Effects of glucagon on myocardial metabolism in patients with and without coronary artery disease

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.

EMPA-REG and Other Cardiovascular Outcome Trials of Glucose-lowering Agents: Implications for Future Treatment Strategies in Type 2 Diabetes Mellitus

During the last decade, the armamentarium for glucose-lowering drugs has increased enormously by the development of DPP-4 inhibitors, GLP-1 receptor agonists and SGLT2 inhibitors, allowing individualization of antidiabetic therapy for patients with type 2 diabetes (T2DM). Some combinations can now be used without an increased risk for severe hypoglycemia and weight gain. Following a request of the US Food and Drug Administration, many large cardiovascular (CV) outcome studies have been performed in patients with longstanding disease and established CV disease. In the majority of CV outcome studies, CV risk factors were well controlled and a high number of patients were already treated with ACE inhibitors/angiotensin receptor blockers, statins and antiplatelet drugs. Most studies with insulin glargine and newer glucose-lowering drugs (saxagliptin, alogliptin, sitagliptin, lixisenatide) demonstrated safety of newer glucose-lowering agents but did not show superiority in the CV outcomes compared with placebo. By contrast, in the EMPA-REG OUTCOME (Empagliflozin Cardiovascular Outcome Event Trial in Type 2 Diabetes Mellitus Patients) study, CV death, all-cause mortality, and hospitalization for heart failure were significantly decreased when empagliflozin was added instead of placebo to therapy for patients with high CV risk and T2DM already well treated with statins, glucose-lowering drugs, and blood pressure-lowering drugs as well as antiplatelet agents. In addition, renal endpoints including endstage renal disease were also significantly reduced when empagliflozin was added instead of placebo. Interestingly, the reduction of these clinically relevant end points was observed after a few months, making antiatherogenic effects an unlikely cause. The fact that the incidence of myocardial infarction (MI) and stroke were not reduced is in line with the hypothesis that hemodynamic factors in particular have contributed to the impressive improvement of the prognosis. To reduce the CV burden of patients with T2DM, drugs influencing factors involved in atherogenesis (eg, insulin resistance, chronic inflammation, increase of HDL, prothrombotic state) are more promising. The recent IRIS (Insulin Resistance Intervention after Stroke) study documented a significant reduction in stroke and MI when pioglitazone instead of placebo was given to nondiabetic patients presenting with both stroke/transient ischemic attack and insulin resistance, confirming results from the PROactive (Prospective Pioglitazone Clinical Trial in Macrovascular Events) study in patients with T2DM. Based on these new data, we suggest that the addition of both empagliflozin and pioglitazone to metformin might be the relative best option to reduce the high CV morbidity and mortality of patients with T2DM and already established CV complications. The very recent announcement that the CV outcome study with liraglutide (LEADER) also demonstrated a significant reduction of the composite endpoint (cardiovascular death, non-fatal myocardial infarction or non-fatal stroke) gives new hope for further beneficial treatment options for T2DM patients with established CVD.

Effects of a low cholesterol eating plan on plasma lipids: results of a three-year community study

In an attempt to demonstrate whether individuals with average plasma lipids would accept a diet low in saturated fat and cholesterol, members of a community organization were taught the HELP Your Heart Eating Plan. Results of 282 individuals suggest that reduced dietary cholesterol from selected foods could be sustained for up to 36 months. While both plasma cholesterol and triglycerides fell during a year of instruction, both rose to above initial values by 36 months. Overall, the results suggest that adults may be willing to accept a new style of eating temporarily but are not committed to making permanent dietary changes.

[The effect of intravenous infusion of glucagon on the contractility of the left ventricular myocardum in man (author's transl)]

In the cases of 10 cardially healthy humans and 5 patients with heart disease, the left ventricular pressure as well as different parameters of contractility - deduced from the pressure curve and its first derivative - were determined by a catheter-tip manometer (Statham SF - 1). In particular the following values were concerned: dP/dtmax,-dP/dtmaxDP, the maximal calculated shortening velocity of the contractile elements according to the 2-component heart muscle model (VCEmaxTP) as well as with the Maxwell model (VCEmaxDP) and finally the (extrapolated) maximum shortening velocity (Vmax) under a fictive zero load. The examinations were carried out before and during a 10-minute infusion of 60 mg/kg glucagon and 10 minutes after completing the infusion. Besides glucagon also digoxin, etilefrin-HCl-1) and orciprenaline-2) were delivered and the same measurements were performed as with glucagon. A definite statement about the priority of any one of the named indices of contractility is rendered more difficult, because the enddiastolic pressure does not change substantially with glucagon. An unequivocal demarcation of frequency and pressure effects and of inotropic mechanisms as just as impossible, because, with the exception of VmaxDP, all parameters react quantitatively and qualitatively in an equal manner. On the basis of VmaxTP the result of glucagon is only a slight increase in the myocardial contractile capability, which would hardley suffice for the treatment of patients, who do not respond to digitalis. The decline of VmaxDP under glucagon cannot be explained. Under digitalis, etilefrin and orciprenaline, a similar dissociation of values for the maximum shortening velocity according to the 2- or 3-component-model of the heart muscle cannot be demonstrated.

[Myocardial metabolism under intravenous infusion of glucagon (author's transl)]

In 7 healthy-hearted probands the arterial-coronary-venous oxygen difference for glucose, K+, lactate, pO2, pCO2 and pH during a glucagon infusion was determined and compared with the values before and 10 minutes after infusion. Contradictory to the unchanged myocardial lactate extraction and the positively or negatively influenced K+-uptake recorded in the literature, in this contingent there was a statistically significant myocardial lactate production and an unchanged potassium uptake. The respiratory quotient of the heart increased. These changes are regarded as the result of a direct hormonal influence on the myocardial metabolism and have nothing to do with the change of an aerobic into an anaerobic metabolic state.