mM respectively. Denervation completely abolished the effect of beta,gamma-meATP. Sympathetic antagonists did not modify the hypotensive effect of beta,gamma-meATP, but parasympathetic antagonists were able to abolish it. Among the series of adenine nucleotide tested, alpha,beta-meATP and beta,gamma-meATP presented hypotensive actions on IOP. beta,gamma-meATP seems to stimulate cholinergic terminals being its final effect the IOP reduction. Therefore, these two nucleotides are interesting pharmacological tools for those pathologies related with high intraocular pressure.