Sex-linked differences in the vasorelaxant effects of anandamide in vascular mesenteric beds: role of oestrogens

Prenatal exposure to methamphetamine in rats induces endothelial dysfunction in male but not female adult offspring

In utero exposure to methamphetamine results in significant developmental, neurological, and behavioral deficits in offspring. However, very little is known about the cardiovascular effects of prenatal methamphetamine exposure in adult offspring. We hypothesized that prenatal methamphetamine exposure causes adverse cardiovascular effects in adult offspring. The aims of this study were to test the effects of prenatal methamphetamine exposure on blood pressure and endothelial function in male and female adult rat offspring. Pregnant rats were injected with methamphetamine (5 mg kg^-1 day^-1) or saline throughout pregnancy. Conscious blood pressure and vascular function in mesenteric-resistance arteries were measured in male and female adult offspring using tail cuff and myography, respectively (beginning at 8 weeks old). In adult male offspring, but not in adult female offspring, endothelium-dependent relaxation to acetylcholine was impaired in methamphetamine-exposed compared to saline-exposed rats. Vascular relaxation to diethylamine NONOate diethylammonium salt was not impacted by gender or prenatal exposure. Prenatal methamphetamine exposure had no effect on systolic blood pressure in offspring of either gender. These data suggest that prenatal methamphetamine exposure adversely affects endothelial function in a sex-dependent manner. Clinically, these data suggest that adult males with a history of prenatal methamphetamine exposure may be at greater risk of developing cardiovascular disease due to endothelial dysfunction.

The role of catecholamines in modulating responses to stress: Sex-specific patterns, implications, and therapeutic potential for post-traumatic stress disorder and opiate withdrawal

Emotional arousal is one of several factors that determine the strength of a memory and how efficiently it may be retrieved. The systems at play are multifaceted; on one hand, the dopaminergic mesocorticolimbic system evaluates the rewarding or reinforcing potential of a stimulus, while on the other, the noradrenergic stress response system evaluates the risk of threat, commanding attention, and engaging emotional and physical behavioral responses. Sex-specific patterns in the anatomy and function of the arousal system suggest that sexually divergent therapeutic approaches may be advantageous for neurological disorders involving arousal, learning, and memory. From the lens of the triple network model of psychopathology, we argue that post-traumatic stress disorder and opiate substance use disorder arise from maladaptive learning responses that are perpetuated by hyperarousal of the salience network. We present evidence that catecholamine-modulated learning and stress-responsive circuitry exerts substantial influence over the salience network and its dysfunction in stress-related psychiatric disorders, and between the sexes. We discuss the therapeutic potential of targeting the endogenous cannabinoid system; a ubiquitous neuromodulator that influences learning, memory, and responsivity to stress by influencing catecholamine, excitatory, and inhibitory synaptic transmission. Relevant preclinical data in male and female rodents are integrated with clinical data in men and women in an effort to understand how ideal treatment modalities between the sexes may be different.

Leveraging Human Microbiome Features to Diagnose and Stratify Children with Irritable Bowel Syndrome

Accurate diagnosis and stratification of children with irritable bowel syndrome (IBS) remain challenging. Given the central role of recurrent abdominal pain in IBS, we evaluated the relationships of pediatric IBS and abdominal pain with intestinal microbes and fecal metabolites using a comprehensive clinical characterization and multiomics strategy. Using rigorous clinical phenotyping, we identified preadolescent children (aged 7 to 12 years) with Rome III IBS (n = 23) and healthy controls (n = 22) and characterized their fecal microbial communities using whole-genome shotgun metagenomics and global unbiased fecal metabolomic profiling. Correlation-based approaches and machine learning algorithms identified associations between microbes, metabolites, and abdominal pain. IBS cases differed from controls with respect to key bacterial taxa (eg, Flavonifractor plautii and Lachnospiraceae bacterium 7_1_58FAA), metagenomic functions (eg, carbohydrate metabolism and amino acid metabolism), and higher-order metabolites (eg, secondary bile acids, sterols, and steroid-like compounds). Significant associations between abdominal pain frequency and severity and intestinal microbial features were identified. A random forest classifier built on metagenomic and metabolic markers successfully distinguished IBS cases from controls (area under the curve, 0.93). Leveraging multiple lines of evidence, intestinal microbes, genes/pathways, and metabolites were associated with IBS, and these features were capable of distinguishing children with IBS from healthy children. These multi-omics features, and their links to childhood IBS coupled with nutritional interventions, may lead to new microbiome-guided diagnostic and therapeutic strategies.

Effect of Testosterone on TRPV1 Expression in a Model of Orofacial Myositis Pain in the Rat

Recent clinical studies have revealed sex differences in response to transient receptor potential vanilloid 1 (TRPV1) agonist-induced pain. However, the mechanism of these differences in TRPV1-related chronic pain remains unclear. In the present study, we investigate the effects of inflammation and gonadal hormones on TRPV1 expression in trigeminal ganglia. Inflammatory pain was modeled by injecting complete Freund's adjuvant (CFA) into the left masseter muscle in rats. TRPV1 mRNA and protein levels in the trigeminal ganglia of male and female rats following CFA injection were assessed. CFA-induced changes in TRPV1 mRNA and protein expression in the trigeminal ganglia from orchidectomized (ODX) male rats and testosterone-replaced ODX rats were examined. Additionally, TRPV1 mRNA levels in the trigeminal ganglia from ovariectomized (OVX) female and ODX male rats treated with tamoxifen were assessed. We found that the levels of TRPV1 mRNA and protein in the trigeminal ganglia from female rats following CFA injection were significantly higher than in the ganglia from naïve female rats. CFA-induced inflammatory hyperalgesia did not alter TRPV1 expression in the trigeminal ganglia from male rats. The TRPV1 mRNA and protein expression levels in the ODX male trigeminal ganglia were significantly upregulated on day 3 following the initiation of inflammation. However, CFA-induced inflammatory pain had no significant effect on TRPV1 mRNA or protein expression in testosterone-replaced ODX rats. Furthermore, tamoxifen was unable to inhibit the upregulation of TRPV1 expression in OVX female and ODX male rats after CFA injection. In summary, these data indicate that gender differences in TRPV1 function may be, in part, mediated by sex-dependent TRPV1 expression in sensory ganglia. Testosterone plays a key role in the inhibition of TRPV1 expression in this rat chronic inflammatory pain model.

Argentinean Society of Experimental Pharmacology: Brief history and main scientific contributions to the discipline

Argentina Biomedical Science has been historically strong. The development of Human and Veterinary Pharmacology in our country as a pivotal discipline has been acknowledged worldwide because of the quality of its contributions. Argentinean Society of Experimental Pharmacology (SAFE) is a non- profit association whose research fields include Experimental and Clinical Pharmacology. SAFE main goals are described as follow (a) To meet active researchers for studying concerns regarding Experimental and Clinical Pharmacology (b) To launch an initiative for development of the discipline in mainly our country and other collaborative countries worldwide (c) To spread the pharmacological know-how obtained from different research teams (d) To strengthen relations between pharmacologists (e) To facilitate the presentation and discussion of scientific papers. This current article shows the SAFE's more important scientific contribution to pharmacology through its former research scientists to the present.

Endocannabinoids and the Cardiovascular System in Health and Disease

The endocannabinoid system is widely distributed throughout the cardiovascular system. Endocannabinoids play a minimal role in the regulation of cardiovascular function in normal conditions, but are altered in most cardiovascular disorders. In shock, endocannabinoids released within blood mediate the associated hypotension through CB(1) activation. In hypertension, there is evidence for changes in the expression of CB(1), and CB(1) antagonism reduces blood pressure in obese hypertensive and diabetic patients. The endocannabinoid system is also upregulated in cardiac pathologies. This is likely to be cardioprotective, via CB(2) and CB(1) (lesser extent). In the vasculature, endocannabinoids cause vasorelaxation through activation of multiple target sites, inhibition of calcium channels, activation of potassium channels, NO production and the release of vasoactive substances. Changes in the expression or function of any of these pathways alter the vascular effect of endocannabinoids. Endocannabinoids have positive (CB(2)) and negative effects (CB(1)) on the progression of atherosclerosis. However, any negative effects of CB(1) may not be consequential, as chronic CB(1) antagonism in large scale human trials was not associated with significant reductions in atheroma. In neurovascular disorders such as stroke, endocannabinoids are upregulated and protective, involving activation of CB(1), CB(2), TRPV1 and PPARα. Although most of this evidence is from preclinical studies, it seems likely that cannabinoid-based therapies could be beneficial in a range of cardiovascular disorders.

Vascular targets for cannabinoids: animal and human studies

Application of cannabinoids and endocannabinoids to perfused vascular beds or individual isolated arteries results in changes in vascular resistance. In most cases, the result is vasorelaxation, although vasoconstrictor responses are also observed. Cannabinoids also modulate the actions of vasoactive compounds including acetylcholine, methoxamine, angiotensin II and U46619 (thromboxane mimetic). Numerous mechanisms of action have been proposed including receptor activation, potassium channel activation, calcium channel inhibition and the production of vasoactive mediators such as calcitonin gene-related peptide, prostanoids, NO, endothelial-derived hyperpolarizing factor and hydrogen peroxide. The purpose of this review is to examine the evidence for the range of receptors now known to be activated by cannabinoids. Direct activation by cannabinoids of CB1 , CBe , TRPV1 (and potentially other TRP channels) and PPARs in the vasculature has been observed. A potential role for CB2, GPR55 and 5-HT1 A has also been identified in some studies. Indirectly, activation of prostanoid receptors (TP, IP, EP1 and EP4 ) and the CGRP receptor is involved in the vascular responses to cannabinoids. The majority of this evidence has been obtained through animal research, but recent work has confirmed some of these targets in human arteries. Vascular responses to cannabinoids are enhanced in hypertension and cirrhosis, but are reduced in obesity and diabetes, both due to changes in the target sites of action. Much further work is required to establish the extent of vascular actions of cannabinoids and the application of this research in physiological and pathophysiological situations.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids 2013. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-6.

Modulation by 17β-estradiol of anandamide vasorelaxation in normotensive and hypertensive rats: a role for TRPV1 but not fatty acid amide hydrolase

Recent studies suggest that endocannabinoid signaling is modulated by 17β-estradiol (17Eβ) however it is unclear if this applies to the cardiovascular actions of anandamide, a major endocannabinoid. This study examined the in vitro effects of 17Eβ on vasorelaxation to anandamide in myograph-mounted small mesenteric arteries obtained from Wistar rats and Spontaneously Hypertensive Rats (SHRs) of both sexes. Treatment with 1μM 17Eβ but not its enantiomer 17Eα significantly enhanced relaxation to anandamide in male Wistar rats. This effect was independent of a functional endothelium but was blocked by the Transient Receptor Potential Vanilloid type 1 (TRPV1) receptor antagonist SB366791 (2μM) or prolonged treatment with the TRPV1 agonist capsaicin (10μM). A TRPV1-dependent potentiation by 17Eβ was also observed in male SHRs, but not in female Wistar rats or female SHRs. Whilst inhibition of anandamide hydrolysis by 1μM URB597 (an inhibitor of fatty acid amide hydrolase; FAAH) similarly augmented anandamide relaxation in male, but not female, Wistar rats and SHRs, URB597 did not affect the 17Eβ-induced potentiation. Female SHRs displayed a larger maximal relaxation to anandamide; however sex difference was not found in Wistar rats. We conclude that pharmacological levels of 17Eβ potentiate mesenteric relaxation to anandamide through mechanisms dependent on TRPV1 receptors but not FAAH-mediated hydrolysis in male Wistar rats and male SHRs. Sexual dimorphism was observed in the modulatory effects of 17Eβ and URB597, which does not necessarily lead to a greater anandamide response in female rats.

Phytoestrogens enhance the vascular actions of the endocannabinoid anandamide in mesenteric beds of female rats

In rat isolated mesenteric beds that were contracted with NA as an in vitro model of the vascular adrenergic hyperactivity that usually precedes the onset of primary hypertension, the oral administration (3 daily doses) of either 10 mg/kg genistein or 20 mg/kg daidzein potentiated the anandamide-induced reduction of contractility to NA in female but not in male rats. Oral treatment with phytoestrogens also restored the vascular effects of anandamide as well as the mesenteric content of calcitonin gene-related peptide (CGRP) that were reduced after ovariectomy. The enhancement of anandamide effects caused by phytoestrogens was prevented by the concomitant administration of the estrogen receptor antagonist fulvestrant (2.5 mg/kg, s.c., 3 daily doses). It is concluded that, in the vasculature of female rats, phytoestrogens produced an estrogen-receptor-dependent enhancement of the anandamide-vascular actions that involves the modulation of CGRP levels and appears to be relevant whenever an adrenergic hyperactivity occurs.

Low omega-6 vs. low omega-6 plus high omega-3 dietary intervention for chronic daily headache: protocol for a randomized clinical trial

BACKGROUND

Targeted analgesic dietary interventions are a promising strategy for alleviating pain and improving quality of life in patients with persistent pain syndromes, such as chronic daily headache (CDH). High intakes of the omega-6 (n-6) polyunsaturated fatty acids (PUFAs), linoleic acid (LA) and arachidonic acid (AA) may promote physical pain by increasing the abundance, and subsequent metabolism, of LA and AA in immune and nervous system tissues. Here we describe methodology for an ongoing randomized clinical trial comparing the metabolic and clinical effects of a low n-6, average n-3 PUFA diet, to the effects of a low n-6 plus high n-3 PUFA diet, in patients with CDH. Our primary aim is to determine if: A) both diets reduce n-6 PUFAs in plasma and erythrocyte lipid pools, compared to baseline; and B) the low n-6 plus high n-3 diet produces a greater decline in n-6 PUFAs, compared to the low n-6 diet alone. Secondary clinical outcomes include headache-specific quality-of-life, and headache frequency and intensity.

METHODS

Adults meeting the International Classification of Headache Disorders criteria for CDH are included. After a 6-week baseline phase, participants are randomized to a low n-6 diet, or a low n-6 plus high n-3 diet, for 12 weeks. Foods meeting nutrient intake targets are provided for 2 meals and 2 snacks per day. A research dietitian provides intensive dietary counseling at 2-week intervals. Web-based intervention materials complement dietitian advice. Blood and clinical outcome data are collected every 4 weeks.

RESULTS

Subject recruitment and retention has been excellent; 35 of 40 randomized participants completed the 12-week intervention. Preliminary blinded analysis of composite data from the first 20 participants found significant reductions in erythrocyte n-6 LA, AA and %n-6 in HUFA, and increases in n-3 EPA, DHA and the omega-3 index, indicating adherence.

TRIAL REGISTRATION

ClinicalTrials.gov (NCT01157208).

A COX-2 metabolite of the endogenous cannabinoid, 2-arachidonyl glycerol, mediates suppression of IL-2 secretion in activated Jurkat T cells

Previous studies from this laboratory have demonstrated that a COX-2 metabolite of the endogenous cannabinoid, 2-arachidonyl glycerol (2-AG), inhibits IL-2 secretion in activated T cells through PPARgamma activation independent of the cannabinoid receptors, CB1/CB2. Because numerous cyclooxygenase (COX) products have been shown to activate PPARgamma, the primary purpose of the present studies was to determine the role of COX metabolism in the inhibition of IL-2 secretion by 2-AG. Pretreatment with nonselective and COX-2-specific inhibitors completely abrogated 2-AG-mediated suppression of IL-2 secretion. In contrast, pretreatment with COX-1-specific inhibitors had no effect upon 2-AG-mediated inhibition of IL-2 secretion. Interestingly, the current studies also demonstrate that while the potency of 2-AG is comparable between human Jurkat T cells and murine splenocytes, anandamide (AEA) is markedly more potent in suppressing IL-2 production in Jurkat T cells compared to murine splenocytes. Additionally, the present studies also demonstrate that COX-2 protein is readily detectable in resting Jurkat T cells, which is in contrast to resting murine splenocytes in which COX-2 protein is virtually undetectable. Furthermore, COX-2 protein and mRNA levels are significantly increased over basal levels by 2h following activation of Jurkat cells, whereas increases in COX-2 protein in murine splenocytes are not observed until 4h after cellular activation. These studies suggest that the potency of AEA in the suppression of IL-2 secretion may correlate with COX-2 protein levels in different T cell models. The present studies are also significant in that they demonstrate 2-AG-mediated inhibition of IL-2 secretion is dependent upon COX-2 metabolism.

Gonadal hormone modulation of the behavioral effects of Delta9-tetrahydrocannabinol in male and female rats

Female rats are more sensitive than males to many behavioral effects of cannabinoids. The purpose of the present study was to determine if sex differences in the antinociceptive and motoric effects of Delta(9)-tetrahydrocannabinol (THC) are due to activational effects of gonadal steroid hormones. THC-induced antinociception (tail withdrawal, paw pressure tests) and motoric effects (horizontal locomotion, catalepsy) were compared in male and female gonadectomized rats that were chronically treated with hormone (testosterone in males, estradiol in females) vs. those that were gonadectomized and had no hormone replacement. THC's effects were also compared between gonadally intact females tested during vaginal estrus vs. diestrus. THC (5 and 10 mg/kg i.p.) produced very similar antinociceptive effects in no-hormone vs. testosterone-treated males, but significantly less locomotor suppression in testosterone-treated males than those with no hormone replacement. In gonadectomized females, estradiol enhanced THC's antinociceptive but not motoric effects. In gonadally intact, cycling females, 5 mg/kg THC produced slightly to significantly greater behavioral effects in estrous than in diestrous females. These results suggest that sex differences in THC-induced behavioral effects in the adult rat can be attributed to activational effects of testosterone in males and/or estradiol in females.

Estrogen recruits the endocannabinoid system to modulate emotionality

Estrogen administration elicits anxiolytic and antidepressant-like effects in female rats; however, the mechanism of this effect is unknown. Fatty acid amide hydrolase (FAAH), the enzyme which degrades the endocannabinoid anandamide, has been shown to be regulated by estrogen. Thus, we examined if the anxiolytic and antidepressant effects of estrogen implicated the endocannabinoid system. In the first experiment, ovariectomized female rats were administered a single injection of 17beta-estradiol (10 microg) or oil, and 48 h later were given an injection of the cannabinoid CB1 receptor antagonist AM251 (1 mg/kg) or vehicle. One hour after AM251 or vehicle administration, subjects were tested in either the open field test (OFT), elevated plus maze (EPM) or the forced swim test (FST). Estradiol treatment resulted in a significant increase in open arm entries in the EPM and time spent in the center quadrant of the OFT, which were reversed by co-treatment with AM251, suggesting that endocannabinoids are integral to the anxiolytic effects of estrogen. No significant effects of estradiol or AM251 were seen in the FST. In the second experiment, administration of the FAAH inhibitor URB597 (0.1 and 0.3 mg/kg) increased open arm entries in the EPM and time spent in the center quadrant in the OFT as well as significantly reduced immobility in the FST. Collectively, these data demonstrate that estrogen may elicit changes in emotional behavior through an endocannabinoid mechanism, and suggest that inhibition of FAAH represents a therapeutic target for anxiety and depression in women.

Cannabinoids as therapeutic agents in cardiovascular disease: a tale of passions and illusions

In addition to their classical known effects, such as analgesia, impairment of cognition and learning and appetite enhancement, cannabinoids have also been related to the regulation of cardiovascular responses and implicated in cardiovascular pathology. Elevated levels of endocannabinoids have been related to the extreme hypotension associated with various forms of shock as well as to the cardiovascular abnormalities that accompany cirrhosis. In contrast, cannabinoids have also been associated with beneficial effects on the cardiovascular system, such as a protective role in atherosclerosis progression and in cerebral and myocardial ischaemia. In addition, it has also been suggested that the pharmacological manipulation of the endocannabinoid system may offer a novel approach to antihypertensive therapy. During the last decades, the tremendous increase in the understanding of the molecular basis of cannabinoid activity has encouraged many pharmaceutical companies to develop more potent synthetic cannabinoid analogues and antagonists, leading to an explosion of basic research and clinical trials. Consequently. not only the synthetic THC dronabinol (Marinol) and the synthetic THC analogue nabilone (Cesamet) have been approved in the United States, but also the standardized cannabis extract (Sativex) in Canada. At least three strategies can be foreseen in the future clinical use of cannabinoid-based drugs: (a) the use of CB(1) receptor antagonists, such as the recently approved rimonabant (b) the use of CB(2)-selective agonists, and (c) the use of inhibitors of endocannabinoid degradation. In this context, the present review examines the effects of cannabinoids and of the pharmacological manipulation of the endocannabinoid system, in cardiovascular pathophysiology.

Participation of CGRP and prostanoids in the sex-linked differences of vascular anandamide effects in mesenteric beds of Sprague-Dawley rats

The in vitro exposure to anandamide elicits greater relaxations in mesenteric beds isolated from female compared to male rats. The present work shows that in mesenteric beds precontracted with noradrenaline the removal of endothelium increased the relaxation caused by anandamide in male and ovariectomized female but not in sham-operated female rats. The nitric oxide synthase inhibition with 100 microM N(omega)-nitro-L-arginine methyl ester hydrochloride (L-NAME) and the sensory in vivo denervation through neonatal administration of capsaicin also reduced anandamide-induced relaxations but these effects had the same extent in male and in female mesenteries. The content of calcitonin gene related peptide (CGRP) in mesenteric beds, that was higher in intact female than in male rats, was reduced by ovariectomy and restored to control values 21 days after a 3 weekly i.m. administration of 450 microg/kg 17beta-oestradiol. This latter treatment also increased CGRP content in mesenteries from males up to the same levels observed in females. The basal release of CGRP in mesenteric beds was equivalent in either sex, but the exposure to anandamide increased CGRP release solely in female mesenteries. The ratio prostacyclin/thromboxane A(2) was selectively reduced in mesenteries from male rats after exposure to anandamide, due to the decrease of the tissue levels of prostacyclin. Moreover, the cyclooxygenase-2 inhibitor 0.1 microM N-[2-(cyclohexyloxy)-4-nitrophenyl]-methanesulphonamide (NS-398) diminished the relaxations caused by anandamide solely in female rats. It is proposed that relaxing factors such as CGRP and prostacyclin contribute to the higher relaxations caused by anandamide in the vasculature of female rats.

Small molecule vanilloid TRPV1 receptor antagonists approaching drug status: can they live up to the expectations?

The cloning of the transient receptor potential vanilloid type-1 (TRPV1) receptor initiated the discovery of potent small molecule antagonists, many of which are in preclinical phase or already undergoing clinical trials. While animal experiments imply a therapeutic value for these compounds as novel analgesic-antiphlogistic drugs, new findings with TRPV1 deficient (trpv1 -/-) mice signal troubles for TRPV1 antagonists as clinical research gains impetus. An emerging concept with important implications for drug development is that TRPV1 may be differentially regulated under physiological and pathological conditions. If so, it is conceivable that such TRPV1 ligands can be synthesized that specifically target TRPV1 in diseased (e.g. inflamed or neoplastic) tissues but spare TRPV1 that subserves its physiological functions in healthy organs. This review explores the current status of this field and seeks an answer to the question how these new discoveries could be factored into TRPV1 drug discovery and development.

Sex differences in behavioral effects of cannabinoids

This review summarizes the existing literature on sex differences in the effects of cannabinoid drugs on behavior, primarily in the adult rodent. These preclinical studies, taken together with preliminary reports of sex differences in cannabinoid effects in humans, suggest that sex of subject may be an important modulating factor in a variety of cannabinoid effects. When sex differences are found, females are usually more sensitive than males to cannabinoids. Both pharmacokinetic and pharmacodynamic variables may contribute to sex differences in behavioral effects of cannabinoids. Given the significant therapeutic potential of cannabinoid agonists and antagonists--as well as their widespread recreational use--it will be important to determine the reliability and functional significance of, as well as mechanisms underlying sex differences in cannabinoid effects.

The effects of Delta9-tetrahydrocannabinol in rat mesenteric vasculature, and its interactions with the endocannabinoid anandamide

1 Delta9-tetrahydrocannabinol (THC) produces varying effects in mesenteric arteries: vasorelaxation (third-order branches, G3), modest vasorelaxation (G2), no effect (G1) and vasoconstriction (the superior mesenteric artery, G0). 2 In G3, vasorelaxation to THC was inhibited by pertussis toxin, but was unaffected by the CB1 receptor antagonist, AM251 (1 microM), incubation with the TRPV1 receptor agonist capsaicin (10 microM, 1 h), the TRPV1 receptor antagonist capsazepine (10 microM) or de-endothelialisation. 3 In G3, vasorelaxation to THC was inhibited by high K+ buffer, and by the following K+ channel inhibitors: charybdotoxin (100 nM), apamin (500 nM) and barium chloride (30 microM), but not by 4-aminopyridine, glibenclamide or tertiapin. 4 In G3, THC (10 and 100 microM) inhibited the contractile response to Ca2+ in a Ca2+-free, high potassium buffer, indicating that THC blocks Ca2+ influx. 5 In G0, the vasoconstrictor responses to THC were inhibited by de-endothelialisation and SR141716A (100 nM), but not by the endothelin (ET(A)) receptor antagonist FR139317 (1 microM).THC (1 and 10 microM) antagonised vasorelaxation to anandamide in G3 but not G0. THC did not antagonise the noncannabinoid verapamil, capsaicin or the CB1 receptor agonist CP55,940. 6 THC (10 and 100 microM) inhibited endothelium-derived relaxing factor (EDHF)-mediated responses to carbachol in a manner similar to the gap junction inhibitor 18alpha-glycyrrhetinic acid. 7 These data show that THC causes vasorelaxation through activation of K+ channels and inhibition of Ca2+ channels, and this involves non-CB1, non-TRPV1 but G-protein-coupled receptors. In G0, THC does not cause relaxation and at high concentrations causes contractions. Importantly, THC antagonises the effects of anandamide, possibly through inhibition of EDHF activity.