Dose-dependent Negative Inotropic Effect Research Articles

Ketamine induced acute systolic heart failure

Background: Studies have shown major cardiovascular effects associated with ketamine use disorder including dose-dependent negative inotropic effects. Preoperative ketamine use has been linked to ketamine-induced stress cardiomyopathy. Case presentation: A 28-year-old female with a history of recurrent cystitis and ketamine use disorder (twice weekly for 14 years) presented with bilateral lower extremity oedema and shortness of breath for 3 months. She was tachycardic with a troponin level of 0.07 ng/ml and a B-type natriuretic peptide (BNP) level of 2511 pg/ml. Electrocardiogram showed normal sinus rhythm and transthoracic echocardiography (TTE) showed left ventricular ejection fraction (EF) of 15%, dilated left ventricle, and severe tricuspid and mitral regurgitation. Computed tomography (CT) scan of the chest and abdomen showed bilateral pleural effusions with congestive hepatopathy and ascites. The patient was started on intravenous furosemide, metoprolol, and sacubitril/valsartan. Rheumatological workup including complement levels, and antinuclear anti-double-stranded DNA was negative. A repeat TTE 2 weeks later revealed an EF of 25% and moderate tricuspid regurgitation. Four months later, the EF was 54% with normal left ventricular cavity size. Conclusion: Although ketamine use disorder is increasing, data on long-term side effects is minimal. Screening for ketamine use disorders should be considered in patients presenting with acute systolic heart failure. Long-term studies are needed to evaluate the benefits of adding ketamine screening to standard urine toxicology.

Adverse effects of hydroxychloroquine and azithromycin on contractility and arrhythmogenicity revealed by human engineered cardiac tissues

The coronavirus disease 2019 (COVID-19) outbreak caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become a global pandemic as declared by World Health Organization (WHO). In the absence of an effective treatment, different drugs with unknown effectiveness, including antimalarial hydroxychloroquine (HCQ), with or without concurrent administration with azithromycin (AZM), have been tested for treating COVID-19 patients with developed pneumonia. However, the efficacy and safety of HCQ and/or AZM have been questioned by recent clinical reports. Direct effects of these drugs on the human heart remain very poorly defined. To better understand the mechanisms of action of HCQ +/- AZM, we employed bioengineered human ventricular cardiac tissue strip (hvCTS) and anisotropic sheet (hvCAS) assays, made with human pluripotent stem cell (hPSC)-derived ventricular cardiomyocytes (hvCMs), which have been designed for measuring cardiac contractility and electrophysiology, respectively. Our hvCTS experiments showed that AZM induced a dose-dependent negative inotropic effect which could be aggravated by HCQ; electrophysiologically, as revealed by the hvCAS platform, AZM prolonged action potentials and induced spiral wave formations. Collectively, our data were consistent with reported clinical risks of HCQ and AZM on QTc prolongation/ventricular arrhythmias and development of heart failure. In conclusion, our study exposed the risks of HCQ/AZM administration while providing mechanistic insights for their toxicity. Our bioengineered human cardiac tissue constructs therefore provide a useful platform for screening cardiac safety and efficacy when developing therapeutics against COVID-19.

Adverse effects of hydroxychloroquine and azithromycin on contractility and arrhythmogenicity revealed by human engineered cardiac tissues

The coronavirus disease 2019 (COVID-19) outbreak caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has become a global pandemic as declared by World Health Organization (WHO). In the absence of an effective treatment, different drugs with unknown effectiveness, including antimalarial hydroxychloroquine (HCQ), with or without concurrent administration with azithromycin (AZM), have been tested for treating COVID-19 patients with developed pneumonia. However, the efficacy and safety of HCQ and/or AZM have been questioned by recent clinical reports. Direct effects of these drugs on the human heart remain very poorly defined. To better understand the mechanisms of action of HCQ +/− AZM, we employed bioengineered human ventricular cardiac tissue strip (hvCTS) and anisotropic sheet (hvCAS) assays, made with human pluripotent stem cell (hPSC)-derived ventricular cardiomyocytes (hvCMs), which have been designed for measuring cardiac contractility and electrophysiology, respectively. Our hvCTS experiments showed that AZM induced a dose-dependent negative inotropic effect which could be aggravated by HCQ; electrophysiologically, as revealed by the hvCAS platform, AZM prolonged action potentials and induced spiral wave formations. Collectively, our data were consistent with reported clinical risks of HCQ and AZM on QTc prolongation/ventricular arrhythmias and development of heart failure. In conclusion, our study exposed the risks of HCQ/AZM administration while providing mechanistic insights for their toxicity. Our bioengineered human cardiac tissue constructs therefore provide a useful platform for screening cardiac safety and efficacy when developing therapeutics against COVID-19.

Sulfur Dioxide: An Endogenous Protector Against Myocardial Injury.

Sulfur dioxide (SO2) was previously known as a harmful gas in air pollution. Recently, it was reported that SO2 can be endogenously generated in cardiovascular tissues. Many studies have revealed that endogenous SO2 has important physiological and pathophysiological significance and pharmacological potential. As a novel gasotransmitter, SO2 has important regulatory effects on the heart. It has a dose-dependent negative inotropic effect on cardiac function, in which L-type calcium channels are involved. SO2 can also attenuate myocardial injury caused by various harmful stimuli and play an important role in myocardial ischemia-reperfusion injury and myocardial hypertrophy. These effects are thought to be linked to its ability to reduce inflammation and as an antioxidant. In addition, SO2 regulates cardiomyocyte apoptosis and autophagy. Therefore, endogenous SO2 plays an important role in maintaining cardiovascular system homeostasis. In the present review, the literature concerning the metabolism of endogenous SO2, its cardiac toxicological effects and physiological regulatory effects, mechanisms for SO2-mediated myocardial protection and its pharmacological applications are summarized and discussed.

Synthesis and Comparative Inotropic Effects of Several Isoquinoline Alkaloids

Compounds 3a [1-(3′,4′-methylenedioxyphenyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline] and 3b [1-(6′-bromo-3′,4′-dimethoxyphenyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline] demonstrated dose-dependent (5-75 μM) negative inotropic effects. Compound 5 [1,3-bis-(6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolin- 1-yl)propane] demonstrated a two-phase inotropic effect. The experimental results and a literature analysis suggested that the negative inotropic effects of the tested compounds (3a, 3b, 5) could be due to their influences on the [Ca2+]i concentration through blocking of cardiomyocyte Na+- and Ca2+-channels. The positive inotropic effect of free base 5 could be related to modulation of cardiomyocyte muscarinic receptor activity.

Inhibitory Effect of Interferons on Contractive Activity of Bovine Mesenteric Lymphatic Vessels and Nodes.

We studied the effect of IFNα-2b and IFNβ-1a on phasic and tonic contractions of isolated bovine mesenteric lymphatic vessels and nodes. IFNα-2b and IFNβ-1a in concentrations of 250-1000 U/ml produced dose-dependent negative chronotropic and inotropic effects on spontaneous phasic contractions and tonus of lymphatic vessels and nodes. In de-endothelialized lymphatic vessels and nodes, IFNα-2b and IFNβ-1a in the same concentrations had less pronounced inhibitory effect on spontaneous contraction and tonus. L-NAME (100 μM) and charybdotoxin (0.1 μM with 0.5 μM apamine) significantly attenuated the inhibitory effect of IFNα-2b on phasic and tonic contractions of lymph nodes. L-NAME (100 μM) and indomethacin (10 μM) significantly reduced the IFNα-2b-induced inhibitory effect on phasic and tonic contractions of lymph node. These results indicate that IFNα-2b and IFNβ-1a have a pronounced inhibitory effect on the phasic and tonic contractions of bovine mesenteric lymphatic vessels and nodes. The responses are endothelium-dependent and are determined by production of NO and endothelium-dependent hyperpolarizing factor by endotheliocytes in lymphatic vessels and by production of NO and prostacyclin by endotheliocytes in the lymphatic nodes.

Effects and mechanisms of curcumin on the hemodynamic variablesof isolated perfused rat hearts.

There is no information on the dose-response relationship of curcumin on the hemodynamic variables of the heart at the organ level in isolated perfused rat hearts. We aimed to investigate the effects and mechanisms of curcumin on the hemodynamic variables of isolated perfused rat hearts. Rats were randomly divided into 9 groups. The isolated rat heart was retrogradely perfused with modified Krebs-Henseleit solution. After the stabilization period, each group was administered one of the following treatments for 25 min: saline, dimethyl sulfoxide, and curcumin (0.2 µM, 1 µM, and 5 µM); atropine (1 µM); atropine (1 µM) + curcumin (1 µM); L-NAME (100 µM); or L-NAME (100 µM) + curcumin (1 µM). Hemodynamic variables of the heart were measured. Curcumin at dose of 1 µM decreased the heart rate (from 271 ± 11.1 to 200.4 ± 14.3 beats/min, P = 0.011) but increased end-diastolic pressure (from 7.0 ± 0.4 to 54.6 ± 7.9 mmHg, P = 0.0008). A dose of 5 µM curcumin caused a decrease in the developed pressure (from 87.58 ± 9.0 to 65.40 ± 7.0 mmHg, P = 0.047) but an increase in the end-diastolic pressure (from 6.8 ± 0.6 to 48.9 ± 7.7 mmHg, P = 0.005). Atropine (1 µM) reversed the effects of curcumin on the heart. Our results suggest that curcumin produces dose-dependent negative chronotropic and inotropic effects in isolated perfused rat hearts.

Hypotensive and antihypertensive effects of a hydroalcoholic extract from Senecio nutans Sch. Bip. (Compositae) in mice: Chronotropic and negative inotropic effect, a nifedipine-like action

Ethnopharmacological relevanceSenecio nutans Sch. Bip. (Compositae) is an endemic plant of South America used in the management of acute mountain sickness in the Andean communities. Currently, the direct effects of hydroalcoholic extract from S. nutans on the cardiovascular system are unknown. The aim of this study was to determine the effects and mechanism of action of S. nutans on cardiovascular function in normotensive and Angiotensin II (1μg/mL) hypertension mice models. Material and methodsBlood pressure and ECG measurements were simultaneously carried out on the mice and rats. The isolated right atrium, papillary muscle of the left ventricle and isolated heart of rat were used to study the cardiac functions and mechanisms. ResultsS. nutans (40mg/Kg) induced a 30% and 12% significant (p<0.05) reduction of the mean arterial pressure (MAP) in normotensive and hypertensive mice respectively. This decrease was as a result of decrease in heart rate (HR) in normotensive (25%) and hypertensive model (31%). It also decreased the sinus rhythm in isolated right atrium of rat. Compared with Losartan, a known anti-hypertensive, S. nutans caused a dose-dependent negative inotropic effect (dP/dtmax) on Langendorff isolated heart system. While Losartan, decreased the MAP by 30% but had no effect on heart rate. The calcium blocker nifedipine had similar effects as S. nutans, decreasing the beat frequency of isolated right atrium and contractility of papillary muscle of the left ventricle of rat. ConclusionThe results suggest an important clinical function in hypertension therapy, as S. nutans could decrease the blood pressure in hypertensive mice by decreasing the HR and contractility, leading to a reduction in myocardial oxygen demand.

Does levobupivacaine have a benefit over bupivacaine in our practice?

Background The well-known toxic effects of bupivacaine on central nervous system and cardiovascular system were a base for the development of new long-acting local anesthetics. Levobupivacaine is the pure S(-)-enantiomer of racemic bupivacaine. This study compares the efficacy of levobupivacaine as against bupivacaine by epidural clinical study and by different routes in animal study. Materials and methods Evaluation of the analgesic activities by the hot plate method was carried out in nine groups of mice. Each four groups were injected intraperitoneally with either levobupivacaine or bupivacaine. The control group received saline. The hemodynamic effects of levobupivacaine and bupivacaine were carried out on the isolated rabbit's heart and anesthetized cats for carotid blood pressure and ECG. Thirty patients undergoing limb surgery were randomized to receive 15 ml of 0.5% levobupivacaine or bupivacaine through epidural needle. Intraoperative blood pressure and heart rate were recorded. Onset time of sensory and motor block, time to T 10 sensory block, complete motor block, quality of analgesia, and times for two segment regressions were detected. Results Experimentally, the intensity and duration of analgesia produced by levobupivacaine was more than that of bupivacaine. Both drugs induced significant dose-dependent negative inotropic effect, but it was lesser in levobupivacaine than in bupivacaine. An amount of 2 mg/kg levobupivacaine produced a significant rise in blood pressure and 4 mg/kg significantly decreased it, whereas 1 and 2 mg/kg bupivacaine produced a significant decrease in blood pressure. The ECG pattern of levobupivacaine showed no abnormalities, but bupivacaine at a dose of 2 mg/kg produced significant bradycardia and ECG changes. Cardiac arrest and death of cats occurred when 4 mg/kg of bupivacaine was injected. Clinically, the onset time of sensory block, time to T 10 sensory block and time to complete motor block are lower with bupivacaine than with levobupivacaine. Conclusion We found, based on the current pharmacodynamics evidence from this experimental and clinical study, that levobupivacaine has good analgesic activity and less cardiodepressant effect, and it offers advantages over bupivacaine.

The hypotensive agent dodoneine inhibits L-type Ca2+ current with negative inotropic effect on rat heart

Agelanthus dodoneifolius is one of the medicinal plants used in African pharmacopeia and traditional medicine for the treatment of cardiovascular diseases. A chemical analysis has identified one of the active principles: Dodoneine (Ddn). It is a new dihydropyranone which exerts hypotensive and vasorelaxant effects on rat. Since the mechanism of the hypotensive effect is unknown, we performed a variety of preclinical and mechanistic studies to characterize the specific cardiac effect of Ddn at tissue (ex-vivo) and cellular levels (in-vitro) in order to determine a molecular target. Ddn effects were evaluated in an isolated rat heart preparation using Langendorff retrograde perfusion and then, the effects of Ddn were characterized in freshly dissociated cardiac ventricular myocytes using the whole-cell patch-clamp configuration. Ex-vivo, Ddn produced a dose-dependent negative inotropic effect with an IC50 value of 10µM without changed heart rate. 100µM Ddn decreased left ventricular developed pressure of about 40%. In isolated cardiac myocytes, Ddn reduced ICa,L density of about 30% with an IC50 value estimated at 3µM. Ddn did not change current–voltage relation but it shifted the inactivation curve toward negative potentials and modified the half inactivation potentials. Furthermore, Ddn induced a phasic-dependent blocking on ICa,L. This study demonstrates that the hypotensive property of dodoneine is likely associated with a negative inotropic effect and the blockade of the L-type calcium channels.

Some Pharmacodynamic Aspects of Cefepime.

Some pharmacodynamic effects of cefepime, a new injectable semisynthetic cephalosporin, were studied in laboratory animals and the following results were obtained. Cefepime maximally stimulated isolated guinea pig's ileum, rat's colon (80 μg/mL bath), and rabbit's duodenum (400 μg/mL bath). Contrarily, complete relaxation of isolated rat's fundic strip was produced by 80 μg/mL bath. Effects of cefepime on isolated rat's uterine muscle were different according to stage of sex cycle. Cefepime did not induce any effects on the resting tonus of isolated guinea pig's tracheal chain and rabbit's aortic strip. Concentrations of 200 and 400 μg/mL bath induced marked inhibition in the force of muscular twitches of the isolated frog's gastrocnemius muscle which was less potent than that induced by procaine hydrochloride 2%. Cefepime completely blocked the neuromuscular transmission of frog's rectus abdominis muscle (40 μg/mL bath) and rat's phrenic nerve hemidiaphragm preparation (200 μg/mL bath). This blockade was reversed by acetylcholine and neostigmine. Cefepime produced dose-dependent negative inotropic effect on isolated rabbit's heart and guinea pig's auricles. There were no changes in blood pressure and rate of respiration in anaesthetized dog after cefepime injection. These findings indicate that cefepime has a low potential to produce adverse reactions at therapeutic doses.

Sunitinib causes dose‐dependent negative functional effects on myocardium and cardiomyocytes

To examine the acute effects of sunitinib on inotropic function, intracellular Ca(2+) transients, myofilament Ca(2+) sensitivity and generation of reactive oxygen species (ROS) in human multicellular myocardium and isolated mouse cardiomyocytes. To search for microRNAs as suitable biomarkers for indicating toxic cardiac effects. After exposure to sunitinib (0.1-10 µg/mL) developed force, diastolic tension and kinetic variables were assessed in isolated human myocardium. Changes in myocyte sarcomere length, whole-cell calcium transients, myofilament force-Ca(2+) relationship, and ROS generation were examined in isolated ventricular mouse cardiomyocytes. Microarray and realtime-PCR were used to screen for differentially expressed microRNAs in cultured cardiomyocytes that were exposed for 24 h to sunitinib. We found that higher concentrations of sunitinib (1 and 10 µg/mL) decreased developed force at 30 minutes 76.9 + 2.8 and 54.5 + 6.3%, compared to 96.1 + 2.6% in controls (P < 0.01). Sunitinib exposure significantly decreased sarcomere shortening and Ca2+ transients. Myofilament Ca(2+) sensitivity was not altered, while ROS levels were significantly increased after exposure to the drug. MicroRNA expression patterns were not altered by sunitinib. Sunitinib elicits a dose-dependent negative inotropic effect in myocardium, accompanied by a decline in intracellular Ca(2+) and increased ROS generation. In clinical practice, these cardiotoxic effects should be considered in cases where cardiac concentrations of sunitinib could be increased.

Cardioprotective Effect of 3-Iodothyronamine in Perfused Rat Heart Subjected to Ischemia and Reperfusion

3-iodothyronamine (T(1)AM) is an endogenous compound which shares structural and functional features with biogenic amines and is able to interact with a specific class of receptors, designed as trace amine associated receptors. T(1)AM has significant physiological effects in mammals and produces a reversible, dose-dependent negative inotropic and chronotropic effect in heart. The aim of the present study was to investigate if T(1)AM is able to reduce irreversible tissue injury in isolated rat hearts subjected to ischemia and reperfusion, as evaluated by triphenyltetrazolium chloride staining. We observed that T(1)AM reduced infarct size at concentrations (125nM to 12.5μM) which did not produce any significant hemodynamic action. The dose-response curve was bell-shaped and peaked at 1.25μM. T(1)AM-induced cardioprotection was completely reversed by the administration of chelerythrine and glibenclamide, suggesting a protein kinase C and K (ATP) (+) -dependent pathway, while it was not additive to the protection induced by cyclosporine A, suggesting modulation of mitochondrial permeability transition. At cardioprotective concentration, T(1)AM reduced the time needed for cardiac attest during ischemia, but it did not affect sarcoplasmatic reticulum Ca(2+) handling, as demonstrated by unaltered ryanodine receptor binding properties. In conclusion, in isolated rat heart T(1)AM produces a cardioprotective effect which is mediated by a protein kinase C and K (ATP) (+) -dependent pathway and is probably linked to modulation of mitochondrial permeability transition and/or ischemic arrest time.

Negative inotropic effect induced by diethylamiloride (DEA) in rabbit myocardium

The effects of the Na+/H+ exchange blocking drug diethylamiloride (DEA) on mechanical function have been studied in the rabbit isolated, arterially perfused interventricular septum. At concentrations of 10(-6)-10(-5) M, DEA induced a significant, dose-dependent, negative inotropic effect (a 54% decrease from control values at the highest concentration), which was slow to develop. After a 45 min washout, recovery was almost complete (95 +/- 3.4%). At concentrations greater than 5 x 10(-5) M, DEA induced a rapid and marked decrease in developed tension, associated with a progressive decrease in excitability and incomplete recovery. Resting tension was not significantly modified at any of the concentrations tested. At greater than 10(-6) M DEA enhanced significantly the transient negative inotropic effect of the brief intracellular acidosis induced by removal of NH4Cl perfusion, both by decreasing the minimal value of developed tension and by increasing the time required to produce this effect. These effects suggest that the dose-dependent DEA negative inotropic effect could be mediated by a progressive intracellular acidosis produced by inhibition of the Na+/H+ exchange system.

Physiological evidence for β3-adrenoceptor in frog ( Rana esculenta) heart

β3-Adrenergic receptors (ARs) have been recently identified in mammalian hearts where, unlike β1- and β2-ARs, induce cardio-suppressive effects. The aim of this study was to describe β3-AR role in the frog ( Rana esculenta) heart and to examine its signal transduction pathway. The presence of β3-AR, by using Western blotting analysis, has been also identified. BRL 37344 , a selective β3-AR agonist, induced a dose-dependent negative inotropic effect at concentrations from 10 −12 to 10 −6 M. This effect was not modified by nadolol (β1/β2-AR antagonist) and by phentolamine (α-AR antagonist), but it was suppressed by the β3-AR-specific antagonist SR 59230 and by exposure to the Gi/o proteins inhibitor Pertussis Toxin. In addition, the involvement of EE-NOS-cGMP-PKG/PDE2 pathway in the negative inotropism of BRL 37344 has been assessed. BRL 37344 treatment induced eNOS and Akt phosphorylation as well as an increase of cGMP levels. β3-ARs activation induce a non-competitive antagonism against ISO stimulation which disappeared in presence of PKG and PDE2 inhibition. Taken together our findings provide, for the first time in the frog, a role for β3-ARs in the cardiac performance modulation which involves Gi/o protein and occurs via an EE-NO-cGMP-PKG/PDE2 cascade.

Cardiac effects of trace amines: Pharmacological characterization of trace amine-associated receptors

Trace amine-associated receptors, a novel class of G-protein coupled receptors which respond to trace amines but not to classical biogenic amines, have been found to be expressed in heart. Therefore, we investigated the cardiac effects of the trace amines p-tyramine, β-phenylethylamine, octopamine, and tryptamine. Isolated rat hearts were perfused in the presence of trace amines, monitoring the hemodynamic variables. In addition, radioligand binding experiments with [ 3H]- p-tyramine and [ 125I]-3-iodothyronamine were performed in rat ventricular tissue. Octopamine, β-phenylethylamine, and tryptamine produced a dose-dependent negative inotropic effect as shown by reduced cardiac output (IC 50 = 109 μM, 159 μM, and 242 μM, respectively). In the same preparation a similar effect was produced by thyronamine and 3-iodothyronamine, with IC 50 = 94 μM and 27 μM, respectively. The negative inotropic effect of octopamine was confirmed in a papillary muscle preparation. All trace amines except tryptamine increased the heart rate, but this action could be attributed to their sympathomimetic properties, since it was abolished by propranolol. The negative inotropic effect of trace amines was significantly increased by the tyrosine kinase inhibitor genistein. Specific and saturable binding of [ 3H]- p-tyramine and [ 125I]-3-iodothyronamine was observed in ventricular tissue. While [ 3H]- p-tyramine was displaced by 3-iodothyronamine, [ 125I]-3-iodothyronamine was not displaced by p-tyramine. In conclusion, trace amines and thyronamines are negative inotropic agents. Their effect appears to be mediated by a subtype of trace amine-associated receptor which is characterized by the rank of potency: 3-iodothyronamine > thyronamine = octopamine = β-phenylethylamine, while tryptamine and p-tyramine are significantly less active.

Combined use of ultra-short acting β-blocker esmolol and intravenous phosphodiesterase 3 inhibitor enoximone

In patients with impaired myocardial contractility associated with downregulation of the β-receptors, compounds inhibiting phosphodiesterase (PDE) 3 may be useful to increase contractility. The PDE3 inhibitor enoximone has been shown to improve pump-function independent from the β-receptor pathway. A simultaneous decrease in ventricular preload and afterload by vasodilation has led to the term ‘inodilator’. Esmolol is the only available ultra-short acting intravenous β-blocking agent. Due to its half-life of ∼ 9 min, β-blockade, and thus, heart rate, can easily be titrated. Esmolol appears to be a helpful tool to avoid myocardial ischemia (e.g., in the perioperative setting). As with all other β-blockers, it has dose-dependent negative inotropic effects, and this limits its use in patients with severe heart failure showing low cardiac output. It seems reasonable that an intravenous combination of both approaches, enoximone-induced positive inotropy and esmolol-associated protection from myocardial ischemia, might offer advantages by producing beneficial hemodynamic effects and by compensating each other's limitations in a complementary way. In spite of some promising results, the place of a combination of enoximone and esmolol in the process of treating patients with (acute) heart failure showing low output is still not entirely clear, and needs further confirmation.

EXISTENCE OF β3‐ADRENOCEPTORS IN RAT HEART: FUNCTIONAL IMPLICATIONS

1. beta(3)-Adrenoceptors (AR) have been reported to be present in numerous species, where they mediate multiple responses. 2. The aim of the present study was to determine whether beta(3)-AR are present in intact rat heart and the functional implications of beta(3)-AR stimulation. The response to the cardiac beta(3)-AR-selective agonist BRL37344 was expressed as the percentage of values measured at baseline. 3. BRL37344 induced dose-dependent negative inotropic effects at concentrations ranging from 10(-11) to 10(-7) mol/L. BRL37344 (10(-8) mol/L) induced a decrease of left ventricular developed pressure (LVDP) from 127 +/- 5 to 89 +/- 16 mmHg (69 +/- 15%; P < 0.01) and +dP/dt from 2594 +/- 59 to 1885 +/- 50 mmHg/s (72 +/- 8%; P < 0.01). Moreover, a significant reduction of -dP/dt from 2176 +/- 42 to 1458 +/- 43 mmHg/s (67 +/- 8%; P < 0.01) was observed. The BRL37344 dose-response curves were not altered by nadolol (10(-5) mol/L), a potent beta(1)- and beta(2)-AR antagonist, but were completely suppressed by the addition of SR59230A (10(-5) mol/L), a potent beta(3)-AR antagonist. 4. The present study provides functional evidence for the presence of beta(3)-AR in rat hearts and shows, for the first time, that a highly specific beta(3)-AR antagonist can block the attenuation of LVDP caused by the specific beta(3)-AR agonist BRL37344 in rat beating hearts.

Cardiac effects of 3‐iodothyronamine: a new aminergic system modulating cardiac function

3-Iodothyronamine T1AM is a novel endogenous thyroid hormone derivative that activates the G protein-coupled receptor known as trace anime-associated receptor 1 (TAAR1). In the isolated working rat heart and in rat cardiomyocytes, T1AM produced a reversible, dose-dependent negative inotropic effect (e.g., 27+/-5, 51+/-3, and 65+/-2% decrease in cardiac output at 19, 25, and 38 microM concentration, respectively). An independent negative chronotropic effect was also observed. The hemodynamic effects of T1AM were remarkably increased in the presence of the tyrosine kinase inhibitor genistein, whereas they were attenuated in the presence of the tyrosine phosphatase inhibitor vanadate. No effect was produced by inhibitors of protein kinase A, protein kinase C, calcium-calmodulin kinase II, phosphatidylinositol-3-kinase, or MAP kinases. Tissue cAMP levels were unchanged. In rat ventricular tissue, Western blot experiments with antiphosphotyrosine antibodies showed reduced phosphorylation of microsomal and cytosolic proteins after perfusion with synthetic T1AM; reverse transcriptase-polymerase chain reaction experiments revealed the presence of transcripts for at least 5 TAAR subtypes; specific and saturable binding of [125I]T1AM was observed, with a dissociation constant in the low micromolar range (5 microM); and endogenous T1AM was detectable by tandem mass spectrometry. In conclusion, our findings provide evidence for the existence of a novel aminergic system modulating cardiac function.

Studies on cardio-suppressant, vasodilator and tracheal relaxant effects ofSarcococca saligna

Sarcococca saligna is a shrub that is traditionally used for its medicinal properties in Pakistan. In this study we report the cardio-suppressant, vasodilator and tracheal relaxant activities of the aqueous-methanolic extract (Ss.Cr) of the plant. Ss.Cr, that tested positive for the presence of saponins, flavonoids, tannins, phenols, and alkaloids, exhibited a dose-dependent (0.3-5 mg/mL) negative inotropic and chronotropic effect on the isolated guinea-pig atrium which was resistant to atropine (1 microM) and aminophylline (10 microM) pretreatment. In rabbit thoracic aorta, Ss.Cr dose-dependently (0.1-3 mg/mL) relaxed the high K+ (80 mM) and phenylephrine (PE, 1 microM)-induced contractions, indicating a possible Ca++ channel blocking (CCB) effect. When tested against PE (1 microM) control peaks in normal Ca++ and Ca++-free Kreb's solution, Ss.Cr exhibited dose-dependent (0.1-3 mg/mL) inhibition, being more potent in relaxing the PE responses in Ca++-free Kreb's solution, thus indicating specific blockade of Ca++ release from the intracellular stores. Ss.Cr also relaxed the agonist-induced contractions in: a) rat aorta irrespective of the presence of endothelium or nitric oxide synthase inhibitor L-NAME and b) rabbit and guinea-pig tracheal strips. The data shows that Ss.Cr possesses possible Ca++ channel blocking activity which might be responsible for its observed cardio-suppressant, vasodilator and tracheal relaxant effects though more tests are required to confirm this Ca++ channel blocking effect.