Direct Negative Inotropic Effect Research Articles

SPICE GOT US IN A PICKLE: A CASE OF SYNTHETIC MARIJUANA-INDUCED CARDIOMYOPATHY AND RHABDOMYOLYSIS

SESSION TITLE: Wednesday Medical Student/Resident Case Report Posters SESSION TYPE: Med Student/Res Case Rep Postr PRESENTED ON: 10/23/2019 09:45 AM - 10:45 AM INTRODUCTION: Spice is a commonly used name for synthetic cannabinoids (SCs) which are chemical analogs of naturally occurring cannabinoids. They are increasingly used for their hallucinogenic effects, low cost and ease of availability. They are not detected in routine urine assays and their detection requires specialized urine drug screens making them an attractive option for young adults. There are case reports of cardiomyopathies associated with their overdose. We discuss the case of a young male who presents with rhabdomyolysis and cardiomyopathy after an intentional overdose of Spice. CASE PRESENTATION: A 21-year-old male with a past medical history of major depressive disorder and substance abuse (heroin, marijuana, spice) was brought in by emergency medical services after being found unresponsive. His vital signs were BP 78/46 mmHg, HR 97 beats per minute, RR 20 times a minute, temperature 100F, saturating 93% on room air. On physical exam, his pupils were pinpoint and he had a Glasgow Coma Scale of 8 (eye 2, verbal 2, motor 4) with decerebrate posturing. Labs showed pH of 6.94, bicarbonate of 12, Urine Drug Screen was positive for opiates and cannabinoids, lactate of 16.4, Creatinine of 2.3, a creatinine kinase of >22,000 and a troponin of 3.35. An EKG on admission showed sinus rhythm with short PR interval and J point elevation most noticeable in lead 1. Bedside ultrasound showed bi-ventricular failure with severe global hypokinesis. He was intubated and started on Dobutamine and Norepinephrine drips. On day 3, pressors were weaned off, he was extubated and Echo showed improved Left Ventricular function off pressors. His acute kidney injury resolved with hemodynamic support and Creatinine of 0.8 on discharge. He admitted to sniffing Heroin and smoking Spice prior to admission and he was discharged home. It was suspected he had spice induced cardiomyopathy and AKI. The patient had no history of coronary artery disease or alcohol use, no evidence of valvular abnormality and no signs of sepsis and the cardiomyopathy was attributed to Spice. He did not have prolonged hypotension, nephrotoxic medication use and his kidney injury was attributed to rhabdomyolysis. DISCUSSION: There are case reports of ST-elevation myocardial infarctions triggered by SC use; most of these have been young patients with normal-appearing coronary arteries on angiography. SCs bind to CBR1 receptors with a higher affinity than natural cannabinoids leading to direct negative inotropic effect on cardiomyocytes. While most case reports of SC-induced nephropathy involve acute tubular necrosis, our patient presented with rhabdomyolysis-induced nephropathy. CONCLUSIONS: SCs are far more dangerous than their natural counterparts and as they require special assays for detection, health care providers should be cognizant of their use and effects. Reference #1: Ting JYS. Reversible cardiomyopathy associated with acute inhaled marijuana use in a young adult. Clin Toxicol (Phila) 2007;45:432–4. https://doi.org/10.1080/15563650601073587. Reference #2: Bhanushali GK, Jain G, Fatima H, Leisch LJ. Thornley-Brown D. AKI associated with synthetic cannabinoids: A case series. Clin J Am Soc Nephrol. 2013;8:5236. https://doi.org/10.2215/CJN.05690612 DISCLOSURES: No relevant relationships by Iman Khan, source=Web Response

Adrenergic and adenosinergic regulation of the cardiovascular system in an Antarctic icefish: Insight into central and peripheral determinants of cardiac output

Icefishes characteristically lack the oxygen-binding protein haemoglobin and therefore are especially reliant on cardiovascular regulation to augment oxygen transport when oxygen demand increases, such as during activity and warming. Using both in vivo and in vitro experiments, we evaluated the roles for adrenaline and adenosine, two well-established cardio- and vasoactive molecules, in regulating the cardiovascular system of the blackfin icefish, Chaenocephalus aceratus. Despite increasing cardiac contractility (increasing twitch force and contraction kinetics in isometric myocardial strip preparations) and accelerating heart rate (ƒH), adrenaline (5 nmol kg−1 bolus intra-arterial injection) did not significantly increase cardiac output (Q̇) in vivo because it elicited a large decrease in vascular conductance (Gsys). In contrast, and despite preliminary data suggesting a direct negative inotropic effect of adenosine on isolated atria and little effect on isolated ventricle strips, adenosine (500 nmol kg−1) generated a large increase in Q̇ by increasing Gsys, a change reminiscent of that previously reported during both acute warming and invoked activity. Our data thus illustrate how Q̇ in C. aceratus may be much more dependent on peripheral control of vasomotor tone than direct regulation of the heart.

Beta-blockers in Septic Shock

The therapy of patients suffering from sepsis and septic shock is one of the greatest challenges in critical care medicine. In the initial phase of septic shock patients often present with hyperdynamic circulatory conditions with elevated cardiac index, tachycardia and progressive hemodynamic instability. The type of tachycardia differs from atrial fibrillation or flatter to sinus tachycardia. The latter might be persistent even in case of adequate volume therapy according to the surviving sepsis campaign recommendations and may represent an independent pathology due to adrenergic overstimulation. Despite predominantly β2-mediated immunomodulatory effects the administration of a selective β1-adrenergic blocker may be beneficial in some cases. On the other hand, incautious administration of beta-blockers especially in case of insufficient volume replacement may result in direct negative inotropic effects rapidly aggravating hypotension and shock. This review focused on pharmacology of the β-adrenergic system, the pathophysiological rationale and current literature on clinical practice of the use of beta-blockers in sepsis and septic shock.

FSCPX, a Chemical Widely Used as an Irreversible A₁ Adenosine Receptor Antagonist, Modifies the Effect of NBTI, a Nucleoside Transport Inhibitor, by Reducing the Interstitial Adenosine Level in the Guinea Pig Atrium.

Based on in silico results, recently we have assumed that FSCPX, an irreversible A1 adenosine receptor antagonist, inhibits the action of NBTI that is apparent on E/c curves of adenosine receptor agonists. As a mechanism for this unexpected effect, we hypothesized that FSCPX might modify the equilibrative and NBTI-sensitive nucleoside transporter (ENT1) in a way that allows ENT1 to transport adenosine but impedes NBTI to inhibit this transport. This assumption implies that our method developed to estimate receptor reserve for agonists with short half-life such as adenosine, in its original form, overestimates the receptor reserve. In this study, therefore, our goals were to experimentally test our assumption on this effect of FSCPX, to improve our receptor reserve-estimating method and then to compare the original and improved forms of this method. Thus, we improved our method and assessed the receptor reserve for the direct negative inotropic effect of adenosine with both forms of this method in guinea pig atria. We have found that FSCPX inhibits the effects of NBTI that are mediated by increasing the interstitial concentration of adenosine of endogenous (but not exogenous) origin. As a mechanism for this action of FSCPX, inhibition of enzymes participating in the interstitial adenosine production can be hypothesized, while modification of ENT1 can be excluded. Furthermore, we have shown that, in comparison with the improved form, the original version of our method overestimates receptor reserve but only to a small extent. Nevertheless, use of the improved form is recommended in the future.

MD-2 is a new predictive biomarker in dilated cardiomyopathy and exerts direct effects in isolated cardiomyocytes

BackgroundMyeloid differentiation factor-2 (MD-2) has been shown to be an important modulator of the innate immune system, but its role in cardiac diseases is unknown. We investigated whether MD-2 plays a role as risk predictor and contributor in dilated cardiomyopathy (DCM). Methods and resultsWe included 174 patients with reduced left ventricular (LV) ejection fraction (LVEF <45%) due to DCM. Coronary artery disease and severe valvular diseases were excluded in all patients by angiography or echocardiography. Cardiac inflammation, viral infection and MD-2 expression were analyzed from right ventricular endomyocardial biopsies. MD-2 was quantified by ELISA in serum upon first hospital admission. Myocyte contractility and inflammatory response after stimulation with recombinant MD-2 protein were analyzed in isolated rat cardiomyocytes.Median follow-up of the patients was 3.51 years (2.73; 4.48) with 34 deaths. Absolute mortality risk increases in patients displaying a MD-2 serum concentration greater than the median (302 ng/ml) was 23% (P < 0.0001). Age- and sex-adjusted Cox regression analyses demonstrated that mortality risk was highly related to MD-2 concentrations (P < 0.001), but not to age or sex. An increase of 100 ng/ml in the MD-2 level was associated with an absolute mortality risk increase of 50.4%. Receiver operating characteristic (ROC) analyses showed no difference between MD-2 and nterminal-pro brain natriuretic peptide (NT-pro-BNP), while the combination of both MD-2 and NT-pro-BNP resulted in a significantly increased capability of risk prediction when compared to NT-pro-BNP alone (P = 0.014). In-vitro, recombinant MD-2 decreases cell shortening and modulates cytokine activation in isolated cardiomyocytes. ConclusionMD-2 predicts long-term outcome in DCM patients and improves mortality risk prediction capability compared to NT-pro-BNP alone. In addition, MD-2 exerts direct negative inotropic effects on isolated cardiomyocytes in-vitro. Further randomized trials should confirm MD-2 as a diagnostic and therapeutic target.

REVERSAL OF PERIPHERAL AND CNS MEDIATED A1 ADENOSINE RECEPTOR HYPOTENSION

IntroductionA1 adenosine receptor (A1AR) agonists such as N6‐cyclohexyladenosine (CHA) are known for their neuroprotective and anti‐convulsant properties and for modulation of thermogenesis. We have demonstrated a neuroprotective, thermolytic effect following systemic administration of CHA combined with the peripherally acting adenosine receptor antagonist, 8‐(p‐sulfophenyl)theophylline (8‐SPT). However, A1AR‐mediated cardiovascular side effects limit the translation of this drug class, and clear understanding of the effects of this drug combination on hypotension and bradycardia are lacking. CHA delivered into the CNS increases para‐sympathetic influence on the heart to produce bradycardia similar to what is seen during onset of hibernation. Systemic administration of A1AR agonist produces bradycardia via direct negative chronotropic and inotropic effects. Evidence also supports other mechanisms of A1AR agonist modulation of blood pressure including indirect activation of peripheral β2 adrenergic receptors and central H1 receptors.HypothesisWe test the hypothesis that CHA lowers blood pressure via increased para‐sympathetic tone to the heart and direct effects on the heart.MethodsRats were implanted with telemetry transmitters to monitor Tb, heart rate (HR), mean arterial pressure (MAP) and administered drugs IP as follows, CHA (1.0mg/kg), 8‐SPT (25.0mg/kg), Atropine (1.0mg/kg), diphenhydramine (4.0mg/kg), or pro‐pranolol (4.0mg/kg), 15min prior to CHA. Cage surface temperature was initially cooled to 4°C and adjusted to maintain Tb at 32°C.Results8‐SPT with atropine reversed hypotension. 8‐SPT alone increased rate of resolution in MAP to baseline value. Pre‐treatment with propranolol, atropine, or diphenhydramine alone did not influence MAP. Diphenhydramine with 8‐SPT reduced the magnitude of hypotension (− 24% average one hour baseline change after CHA) compared to pre‐treatment with 8‐SPT (− 36%) alone.ConclusionsOur results suggest that A1AR induced hypotension is mediated through increased parasympathetic tone to the heart in addition to direct effect on the heart. Histamine receptor activation may also play a role, although the resolution of MAP seen may have been due to the anticholinergic effect of diphenhydramine instead of H1 receptor antagonism. Reversing hypotension necessitates addressing both mechanism with atropine and 8‐SPTSupport or Funding InformationNIH U54GM115371, NIH R15 NS070779, NIH: RL5GM118900, TL4 GM 18992, 1UL1GN118991This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

English

Numerous studies suggested that propofol anesthesia is intuitively appealing for its simplicity, stability and safety, permitting the rapid recovery of patients undergoing cardiac surger. However, its use for induction of anesthesia is often results in transient hypotension. The aim of this study was to determine the safety of modified propofol protocol for induction in low ejection fraction cardiac patients undergoing CABG surgery. Fifty patients with ejection fraction between 30% - 60% who were planned for coronary artery bypass graft surgery were included in this study. Patients were divided into two groups of 25 patients each, according to their left ventricular ejection fractions (EF). Group N (EF between 60%-45%) and Group L (EF between 30%-45%). All the patients were given midazolam/fentanyl/vecuronium and propofol for induction according to pre-defined protocol to prevent hypotension and facilitate early intubation. Hemodynamic variables were registered at fixed points. To prevent hemodynamic compromised situation rescue noradrenaline in 5µg/ml aliquots was kept ready. Amount of propofol used, time taken for successful intubation and grading of jaw relaxation was also done. RESULTS: Four patients in Group L and one patients in Group N encountered significant hypotension (>20% of preoperative value). Amount of vasoconstriction agents used were high in group L. Cardiac index was changed 17.4% from preoperative value and returned to baseline values within 6 min in group L while in group N cardiac index was changed 12.9% from preoperative value and also returned to baseline values within 6 min. Propofol 0.5-1 mg/kg was used to induce hypnosis and all patients were intubated in less than ninety seconds. CONCLUSION: Propofol as induction agent is safe in both low and normal ejection fraction cardiac patients when used judiciously and in titrated doses. Immediate changes in hemodynamic changes can be corrected with mild doses of vasoconstriction agents. BACKGROUND: Total intravenous anesthesia with propofol and low- dose opioids for CABG surgery is now commonly used and is one of the methods that allows early extubation. Fixed dose propofol induction may cause hypotension for about 5−10 min, which is mainly due to the decrease in sympathetic activity and direct vascular smooth muscle relaxation without any direct negative inotropic effect. 1 Even minor haemodynamic changes during induction may lead to severe circulatory problem in patients posted for CABG surgery. This effect is more profound in patients with low left ventricular ejection fraction. Therefore propofol is not routinely used as sole induction agent in that situation. Modified induction technique judicious doses of propofol along with rescue vasopressor agent was described in literature for non-coronary artery cardiac surgery. 2 Preoperative optimization of intravascular fluid status, tredenlenburg position

Cardiac and hepatic role of r-AtHSP70: basal effects and protection against ischemic and sepsis conditions.

Heat shock proteins (HSPs), highly conserved in all organisms, act as molecular chaperones activated by several stresses. The HSP70 class of stress-induced proteins is the most studied subtype in cardiovascular and inflammatory disease. Because of the high similarity between plant and mammalian HSP70, the aim of this work was to evaluate whether recombinant HSP70 of plant origin (r-AtHSP70) was able to protect rat cardiac and hepatic function under ischemic and sepsis conditions. We demonstrated for the first time that, in ex vivo isolated and perfused rat heart, exogenous r-AtHSP70 exerted direct negative inotropic and lusitropic effects via Akt/endothelial nitric oxide synthase pathway, induced post-conditioning cardioprotection via Reperfusion Injury Salvage Kinase and Survivor Activating Factor Enhancement pathways, and did not cause hepatic damage. In vivo administration of r-AtHSP70 protected both heart and liver against lipopolysaccharide-dependent sepsis, as revealed by the reduced plasma levels of interleukin-1β, tumour necrosis factor alpha, aspartate aminotransferase and alanine aminotransferase. These results suggest exogenous r-AtHSP70 as a molecular modulator able to protect myocardial function and to prevent cardiac and liver dysfunctions during inflammatory conditions.

The effect of adenosine deaminase inhibition on the A1 adenosinergic and M2 muscarinergic control of contractility in eu- and hyperthyroid guinea pig atria.

The A1 adenosine and M2 muscarinic receptors exert protective (including energy consumption limiting) effects in the heart. We investigated the influence of adenosine deaminase (ADA) inhibition on a representative energy consumption limiting function, the direct negative inotropic effect elicited by the A1 adenosinergic and M2 muscarinergic systems, in eu- and hyperthyroid atria. Furthermore, we compared the change in the interstitial adenosine level caused by ADA inhibition and nucleoside transport blockade, two well-established processes to stimulate the cell surface A1 adenosine receptors, in both thyroid states. A classical isolated organ technique was applied supplemented with the receptorial responsiveness method (RRM), a concentration estimating procedure. Via measuring the contractile force, the direct negative inotropic capacity of N6-cyclopentyladenosine, a selective A1 receptor agonist, and methacholine, a muscarinic receptor agonist, was determined on the left atria isolated from 8-day solvent- and thyroxine-treated guinea pigs in the presence and absence of 2′-deoxycoformycin, a selective ADA inhibitor, and NBTI, a selective nucleoside transporter inhibitor. We found that ADA inhibition (but not nucleoside transport blockade) increased the signal amplification of the A1 adenosinergic (but not M2 muscarinergic) system. This action of ADA inhibition developed in both thyroid states, but it was greater in hyperthyroidism. Nevertheless, ADA inhibition produced a smaller rise in the interstitial adenosine concentration than nucleoside transport blockade did in both thyroid states. Our results indicate that ADA inhibition, besides increasing the interstitial adenosine level, intensifies the atrial A1 adenosinergic function in another (thyroid hormone-sensitive) way, suggesting a new mechanism of action of ADA inhibition.

Negative inotropic and hypotensive effects of the superoxide dismutase mimetic tempol in pigs

Through interference with free radicals, the nitroxide tempol potentially increases bioavailability of nitric oxide (NO) and along with modulation of potassium channels reduces blood pressure (BP). We studied whether tempol in pigs lowers BP by mechanisms sensitive to inhibition of NO synthase or large conductance calcium-activated potassium channels (BKCa). The cardiovascular effects of intravenous tempol (25–50mg/kg) were examined in anesthetized pigs with myocardial function being evaluated by echocardiography. While saline-treated animals remained hemodynamically stable, tempol induced fast, dose-dependent and transient reductions in BP lasting 5–10min with a simultaneous impairment of left ventricular contraction. Pretreatment with the NO synthase (NOS) inhibitor NG-nitro-l-arginine methyl ester (l-NAME, 4mg/kg) or a blocker of BKCa (tetraethylammonium (TEA), 100mg/h) increased baseline BP but also enhanced BP reductions to tempol. Isolated myocardial trabeculae subjected to an identical protocol also demonstrated dose-related reductions in contractility to tempol. This effect was not affected by l-NAME, but attenuated by TEA. In isolated mesenteric resistance arteries contracted with noradrenaline, tempol caused small postjunctional l-NAME sensitive relaxations, while neurogenic contractions were inhibited by tempol by TEA-sensitive mechanisms and mechanisms insensitive to TEA and l-NAME. In conclusion intravenous tempol induces fast transient reductions in BP associated with simultaneous reductions in myocardial contraction. Tempol exerts direct negative inotropic effects which are partly sensitive to BKCa-blockade but independent of NOS inhibition. In addition tempol has direct vasodilatory effects despite NOS and potassium channel blockade. The negative inotropic and hypotensive effects raise concerns using tempol, or structurally similar drugs, for intravenous use.

Approximation of A1 adenosine receptor reserve appertaining to the direct negative inotropic effect of adenosine in hyperthyroid guinea pig left atria

Hyperthyroidism elevates cardiovascular mortality by several mechanisms, including increased risk of ischemic heart disease. Therefore, therapeutic strategies, which enhance tolerance of heart to ischemia-reperfusion injury, may be particularly useful for hyperthyroid patients. One promising cardioprotective approach is use of agents that cause (directly or indirectly) A1 adenosine receptor (A1 receptor) activation, since A1 adenosinergic pathways initiate protective mechanisms such as ischemic preconditioning. However, previously we found great A1 receptor reserve for the direct negative inotropic effect of adenosine in isolated guinea pig atria. This phenomenon suggests that weakening of atria is a possible side effect of A1 adenosinergic stimulant agents. Thus, the goal of the present investigation was to explore this receptor reserve in hyperthyroidism. Our recently developed method was used that prevents the rapid intracellular elimination of adenosine, allowing sufficient time for exogenous adenosine administered for the generation of concentration-response curves to exert its effect. Our method also allowed correction for the bias caused by the consequent endogenous adenosine accumulation. Our results demonstrate that thyroxine treatment does not substantially affect the A1 receptor reserve for the direct negative inotropic effect of adenosine. Consequently, if an agent causing A1 receptor activation is administered for any indication, the most probable adverse effect affecting the heart may be a decrease of atrial contractility in both eu- and hyperthyroid conditions.

The guinea pig atrial A1 adenosine receptor reserve for the direct negative inotropic effect of adenosine

Although the A1 adenosine receptor (A1 receptor), the main adenosine receptor type in cardiac muscle, is involved in powerful cardioprotective processes such as ischemic preconditioning, the atrial A1 receptor reserve has not yet been quantified for the direct negative inotropic effect of adenosine. In the present study, adenosine concentration-effect (E/c) curves were constructed before and after pretreatment with FSCPX (8-cyclopentyl-N3-[3-(4-(fluorosulfonyl)benzoyloxy)propyl]-N1-propylxanthine), an irreversible A1 receptor antagonist, in isolated guinea pig atria. To prevent the intracellular elimination of the administered adenosine, NBTI (S-(2-hydroxy-5-nitrobenzyl)-6-thioinosine), a nucleoside transport inhibitor, was used. As expected, NBTI alone and FSCPX-pretreatment alone shifted the adenosine E/c curve to the left and right, respectively. However, in the presence of NBTI, FSCPX-pretreatment appeared to increase the maximal response to adenosine. By means of the receptorial responsiveness method (RRM), our recently developed procedure, adenosine E/c curves generated in the presence of NBTI were corrected for the bias caused by the endogenous adenosine accumulated by NBTI. The corrected curves indicate a substantial A1 receptor reserve for the direct negative inotropy evoked by adenosine. In addition, our results suggest that accumulation of an endogenous agonist may bias the E/c curve constructed with the same or similar agonist that can lead to seemingly paradoxical results.

Comparison of the Intrinsic Vasorelaxant and Inotropic Effects of the Antiarrhythmic Agents Vernakalant and Flecainide in Human Isolated Vascular and Cardiac Tissues

This study explored the intrinsic vasorelaxant and inotropic effects of the mixed potassium and sodium channel blocker atrial antiarrhythmic vernakalant and the class IC antiarrhythmic agent flecainide in human isolated subcutaneous resistance artery and in ventricular trabecular muscle preparations. At test concentrations encompassing free plasma concentrations associated with clinical efficacy for conversion of atrial fibrillation, vernakalant (1-10 μM) displayed no significant direct effects on human resistance artery tone or ventricular contractility. In contrast, tested at equimolar concentrations, flecainide significantly reduced peak isometric contractile force (10 μM) and maximal rates of force development and decline (3 and 10 μM) in the human ventricular muscle preparation while displaying no significant effect on human resistance artery tone. The lack of effects of vernakalant on human resistance artery tone and ventricular muscle contractile function suggests that direct vasorelaxant and inotropic effects do not underlie the rare hypotensive events observed clinically with vernakalant, raising the possibility that secondary (eg, reflex) effects may mediate these events. The demonstration of negative inotropic effects with flecainide in the human ventricular muscle preparations in the absence of an effect on resistance artery tone suggests that the hemodynamic effects of flecainide observed clinically result primarily from direct negative inotropic effects.

The surmountable effect of FSCPX, an irreversible A1 adenosine receptor antagonist, on the negative inotropic action of A1 adenosine receptor full agonists in isolated guinea pig left atria

A1 adenosine receptors (A1 receptors) are widely expressed in mammalian tissues; therefore attaining proper tissue selectivity is a cornerstone of drug development. The fact that partial agonists chiefly act on tissues with great receptor reserve can be exploited to achieve an appropriate degree of tissue selectivity. To the best of our knowledge, the A1 receptor reserve has not been yet quantified for the atrial contractility. A1 receptor reserve was determined for the direct negative inotropic effect of three A1 receptor full agonists (NECA, CPA and CHA) in isolated, paced guinea pig left atria, with the use of FSCPX, an irreversible A1 receptor antagonist. FSCPX caused an apparently pure dextral displacement of the concentration-response curves of A1 receptor agonists. Accordingly, the atrial A1 receptor function converging to inotropy showed a considerably great, approximately 80-92 % of receptor reserve for a near maximal (about 91-96 %) effect, which is greater than historical atrial A1 receptor reserve data for any effects other than inotropy. Consequently, the guinea pig atrial contractility is very sensitive to A1 receptor stimulation. Thus, it is worthwhile considering that even partial A1 receptor agonists, given in any indication, might decrease the atrial contractile force, as an undesirable side effect, in humans.

Itraconazole decreases left ventricular contractility in isolated rabbit heart: Mechanism of action

Itraconazole (ITZ) is an approved antifungal agent that carries a “black box warning” in its label regarding a risk of negative cardiac inotropy based on clinical findings. Since the mechanism of the negative inotropic effect is unknown, we performed a variety of preclinical and mechanistic studies to explore the pharmacological profile of ITZ and understand the negative inotropic mechanism. ITZ was evaluated in: (1) an isolated rabbit heart (IRH) preparation using Langendorff retrograde perfusion; (2) ion channel studies; (3) a rat heart mitochondrial function profiling screen; (4) a mitochondrial membrane potential (MMP) assay; (5) in vitro pharmacology profiling assays (148 receptors, ion channels, transporters, and enzymes); and (6) a kinase selectivity panel (451 kinases). In the IRH, ITZ decreased cardiac contractility (>30%) at 0.3μM, with increasing effect at higher concentrations, which indicated a direct negative inotropic effect upon the heart. It also decreased heart rate and coronary flow (≥1μM) and prolonged PR/QRS intervals (3μM). In mechanistic studies, ITZ inhibited the cardiac NaV channel (IC50: 4.2μM) and was devoid of any functional inhibitory effect at the remaining pharmacological targets. Lastly, ITZ did not affect MMP, nor interfere with mitochondrial enzymes or processes involved with fuel substrate utilization or energy formation. Overall, the cardiovascular and mechanistic data suggest that ITZ-induced negative inotropy is a direct effect on the heart, in addition, the potential involvement of mitochondria function and L-type Ca2+ channels are eliminated. The exact mechanism underlying the negative inotropy is uncertain, and requires further study.

Effects of propofol on left ventricular mechanoenergetics in the excised cross-circulated canine heart.

Although propofol is commonly used for general anesthesia, its direct effects on left ventricular (LV) contractility and energetics remain unknown. Accordingly, we studied the effects of intracoronary propofol on excised cross-circulated canine hearts using the framework of the Emax (a contractility index)-PVA (systolic pressure-volume area, a measure of total mechanical energy)-V(O2) (myocardial oxygen consumption per beat) relationship. We obtained 1) the V(O2)-PVA relationship of isovolumic contractions with varied LV volumes at a constant Emax, 2) the V(O2)-PVA relationship with varied LV volumes at a constant intracoronary concentration of propofol, and 3) the V(O2)-PVA relationship under increased intracoronary concentrations of either propofol or CaCl(2) at a constant LV volume to assess the cardiac mechanoenergetic effects of propofol. We found that propofol decreased Emax dose-dependently. The slope of the linear V(O2)-PVA relationship (oxygen cost of PVA) remained unchanged by propofol. The PVA-independent V(O2)-Emax relationship (oxygen cost of Emax) was the same for propofol and Ca(2+). In conclusion, propofol showed a direct negative inotropic effect on LV. At its clinical concentrations, decreases in contractility by propofol were relatively small. Propofol shows mechanoenergetic effects on the LV that are similar to those of Ca(2+) blockers or ß-antagonists-i.e., it exerts negative inotropic effects without changing the oxygen costs of Emax and PVA.

Negative Inotropic Effect of a CB2 Agonist A-955840 in Isolated Rabbit Ventricular Myocytes is Independent of CB1 and CB2 Receptors

A-955840, a selective CB2 agonist, has been shown to elicit concentration-dependent decreases in cardiac contractility in the anesthetized dog (decreased maximal velocity of left ventricular pressure development [LV dP/dt max]). However, it is unknown whether this represents a direct effect or a response dependent on other factors (such as autonomic tone and neurohumoral factors) present in vivo. This study examined if A-955840 had a direct effect on contractility of isolated cardiac myocytes, and if so to determine the potential mechanisms. Contractility was assessed in vitro using percent changes in maximal shortening velocity of sarcomeres (dL/dt max) and fractional shortening of sarcomere length (FS) in rabbit left ventricular myocytes. L-type calcium current in myocytes was recorded using wholecell voltage-clamp techniques. A-955840 reduced dL/dt max and FS in a reversible and concentration-dependent manner with an IC50 of 11.4 μg/mL (based on dL/dt max) which is similar to the estimated IC50 value of 9.8 μg/mL based on the effects of A-955840 on LV dP/dt max in anesthetized dogs. A-955840 (4.1 μg/mL) reduced myocyte contractility (%FS) to a similar extent in the absence and presence of a CB2 antagonist, SR-2 (24.0 ± 3.4 vs 23.1 ± 3.0 %, n=5) or a CB1 antagonist, Rimonabant (18.8 ± 2.3 vs 19.8 ± 2.7 %, n=5). A-955840 (4.1 μg/mL) also reduced L-type calcium current of rabbit ventricular myocytes (1.05 ± 0.11 vs 0.70 ± 0.12 nA, n=5, P < 0.01). These results suggest that A-955840 exerts direct negative inotropic effects on isolated rabbit ventricular myocytes, which is mediated by neither CB2 nor CB1 receptors, and consistent with off-target negative inotropy mediated by inhibition of the cardiac L-type calcium current.

Metronidazole-induced myocardial depression: chemical and pharmacological studies on the role of calcium in-vitro.

The interaction of metronidazole with calcium to form a water-soluble complex has been studied by titration with ethylenediaminetetraacetate (EDTA), direct current and pulse polarographic reduction steps of the nitro-group at pH 5 and 7, and by ultraviolet absorption. Stoichiometric calculations, X-ray powder diffraction pattern of the synthesized metronidazole-calcium complex, and molecular ion peak at m/z 381 in the mass spectrum of this product, showed that a 2:1 complex is formed. The interaction of metronidazole with calcium on myocardial contractile performance of guinea-pig electrically-driven isolated left atria in physiological solution was also examined. Metronidazole induced a sustained, concentration-dependent depression of the tension that was reversed by changing the bathing fluid to physiological solution, and/or by adding excess calcium ion. The drug-induced negative inotropic response was antagonized competitively by increasing calcium ion in the bath, whereas noradrenaline antagonized metronidazole-induced negative inotropic responses non-competitively. Addition of the metronidazole-calcium complex to the bath did not affect normal myocardial contractile performance. The results show that metronidazole produces a direct negative inotropic effect on isolated atrial muscles by interfering with Ca2+, and by preventing Ca2+ function in the events leading to contractile activity of atrial muscles.

Cardiovascular Profile of Oligomycin, a Mitochondial Complex‐V inhibitor, in Anesthetized Dogs

Oligomycin A (oligo) is an antibiotic that inhibits mitochondrial complex‐V, leading to impaired energy formation in cells. Cells that have high energy demands, such as cardiac myocytes, may be sensitive to mitochondrial toxins, like oligo. Our goal was to determine the effect of oligo on hemodynamics and heart rate in the anesthetized dog preparation. Oligo was infused at 0, 0.01, 0.1 and 1 mg/kg IV (30 min/dose) and caused a dose‐related tachycardia (39–176%) and hypotension (19–36%). An increase in cardiac contractility (18–39%) was secondary to the heart rate increase (Bowditch phenomena). ATP depletion can stimulate norepinephrine release from sympathetic neurons, therefore, a follow‐up study evaluated whether atenolol could block oligo‐induced tachycardia. Atenolol (5 mg/kg, IV) demonstrated that the tachycardia induced by 1 mg/kg oligo was sensitive to cardiac b1‐blockade, but negative inotropy was not observed. These findings show that acute administration of oligo in this model elicits a profound sympathomimetic response, including an increase in cardiac contractility. Since energy depletion would be expected to reduce cardiac contractility, it is plausible that an acute cardiac sympathomimetic response masks negative inotropy. Evaluation of oligo in isolated heart preparations, are needed to address whether complex‐V inhibition has a direct negative inotropic effect on cardiac myocytes.

A case of coronary hypersensitivity (Kounis) syndrome associated with mid-ventricular ballooning pattern, intracoronary thrombosis and troponin elevation

A 76-years oldwomanaffected since15 years byahairycell leukemia underwent a treatmentwith rituximab. The patient had beenpreviously treated with several chemotherapy and immunosuppressive regimens with inconstant results, and she had a history of multiple drug intolerance or allergy. During previous infusions of rituximab, she had presented mild, self-resolving, allergic reactions (cutaneous manifestations, mild dyspnea). During the current infusion of the monoclonal antibody, she reported more severe signs of allergic reaction, including chills, erythema, and dyspnea along with precordial pain. Although initially severe, the anaphylactic reaction regressed after administration of corticosteroids and histamine antagonists and the patient did not require treatment with adrenergic medications. An ECG showed a left anterior hemiblock and a right bundle branch block but no ischemiaspecific ST-segment change. Repeated blood samples were collected, which showed an elevation of cardiac biomarkers (troponin Imaximum of 4.4 ng/ml at 6 h, with a normal value of b0.1). C-reactive protein was mildly elevated (16 mg/l, normal b5) and D-dimer and B-Natriuretic peptide were more consistently elevated (respectively, 6.8 mg/l and 1139 pg/ml). The patient was treated with aspirin of 300 m i.v., heparin 5000 IU i.v., and clopidogrel 600 mg per os and was scheduled for coronary angiography. During angiography no significant stenosis was evident, but a mobile structure suggestive of intracoronary thrombus (and compatible with the acute coronary presentation, Fig. 1) was present in the proximal left anterior descending coronary. Also, an atypical left mid-ventricular ballooning pattern was present, with dyskinesia of the mid anterior and inferior walls and hyperkinesia of the apex of the left ventricle (Fig. 2). Given the evidence of thrombus in the left anterior descending (LAD), angioplasty and stenting (Liberte 3.0x20mm, Boston Scientific) were successfully performed. Two days later, the symptoms had subsided and the cardiac biomarkers had returned to normal. The patient was discharged and is currently well. The “Kounis” or “coronary hypersensitivity” syndrome has been described as the occurrence of angina pectoris in the setting of allergic reactions with or without anaphylactic shock. Clinical and laboratory findings of classical acute coronary syndrome (for instance STsegment elevation in the ECG or elevated troponin markers), or a “left ventricular apical ballooning” syndrome presentation have been reported in this setting [1]. The mechanism(s) proposed for this phenomenon include intracoronary thrombosis or coronary spasm induced by cardiac mast cell-derived histamine and/or a depression of cardiac systolic function induced by the direct negative inotropic effect of TNF-α or IL-1β also released by activated mast cells [2,3]. International Journal of Cardiology 149 (2011) 377–402