Haemodynamic effects of glucagon

Glucagon receptor antagonist volagidemab in type 1 diabetes: a 12-week, randomized, double-blind, phase 2 trial

Hyperglucagonemia contributes to hyperglycemia in patients with type 1 diabetes (T1D); however, novel therapeutics that block glucagon action could improve glycemic control. This phase 2 study evaluated the safety and efficacy of volagidemab, an antagonistic monoclonal glucagon receptor (GCGR) antibody, as an adjunct to insulin therapy in adults with T1D. The primary endpoint was change in daily insulin use at week 12. Secondary endpoints included changes in hemoglobin A1c (HbA1c) at week 13, in average daily blood glucose concentration and time within target range as assessed by continuous blood glucose monitoring (CGM) and seven-point glucose profile at week 12, incidence of hypoglycemic events, the proportion of subjects who achieve HbA1c reduction of ≥0.4%, volagidemab drug concentrations and incidence of anti-drug antibodies. Eligible participants (n = 79) were randomized to receive weekly subcutaneous injections of placebo, 35 mg volagidemab or 70 mg volagidemab. Volagidemab produced a reduction in total daily insulin use at week 12 (35 mg volagidemab: -7.59 units (U) (95% confidence interval (CI) -11.79, -3.39; P = 0.040 versus placebo); 70 mg volagidemab: -6.64 U (95% CI -10.99, -2.29; P = 0.084 versus placebo); placebo: -1.27 U (95% CI -5.4, 2.9)) without meeting the prespecified significance level (P < 0.025). At week 13, the placebo-corrected reduction in HbA1c percentage was -0.53 (95% CI -0.89 to -0.17, nominal P = 0.004) in the 35 mg volagidemab group and -0.49 (95% CI -0.85 to -0.12, nominal P = 0.010) in the 70 mg volagidemab group. No increase in hypoglycemia was observed with volagidemab therapy; however, increases in serum transaminases, low-density lipoprotein (LDL)-cholesterol and blood pressure were observed. Although the primary endpoint did not meet the prespecified significance level, we believe that the observed reduction in HbA1c and tolerable safety profile provide a rationale for further randomized studies to define the long-term efficacy and safety of volagidemab in patients with T1D.

Emergence of Mechano-Sensitive Contraction Autoregulation in Cardiomyocytes

The heart has two intrinsic mechanisms to enhance contractile strength that compensate for increased mechanical load to help maintain cardiac output. When vascular resistance increases the ventricular chamber initially expands causing an immediate length-dependent increase of contraction force via the Frank-Starling mechanism. Additionally, the stress-dependent Anrep effect slowly increases contraction force that results in the recovery of the chamber volume towards its initial state. The Anrep effect poses a paradox: how can the cardiomyocyte maintain higher contractility even after the cell length has recovered its initial length? Here we propose a surface mechanosensor model that enables the cardiomyocyte to sense different mechanical stresses at the same mechanical strain. The cell-surface mechanosensor is coupled to a mechano-chemo-transduction feedback mechanism involving three elements: surface mechanosensor strain, intracellular Ca2+ transient, and cell strain. We show that in this simple yet general system, contractility autoregulation naturally emerges, enabling the cardiomyocyte to maintain contraction amplitude despite changes in a range of afterloads. These nontrivial model predictions have been experimentally confirmed. Hence, this model provides a new conceptual framework for understanding the contractility autoregulation in cardiomyocytes, which contributes to the heart's intrinsic adaptivity to mechanical load changes in health and diseases.

High-Dose Glucagon Has Hemodynamic Effects Regardless of Cardiac Beta-Adrenoceptor Blockade: A Randomized Clinical Trial

Background Intravenous high-dose glucagon is a recommended antidote against beta-blocker poisonings, but clinical effects are unclear. We therefore investigated hemodynamic effects and safety of high-dose glucagon with and without concomitant beta-blockade. Methods and Results In a randomized crossover study, 10 healthy men received combinations of esmolol (1.25 mg/kg bolus+0.75 mg/kg/min infusion), glucagon (50 µg/kg), and identical volumes of saline placebo on 5 separate days in random order (saline+saline; esmolol+saline; esmolol+glucagon bolus; saline+glucagon infusion; saline+glucagon bolus). On individual days, esmolol/saline was infused from -15 to 30 minutes. Glucagon/saline was administered from 0 minutes as a 2-minute intravenous bolus or as a 30-minute infusion (same total glucagon dose). End points were hemodynamic and adverse effects of glucagon compared with saline. Compared with saline, glucagon bolus increased mean heart rate by 13.0 beats per minute (95% CI, 8.0-18.0; P<0.001), systolic blood pressure by 15.6 mm Hg (95% CI, 8.0-23.2; P=0.002), diastolic blood pressure by 9.4 mm Hg (95% CI, 6.3-12.6; P<0.001), and cardiac output by 18.0 % (95% CI, 9.7-26.9; P=0.003) at the 5-minute time point on days without beta-blockade. Similar effects of glucagon bolus occurred on days with beta-blockade and between 15 and 30 minutes during infusion. Hemodynamic effects of glucagon thus reflected pharmacologic glucagon plasma concentrations. Glucagon-induced nausea occurred in 80% of participants despite ondansetron pretreatment. Conclusions High-dose glucagon boluses had significant hemodynamic effects regardless of beta-blockade. A glucagon infusion had comparable and apparently longer-lasting effects compared with bolus, indicating that infusion may be preferable to bolus injections. Registration Information URL: https://www.clinicaltrials.gov; Unique identifier: NCT03533179.

The role of glucagon in the possible mechanism of cardiovascular mortality reduction in type 2 diabetes patients

AIM

Type 2 diabetes (T2D) is one of the major public health issues worldwide. The main cause of mortality and morbidity among T2D patients are cardiovascular (CV) causes. Various antidiabetics are used in T2D treatment, but until recently they lacked clear evidence of the reduction in CV mortality and all-cause mortality as independent study end-points. The aim of this article was to present and critically evaluate potential mechanisms behind the remarkable results documented in trials with new antidiabetics for the treatment of T2D.

METHODS

Relevant data were collected using the MEDLINE, PubMed, EMBASE, Web of Science, Science Direct, and Scopus databases with the key words: "type 2 diabetes," "mortality," "glucagon," "empagliflozin," "liraglutide," "insulin" and "QTc." Searches were not limited to specific publication types or study designs.

RESULTS

The EMPA-REG OUTCOME trial with empagliflozin and LEADER trial with liraglutide presented remarkable results regarding the reduction in mortality in T2D treatment. However, the potential mechanism for those beneficial effects is difficult to determine. It is not likely that improvements in classic CV risk factors are responsible for the observed effect. A potential mechanism may be caused by the elevation of postprandial (PP) glucagon concentrations that can be seen with an empagliflozin and liraglutide therapy, which could have beneficial effects considering the myocardial electrical stability in T2D patients.

CONCLUSION

This hypothesis throws new light upon possible mechanisms of reduction in mortality in T2D patients.

Does glucagon have a positive inotropic effect in the human heart?

Glucagon is considered to exert cardiostimulant effects, most notably the enhancement of heart rate and contractility, due to the stimulation of glucagon receptors associated with Gs protein stimulation which causes adenylyl cyclase activation and the consequent increase in 3′,5′-cyclic adenosine monophosphate production in the myocardium. These effects have been extensively demonstrated in experimental studies in different animal species. However, efforts to extrapolate the experimental data to patients with low cardiac output states, such as acute heart failure or cardiogenic shock, have been disappointing. The experimental and clinical data on the cardiac effects of glucagon are described here.

Sodium-glucose cotransporter-2 inhibition for the reduction of cardiovascular events in high-risk patients with diabetes mellitus

Patients with type 2 diabetes mellitus (T2DM) exhibit an increased risk for cardiovascular (CV) events. Hyperglycemia itself contributes to the pathogenesis of atherosclerosis and heart failure (HF) in these patients, but glucose-lowering strategies studied to date have had little or no impact on reducing CV risk, especially in patients with a long duration of T2DM and prevalent CV disease (CVD). Sodium-glucose cotransporter-2 (SGLT2) inhibitors are the new class of glucose-lowering medications that increase urinary glucose excretion, thus improving glycemic control, independent of insulin. The recently published CV outcome trial, Empagliflozin Cardiovascular Outcome Event Trial in Type 2 Diabetes Mellitus Patients-Removing Excess Glucose (EMPA-REG OUTCOME), demonstrated that the SGLT2 inhibitor empagliflozin significantly reduced the combined CV end point of CV death, nonfatal myocardial infarction, and nonfatal stroke vs. placebo in a population of patients with T2DM and prevalent atherosclerotic CVD. In addition, and quite unexpectedly, empagliflozin significantly and robustly reduced the individual end points of CV death, overall mortality, and hospitalization for HF in this high-risk population. Several beneficial factors beyond glucose control, such as weight loss, lowering blood pressure, sodium depletion, renal hemodynamic effects, effects on myocardial energetics, and/or neurohormonal effects, have been seen with SGLT2 inhibition.

Hemodynamic Effects of Glucagon: A Literature Review

CONTEXT

Glucagon's effects on hemodynamic parameters, most notably heart rate and cardiac contractility, are often overlooked. The glucagon receptor is a central target in novel and anticipated type 2 diabetes therapies, and hemodynamic consequences of glucagon signaling have therefore become increasingly important. In this review, we summarize and evaluate published studies on glucagon pharmacology with a focus on clinical hemodynamic effects in humans.

EVIDENCE ACQUISITION

PubMed, Embase, and the Cochrane Library were searched for clinical studies concerning hemodynamic effects of glucagon (no year restriction). Papers reporting effects of a defined glucagon dose on any hemodynamic parameter were included. Reference searches were conducted in retrieved articles.

EVIDENCE SYNTHESIS

Hemodynamic effects of glucagon have been investigated mainly in cohort studies of patients suffering from heart failure receiving large glucagon bolus injections. The identified studies had shortcomings related to restricted patient groups, lack of a control group, randomization, or blinding. We identified no properly conducted randomized clinical trials. The majority of human studies report stimulating effects of pharmacological glucagon doses on heart rate, cardiac contractility, and blood pressure. The effects were characterized by short duration, interindividual variation, and rapid desensitization. Some studies reported no measurable effects of glucagon.

CONCLUSIONS

The level of evidence regarding hemodynamic effects of glucagon is low, and observations in published studies are inconsistent. Actual effects, interindividual variation, dose-response relationships, and possible long-term effects of supraphysiological glucagon levels warrant further investigation.

Glucagon and heart in type 2 diabetes: new perspectives

Increased levels of glucagon in type 2 diabetes are well known and, until now, have been considered deleterious. However, glucagon has an important role in the maintenance of both heart and kidney function. Moreover, in the past, glucagon has been therapeutically used for heart failure treatment. The new antidiabetic drugs, dipeptidyl peptidase-4 inhibitors and sodium-glucose co-transporter-2 inhibitors, are able to decrease and to increase glucagon levels, respectively, while contrasting data have been reported regarding the glucagon like peptide 1 receptors agonists. The cardiovascular outcome trials, requested by the FDA, raised some concerns about the possibility that the dipeptidyl peptidase-4 inhibitors can precipitate the heart failure, while, at least for empagliflozin, a positive effect has been shown in decreasing both cardiovascular death and heart failure. The recent LEADER Trial, showed a significant reduction of cardiovascular death with liraglutide, but a neutral effect on heart failure. A possible explanation of the results with the DPPIV inhibitors and empagliflozin might be related to their divergent effect on glucagon levels. Due to unclear effects of glucagon like peptide 1 receptor agonists on glucagon, the possible role of this hormone in the Leader trial remains unclear.

Sodium Glucose Cotransporter 2 Inhibitors in the Treatment of Diabetes Mellitus: Cardiovascular and Kidney Effects, Potential Mechanisms, and Clinical Applications

Sodium-glucose cotransporter-2 (SGLT2) inhibitors, including empagliflozin, dapagliflozin, and canagliflozin, are now widely approved antihyperglycemic therapies. Because of their unique glycosuric mechanism, SGLT2 inhibitors also reduce weight. Perhaps more important are the osmotic diuretic and natriuretic effects contributing to plasma volume contraction, and decreases in systolic and diastolic blood pressures by 4 to 6 and 1 to 2 mm Hg, respectively, which may underlie cardiovascular and kidney benefits. SGLT2 inhibition also is associated with an acute, dose-dependent reduction in estimated glomerular filtration rate by ≈5 mL·min(-1)·1.73 m(-2) and ≈30% to 40% reduction in albuminuria. These effects mirror preclinical observations suggesting that proximal tubular natriuresis activates renal tubuloglomerular feedback through increased macula densa sodium and chloride delivery, leading to afferent vasoconstriction. On the basis of reduced glomerular filtration, glycosuric and weight loss effects are attenuated in patients with chronic kidney disease (estimated glomerular filtration rate <60 mL·min(-1)·1.73 m(-2)). In contrast, blood pressure lowering, estimated glomerular filtration rate, and albuminuric effects are preserved, and perhaps exaggerated in chronic kidney disease. With regard to long-term clinical outcomes, the EMPA-REG OUTCOME trial (Empagliflozin, Cardiovascular Outcomes, and Mortality in Type 2 Diabetes) in patients with type 2 diabetes mellitus and established cardiovascular disease randomly assigned to empagliflozin versus placebo reported a 14% reduction in the primary composite outcome of cardiovascular death, nonfatal myocardial infarction, nonfatal stroke, and >30% reductions in cardiovascular mortality, overall mortality, and heart failure hospitalizations associated with empagliflozin, even though, by design, the hemoglobin A1c difference between the randomized groups was marginal. Aside from an increased risk of mycotic genital infections, empagliflozin-treated patients had fewer serious adverse events, including a lower risk of acute kidney injury. In light of the EMPA-REG OUTCOME results, some diabetes clinical practice guidelines now recommend that SGLT2 inhibitors with proven cardiovascular benefit be prioritized in patients with type 2 diabetes mellitus who have not achieved glycemic targets and who have prevalent atherosclerotic cardiovascular disease. With additional cardiorenal protection trials underway, sodium-related physiological effects of SGLT2 inhibitors and clinical correlates of natriuresis, such as the impact on blood pressure, heart failure, kidney protection, and mortality, will be a major management focus.

Effects of subcutaneous, low-dose glucagon on insulin-induced mild hypoglycaemia in patients with insulin pump treated type 1 diabetes

AIM

To investigate the dose-response relationship of subcutaneous (s.c.) glucagon administration on plasma glucose and on counter-regulatory hormone responses during s.c. insulin-induced mild hypoglycaemia in patients with type 1 diabetes treated with insulin pumps.

METHODS

Eight insulin pump-treated patients completed a blinded, randomized, placebo-controlled study. Hypoglycaemia was induced in the fasting state by an s.c. insulin bolus and, when plasma glucose reached 3.4 mmol/l [95% confidence interval (CI) 3.2-3.5], an s.c. bolus of either 100, 200, 300 µg glucagon or saline was administered. Plasma glucose, counter-regulatory hormones, haemodynamic variables and side effects were measured throughout each study day. Peak plasma glucose level was the primary endpoint.

RESULTS

Plasma glucose level increased significantly by a mean (95% CI) of 2.3 (1.7-3.0), 4.2 (3.5-4.8) and 5.0 (4.3-5.6) mmol/l to 6.1 (4.9-7.4), 7.9 (6.4-9.3) and 8.7 (7.8-9.5) vs 3.6 (3.4-3.9) mmol/l (p < 0.001) after the three different glucagon doses as compared with saline, and the increase was neither correlated with weight nor insulin levels. Area under the plasma glucose curve, peak plasma glucose, time to peak plasma glucose and duration of plasma glucose level above baseline were significantly enhanced with increasing glucagon doses; however, these were not significantly different between 200 and 300 µg glucagon. Free fatty acids and heart rates were significantly lower initially after glucagon than after saline injection. Other haemodynamic variables, counter-regulatory hormones and side effects did not differ between interventions.

CONCLUSIONS

An s.c. low-dose glucagon bolus effectively restores plasma glucose after insulin overdosing. Further research is needed to investigate whether low-dose glucagon may be an alternative treatment to oral carbohydrate intake for mild hypoglycaemia in patients with type 1 diabetes.

Addition of glucagon to adrenaline improves hemodynamics in a porcine model of prolonged ventricular fibrillation

OBJECTIVE

Cardiac arrest is a daunting medical emergency. The aim of the present study was to assess whether the combination of adrenaline and glucagon would improve initial resuscitation success, 48-hour survival, and neurologic outcome compared with adrenaline alone in a porcine model of ventricular fibrillation.

METHODS

Ventricular fibrillation was induced in 20 healthy Landrace/Large White piglets, which were subsequently left untreated for 8 minutes. The animals were randomized to receive adrenaline alone (n = 10, group C) and adrenaline plus glucagon (n = 10, group G). All animals were resuscitated according to the 2010 European Resuscitation Council guidelines. Hemodynamic variables were measured before arrest, during arrest and resuscitation, and during the first 60 minutes after return of spontaneous circulation. Survival and a neurologic alertness score were measured at 48 hours after return of spontaneous circulation.

RESULTS

Return of spontaneous circulation was achieved in 8 animals (80%) from group C and 10 animals (100%) from group G (P = .198). A significant gradual increase in coronary perfusion pressure and diastolic aortic pressure over time, which started 1 minute after the onset of cardiopulmonary resuscitation, was observed. Three animals (30%) from group C and 9 animals (90%) from group G survived after 48 hours (P = .006), whereas neurologic examination was significantly better in the animals of group G (P < .001).

CONCLUSIONS

In this porcine model of prolonged ventricular fibrillation, the addition of glucagon to adrenaline improves hemodynamics during resuscitation and early postresuscitation period and may increase survival.

Glucagon therapy in the treatment of symptomatic bradycardia

Symptomatic bradycardia is commonly seen in the emergency department. Effective drug therapy for this clinical scenario is limited. Although glucagon has been used in no clinical trial in this setting, its cardiac activity may prove useful, particularly in the setting of beta-adrenergic blockade. We report a case series comprising three patients taking maintenance beta-blocker therapy who presented to the ED with symptomatic bradycardia and hypotension and in whom glucagon therapy obviated the need for further treatment. Further study is warranted to evaluate and define the role of glucagon in the treatment of symptomatic bradycardia.

Mediators, cytokines, and growth factors in liver-lung interactions

Multiple mediators have been implicated in the interactions between the liver and the lungs in various disease states. The best characterized mediator of liver-lung interaction is alpha 1-antitrypsin. Several cytokines and mediators may be involved in the pathogenesis of the hepatopulmonary syndrome and in the cytokine cascades that are activated in systemic inflammatory states such as acute respiratory distress syndrome. Hepatocyte growth factor or scatter factor is a recently described peptide with a broad range of biologic effects that may mediate lung-liver interactions.

Inotropic drugs in acute circulatory failure

The use of inotropic drugs in patients requiring acute circulatory support is reviewed. A knowledge of their various peripheral effects is essential if the appropriate drug is to be used. The place or pressor amines, digitalis, salbutamol and glucagon in the treatment of patients with poor tissue perfusion is limited. Of the catecholamines, adrenaline causes excessive renal vasoconstriction and peripheral gangrene, noradrenaline increase myocardial work and diminishes peripheral perfusion and isoprenaline distributes blood away from the vital organs, namely: brain, kidneys, heart and mesentery. Dopamine is a useful agent as it enhances renal blood flow in low doses and is not excessively chronotropic. Dobutamine has not yet been shown to have significant advantages over other inotropes and requires further examination.

Influence of glucagon on the cardiovascular effects of procainamide

Effects of glucagon on procainamide-induced cardiac toxicity were studied in anesthetized dogs. Procainamide in doses of 50 and 100 mg/kg produced dose-dependent decreases in the blood pressure, cardiac output, left ventricular work index, and left ventricular systolic pressure; and increases in the left ventricular end diastolic and right atrial pressure, and total systemic vascular resistance. Glucagon antagonized most of the effects of procainamide on the cardiovascular system. Glucagon may be effective in antagonizing procainamide-induced cardiac toxicity.

Haemodynamic effects of glucagon after mitral valve replacement

We have studied six patients who had undergone mitral valve replacement. Estimations of cardiac output and of pulmonary vascular resistance were made, beginning two hours after the finish of the operation. Glucagon, 10 mg, was given intravenously, and cardiac output and pulmonary vascular resistance were measured 5 minutes and 30 minutes later. In all six cases there was a significant decrease in pulmonary vascular resistance and this occurred whether the resistance was slightly, moderately or greatly elevated. There was a highly significant increase in cardiac output in all cases.

Use of drugs in cardiogenic shock due to acute myocardial infarction

As a plan of therapy for shock associated with acute myocardial infarction in a general hospital and assuming that septic and hemorrhagic shock has been eliminated as diagnostic possibilities we would suggest the following:

(1) Pain should be relieved using morphine or pentazocine, and atropine if brady-cardia is present. Oxygen by mask should be administered to bring the arterial oxygen tension to about 100 mm Hg. The airway must be examined and, if air exchange is poor and the arterial oxygen very low or carbon dioxide high, respiratory assistance and occasionally intubation may be required.

(2) Blood pressure must be stabilized at an adequate level for perfusion of vital organs, or progression may be so rapid that death will occur before proper evaluation can be made and more rational therapy started. For this purpose we would start a norepinephrine infusion at a rate just sufficient to keep the systolic blood pressure near 100 mm Hg. If the shock syndrome is present but arterial pressure is normal or only slightly reduced, we would eliminate this step in therapy.

(3) Arrhythmias or heart block should be corrected by methods discussed elsewhere in this symposium.

(4) A venous catheter should be inserted so that the catheter tip is just within the thorax. If the central venous pressure (CVP) is below 10 cm H 2 O we would begin a regimen of plasma volume expansion giving 100 cc of 40 dextran over a period of 10 min, waiting 10 min, and if the CVP has not risen 1 cm H 2 O repeat the process until shock is relieved, the CVP continues to increase or is above 15 cm H 2 O, or 1000 cc of 40 dextran has been given. If the patient accepts more than 1000 cc of fluid in this manner without elevating the CVP it is most likely that some other major process causing fluid loss is complicating the myocardial infarction.

(5) If or when CVP is above 10 cm H 2 O, and if the patient remains in shock and is hypotensive, we would add norepinephrine infusion at a rate just sufficient to bring the systolic pressure between 100 and 110 mm Hg. If this cannot be accomplished with small amounts of norepinephrine then intraarterial pressure must be measured since the discrepancy between the cuff pressure and actual pressure may be increasing with further pressor infusion.

(6) If the patient is normotensive and has a CVP above 10 cm H 2 O but manifests the shock syndrome, an isoproterenol infusion should be instituted, but to use this regimen one must be able to measure intraarterial pressure. If CVP falls, simultaneous plasma volume expansion may be necessary. If arterial pressure begins to fall, norepinephrine should be substituted. We would use dopamine first in this particular situation, but this agent is not as yet generally available.

(7) With the CVP elevated and blood pressure stable, arterial oxygenation established, and arrhythmias corrected, if the patient is still in a low cardiac output state with continued oliguria and poor tissue perfusion, digitalization with about half to two thirds the normal digitalizing dose should be undertaken.

(8) If a further inotropic response is needed glucagon may be added at this point. With an initial bolus injection efficacy should be established and if found helpful a constant infusion should follow. Aminophylline should be given simultaneously to potentiate the action of glucagon.

(9) The patient who at this point remains oliguric and with a small pulse pressure may be benefited by cautious vasodilation with chlorpromazine or phentolamine and simultaneous further plasma volume expansion.

(10) A patient who remains pressor-dependent or responds poorly to pressors will probably need circulatory assistance. However, unless some definitive measure can be undertaken to restore or replace nonfunctioning myocardium this too will be of little benefit.

(11) A patient who stabilizes well but experiences a fall in blood pressure as the pressor infusion is being discontinued should have plasma volume expansion as the pressor infusion is decreased. The physician must resist the temptation to restart the infusion as the pressure falls, unless the shock syndrome accompanies the hypotension.

Effect of glucagon on ventricular arrhythmias after coronary artery occlusion and on ventricular automaticity in the dog

1. In anaesthetized dogs, glucagon (100 mug/kg i.v.), caused a significant increase in heart rate and decrease in mean arterial blood pressure. Ventricular automaticity, as determined by the time to the onset of first vagal escape beat and the number of such indioventricular beats during the 30 s period of vagal stimulation, was not significantly altered.2. In unanaesthetized dogs with ventricular arrhythmias produced by two-stage ligation of the anterior descending branch of the left coronary artery, glucagon (30 and 100 mug/kg i.v.), restored normal sinus rhythm in a few animals. In the remaining dogs, there was a significant reduction in the ventricular ectopic activity.3. The significant positive chronotropic response to glucagon elicited in anaesthetized animals was not observed in conscious dogs whose coronary arteries had been ligated.4. These findings enhance the potential usefulness of glucagon in the treatment of acute myocardial infarction, which may often be associated with disturbances of ventricular rhythm.5. In the light of observations made by other workers, it is suggested that the antiarrhythmic effect of glucagon may be due to movement of potassium ions into the cardiac cell.

Glucagon in prevention and abolition of ouabain-induced ventricular tachycardia in normokalemic and hypokalemic dogs

A recent study suggested that glucagon has antiarrhythmic properties in addition to its positive inotropic effect. The present study was designed to evaluate the efficacy of glucagon in preventing and converting ouabain-induced ventricular tachycardia (VT) in normokalemic and hypokalemic dogs. Paired studies were made in ten normokalemic dogs and in eight dogs rendered hypokalemic by diet and hydrochlorothiazide. All dogs were pretreated with glucagon, and the amount of ouabain required to produce VT was measured. Each dog served as its own control in a second study in which normal saline was substituted for glucagon. When VT was produced during the control study, the response to a bolus injection of glucagon was evaluated. (1) Pretreatment with glucagon delayed the appearance of VT in hypokalemic dogs but not in normokalemic dogs. (2) Glucagon, by bolus injection, converted VT to sinus rhythm in 78% of the normokalemic dogs and in 100% of the hypokalemic dogs. (3) The mechanisms by which glucagon exerts its antiarrhythmic effect are not clearly defined.

Hemodynamic evaluation of glucagon in symptomatic heart disease

Glucagon was administered as a 5 mg intravenous bolus in 26 patients. Studies were performed in the Cardiac Catheterization Laboratory and soon after cardiac surgery. When the response to glucagon was compared on the basis of functional classification, patients with class I and II heart disease had a significantly greater increase in cardiac output (+700 ml) than patients with class III and IV heart disease (+100 ml). Isoproterenol augmented cardiac output by a significantly greater amount (+2500 ml) than glucagon in eight of these patients. It is concluded that glucagon is a less effective inotropic agent than isoproterenol and that glucagon's usefulness is limited in patients with advanced symptomatic heart disease.