Post-coronary Artery Ligation Research Articles

Effects of CD8 T-cell transfer on biomechanics of post-myocardial infarction scar formation

CD8+ T-cells are adverse regulators of post-MI remodeling, resulting in attenuated cardiac function and overall survival. Based on previous studies, we hypothesize that CD8+ T-cells impair cardiac function by altering scar composition. MI was induced by ligating the left anterior descending coronary artery on C57BL6/J wildtype (WT; 3-7 months of age, n≥2/sex) and CD8atm1mak (CD8−/−; 3-7 months of age, n≥2/sex/ group) mice. CD8−/− mice were injected with either vehicle or naïve splenic CD8+ T-cells via tail vein, 4-hours post-coronary artery ligation to assess potential effects on the scar. On day 7 post-MI, infarct tissue was collected, undergoing either passive stretch biomechanical analysis or histological and biochemical assays for collagen composition. Effects of granzyme (Gzm) B and K on collagen cleavage were tested using a fluorogenic collagen cleavage assay to examine possible mechanisms of scar alteration. Mice lacking CD8+ T-cells had improved ejection fraction and decreased dilation compared to WT mice at post-MI Day 7. This protective effect was lost in CD8−/− mice that received splenic CD8+ T-cells. Biomechanical analysis demonstrated CD8−/− mice had a 2-fold increase in regional stiffness compared to WT mice. Re-supplementation with splenic CD8+ T-cells decreased scar tissue stiffness mimicking biomechanics of WT mice. Picrosirius red staining surprisingly showed no significant differences in total collagen levels (p=0.51). Immunoblotting for Collagen 1 trended an increase in the 250 kDa band in CD8−/− mice that decreased after supplementation indicating a loss of pro-collagen formation (p=0.051). Ex-vivo cleavage assay demonstrated GzmK cleaved collagen in a concentration (0-50 AU) and temporal-dependent manner (0-24 hrs). Moreover, GzmK demonstrated a 10-fold greater capacity in collagen cleavage compared to GzmB at 25 AU, indicating the role GzmK plays during post-MI remodeling may be distinctly separate from that of GzmB. In conclusion, our data demonstrates that CD8+ T-cells regulate cardiac fibrosis potentially in part through the release of granzymes, leading to alterations in biomechanical capability of the left ventricle. This work was supported by the National Institutes of Health T32GM123055, R25GM113278; the Biomedical Laboratory Research and Development Service of the Veterans Affairs Offce of Research and Development Award IK2BX003922 and BX003922; and South Carolina Translational Research Center UL1TR001450. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Protective role of arachidonic acid against diabetic myocardial ischemic injury: a translational study of pigs, rats, and humans

AimPatients with diabetes mellitus have poor prognosis after myocardial ischemic injury. However, the mechanism is unclear and there are no related therapies. We aimed to identify regulators of diabetic myocardial ischemic injury.Methods and resultsMass spectrometry-based, non-targeted metabolomic approach was used to profile coronary sinus blood from diabetic and non-diabetic Bama-mini pigs at 0.5-h post coronary artery ligation. Six metabolites had a |log2 (Fold Change)|> 1.3. Among them, the most changed is arachidonic acid (AA), levels of which were 32 times lower in diabetic pigs than in non-diabetic pigs. The AA-derived products, PGI2 and 6-keto-PGF1α, were also significantly reduced. AA treatment of cultured cardiomyocytes protected against cell death by 30% at 48 h of high glucose and oxygen deprivation, which coincided with increased mitophagic activity (as indicated by increased LC3II/LC3I, decreased p62 and increased parkin & PINK1), improved mitochondrial renewal (upregulation of Drp1 and FIS1), reduced ROS generation and increased ATP production. These cardioprotective effects were abolished by PINK1(a crucial mitophagy protein) knockdown or the autophagy inhibitor 3-Methyladenine. The protective effect of AA was also inhibited by indomethacin and Cay10441, a prostacyclin receptor antagonist. Furthermore, diabetic Sprague Dawley rats were subjected to coronary ligation for 40 min and AA treatment (10 mg/day per animal gavaged) decreased myocardial infarct size, cell apoptosis index, inflammatory cytokines and improved heart function. Scanning electron microscopy showed more intact mitochondria in the border zone of infarcted myocardium in AA treated rats. Lastly, diabetic patients after myocardial infarction had lower plasma levels of AA and 6-keto-PGF1α and reduced cardiac ejection fraction, compared with non-diabetic patients after myocardial infarction. Plasma AA level was inversely correlated with fasting blood glucose.ConclusionsAA protects against diabetic ischemic myocardial damage by promoting mitochondrial autophagy and renewal, which is related to AA derived PGI2 signaling. AA may represent a new strategy to treat diabetic myocardial ischemic injury.

A Clinically Relevant Functional Model of Type-2 Cardio-Renal Syndrome with Paraventricular Changes consequent to Chronic Ischaemic Heart Failure

Cardiorenal syndrome, de novo renal pathology arising secondary to cardiac insufficiency, is clinically recognised but poorly characterised. This study establishes and characterises a valid model representative of Type 2 cardiorenal syndrome. Extensive permanent left ventricular infarction, induced by ligation of the left anterior descending coronary artery in Lewis rats, was confirmed by plasma cardiac troponin I, histology and cardiac haemodynamics. Renal function and morphology was assessed 90-days post-ligation when heart failure had developed. The involvement of the paraventricular nucleus was investigated using markers of inflammation, apoptosis, reactive oxygen species and of angiotensin II involvement. An extensive left ventricular infarct was confirmed following coronary artery ligation, resulting in increased left ventricular weight and compromised left ventricular diastolic function and developed pressure. Glomerular filtration was significantly decreased, fractional excretion of sodium and caspase activities were increased and basement membrane thickening, indicating glomerulosclerosis, was evident. Interestingly, angiotensin II receptor I expression and reactive oxygen species levels in the hypothalamic paraventricular nucleus remained significantly increased at 90-days post-coronary artery ligation, suggesting that these hypothalamic changes may represent a novel, valuable pharmacological target. This model provides conclusive morphological, biochemical and functional evidence of renal injury consequent to heart failure, truly representative of Type-2 cardiorenal syndrome.

Slow antegrade excitation and delayed retrograde activation through an "inexcitable zone": A basis for arrhythmia formation in infarcted myocardium ex vivo.

The electrophysiologic mechanism for rate-dependent PVBs associated with double potentials (DPs) was investigated in infarcted canine hearts using bipolar and intracellular microelectrode recordings. Dogs exhibiting rate-related ventricular ectopic beats (coupling interval, 390 ± 54 milliseconds) during sinus rhythm or atrial pacing were studied 4-5 days (N = 63) or 25 days (N = 16) following anterior descending coronary artery ligation. Sites of DP and rate-dependent arrhythmia formation were identified in vivo using bipolar recordings for subsequent ex vivo studies. Rate-dependent conduction delays with increasing duration isoelectric intervals representing very slow conduction were observed at sites of DP formation, frequently provoking both manifest and concealed reentry (non-stimulated beats) over a narrow range of paced cycle lengths. Both slow antegrade and retrograde activation across an inexcitable gap (reflection) were integral components of extrasystole formation. Retrograde reflection to a region of very slow conduction (mid-potential) during antegrade activation was routinely observed at 4-5 days (42 of 63 preparations, 67%) and 25 days (22 of 26 preparations, 85%) postcoronary artery ligation. Reflection and premature re-activation of the proximal site was then observed in 6 of 63 (9%), and 3 of 26 preparations (12%). The present experiments demonstrate DP formation and rate-dependent constant-coupled late epicardial premature beats in infarcted dog hearts. Microelectrode recordings at DP sites demonstrating prolonged isoelectric intervals display very slow conduction preceding distal activation and "reentrant" re-activation of more proximal sites, representing reflection as an arrhythmia mechanism in ischemically injured epicardium during subacute myocardial infarction.

Salubrinal improves cardiac function in rats with heart failure post myocardial infarction through reducing endoplasmic reticulum stress-associated apoptosis

Endoplasmic reticulum (ER) stress plays an important role in ischemia-mediated cell death. The aim of the current study is to investigate the effects of salubrinal (Sal), a selective eIF2a dephosphorylation inhibitor, on heart failure rats and related mechanisms. Heart failure was induced by coronary artery ligation (MI) in adult male Sprague-Dawley rats. To ensure comparable MI sizes post coronary artery ligation on various groups, echocardiography examination was performed before and 30 minutes after ligation in MI groups. Then rats were randomly assigned to 4 groups: Sham group (n=12), MI group (n=10), MI plus vehicle injections group (DMSO group, n=12) and MI plus Sal injection group (Sal group, n=12). Sal (1 mg/kg) or DMSO was injected via the tail vein daily for the first 3 days (starting at 30 minutes after ligation of the left coronary artery), followed by subcutaneous injections twice per week for 8 weeks. Cardiac function was assessed by echocardiography and cell apoptosis assessed by flow cytometric analysis after 8 weeks. Protein and mRNA levels of ER stress markers were evaluated by immunohistochemistry and real time RT-PCR respectively. Eight weeks later, LVEF was significantly higher, while LVESD and LVEDD values were significantly lower in Sal group compared to MI and DMSO groups (all P<0.05); LV/BW ratio was significantly higher in MI group than in Sham group ((2.30±0.40) mg/g vs.(1.78±0.31) mg/g, P<0.05), which was significantly reduced in Sal group ((1.88±0.25) mg/g), but not in DMSO group((2.25±0.36) mg/g, P<0.05 vs. MI). In addition, flow cytometric analysis showed that Sal treatment significantly reduced apoptosis but not necrosis in post MI. Immunohistochemistry and real time PCR analysis showed that the myocardial protein and mRNA expression of ER stress markers were significantly lower in Sal group than in MI group, myocardial caspase-12 expression was significantly upregulated in MI group and significantly reduced by Sal treatment. Our results suggest that reduction of ER stress and myocardial apoptosis through inhibition of eIF2α dephosphorylation may serve as the potential mechanisms for the improved cardiac function and attenuated cardiac remodeling post Sal treatment in this heart failure rat model.

Abstract 15610: The Infusion of Mesenchymal Stromal Cells Post Myocardial Infarction Increases Myocardial S100A6, Attenuates Myocyte Hypertrophy, Reduces Myocyte Apoptosis and Improves Cardiac Function

The beneficial effects originally attributed to the ability of bone-marrow derived mesenchymal stromal cells (BM-MSCs) to differentiate into cardiomyocytes have been questioned due to the transient presence of donor cells at injury site following myocardial infarction (MI) suggesting that the MSC-induced improvement in hemodynamic function may be attributable to paracrine effects. We showed that S100A6, a 20 kDa EF-hand calcium-binding dimer, is upregulated and secreted following MI and forced expression post-MI was beneficial to the preservation of cardiac function. The aim of this study was to determine whether the beneficial effects of infused BM-MSCs may be related to the autocrine secretion of S100A6. Balb/c murine cultured green fluorescence protein (GFP)-marked BM-MSCs express S100A6 at baseline and in response to hypoxia (5%C02/95% N2) for 1 hr increase S100A6 mRNA and protein (2-3 fold, and release S100A6 (1 nM) in the culture media, responses inhibited in BM-MSCs transfected with S100A6 siRNA. Treatment of neonatal Balb/c cardiac myocytes with human recombinant S100A6 (1nM) for 1-24 hrs attenuated baseline apoptosis (30 per cent decrease in BAX/BCL2 ratio), induced cyclin-dependent kinase 1(CDK1) mRNA 1.5 fold, miR199a 2 fold and myocyte proliferation 2.5 fold, the latter inhibited by anti-miR 199a. In 12 week old Balb/c mice, saline or GFP-marked BM-MSCs transfected with either a scrambled or S100A6 siRNA were infused intravenously 3-4 hrs post coronary artery ligation. After 3-4 days the GFP-marked cells were confined to ischemic areas and represented approximately 10% of total cellularity and co-expressed collagen type IV and myosin heavy chain, characteristic of MSCs and cardiomyocytes, respectively, and were CD45(-). Despite the absence of donor cells in the infarcted myocardium 21 days after infusion, mice that have received MSCs alone compared to MSCs transfected with an S100A6 siRNA or saline alone showed a 6-fold increase in S100A6 mRNA and protein, 3-fold increase in miR199a in peri-infarcted myocardium, attenuated myocyte hypertrophy, decreased fibrosis and apoptosis, and preservation of cardiac function. In conclusion, the secretion of S100A6 by infused BM-MSCs may contribute in limiting adverse LV remodeling post-MI.

THE INFUSION OF MESENCHYMAL STROMAL CELLS INCREASES MYOCARDIAL S100A6 AND LIMITS ADVERSE LEFT VENTRICULAR REMODELING POST MYOCARDIAL INFARCTION

The beneficial effects originally attributed to the ability of bone-marrow derived mesenchymal stromal cells BM-MSCs to differentiate into cardiomyocytes, both in vitro and in vivo experimental models has been questioned due to the transient presence of donor cells at injury site following myocardial infarction (MI) suggesting that the MSC-induced improvement in hemodynamic function may be attributable to paracrine effects. We have shown that S100A6, a 20 kDa EF-hand Ca++-binding dimer, is upregulated and secreted following MI and forced expression post-MI attenuated myocyte hypertrophy, decreased fibrosis and apoptosis and was beneficial to the preservation of cardiac function. The aim of this study was to determine whether the beneficial effects of infused BM-MSCs may be related to the secretion of S100A6. In 12 week old Balb/c mice, saline or green fluorescence protein (GFP)-marked BM-MSCs transfected with either a scrambled or S100A6 siRNA were infused intravenously 3-4 hrs post coronary artery ligation. Balb/c murine cultured GFP-marked BM-MSCs express cytoplasmic and nuclear S100A6 at baseline and in response to a hypoxia (5%C02/95% N2) for 1 hr increase S100A6 mRNA and protein approximately 2-3 fold, and release S100A6 (1 nM) in the culture media, responses inhibited in BM-MSCs transfected with S100A6 siRNA. Treatment of neonatal Balb/c cardiac myocytes with human recombinant S100A6 (1nM) for 1-24 hrs attenuated baseline apoptosis (30 per cent decrease in BAX/BCL2 ratio), induced cyclin-dependent kinase 1(CDK1) mRNA 1.5 fold, miR199a 2 fold and myocyte proliferation 2.5 fold, the latter inhibited in the presence of anti-miR 199a. In Balb/c mice, 3-4 days post infusion, the GFP-marked cells were confined strictly to ischemic areas and represented approximately 10 % of total cellularity and coexpressed collagen type IV and troponin T or myosin heavy chain, characteristic of MSCs and cardiomyocytes, respectively, and were CD45(-). Despite the absence of donor cells in the infarcted myocardium 21 days after infusion, mice that have received MSCs alone compared to MSCs transfected with an S100A6 siRNA or saline alone showed a 6-fold increase in S100A6 in peri-infarcted myocardium, attenuated myocyte hypertrophy, decreased fibrosis and apoptosis and preservation of cardiac function. The secretion of S100A6 by infused BM-MSCs may contribute in limiting adverse left ventricular remodeling post-MI.

Suppression of Autonomic‐Mediated Triggered Firing in Pulmonary Vein Preparations, 24 Hours Postcoronary Artery Ligation in Dogs

Rapid arrhythmia originating within pulmonary veins (PVs) precipitates atrial fibrillation (AF) in man. To determine a possible basis for an increased incidence of AF observed peri-myocardial infarction in man, we compared AF induction in vivo and triggered arrhythmia formation within isolated PVs in vitro in normal dogs and dogs studied 24 hours postcoronary artery ligation. The incidence of AF initiated by atrial premature stimuli was increased in dogs postcoronary artery ligation (6/9) versus normal (2/12) (P = 0.03). In isolated PVs from normal hearts, pause-dependent early afterdepolarizations (EADs) were enhanced by catecholamines. Rapid arrhythmia (1,182 +/- 213 beats/min) was triggered during isoproterenol/norepinephrine (32 nM) + acetylcholine (100 nM) (N = 16/23) using the same pacing pauses eliciting EADs. Rapid arrhythmia (802 +/- 161 beats/min) was also triggered by local autonomic nerve stimulation (ANS; N = 18/23). Despite equivalent pause-dependent afterdepolarization formation in PVs from infarcted hearts, a rightward 45-fold and 28-fold shift in the dose-response curve for afterdepolarization enhancement was observed for isoproterenol and norepinephrine, respectively (P < 0.02). ANS (N = 1/19) and isoproterenol/norepinephrine (32 nM) + acetylcholine (100 nM) (N = 0/9 and 0/12, respectively) (P = 0.0001) failed to elicit arrhythmia formation. Beta-adrenergic receptor desensitization was associated with a 2.5-fold increase in PV beta-adrenergic receptor kinase (ARK). The data demonstrate decreased susceptibility of isolated canine PVs for arrhythmia triggered by local ANS, or pacing pauses in the presence of a catecholamine + acetylcholine, postmyocardial infarction, despite a greater susceptibility of the intact heart to AF. The decreased arrhythmia susceptibility was observed coincident with an increase in beta-ARK and a decreased responsiveness to beta-adrenergic receptor agonists.

Expression of S100B in murine cardiovascular tissues post coronary artery ligation and aortic banding

Expression of S100B in murine cardiovascular tissues post coronary artery ligation and aortic banding

Haemodynamic effects of a selective adenosine A2A receptor agonist, CGS 21680, in chronic heart failure in anaesthetized rats.

1. Recently we demonstrated that the administration of an A2A adenosine receptor agonist, CGS 21680, to anaesthetized rats with acute heart failure (1 h post-coronary artery ligation) resulted in an increase in cardiac output. In the present investigation, the effects of CGS 21680 on cardiac output, vascular resistance, heart rate, blood pressure and mean circulatory filling pressure (Pmcf) were investigated in anaesthetized rats with chronic heart failure (8 weeks post-coronary artery ligation). 2. Experiments were conducted in five groups (n = 6) of animals: sham-operated vehicle-treated (0.9% NaCl; 0.037 mL kg(-1) min(-1)) animals in which the occluder was placed but not pulled to ligate the coronary artery; coronary artery-ligated vehicle-treated animals; and coronary artery-ligated CGS 21680-treated (0.1. 0.3 or 1.0 microg kg(-1) min(-1)) animals. 3. Baseline blood pressure, cardiac output and rate of rise in left ventricular pressure (+dP/dt) were significantly reduced in animals with coronary artery ligation when compared to sham-operated animals. Coronary artery ligation resulted in a significant increase in left ventricular end-diastolic pressure, Pmcf and venous resistance when compared to sham-operated animals. 4. Administration of CGS 21680 at 0.3 and 1.0 microg kg(-1) min(-1) significantly (n = 6; P<0.05) increased cardiac output by 19+/-4% and 39+/-5%, and heart rate by 14+/-2% and 15+/-1%, respectively, when compared to vehicle treatment in coronary artery-ligated animals. Administration of CGS 21680 also significantly reduced blood pressure and arterial resistance when compared to coronary artery-ligated vehicle-treated animals. Infusion of CGS 21680 also significantly reduced venous resistance when compared to vehicle-treated coronary artery-ligated animals. 5. The results show that heart failure is characterized by reduced cardiac output, and increased left ventricular end-diastolic pressure, venous resistance and Pmcf. Acute treatment with CGS 21680 in animals with chronic heart failure decreased left ventricular end-diastolic pressure and increased cardiac output. This increase in cardiac output was the result of reduced arterial and venous resistances and increased heart rate.

Post-infarction Heart Failure in the Rat is Associated with Distinct Alterations in Cardiac Myocyte Molecular Phenotype

The myocardial molecular and cellular responses to hemodynamic and other hypertrophic stimuli have been characterized extensively, but less is known of the alterations in gene expression during the evolution of heart failure following myocardial infarction, and specifically those affecting the cardiac myocytes. Therefore, the present study was undertaken to test the hypothesis that post-infarction heart failure and remodeling in the rat is associated with a distinct myocyte molecular phenotype. To address this question, hemodynamic measurements were performedin vivo; and myocytes isolated from the non-infarcted myocardium 1 day, 1 week, and 6 weeks post-coronary artery ligation in post-infarct rats and sham controls. Myocyte size, mRNA levels for immediate early genes, contractile proteins, and sarcoplasmic reticulum Ca2+-ATPase (SERCA) and phospholamban were assayed by Northern analyses, and SERCA and phospholamban proteins were examined by Western blotting. Hemodynamic evidence of heart failure was present at all post-infarct time points. Myocyte size was increased significantly at 6 weeks.c-mycexpression was increased at 1 day and 1 week in the infarcted rats, but returned to baseline by 6 weeks. Atrial natriuretic peptide and VEGF mRNAs were elevated at 1 and 6 weeks. Bothβ-myosin heavy chain and skeletalα-actin expression were increased at all post-MI time points. In contrast, neither changes in the expression of the calcium-handling proteins (SERCA and phospholamban) were not observed, nor was there a change in TGFβ1or TGFβ3. These results demonstrate that in rats with post-MI heart failure, there was an immediate induction of the fetal/embryonic transcriptional gene program which preceded myocyte hypertrophy and appeared to persist longer than in pressure-overload models. In further contrast to pressure-overload, expression of sarcoplasmic reticulum Ca2+-ATPase and phospholamban, was not altered despite a comparable degree of cellular hypertrophy and more severe hemodynamic decompensation. These findings suggest that there may be important differences in the regulatory mechanisms underlying these two forms of myocardial hypertrophy and heart failure.

Ischemia and reperfusion-induced arrhythmias in rabbits with chronic heart failure

The incidence of ventricular arrhythmias occurring during acute myocardial ischemia and reperfusion was studied in anesthetized rabbits with chronic heart failure. Cardiac failure was induced by volume and pressure overload and was characterized by marked hypertrophy (84%) and lower systolic aortic blood pressure (112 +/- 3 mmHg) than in controls (124 +/- 2 mmHg, P less than 0.01). During the first 20 min postcoronary artery ligation, the incidence and duration of ventricular fibrillation were greater in the heart failure group (76% and 485 +/- 77 s, respectively) compared with the control group (27% and 86 +/- 37 s, respectively, P less than 0.01). Reperfusion-induced arrhythmias after various ischemic durations were also more frequent in the heart failure group than in the control group. Papillary muscles taken from rabbits with heart failure showed a reduced diastolic potential and a prolonged action potential duration (APD90) compared with the control group (by 7 and 46%, respectively), but there was no change in maximum upstroke velocity. The present study established that rabbits with pronounced morphological signs of chronic heart failure have an enhanced susceptibility to ischemia and reperfusion-induced arrhythmias. As already described in situations of uncomplicated cardiac hypertrophy, a delay in the repolarization process could represent an arrhythmogenic mechanism in this model.

Adrenergic influences on the spinal cardiovascular neurones.

In cervical spinal cord transected and bilaterally vagotomized dogs, intrathecal (i.t.) injection of clonidine decreased the resting heart rate and mean arterial pressure (MAP) while isoprenaline increased the heart rate. The clonidine induced bradycardia and hypotension were antagonized by piperoxan pretreatment. Similarly, the isoprenaline induced tachycardia was antagonized by pretreatment (i.t.) with atenolol. Intrathecal atenolol per se decreased the heart rate and MAP while piperoxan had no effect. The post-coronary artery ligation cardiac arrhythmia, in the cervical spinal cord transected and bilaterally vagotomized dogs, was inhibited by clonidine, phenylephrine and methoxamine and facilitated by isoprenaline. beta-Adrenoreceptor antagonists propranolol, atenolol and acebutolol, given intrathecally, inhibited while piperoxan facilitated the cardiac arrhythmia. The clonidine and isoprenaline induced changes in the arrhythmia were antagonized by i.t. pretreatment with piperoxan and atenolol respectively. It appears that the alpha-adrenoreceptors are inhibitory while beta-adrenoreceptors are facilitatory for spinal control of heart rate and blood pressure and for post-coronary artery ligation cardiac arrhythmia.

Electrophysiological actions of amrinone in dogs with cardiac lesions.

We examined the actions of amrinone in five models using dogs to determine under what circumstances intravenous amrinone might exert arrhythmogenic or antiarrhythmic properties. In dogs with 24-h post-coronary artery ligation arrhythmias, amrinone, given at incrementally increasing doses of 1.5, 3.0, and 6.0 mg/kg at 30-min intervals, produced significant increases of cardiac contractility without altering the severity of the arrhythmia. In dogs with 2- to 6-day-old ischemic lesions and 90-100% sinus beats, a bolus dose of 3.0 mg/kg amrinone was followed by an increased incidence of abnormal beats (p = 0.013); neither 1.5 nor 6.0 mg/kg caused a significant incidence of arrhythmias. Acute occlusion of the left anterior descending coronary artery followed by reperfusion caused fibrillation in nine of 15 control dogs and two of 14 dogs treated with 2.3 mg/kg amrinone. This difference was significant at the level p less than 0.05. In ouabain-intoxicated dogs, amrinone at 1.0 and 3.0 mg/kg neither worsened nor improved the arrhythmias. In the atrial circus flutter arrhythmia, amrinone increased ventricular heart rate by a significantly greater amount than it increased atrial rate, suggesting that amrinone facilitates atrioventricular conduction.

Cholinergic influences on the spinal cardiovascular neurones.

1 In bilaterally vagotomized and spinal cord (C1) transected dogs, intrathecal (i.t.) injection of pilocarpine decreased while DMPP increased the blood pressure. These responses were antagonized by i.t. pretreatment with ethylbenztropine and chlorisondamine respectively. 2 No change in the resting heart rate occurred after intrathecal injection of cholinergic drugs in these animals. 3 The post-coronary artery ligation cardiac arrhythmia, in bilaterally vagotomized and spinal (C1) transected dogs, was inhibited by i.t. pilocarpine and chlorisondamine and facilitated by ethylbenztropine and DMPP. 4 The effects of muscarinic and nicotinic receptor agonists on the arrhythmia were blocked by their respective blockers. 5 It appears that the muscarinic receptors are inhibitory while nicotinic receptors are facilitatory for spinal control of vasomotor tone and the post-coronary artery ligation cardiac arrhythmia. However, the spinal muscarinic and nicotinic receptors do not appear to have a significant role in the regulation of normal heart rate.