Re-evaluation of the cardioprotective effects of cannabinoids against ischemia-reperfusion injury according to the IMproving Preclinical Assessment of Cardioprotective Therapies (IMPACT) criteria.

Ischemic heart disease, associated with high morbidity and mortality, represents a major challenge for the development of drug-based strategies to improve its prognosis. Results of pre-clinical studies suggest that agonists of cannabinoid CB2 receptors and multitarget cannabidiol might be potential cardioprotective strategies against ischemia-reperfusion injury. The aim of our study was to re-evaluate the cardioprotective effects of cannabinoids against ischemia-reperfusion injury according to the IMproving Preclinical Assessment of Cardioprotective Therapies (IMPACT) criteria published recently by the European Union (EU) CARDIOPROTECTION COST ACTION. To meet the minimum criteria of those guidelines, experiments should be performed (i) on healthy small animals subjected to ischemia with reperfusion lasting for at least 2 hours and (ii) confirmed in small animals with comorbidities and co-medications and (iii) in large animals. Our analysis revealed that the publications regarding cardioprotective effects of CB2 receptor agonists and cannabidiol did not meet all three strict steps of IMPACT. Thus, additional experiments are needed to confirm the cardioprotective activities of (endo)cannabinoids mainly on small animals with comorbidities and on large animals. Moreover, our publication underlines the significance of the IMPACT criteria for a proper planning of preclinical experiments regarding cardiac ischemia-reperfusion injury.

Concentration-Dependent Attenuation of Pro-Fibrotic Responses after Cannabigerol Exposure in Primary Rat Hepatocytes Cultured in Palmitate and Fructose Media.

Hepatic fibrosis is a consequence of liver injuries, in which the overproduction and progressive accumulation of extracellular matrix (ECM) components with the simultaneous failure of matrix turnover mechanisms are observed. The aim of this study was to investigate the concentration-dependent influence of cannabigerol (CBG, Cannabis sativa L. component) on ECM composition with respect to transforming growth factor beta 1 (TGF-ß1) changes in primary hepatocytes with fibrotic changes induced by palmitate and fructose media. Cells were isolated from male Wistar rats' livers in accordance with the two-step collagenase perfusion technique. This was followed by hepatocytes incubation with the presence or absence of palmitate with fructose and/or cannabigerol (at concentrations of 1, 5, 10, 15, 25, 30 µM) for 48 h. The expression of ECM mRNA genes and proteins was determined using PCR and Western blot, respectively, whereas media ECM level was evaluated using ELISA. Our results indicated that selected low concentrations of CBG caused a reduction in TGF-ß1 mRNA expression and secretion into media. Hepatocyte exposure to cannabigerol at low concentrations attenuated collagen 1 and 3 deposition. The protein and/or mRNA expressions and MMP-2 and MMP-9 secretion were augmented using CBG. Considering the mentioned results, low concentrations of cannabigerol treatment might expedite fibrosis regression and promote regeneration.

Evaluation of the Expression and Localization of the Multifunctional Protein CacyBP/SIP and Elements of the MAPK Signaling Pathway in the Adrenal Glands of Rats with Primary and Secondary Hypertension.

Hypertension is a global civilization disease and one of the most common causes of death in the world. Organ dysfunction is a serious health consequence of hypertension, which involves damage to the heart, kidneys and adrenals. The interaction of recently discovered multifunctional protein-CacyBP/SIP with ERK1/2 and p38 kinases by regulating the activity and intracellular localization of these kinases may play an important role in the signaling pathways involved in the pathogenesis of hypertension. Due to the lack of data on this subject, we decided to investigate the localization, expression and possible relationship between the studied parameters in the adrenals under arterial hypertension. The study was conducted on the adrenals of rats with spontaneous and DOCA-salt hypertension. The expression of CacyBP/SIP, p-ERK1/2 and p-p38 was detected by immunohistochemistry and qRT-PCR. The results show a statistically significant decrease in CacyBP/SIP expression in the adrenal glands of hypertensive rats. With ERK1/2, there was a decrease in cortical immunoreactivity and an increase in the adrenal medulla of primary hypertensive rats. In contrast, in the adrenals of DOCA-salt rats, ERK1/2 immunoreactivity increased in the cortex and decreased in the medulla. In turn, p38 expression was higher in the adrenal glands of rats with primary and secondary hypertension. The obtained results may suggest the involvement of CacyBP/SIP in the regulation of signaling pathways in which MAP kinases play an important role and provide new insight into molecular events in hypertension. Moreover, they show the participation of CacyBP/SIP in response to oxidative stress.

Effects of the peripheral CB1 receptor antagonist JD5037 in mono- and polytherapy with the AMPK activator metformin in a monocrotaline-induced rat model of pulmonary hypertension.

Pulmonary hypertension (PH) is a disease leading to increased pressure in the pulmonary artery and right heart failure. The adenosine monophosphate-activated protein kinase (AMPK) activator, metformin, has a protective effect against PH. CB1 receptor blockade reduces the number of pathological alterations in experimental lung fibrosis. The current study evaluates the effect of the peripheral cannabinoid CB1 receptor antagonist JD5037 in mono- and polytherapy with metformin in rat monocrotaline-induced mild PH. Animals received metformin (100 mg/kg), JD5037 (3 mg/kg), or a combination of both once daily for 21 days. Monocrotaline (60 mg/kg) increased right ventricular (RV) systolic pressure (RVSP), led to RV and lung hypertrophy and remodeling, and decreased oxygen saturation. Metformin partially restored the monocrotaline-induced effects, i.e., decreased RVSP, increased oxygen saturation, and counteracted cardiac fibrotic, hypertrophic, and inflammatory changes. JD5037 modified parameters related to inflammation and/or fibrosis. Only polytherapy with metformin and JD5037 improved Fulton's index and coronary artery hypertrophy and tended to be more effective than monotherapy against alterations in RVSP, oxygen saturation and coronary artery tunica media vacuolization. In conclusion, monotherapy with JD5037 does not markedly influence the PH-related changes. However, polytherapy with metformin tends to be more efficient than any of these compounds alone.

Why Do Marijuana and Synthetic Cannabimimetics Induce Acute Myocardial Infarction in Healthy Young People?

The use of cannabis preparations has steadily increased. Although cannabis was traditionally assumed to only have mild vegetative side effects, it has become evident in recent years that severe cardiovascular complications can occur. Cannabis use has recently even been added to the risk factors for myocardial infarction. This review is dedicated to pathogenetic factors contributing to cannabis-related myocardial infarction. Tachycardia is highly important in this respect, and we provide evidence that activation of CB1 receptors in brain regions important for cardiovascular regulation and of presynaptic CB1 receptors on sympathetic and/or parasympathetic nerve fibers are involved. The prototypical factors for myocardial infarction, i.e., thrombus formation and coronary constriction, have also been considered, but there is little evidence that they play a decisive role. On the other hand, an increase in the formation of carboxyhemoglobin, impaired mitochondrial respiration, cardiotoxic reactions and tachyarrhythmias associated with the increased sympathetic tone are factors possibly intensifying myocardial infarction. A particularly important factor is that cannabis use is frequently accompanied by tobacco smoking. In conclusion, additional research is warranted to decipher the mechanisms involved, since cannabis use is being legalized increasingly and Δ9-tetrahydrocannabinol and its synthetic analogue nabilone are indicated for the treatment of various disease states.

The potential of cannabinoids and inhibitors of endocannabinoid degradation in respiratory diseases.

The global incidence of respiratory diseases and complications is increasing. Therefore, new methods of treatment, as well as prevention, need to be investigated. A group of compounds that should be considered for use in respiratory diseases is cannabinoids. There are three groups of cannabinoids - plant-derived phytocannabinoids, synthetic cannabinoids, and endogenous endocannabinoids including the enzymes responsible for their synthesis and degradation. All cannabinoids exert their biological effects through either type 1 cannabinoid receptors (CB1) and/or type 2 cannabinoid receptors (CB2). In numerous studies (in vitro and in vivo), cannabinoids and inhibitors of endocannabinoid degradation have shown beneficial anti-inflammatory, antioxidant, anti-cancer, and anti-fibrotic properties. Although in the respiratory system, most of the studies have focused on the positive properties of cannabinoids and inhibitors of endocannabinoid degradation. There are few research reports discussing the negative impact of these compounds. This review summarizes the properties and mechanisms of action of cannabinoids and inhibitors of endocannabinoid degradation in various models of respiratory diseases. A short description of the effects selected cannabinoids have on the human respiratory system and their possible use in the fight against COVID-19 is also presented. Additionally, a brief summary is provided of cannabinoid receptors properties and their expression in the respiratory system and cells of the immune system.

Beneficial and harmful effects of CB1 and CB2 receptor antagonists on chronotropic and inotropic effects related to atrial ß-adrenoceptor activation in humans and in rats with primary hypertension.

We have previously shown that cannabinoid CB1 and CB2 receptor antagonists, AM251 and AM630, respectively, modulate cardiostimulatory effects of isoprenaline in atria of Wistar rats. The aim of the present study was to examine whether such modulatory effects can also be observed (a) in the human atrium and (b) in spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY). Inotropic effects of isoprenaline and/or CGP12177 (that activate the high- and low-affinity site of ß1 -adrenoceptors, respectively) were examined in paced human atrial trabeculae and rat left atria; chronotropic effects were studied in spontaneously beating right rat atria. AM251 modified cardiostimulatory effects more strongly than AM630. Therefore, AM251 (1 µM) enhanced the chronotropic effect of isoprenaline in WKY and SHR as well as inotropic action of isoprenaline in WKY and in human atria. It also increased the inotropic influence of CGP12177 in SHR. AM630 (1 µM) decreased the inotropic effect of isoprenaline and CGP12177 in WKY, but enhanced the isoprenaline-induced inotropic effect in SHR and human atria. Furthermore, AM251 (0.1 and 3 µM) and AM630 (0.1 µM) reduced the inotropic action of isoprenaline in human atria. In conclusion, cannabinoid receptor antagonists have potentially harmful and beneficial effects through their amplificatory effects on ß-adrenoceptor-mediated positive chronotropic and inotropic actions, respectively.

Chronic cannabidiol treatment reduces the carbachol-induced coronary constriction and left ventricular cardiomyocyte width of the isolated hypertensive rat heart.

Cannabidiol (CBD) is suggested to possess cardioprotective properties. We examined the influence of chronic (10 mg/kg once daily for 2 weeks) CBD administration on heart structure (e.g. cardiomyocyte width) and function (e.g. stimulatory and inhibitory responses induced by ß-adrenoceptor (isoprenaline) and muscarinic receptor (carbachol) activation, respectively). Experiments were performed on hearts and/or left atria isolated from spontaneously (SHR) and deoxycorticosterone (DOCA-salt) hypertensive rats; Wistar-Kyoto (WKY) and sham-operated rats (SHAM) served as the respective normotensive controls. CBD diminished the width of cardiomyocytes in left ventricle and reduced the carbachol-induced vasoconstriction of coronary arteries both in DOCA-salt and SHR. However, it failed to affect left ventricular hypertrophy and even aggravated the impaired positive and negative lusitropic effects elicited by isoprenaline and carbachol, respectively. In normotensive hearts CBD led to untoward structural and functional effects, which occurred only in WKY or SHAM or, like the decrease in ß1-adrenoceptor density, in either control strain. In conclusion, due to its modest beneficial effect in hypertension and its adverse effects in normotensive hearts, caution should be taken when using CBD as a drug in therapy.

Chronic Cannabidiol Administration Fails to Diminish Blood Pressure in Rats with Primary and Secondary Hypertension Despite Its Effects on Cardiac and Plasma Endocannabinoid System, Oxidative Stress and Lipid Metabolism.

We investigated the influence of cannabidiol (CBD) on blood pressure (BP) and heart rate (HR) in spontaneously (SHR) and deoxycorticosterone (DOCA-salt) hypertensive rats. Hypertension was connected with increases in cardiac and plasma markers of lipid peroxidation in both models, whereas cardiac endocannabinoid levels decreased in SHR and increased in DOCA-salt. CBD (10 mg/kg once a day for 2 weeks) did not modify BP and HR in hypertension but counteracted pro-oxidant effects. Moreover, it decreased cardiac or plasma levels of anandamide, 2-arachidonoylglycerol and oleoyl ethanolamide in DOCA-salt and inhibited the activity of fatty acid amide hydrolase (FAAH) in both models. In the respective normotensive control rats, CBD increased lipid peroxidation, free fatty acid levels and FAAH activity. In conclusion, chronic CBD administration does not possess antihypertensive activity in a model of primary and secondary (DOCA-salt) hypertension, despite its antioxidant effect. The latter may be direct rather than based on the endocannabinoid system. The unexpected CBD-related increase in lipid peroxidation in normotensive controls may lead to untoward effects; thus, caution should be kept if CBD is used therapeutically.

Effects of hypertension and FAAH inhibitor treatment of rats with primary and secondary hypertension considering the physicochemical properties of erythrocytes.

Hypertension is one of the most common cardiovascular diseases in the world and is associated with oxidative stress. The aim of this study was to examine the effect of the chronic administration of the fatty-acid amide hydrolase inhibitor (URB597-[3-(3-carbamoylphenyl)phenyl]N-cyclohexylcarbamate) to rats with primary (SHRs - spontaneously hypertensive rats) and secondary (DOCA-salt - 11-desoxycorticosterone acetate-salt-induced hypertension) hypertension on the composition and physicochemical properties of erythrocytes membrane. Because changes in membrane composition lead to modifications of electrical charge what may affect cell functions, the levels of following components were determined: four classes of membrane phospholipids (by HPLC - high-performance liquid chromatograph), sialic acid (by resorcinol method), lipid peroxidation product - malondialdehyde (by GCMS - gas chromatography-mass spectrometry). The reduced levels of phospholipids and sialic acid, as well as the increased levels of malonodialdehyde observed in the erythrocyte membrane of rats with primary and secondary hypertension led to a decrease in the negative electrical charge of the membrane. Long-term administration of URB597 to SHRs and DOCA-salt-treated rats partially prevented changes caused by hypertension. Using theoretical equations and the dependence of cell surface charge density as a function of pH, total surface concentrations of acid and base groups and their association constants have been determined. Considering the changes in physicochemical parameters of erythrocyte membranes, URB597 can be considered a potential protective factor for erythrocytes in situations of metabolic changes associated with oxidative stress.

Cannabinoid CB1 and CB2 receptors antagonists AM251 and AM630 differentially modulate the chronotropic and inotropic effects of isoprenaline in isolated rat atria.

BACKGROUND: Drugs targeting CB1 and CB2 receptors have been suggested to possess therapeutic benefit in cardiovascular disorders associated with elevated sympathetic tone. Limited data suggest cannabinoid ligands interact with postsynaptic ß-adrenoceptors. The aim of this study was to examine the effects of CB1 and CB2 antagonists, AM251 and AM630, respectively, at functional cardiac ß-adrenoceptors. METHODS: Experiments were carried out in isolated spontaneously beating right atria and paced left atria where inotropic and chronotropic increases were induced by isoprenaline and selective agonists of ß1 and ß2-adrenergic receptors. RESULTS: We found four different effects of AM251 and AM630 on the cardiostimulatory action of isoprenaline: (1) both CB receptor antagonists 1 µM enhanced the isoprenaline-induced increase in atrial rate, and AM630 1 µM enhanced the inotropic effect of isoprenaline; (2) AM251 1 µM decreased the efficacy of the inotropic effect of isoprenaline; (3) AM251 0.1 and 3 µM and AM630 3 µM reduced the isoprenaline-induced increases in atrial rate; (4) AM630 0.1 and 3 µM enhanced the inotropic effect of isoprenaline, which was not changed by the same concentrations of AM251. CONCLUSIONS: Our results show that the CB1 and CB2 receptor antagonists AM251 and AM630 have bidirectional effects on the cardiostimulatory action of isoprenaline, most likely related to an interaction with ß1-adrenoceptors. Provided that the results translate to human heart, caution should be taken when using CB1 and CB2 receptor antagonists, as an enhanced sympathetic tone accompanies many cardiovascular disorders.

Fatty acid amide hydrolase inhibitor (URB597) as a regulator of myocardial lipid metabolism in spontaneously hypertensive rats.

Pressure overload, which is typical of hypertension, is known to evoke alterations not only in the morphology of the heart but also in the preference of myocardial energetic substrates usage. Nowadays, the endocannabinoid system (ECS) serves as a potential therapeutic target for cardiovascular disorders and, simultaneously, affects whole body metabolism homeostasis. Therefore, an open question is whether ECS, apart from decreasing blood pressure, also affects cardiac muscle metabolism in hypertensive conditions. All experiments were conducted on a genetic model of primary hypertension i.e. spontaneously hypertensive rats (SHRs) and Wistar Kyoto rats (WKY) served as a normotensive control. ECS was chronically activated by 2-weeks intraperitoneal injections of fatty acid amide hydrolase (FAAH) inhibitor - URB597. Lipid analyses in the left ventricle and serum were based on ex vivo heart perfusion in Langendorff perfusion system, thin layer chromatography, and gas liquid chromatography. The total expression of selected proteins was determined using Western blot as well as immunohistochemical techniques. As expected, URB597 markedly reduced systolic as well as mean blood pressures in SHRs. Moreover, prolonged FAAH inhibition resulted in stimulation of 3H-palmitate uptake and incorporation into different lipid fractions in cardiomyocytes in the hypertensive as well as normotensive conditions. An increase in fatty acid oxidation caused by URB597 treatment was observed only in WKY rats, but not SHRs, and was accompanied by an elevation in peroxisome proliferator-activated receptor alpha (PPARα) and ß-hydroxyacyl-CoA dehydrogenase (ß-HAD) expressions. Chronic activation of ECS significantly upregulates palmitate uptake and its esterification but not oxidation in the SHR's myocardium.

The effects of chronic FAAH inhibition on myocardial lipid metabolism in normotensive and DOCA-salt hypertensive rats.

AIMS: There is significant evidence that the endocannabinoid system (ECS) takes part in the regulation of the cardiovascular system in hypertension. It is quite well established that hypertension causes several changes in the heart metabolism, but it is still unknown whether the ECS affects this process. Therefore, we investigated the influence of prolonged ECS activation on myocardial lipid metabolism in deoxycorticosterone acetate (DOCA)-salt hypertensive rats by chronic fatty acid amide hydrolase (FAAH) inhibition. MATERIALS AND METHODS: We examined the uptake and oxidation of palmitic acid during the heart perfusion as well as intramyocardial and plasma lipid contents using gas liquid chromatography. Total, plasmalemmal and intracellular expressions of selected proteins were estimated by the Western blot technique. Moreover, the left ventricle's morphology, including myocardial vessels density, was measured using immunohistochemistry. KEY FINDINGS: We demonstrated that hypertension induced cardiomyocytes and myocardial blood vessels hypertrophy, followed by a reduction in myocardial palmitate oxidation. Interestingly, prolonged activation of the ECS in the normotensive rats induced cardiomyocyte enlargement and intensified fatty acids metabolism. We have also shown that FAAH inhibition improved morphology of coronary blood vessels and only partially maintained its effect on lipid metabolism in the DOCA-salt hearts (i.e. elevated plasma and intramyocardial TAG contents as well as plasmalemmal FAT/CD36 and total FATP1 expressions). SIGNIFICANCE: This study revealed that chronic FAAH inhibition has no protective effects on the heart lipid metabolism in hypertension.

Chronic inhibition of fatty acid amide hydrolase by URB597 produces differential effects on cardiac performance in normotensive and hypertensive rats.

BACKGROUND AND PURPOSE: Fatty acid amide hydrolase (FAAH) inhibitors are postulated to possess anti-hypertensive potential, because their acute injection decreases BP in spontaneously hypertensive rats (SHR), partly through normalization of cardiac contractile function. Here, we examined whether the potential hypotensive effect of chronic FAAH inhibition by URB597 in hypertensive rats correlated with changes in cardiac performance. EXPERIMENTAL APPROACH: Experiments were performed using perfused hearts and left atria isolated from 8- to 10-week-old SHR, age-matched deoxycorticosterone acetate (DOCA)-salt rats and normotensive controls chronically treated with URB597 (1 mg·kg-1 ) or vehicle. KEY RESULTS: URB597 decreased BP only in the DOCA-salt rats, along with a reduction of ventricular hypertrophy and diastolic stiffness, determined in hypertension. We also observed normalization of the negative inotropic atrial response to the cannabinoid receptor agonist CP55940. In the SHR model, URB597 normalized (atria) and enhanced (hearts) the positive ino- and chronotropic effects of the ß-adrenoceptor agonist isoprenaline respectively. Ventricular CB1 and CB2 receptor expression was decreased only in the DOCA-salt model, whereas FAAH expression was reduced in both models. URB597 caused translocation of CB1 receptor immunoreactivity to the intercalated discs in the hearts of SHR. URB597 increased cardiac diastolic stiffness and modified the ino- and lusitropic effects of isoprenaline in normotensive rats. CONCLUSION AND IMPLICATIONS: Hypotensive effect of chronic FAAH inhibition depend on the model of hypertension and partly correlate with improved cardiac performance. In normotensive rats, chronic FAAH inhibition produced several side-effects. Thus, the therapeutic potential of these agents should be interpreted cautiously.

Altered uterine contractility in response to ß-adrenoceptor agonists in ovarian cancer.

We aimed to prospectively examine ß-adrenoceptor-mediated uterine contractility in women suffering from gynecological malignancies. Myometrial specimens were obtained from non-pregnant women undergoing hysterectomy for benign gynecological disorders, and ovarian, endometrial, synchronous ovarian-endometrial, and cervical cancer. Contractions of myometrial strips in an organ bath before and after cumulative dosages of ß2- and ß3-adrenoceptor agonists with preincubation of propranolol, SR 59230A, and butoxamine were studied. All agonists induced a dose-dependent attenuation for uterine contractility in endometrial or cervical cancer, similar to that observed in the reference group. Contradictory effects were observed for ovarian cancer alone or in combination with endometrial cancer. CL 316243 or ritodrine abolished the relaxation, whereas BRL 37344 increased the uterine contractility in ovarian cancer. Moreover, ß-adrenoceptor antagonists caused varied effects for ß2- or ß3-adrenoceptor agonists. Our experiments demonstrate that ovarian cancer, alone or as synchronous ovarian-endometrial cancer, substantially alters uterine contractility in response to ß-adrenoceptor agonists.

Age-specific influences of chronic administration of the fatty acid amide hydrolase inhibitor URB597 on cardiovascular parameters and organ hypertrophy in DOCA-salt hypertensive rats.

BACKGROUND: The endocannabinoid system has been suggested to be up-regulated in hypertension. Fatty acid amide hydrolase (FAAH) is the main hydrolytic enzyme for the encocannabinoid anandamide. The aim of our study was to examine the age-specific influence of the chronic administration of the FAAH inhibitor URB597 on blood pressure (BP), heart rate (HR) and cardiac and renal hypertrophy in hypertensive rats during two critical periods for the development of hypertension. METHODS: Experiments were performed on uninephrectomised 4 (younger) and 6-7 (older) weeks old rats rendered hypertensive by a high salt diet and deoxycorticosterone acetate (DOCA) injections and on normotensive animals (unilateral nephrectomy only). URB597 1mg/kg or its vehicle were injected twice daily for 2 weeks. RESULTS: The DOCA-salt procedure caused comparable increases in BP (but not HR) in both age groups and more strongly increased cardiac and renal hypertrophic indices in younger than in older animals. Chronic URB597 administration reduced BP and HR in older but not in younger rats. In contrast, the inhibitor diminished the cardiac and renal hypertrophy in younger but not in older animals. URB597 did not affect body weight gain, and food and water intake in normotensive or hypertensive rats. CONCLUSION: Two weeks of URB597 administration to DOCA-salt hypertensive rats caused an age-specific reduction in BP, HR and cardiac and renal hypertrophy and did not affect the body weight, and water and food intake. Thus, caution should be taken during studies of FAAH inhibitors because of their potential age-specific effects.

[Serotonin hypothesis and pulmonary artery hypertension]. / Teoria serotoninowa a tetnicze nadcisnienie plucne.

Pulmonary arterial hypertension (PAH) is a progressive, complex disease leading to the right ventricular failure and premature death. PAH is characterized by increased pulmonary arterial pressure, increased vascular resistance, pulmonary vascular remodeling and endothelial dysfunction. Pathomechanism of this disease is still unknown. It has been suggested, that endothelial dysfunction is caused by unbalance between vasodilators and vasoconstrictors e.g. serotonin (5-HT). Previously, serotonin hypothesis was linked to the anorexigens, derivatives of fenfluramine, which are serotonin transporter (SERT) substrates. Nowadays, it has been proved that all elements of serotonergic system within pulmonary circulation participate in the developement of PAH. The tryptophan hydroxylase 1 (Tph-1) catalyses synthesis of 5-HT from tryptophan in the pulmonary arterial endothelial cells. 5-HT mediates contraction of pulmonary vessels via 5-HT1B and 5-HT2A receptors. 5-HT is also transported into pulmonary arterial smooth muscle cells via SERT and through activation of reactive oxygen species and Rho-kinase may contribute to contraction or/and, via stimulation of transcription factors, lead to proliferation and remodelling. There is also increasing number of evidence about functional interaction between 5-HT1B receptor and SERT in modulation of vasoconstriction and proliferation in pulmonary arteries. This review discusses the role of 5-HT in the development of PAH and highlights possible therapeutic targets within serotonergic system.

MH-3: evidence for non-competitive antagonism towards the low-affinity site of ß1-adrenoceptors.

ß-Adrenoceptor antagonists are important drugs for the treatment of cardiovascular diseases and some of those drugs also block the so-called low-affinity site of ß1-adrenoceptors although at much higher concentrations. This low-affinity site, also identified in vivo and in human tissue, may come into play under certain pathophysiological situations including arrhythmias. The aim of our study was to determine the potency of 14 compounds chemically related to bupranolol or bevantolol and two xanthone derivatives at the low-affinity site of the ß1-adrenoceptor. The potency of the compounds at the low- and high-affinity site of ß1-adrenoceptors (ß1L and ß1H; both increasing heart rate) was compared in the pithed rat. One compound was also studied in the isolated rat heart and its α1-adrenolytic effect determined in the isolated rat mesenteric artery. In the pithed rat, four compounds blocked the ß1L-adrenoceptor at a ≥10-fold lower potency than the ß1H-adrenoceptor whereas the xanthone derivative (-)-MH-3 was equipotent. In the spontaneously beating right atrium (-)-MH-3 was a non-competitive antagonist of comparable potency at either receptor; its apparent pD'2 value for the ß1L-adrenoceptor ranged from 5.6 to 6.4 under various conditions, including the Langendorff preparation. Its apparent pA2 at the α1-adrenoceptor in the mesenteric artery was 8.4. (-)-MH-3 is the first compound with virtually the same potency at the low- and high-affinity site of ß1-adrenoceptors in vivo; it appears to be a non-competitive antagonist at either site in vitro.