The actions of insulin on cardiac contractility

Propofol (Diprivan®) and Intralipid® exacerbate insulin resistance in type-2 diabetic hearts by impairing GLUT4 trafficking

BACKGROUND

The IV anesthetic, propofol, when administered as fat emulsion-based formulation (Diprivan) promotes insulin resistance, but the direct effects of propofol and its solvent, Intralipid, on cardiac insulin resistance are unknown.

METHODS

Hearts of healthy and type-2 diabetic rats (generated by fructose feeding) were aerobically perfused for 60 minutes with 10 μM propofol in the formulation of Diprivan or an equivalent concentration of its solvent Intralipid (25 μM) ± insulin (100 mU•L). Glucose uptake, glycolysis, and glycogen metabolism were measured using [H]glucose. Activation of Akt, GSK3β, AMPK, ERK1/2, p38MAPK, S6K1, JNK, protein kinase Cθ (PKCθ), and protein kinase CCβII (PKCβII) was determined using immunoblotting. GLUT4 trafficking and phosphorylations of insulin receptor substrate-1 (IRS-1) at Ser307(h312), Ser1100(h1101), and Tyr608(hTyr612) were measured. Mass spectrometry was used to determine acylcarnitines, phospholipids, and sphingolipids.

RESULTS

Diprivan and Intralipid reduced insulin-induced glucose uptake and redirected glucose to glycogen stores in diabetic hearts. Reduced glucose uptake was accompanied by lower GLUT4 trafficking to the sarcolemma. Diprivan and Intralipid inactivated GSK3β but activated AMPK and ERK1/2 in diabetic hearts. Only Diprivan increased phosphorylation of Akt(Ser473/Thr308) and translocated PKCθ and PKCβII to the sarcolemma in healthy hearts, whereas it activated S6K1 and p38MAPK and translocated PKCβII in diabetic hearts. Furthermore, only Diprivan phosphorylated IRS-1 at Ser1100(h1101) in healthy and diabetic hearts. JNK expression, phosphorylation of Ser307(h312) of IRS-1, and PKCθ expression and translocation were increased, whereas GLUT4 expression was reduced in insulin-treated diabetic hearts. Phosphatidylglycerol, phosphatidylethanolamine, and C18-sphingolipids accumulated in Diprivan-perfused and Intralipid-perfused diabetic hearts.

CONCLUSIONS

Propofol and Intralipid promote insulin resistance predominantly in type-2 diabetic hearts.

Management of calcium channel blocker overdoses

Calcium channel blockers (CCBs) are some of the most commonly used medications in clinical practice to treat hypertension, angina, cardiac arrhythmias, and some cases of heart failure. Recent data show that CCBs are the most common of the cardiovascular medications noted in intentional or unintentional overdoses.(1) Novel treatment approaches in the form of glucagon, high-dose insulin therapy, and intravenous lipid emulsion therapies have been tried and have been successful. However, the evidence for these are limited to case reports and case series. We take this opportunity to review the various treatment options in the management of CCB overdoses with a special focus on high-dose insulin therapy as the emerging choice for initial therapy in severe overdoses.

Toxicologic emergencies in the intensive care unit: management using reversal agents and antidotes

PURPOSE

To review the most common drugs implicated in overdoses admitted to the intensive care unit focusing on antidotes and reversal agents used in their management.

SUMMARY

Poisonings and overdoses due to pharmaceutical agents result in more than 100 000 critical care unit admissions each year. Ingestion of toxic alcohols, calcium channel blockers, beta-adrenergic antagonists, benzodiazepines, opioids, acetaminophen, tricyclic antidepressants, and salicylates are associated with a high rate of morbidity and mortality. Reviewing the mechanism of toxicity due to specific agents along with the mechanism of action, dosing, and adverse effects of appropriate antidotes is important for the successful management of these patients within the critical care unit.

CONCLUSION

Understanding the most prevalent overdoses and their management using reversal agents and antidotes is essential to the overall treatment of these critically ill patients.

High dose insulin therapy, an evidence based approach to beta blocker/calcium channel blocker toxicity

Poison-induced cardiogenic shock (PICS) as a result of beta-blocker (β-blocker) or calcium channel blocker (CCB) overdose is a common and potentially life-threatening condition. Conventional therapies, including fluid resuscitation, atropine, cardiac pacing, calcium, glucagon, and vasopressors often fail to improve hemodynamic status. High-dose insulin (HDI) is an emerging therapeutic modality for PICS. In this article, we discuss the existing literature and highlight the therapeutic success and potential of HDI. Based on the current literature, which is limited primarily to case series and animal models, the authors conclude that HDI can be effective in restoring hemodynamic stability, and recommend considering its use in patients with PICS that is not responsive to traditional therapies. Future studies should be undertaken to determine the optimal dose and duration of therapy for HDI in PICS.

Cardioprotective effect of glucose-insulin on acute propafenone toxicity in rat

OBJECTIVE

We recently observed a case of propafenone self-poisoning in which the patient was initially unresponsive to conventional therapies such as sodium bicarbonate, dopamine, and norepinephrine but recovered with intravenous glucose-insulin infusion. We raised the hypothesis that insulin may have a cardioprotective effect in acute propafenone toxicity.

METHODS

We evaluated the effect of glucose-insulin infusion on mortality and electrocardiographic abnormalities during acute propafenone toxicity in rats. After measurements of basal mean arterial pressure, heart rate, PR interval, and QRS duration, rats received intravenous propafenone (36 mg/kg per hour) for 12 minutes. Two minutes after the induction of toxicity, the rats (n=10 per group) received either normal saline solution (NSS) or insulin with glucose. Rats in the insulin-treated (Insulin group) and the NSS-treated (NSS group) groups received an intravenous infusion of 36 mg/kg per hour of propafenone until death occurred. Rats receiving only NSS intravenously without propafenone toxicity served as control (Control group, n=10).

RESULTS

Insulin treatment improved survival and delayed the hemodynamic and electrocardiographic consequences of propafenone toxicity. Survival was significantly greater in the insulin group than that in the NSS group (P<.001). Insulin prevented the decline in mean arterial pressure and heart rate (P<.05). Insulin also prevented the increase of the PR interval and the QRS duration (P<.05).

CONCLUSION

Glucose-insulin infusion delayed the abnormalities in cardiac conduction and improved rat survival after acute propafenone toxicity. These results suggest a cardioprotective effect of glucose-insulin in acute propafenone toxicity.

Massive calcium channel blocker overdose: intravenous insulin and glucose as a therapy

We describe a case of massive overdosage with cardiac medications that proved resistant to conventional support, including fluid replacement, inotropes, mechanical ventilation, cardiac pacing and haemofiltration. The use of a high-dose insulin and glucose infusion proved to be beneficial in the acute management although the patient has been left with significant impairment of cardiac function.

Antidotes for toxicological emergencies: a practical review

PURPOSE

Appropriate therapies for commonly encountered poisonings, medication overdoses, and other toxicological emergencies are reviewed, with discussion of pharmacists' role in ensuring their ready availability and proper use.

SUMMARY

Poisoning is the second leading cause of injury-related morbidity and mortality in the United States, with more than 2.4 million toxic exposures reported each year. Recently published national consensus guidelines recommend that hospitals providing emergency care routinely stock 24 antidotes for a wide range of toxicities, including toxic-alcohol poisoning, exposure to cyanide and other industrial agents, and intentional or unintentional overdoses of prescription medications (e.g., calcium-channel blockers, β-blockers, digoxin, isoniazid). Pharmacists can help reduce morbidity and mortality due to poisonings and overdoses by (1) recognizing the signs and symptoms of various types of toxic exposure, (2) guiding emergency room staff on the appropriate use of antidotes and supportive therapies, (3) helping to ensure appropriate monitoring of patients for antidote response and adverse effects, and (4) managing the procurement and stocking of antidotes to ensure their timely availability.

CONCLUSION

Pharmacists can play a key role in reducing poisoning and overdose injuries and deaths by assisting in the early recognition of toxic exposures and guiding emergency personnel on the proper storage, selection, and use of antidotal therapies.

Insulin versus Lipid Emulsion in a Rabbit Model of Severe Propranolol Toxicity: A Pilot Study

Background and objective. Beta-blocker overdose may result in intractable cardiovascular collapse despite conventional antidotal treatments. High dose insulin/glucose (ING), and more recently intravenous lipid emulsion (ILE), have been proposed as potentially beneficial therapies in beta blocker intoxication. We compare efficacy of the novel antidotes ING, with ILE, in a rabbit model of combined enteric/intravenous propranolol toxicity. Methods. Sedated, mechanically ventilated and invasively monitored New Zealand White rabbits underwent mini-laparotomy and enterostomy formation with 40 mg/kg propranolol instilled into the proximal small bowel. At 30 minutes propranolol infusion was commenced at 4 mg/kg/hr and continued to a target mean arterial pressure (MAP) of 50% baseline MAP. Animals were resuscitated with insulin at 3 U/kg plus 0.5 g/kg glucose (ING group), or 10 mL/kg 20% Intralipid (ILE group). Results. Rate pressure product (RPP; RPP = heart rate × mean arterial pressure) was greatest in the ING group at 60 minutes (P < .05). A trend toward greater heart rate was observed in the ING group (P = .06). No difference was observed in survival between groups (4/5 ING versus 2/5 ILE; P = .524). Conclusions. High dose insulin resulted in greater rate pressure product compared with lipid emulsion in this rabbit model of severe enteric/intravenous propranolol toxicity.

Severe amlodipine intoxication treated by hyperinsulinemia euglycemia therapy

The objective of this study was to report a use of hyperinsulinemia euglycemia therapy in severe amlodipine intoxication. Intoxication with 420 mg of amlodipine caused severe hypotension in a 20-year-old female patient. The patient was initially treated with fluids, calcium gluconate, and epinephrine without effect. She was then given hyperinsulinemia euglycemia therapy. We observed a rise in blood pressure (BP) approximately 30 min after insulin was given and the BP was subsequently responsive to epinephrine. The patient was weaned from pressors 5 h after insulin therapy. The trachea was extubated 24 h after ingesting amlodipine, and the patient was transferred for psychiatric treatment 3 days later. This possible positive inotropic effect of insulin therapy in patients with calcium channel blocker intoxication supports previous findings. It is suggested that hyperinsulinemia euglycemia therapy may be considered as a first-line therapy in amlodipine intoxication.

Hyperinsulinemic Euglycemia Therapy for Verapamil Poisoning: A Review

Treatment of patients with verapamil overdose remains challenging. Traditional decontamination and supportive measures with intravenous calcium and vasopressors are the mainstays in initial care. Recently, the successful use of rescue hyperinsulinemic euglycemia therapy has been described in multiple cases. Treatment resulted in improved hemodynamic parameters and increased metabolic efficiency in patients with a low-output, myocardial shock state. Information on clinical use of hyperinsulinemic euglycemia therapy in humans is limited to case reports and small case series; no controlled clinical trials have been done. Hyperinsulinemic euglycemia therapy should be considered for patients with calcium channel blocker overdose who do not respond to initial supportive therapy.

Management of beta-adrenergic blocker and calcium channel antagonist toxicity

State-of-the-art therapy for beta-adrenergic receptor blocker and calcium channel antagonist toxicity is reviewed in the light of new insights into drug-induced shock. A brief discussion of pathophysiology, including cardiac, hemodynamic, and metabolic effects of cardiac drug toxicity, provides a foundation for understanding the basis of therapy. The major focus of this review is a critical evaluation of antidotal use of calcium, glucagon, catecholamines, insulin-euglycemia, and other novel therapies based on investigational studies and cumulative clinical experience.

Myocardial insulin action and the contribution of insulin resistance to the pathogenesis of diabetic cardiomyopathy

Heart disease is the leading cause of death in patients with insulin resistance and type 2 diabetes (DM2). Even in the absence of coronary artery disease and hypertension, functional and structural abnormalities exist in patients with well-controlled and uncomplicated DM2. These derangements are collectively designated by the term diabetic cardiomyopathy (DCM). Changes in myocardial energy metabolism, due to altered substrate supply and utilization, largely underlie the development of DCM. Insulin is an important regulator of myocardial substrate metabolism, but also exerts regulatory effects on intracellular Ca2+ handling and cell survival. The current paper reviews the multiple functional and molecular effects of insulin on the heart, all of which ultimately seem to be cardioprotective both under normal conditions and under ischemia. In particular, the dismal consequences of myocardial insulin resistance contributing to the development of DCM will be discussed.

Metabolic therapy for patients with diabetes mellitus and coronary artery disease

Patients with diabetes mellitus and ischemic heart disease more frequently develop heart failure and have a greater amount of myocardial ischemia, often silent, compared with patients without diabetes. Furthermore, patients with coronary artery disease (CAD) and diabetes or insulin resistance have altered myocardial metabolism and accelerated and diffuse atherogenesis with involvement of distal coronary segments that causes chronic hypoperfusion and hibernation. Therefore, in patients with diabetes and CAD, the ischemic metabolic changes are heightened by the metabolic changes in patients with diabetes. An important metabolic alteration in patients with diabetes is the increase in free fatty acid (FFA) concentrations and the increased skeletal muscle and myocardial FFA uptake and oxidation. The increased uptake and utilization of FFA and the reduced utilization of glucose as a source of energy during stress and ischemia contribute to the increased susceptibility of diabetic hearts to myocardial ischemia and to a greater decrease of myocardial performance for a given amount of ischemia compared with nondiabetic hearts. A therapeutic approach aimed at an improvement in cardiac metabolism through manipulations of the use of metabolic substrates should result in an improvement in myocardial ischemia and left ventricular (LV) function. The inhibition of FFA oxidation with trimetazidine improves cardiac metabolism at rest, increases cardiac resistance to ischemia, and therefore reduces the decrease of LV function caused by chronic hypoperfusion and repetitive episodes of myocardial ischemia in patients with and without diabetes. Thus, modulation of myocardial FFA metabolism should be the key target for metabolic interventions in patients with CAD with and without diabetes. In patients with diabetes, the effects of modulation of FFA metabolism should be even greater compared with those observed in patients without diabetes. Because of its effect on cardiac metabolism at rest and its effects on myocardial ischemia and LV function, trimetazidine should always be considered for the treatment of patients with diabetes with CAD with or without LV dysfunction.

Metabolic therapy for the diabetic patients with ischaemic heart disease

Diabetic patients with ischaemic heart disease have a greater amount of myocardial ischaemia, often silent, and an increased incidence of heart failure compared to nondiabetic patients. This is the result of altered myocardial metabolism and accelerated atherogenesis with involvement of peripheral coronary segments causing chronic hypoperfusion and diffuse hybernation. In patients with diabetes mellitus and myocardial ischaemia, the metabolic changes occurring as a consequence of the mismatch between blood supply and cardiac metabolic requirements are heightened by the diabetic metabolic changes. An important metabolic alteration of diabetes is the increase in free fatty acid concentrations and increased muscular and myocardial free fatty acid uptake and oxidation. This increased uptake and utilization of free fatty acid during stress and ischaemia is responsible for the increased susceptibility of the diabetic heart to myocardial ischaemia and to a greater decrease of myocardial performance for a given amount of ischaemia compared to nondiabetic hearts. Given the metabolic alterations of the diabetic heart at rest and during episodes of myocardial ischaemia, a therapeutic approach aimed at an improvement of cardiac metabolism through manipulations of the utilization of metabolic substrates should result in an improvement of myocardial ischaemia and of left ventricular function. Modulation of myocardial free fatty acid metabolism should be the key target for metabolic interventions in patients with coronary artery disease with and without diabetes. In diabetic patients, the effects of modulation of free fatty acid metabolism should be even greater than those observed in patients without diabetes. The inhibition of FFA oxidation with trimetazidine improves cardiac metabolism at rest, decreases cardiac ischaemia and therefore prevents the decline of left ventricular function due to chronic hypoperfusion and repetitive episodes of myocardial ischaemia. Because of its effect on cardiac metabolism at rest, its effects on myocardial ischaemia and left ventricular function trimetazidine should always be considered for the treatment of diabetic patients with ischaemic heart disease with or without left ventricular dysfunction.

Metaraminol (Aramine) in the management of a significant amlodipine overdose

OBJECTIVE

To report a patient with a significant amlodipine self-poisoning who failed to clinically respond to conventional treatment and was managed with metaraminol (Aramine).

PATIENT

A 43-year old male presenting after ingestion of 560 mg amlodipine, who failed to respond clinically to treatment with fluid resuscitation, calcium salts, glucagon and norepinephrine/epinephrine inotropic support.

MAIN RESULTS

Following a loading bolus of 2 mg and intravenous infusion (83 microg/min) of metaraminol (Aramine) there was improvement in his blood pressure, cardiac output and urine output.

CONCLUSIONS

This is the first case report of the beneficial use of metaraminol (aramine) in the management of significant amlodipine poisoning unresponsive to conventional therapy.

The role of insulin and glucose (hyperinsulinaemia/euglycaemia) therapy in acute calcium channel antagonist and beta-blocker poisoning

The inotropic effect of insulin has been long established. High-dose (0.5-1 IU/kg/hour) insulin, in combination with a glucose infusion to maintain euglycaemia (hyperinsulinaemia/euglycaemia therapy), has been proposed as a treatment for calcium channel antagonist (CCA) and beta-adrenoceptor antagonist (beta-blocker) poisonings. However, the basis for its beneficial effect is poorly understood.CCAs inhibit insulin secretion, resulting in hyperglycaemia and alteration of myocardial fatty acid oxidation. Similarly, blockade of beta(2)-adrenoceptors in beta-blocker poisoning results in impaired lipolysis, glycogenolysis and insulin release. Insulin administration switches cell metabolism from fatty acids to carbohydrates and restores calcium fluxes, resulting in improvement in cardiac contractility. Experimental studies in verapamil poisoning have shown that high-dose insulin significantly improved survival compared with calcium salts, epinephrine or glucagon. In several life-threatening poisonings in humans, the administration of high-dose insulin produced cardiovascular stabilisation, decreased the catecholamine vasopressor infusion rate and improved the survival rate. In a canine model of propranolol intoxication, high-dose insulin provided a sustained increase in systemic blood pressure, cardiac performance and survival rate compared with glucagon or epinephrine. In contrast, insulin had no effect on heart rate and electrical conduction in the myocardium. In another study, high-dose insulin reversed the negative inotropic effect of propranolol to 80% of control function and normalised heart rate. High-dose insulin produced a significant decrease in the left ventricular end-diastolic pressure and a significant increase in the stroke volume and cardiac output. The vasodilator effect was explained by an enhanced cardiac output leading to withdrawal of compensatory vasoconstriction. No clinical studies have yet been performed. Although not effective in all cases, we recommend hyperinsulinaemia/euglycaemia therapy in patients with severe CCA poisoning who present with hypotension and respond poorly to fluid, calcium salts, glucagon and catecholamine infusion. However, careful monitoring of blood glucose and serum potassium concentrations is required to avoid serious adverse effects. More clinical data are needed before this therapy can be recommended in beta-blocker poisoning. There is a need for large prospective clinical trials to confirm safety and efficacy of hyperinsulinaemia/euglycaemia therapy in both CCA and beta-blocker poisoning.

High-Dose Insulin Therapy for Calcium-Channel Blocker Overdose

OBJECTIVE:

To evaluate the evidence for using high-dose insulin therapy with supplemental dextrose and potassium in calcium-channel blocker (CCB) overdose.

DATA SOURCES:

Evidence of efficacy for high-dose insulin therapy with supplemental dextrose and potassium was sought by performing a search of MEDLINE and Toxline between 1966 and July 2004 using combinations of the terms calcium-channel blocker, overdose, poisoning, antidote, and insulin. Abstracts from the North American Congress of Clinical Toxicology for the years 1996–2003 were also reviewed.

STUDY SELECTION AND DATA EXTRACTION:

Identified articles, including animal studies, case reports, and case series, were evaluated for this review. No clinical trials were available.

DATA SYNTHESIS:

Animal models of CCB overdose demonstrate that high-dose insulin with supplemental dextrose and potassium was a more effective therapy than calcium, glucagon, or catecholamines. High-dose insulin appears to enhance cardiac carbohydrate metabolism and has direct inotropic effects. Published clinical experience is limited to 13 case reports where insulin was used after other therapies were failing; 12 of these patients survived. High-dose insulin therapy was beneficial for CCB-induced hypotension, hyperglycemia, and metabolic acidosis. Bradycardia and heart block resolved in some patients, but persisted in others.

CONCLUSIONS:

Based on animal data and limited human experience, as well as the inadequacies of available alternatives for patients with significant poisoning, high-dose insulin therapy warrants further study and judicious use in patients with life-threatening CCB poisoning.

Reversal of Glucose-Insulin-Potassium-Induced Hyperglycemia by Aggressive Insulin Treatment in Postoperative Heart Failure

Metabolic support with glucose-insulin-potassium (GIK) significantly reduces the morbidity and mortality of patients in cardiogenic shock after hypothermic ischemic arrest for aortocoronary bypass surgery. However, a small subset of these patients develops postoperative insulin resistance regardless of their preoperative diabetic status. Whether GIK directly contributes to higher mortality in these patients is unknown. We reviewed the records of 322 patients whose treatment for postoperative cardiogenic shock included GIK. Ten patients (3%) had postoperative hyperglycemia (serum glucose > or =250 mg/dl or 13.9 mmol/l) due to insulin resistance. These were compared to randomly selected GIK-treated, insulin-responsive patients (n = 10) and non-GIK-treated patients (n = 10) for comparison. The insulin-resistant patients required increasing amounts of regular insulin up to 130 U/h until blood glucose levels fell below 250 mg/dl. However, short-term outcomes (IABP support time, length of stay in ICU, 7-day mortality) for insulin- resistant patients were indistinguishable from those for insulin-responsive patients. These data indicate that postoperative iatrogenic hyperglycemia in patients after cardiopulmonary bypass may not be detrimental per se and is reversible when treated with supplemental insulin.

Pharmacology, Pathophysiology and Management of Calcium Channel Blocker and ??-Blocker Toxicity

Calcium channel blockers (CCB) and beta-blockers (BB) account for approximately 40% of cardiovascular drug exposures reported to the American Association of Poison Centers. However, these drugs represent >65% of deaths from cardiovascular medications. Yet, caring for patients poisoned with these medications can be extremely difficult. Severely poisoned patients may have profound bradycardia and hypotension that is refractory to standard medications used for circulatory support.Calcium plays a pivotal role in cardiovascular function. The flow of calcium across cell membranes is necessary for cardiac automaticity, conduction and contraction, as well as maintenance of vascular tone. Through differing mechanisms, CCB and BB interfere with calcium fluxes across cell membranes. CCB directly block calcium flow through L-type calcium channels found in the heart, vasculature and pancreas, whereas BB decrease calcium flow by modifying the channels via second messenger systems. Interruption of calcium fluxes leads to decreased intracellular calcium producing cardiovascular dysfunction that, in the most severe situations, results in cardiovascular collapse.Although, CCB and BB have different mechanisms of action, their physiological and toxic effects are similar. However, differences exist between these drug classes and between drugs in each class. Diltiazem and especially verapamil tend to produce the most hypotension, bradycardia, conduction disturbances and deaths of the CCB. Nifedipine and other dihydropyridines are generally less lethal and tend to produce sinus tachycardia instead of bradycardia with fewer conduction disturbances.BB have a wider array of properties influencing their toxicity compared with CCB. BB possessing membrane stabilising activity are associated with the largest proportion of fatalities from BB overdose. Sotalol overdoses, in addition to bradycardia and hypotension, can cause torsade de pointes. Although BB and CCB poisoning can present in a similar fashion with hypotension and bradycardia, CCB toxicity is often associated with significant hyperglycaemia and acidosis because of complex metabolic derangements related to these medications. Despite differences, treatment of poisoning is nearly identical for BB and CCB, with some additional considerations given to specific BB. Initial management of critically ill patients consists of supporting airway, breathing and circulation. However, maintenance of adequate circulation in poisoned patients often requires a multitude of simultaneous therapies including intravenous fluids, vasopressors, calcium, glucagon, phosphodiesterase inhibitors, high-dose insulin, a relatively new therapy, and mechanical devices. This article provides a detailed review of the pharmacology, pathophysiology, clinical presentation and treatment strategies for CCB and BB overdoses.

Pediatric toxicologic concerns

Pediatric poisonings account for significant morbidity in the United States each year. Clinicians must keep current with advances in toxicology to be familiar with the latest recommended treatment regimens and antidotes. They also must be familiar in identifying toxidromes and important physical examination findings. Having these skills can enable the clinician to determine who is at risk for significant morbidity or mortality and to provide the appropriate medical care.

Insulin-glucose as adjunctive therapy for severe calcium channel antagonist poisoning

CASE REPORT

This case series documents the clinical courses of 4 patients after verapamil overdose and 1 patient after amlodipine-atenolol overdose. All subjects had hypodynamic circulatory shock (hypotension, bradycardia, and acidosis) that was not adequately responsive to conventional treatment. After initiation of insulin-dextrose infusion, the hemodynamic status of all 5 patients stabilized and all patients survived. Plasma drug concentrations are reported for all cases and verapamil levels were extremely high in 2 patients (3710 ng/mL and 3980 ng/mL). However, because patients were not treated according to a standard protocol, each patient received variable other supportive measures and inotropic agents, and the infusion rates of insulin were variable among patients. This report provides preliminary evidence toward a larger trial of insulin-dextrose to treat hypodynamic shock from calcium channel blocker overdose.

Augmentation of the inotropic response to insulin in diabetic rat hearts

Insulin participates in the modulation of myocardial function, but its inotropic action in diabetes mellitus is not fully clear. In the present study, we examined contractile responses to insulin in left-ventricular papillary muscles and ventricular myocytes isolated from hearts of normal or short-term (5-7 days) streptozotocin-induced (65 mg/kg) diabetic rats. Mechanical properties of papillary muscles and ventricular myocytes were evaluated using a force transducer and an edge-detector, respectively. Contractile properties of papillary muscles or cardiac myocytes, electrically stimulated at 0.5 Hz, were analyzed in terms of peak tension development (PTD) or peak twitch amplitude (PTA), time-to-peak contraction (TPT) and time-to-90% relaxation (RT90). Intracellular Ca2+ transients were measured as fura-2 fluorescence intensity change (deltaFFI). Insulin (1-500 nM) had no effect on PTD in normal myocardium, whereas it produced a positive inotropic response in preparations from diabetic animals, with a maximal increase of 11%. Insulin did not modify TPT or RT90 in either group. Further studies revealed that insulin enhanced cell shortening in diabetic but not normal myocytes, with a maximal increase of 21%. Consistent with its action on the mechanical properties of papillary muscles and cardiac myocytes, insulin also induced a dose-dependent increase in the intracellular Ca2+ transient in diabetic but not normal myocytes. Collectively, these data suggest that the myocardial contractile response to insulin may be altered in diabetes.

Insulin effects on the left ventricle in older hypertensive subjects

BACKGROUND

To evaluate the effects of hyperinsulinemia on left ventricular (LV) structure and function in older hypertensive subjects

METHODS

Thirty-seven hypertensive subjects (17 men/20 women) aged 50 to 80, were studied. LV mass were evaluated echocardiographically according to the Penn convention. A 75-g oral glucose tolerance test (OGTT) was performed after overnight fasting, and both blood glucose and insulin concentrations were assayed at 0, 30, 60, 90, 120, and 180 minutes. Comparison between groups was performed by analysis of variance. A P value of .05 was considered statistically significant.

RESULTS

When the hypertensive patients were divided into two groups according to the median value of 2-hour post-loading plasma insulin, there was no difference in blood pressure levels between the groups. However, hyperinsulinemic hypertensive subjects had an increased LV mass (P < .05), mean wall thickness, and interventricular septum thickness (P < .05 for both parameters) and had better systolic function-ejection and shortening fractions (P < .0001 for both indices).

CONCLUSIONS

Hyperinsulinemia may be associated with increased left ventricular mass and with a better systolic performance in older hypertensive subjects.

Insulin improves survival in a canine model of acute beta-blocker toxicity

STUDY OBJECTIVE

To compare the efficacy of a novel antidote, insulin, with standard treatments, glucagon and epinephrine, in a canine model of acute beta-blocker toxicity.

METHODS

Anesthetized dogs were fitted with instruments by means of thoracotomy and vascular cutdown for multiple cardiodynamic, hemodynamic, metabolic, and electrical measures. After basal measurements were taken, animals received intravenous propranolol (.25 mg/kg/minute) continuously for the remainder of the experiment. Toxicity was defined as a 25% decrease in the product of heart rate times mean blood pressure. Thirty minutes after the development of toxicity, toxic measures were taken (treatment 0 minutes), and then the animals (n = 6 each group) received either sham (saline solution), insulin (4 IU/minute with glucose clamped), glucagon (50 micrograms/kg bolus, then 150 micrograms/kg/hour infusion), or epinephrine (1 microgram/kg/minute). Animals were monitored until death or for 240 minutes.

RESULTS

Propranolol decreased contractility, left ventricular pressure, and systemic blood pressure, and resulted in death of all sham-treated animals by 150 minutes. Six of six insulin-treated, four of six glucagon-treated, and one of six epinephrine-treated animals survived. Survival was greater for insulin-treated animals, compared with either glucagon-treated (P < .05) or epinephrine-treated animals (P < .02) by the log-rank test. Insulin-treated animals were characterized by improved cardiodynamics and hemodynamics, increased myocardial glucose uptake, and decreased serum potassium.

CONCLUSION

Insulin is a superior antidote compared with glucagon or epinephrine in an anesthetized canine model of acute beta-blocker toxicity.

Insulin increases distinct species of 1,2-diacylglycerol in isolated perfused rat heart

Insulin and glucose increase the synthesis of 1,2-diacylglycerol (1,2-DAG), the physiological activator of protein kinase C (PKC) in a variety of tissues and cells. The effects of insulin and glucose on the abundance and fatty acid composition of 1,2-DAG were investigated in isolated perfused rat hearts with the use of capillary gas chromatography and 1,2-dipentadecanoin as an internal standard. A high concentration of insulin (25 mU/ mL) significantly increased cardiac contractility and reduced coronary flow. In addition, perfusion with 25 mU/mL insulin induced significant increases of 18.2% and 26.4% in 1,2-DAG mass after 5 and 30 minutes, respectively, in the presence of 8.6 mmol/L glucose, whereas there was no increase in 1,2-DAG with 2.5 mU/mL insulin. Analysis of the fatty acid composition of 1,2-DAG showed that only species containing specific fatty acids (16:0, 18:1, and 18:2) were increased in response to insulin. In contrast, an increase in glucose concentration in the perfusion medium from 3 to 17 mmol/L had no effect on the total mass or fatty acid composition of 1,2-DAG, cardiac contractility, or coronary flow. Addition of a high insulin concentration to the high-glucose medium increased the abundance of 1,2-DAG containing 16:0, 18:1, and 18:2 fatty acids, as well as cardiac contractility. It is concluded that the effect of insulin on cardiac contractility may be related to the associated increase in 1,2-DAG abundance.

Myocardial metabolism during graded intraportal verapamil infusion in awake dogs

Verapamil produces comparatively greater in vivo left ventricular (LV) depression than other calcium channel antagonists produce, possibly because of myocardial metabolic derangements in addition to L-channel antagonism. Therefore, we studied myocardial lipid and carbohydrate usage and the effect of insulin treatment during progressive verapamil toxicity. Verapamil was infused through the portal vein to simulate oral overdose. Eighteen mongrel dogs were instrumented to measure multiple hemodynamic and metabolic parameters. After 1-week recovery, dogs underwent control euglycemic insulin dose-response studies (n = 6) in the conscious state: at 1,000 mU/mm insulin infusion rate, myocardial glucose and lactate extraction increased seven- and threefold, respectively with no change in coronary artery blood flow or ventricular elasticity and end-systole (Ees). In 12 separate dogs, intraportal graded verapamil toxicity was induced in 3 h by increasing the infusion rate hourly: 0.04 -- 0.08 -- 0.1 mg/kg/mm. At the end of hour 3, myocardial extraction of free fatty acids decreased from 33 +/- 4 to 9 +/- 3% (mean +/- SEM, p < 0.05), without significant change in myocardial blood flow or arterial free fatty acid concentration. Verapamil toxicity increased arterial glucose from 3.5 +/- 0.16 to 6.1 +/- 1.1 mM; simultaneously, myocardial glucose extraction doubled, although endogenous insulin concentrations did not increase. Arterial lactate concentrations and net myocardial lactate uptake both increased (p < 0.05 vs basal blue). Ees decreased from 28 +/- 1 mm Hg/mm (basal) to 20 +/- 2 mm Hg/mm (end of hour 3, p <0.05). Animals were randomized into two treatment groups; either (a) insulin-glucose (1,000 mU/mm, n 6; arterial glucose was clamped +/- 10% with 50% dextrose), or (b) saline controls (n = 6) that received equivalent volume of saline. After 1-h insulin treatment, Ees increased to 34 + 3 mm Hg; in controls, Ees was 15 +/- 3 mm Hg/mm (p < 0.05). With insulin-glucose treatment, neither myocardial glucose nor lactate extraction increased significantly (p = 0.06 for lactate). Verapamil therefore inhibits myocardial fatty acid uptake and impedes insulin-stimulated myocardial glucose uptake; under these conditions, insulin-glucose treatment increases myocardial contractile function independent of increased sugar transport. These findings indicate that verapamil toxicity produces myocardial insulin resistance and, potentially, nutrient deprivation that may contribute to clinically relevant negative inotropy.

Calcium channel blocker overdose

A case of diltiazem overdose with significant hemodynamic compromise is presented. Multiple therapeutic modalities were attempted with limited results. Control was finally achieved with a combination of norepinephrine, dobutamine, and cardiac pacing. Invasive pulmonary monitoring parameters are reported and were important in the management of this patient. The management of calcium channel blocker overdose and the various available therapeutic modalities are discussed.

Beneficial myocardial metabolic effects of insulin during verapamil toxicity in the anesthetized canine

OBJECTIVE

Myocardial depression from verapamil toxicity may result from alterations in carbohydrate metabolism as well as calcium-channel antagonism. We hypothesized that pharmacologic doses of insulin may be effective in reversing both of these deficits.

DESIGN

Randomized, controlled, prospective study.

SETTING

Laboratory of an urban hospital.

SUBJECTS

Thirty mongrel dogs.

INTERVENTIONS

Thirty mongrel canines were anesthetized with alpha-chloralose. Toxicity was induced by the administration of 0.1 mg/kg/min iv of verapamil, until there was a 50% reduction in mean arterial pressure, for 30 mins (titration), followed by a continuous verapamil infusion of 1 mg/kg/hr. Animals (n = 6 per group) were randomized to the control group (saline only) or to one of four treatment protocols: a) calcium chloride (20 mg/kg), then 0.6 mg/kg/hr; b) hyperinsulinemia-euglycemia (4.0 U/min of recombinant insulin, with arterial glucose concentration clamped to +/- 10 mg/dL [+/- 0.5 mmol/L] of the basal value); c) epinephrine, with a starting rate of 1.0 microgram/kg/min, titrated to maintain left ventricular pressure at basal values; or d) glucagon, a 0.2-mg/kg bolus, followed by a 150-microgram/kg/hr infusion. Animals were monitored until death or 240 mins; infusate volumes were held constant for all groups.

MEASUREMENTS AND MAIN RESULTS

During verapamil titration, the myocardial respiratory quotient increased from 0.84 +/- 0.05 to 1.07 +/- 0.11 (p < .05, paired t-test) and myocardial glucose uptake doubled, despite a reduction in cardiac work (p < .05, paired t-test). Net myocardial lactate uptake also increased significantly, excluding myocardial ischemia. In controls, this trend continued, indicating preferential carbohydrate metabolism during untreated verapamil toxicity. Despite hyperglycemia, the plasma insulin concentration was not significantly different in controls (basal value 11 +/- 2 vs. 39 +/- 21 microU/mL at 30 mins). Hyperinsulinemia-euglycemia increased both myocardial glucose and lactate uptake five-fold, and significantly increased the ratio of myocardial oxygen delivery/work, along with superior improvements in maximal left ventricular elastance at end systole compared with other treatments (p < .05 vs. other treatments, contrast analysis).

CONCLUSIONS

Verapamil toxicity renders the heart dependent on carbohydrate metabolism. Inasmuch as the positive inotropic effects of all treatments were coincident with increased indices of myocardial carbohydrate uptake, adequate treatment of verapamil toxicity appeared to require maximal myocardial carbohydrate utilization. Hyperinsulinemia-euglycemia allows larger increases in myocardial carbohydrate metabolism and myocardial contractility than calcium chloride, epinephrine, or glucagon, resulting in improved survival rates during severe verapamil toxicity.

Signal transduction mechanism for the stimulation of the sarcolemmal Na(+)-Ca2+ exchanger by insulin

The signal transduction pathway for insulin-mediated activation of sarcolemmal Na(+)-Ca2+ exchange was examined. Insulin stimulated Na(+)-Ca2+ exchanger activity in a dose-dependent manner, with the EC50 being about 0.7 U/l. The insulin effect was blocked by the protein kinase inhibitor, staurosporine, indicating possible involvement of a protein kinase in insulin action. Also, the relationship between the insulin effect and activation of a G protein was examined by testing the effects of 5' guanylyl imidodiphosphate (Gpp(NH))p) on Na(+)-Ca2+ exchange in the presence and absence of insulin. When exchanger activity was assayed at a calcium concentration of 40 microM, insulin alone had no effect whereas ATP and Gpp(NH)p increased exchanger activity. However, insulin responsiveness was restored in vesicles preloaded with either ATP or Gpp(NH)p, suggesting that insulin may act through a combination of G protein coupling and protein phosphorylation to enhance Na(+)-Ca2+ exchanger activity. We conclude that calcium overload in the diabetic heart may involve a defect in acute activation of the exchanger by insulin.

Ex vivo effect of insulin on normal and diabetic rat hearts hypoperfused with norepinephrine

The effect of ex vivo insulin on contractile and energy metabolism dysfunctions was examined during hypoperfusion (0.6 ml/min per g heart weight) with 10(-6) M norepinephrine in isolated non-diabetic and streptozotocin-diabetic rats hearts. Insulin (2 mU/min per g heart weight) was infused for 15 min before as well as during 60-min hypoperfusion. Insulin significantly reduced the elevated diastolic tension in diabetic hearts (from 3.8 to 0.7 delta g), but not in non-diabetic hearts (from 1.4 to 1.2 delta g). Insulin partly improved the ATP decrease in the subendocardium of the left ventricle of the diabetic hearts (from 3.5 to 10.2 mumol/g dry weight) but did not affect non-diabetic hearts (from 6.9 to 6.8 mumol/g dry weight). Insulin also partly improved the creatine phosphate decrease and the inorganic phosphate increase in diabetic hearts only. Lactate accumulation was greater in non-diabetic than in diabetic hearts, even in the presence of insulin (77 vs. 45 mumol/g dry weight). The results indicate that acute intracoronary application of insulin in diabetic hearts improves hypoperfusion with norepinephrine injury to a level above that of non-diabetic hearts, but does not improve a less severe injury in non-diabetic hearts.

Behavior of embryonic chick heart cells in culture. 2. Cellular responses to epidermal growth factor and other growth signals

Muscle cell-enriched primary cell cultures were prepared from 8-day embryonic chick heart ventricles (74% of these cells showed positive staining with anti-cardiac myosin antibody). To determine if Epidermal Growth Factor (EGF) affects cardiac muscle cells, immunostaining and autoradiography were performed to find the Muscle Cell Labeling Index (MLI). MLI represents the proportion of cardiac myosin-positive cells that specifically incorporated [3H]thymidine. The MLI for EGF-treated cells was 51%. Controls in Serum-free Nutrient Medium (SFNM) had a MLI of 34.5%. Combinations of growth signals also were tested. EGF, IGF-I (Insulin-like Growth Factor-I), or PDGF (Platelet-derived Growth Factor) alone increased [3H]thymidine incorporation in the cells. Adding IGF-I or PDGF simultaneously with EGF enhanced the response of the cells to EGF by increasing [3H]thymidine incorporation. TGF-beta (Transforming Growth Factor-beta) alone was shown to have an inhibitory effect on [3H]thymidine incorporation, and when TGF-beta was added together with EGF, it attenuated the stimulatory effect of EGF on [3H]thymidine incorporation. Phorbol 12-Myristate 13-Acetate (PMA), a tumor promoter, alone had no effect on [3H]thymidine incorporation, but its addition suppressed the stimulatory effect of EGF when they were added simultaneously in the presence of 5% FBS. Developmental response of the heart cells to growth signals also was tested. Heart cells from 18-day embryos were used to test the effect of insulin and EGF. Although both insulin and EGF increased [3H]thymidine incorporation in heart cells from 8-day embryos, different responses to insulin and EGF occurred with heart cells from 18-day embryos. Whereas the heart cells from 18-day embryos still responded to EGF by increasing [3H]thymidine incorporation, they did not show a response to insulin as measured by [3H]thymidine incorporation, suggesting that the loss of response of the heart cells to growth signals may occur at the receptor level. Further studies show that EGF, TGF-alpha, aFGF, and PDGF increased the total numbers of heart cells, and that aFGF and PDGF also increased the percentages of heart muscle cells.

Behavior of embryonic chick heart cells in culture. 1. Cellular responses to insulin-transferrin-selenium

Muscle cell-enriched primary cell cultures were prepared from 8-day embryonic chick heart ventricles (74% of these cells showed positive staining with anti-cardiac myosin antibody). To determine if ITS (a commercial mixture of insulin, transferrin, and selenium) affects these cardiac muscle cells, immunostaining and autoradiography were performed to determine the Muscle Cell Labeling Index (MLI). MLI represents the proportion of cardiac myosin-positive cells that specifically incorporated [3H]thymidine. The MLI for ITS-treated cells was 52%. Controls in Serum-free Nutrient Medium (SFNM) had a MLI of 27%. Combinations of growth signals also were tested. Whereas 5% Fetal Bovine Serum (FBS) was optimal for stimulation of [3H]thymidine incorporation, 10 and 20% FBS elicited an inhibitory effect. Addition of ITS enhanced the stimulatory effect of FBS and relieved some of the inhibitory effect. TGF-beta also was shown to have inhibitory effect on [3H]thymidine incorporation in these heart cells, but the inhibitory effect was not seen when it was added with ITS. Staining with anti-cardiac myosin antibody revealed that when the cells were cultured with ITS for 6 or 10 days, the percentages of muscle cells were 65 and 59%, whereas the percentages of muscle cells of controls in SFNM dropped to 44 and 31% respectively. Additional experiments showed that cell number increased in the presence of 5% FBS. In contrast, although ITS stimulated DNA synthesis, it did not immediately stimulate complete cell division. The percentage of muscle cells remained around 74% in the presence of 5% FBS, whereas it fell slightly (to 65%) in SFNM. This study showed that cardiac muscle cells from 8-day embryos in culture were responsive to ITS, FBS and TGF-beta and that ITS may be permissive for continued expression of differentiation of embryonic cardiac muscle cells.

The endogenous cyclic AMP antagonist, cyclic PIP: its ubiquity, hormone-stimulated synthesis and identification as prostaglandylinositol cyclic phosphate

This report shows that the cyclic AMP antagonist cyclic PIP is present in all organs and tissues of the rat so far examined: brain, heart, lung, intestine, kidney, liver, spleen, skeletal muscle and fat. The synthesis of cyclic PIP is stimulated by insulin or noradrenaline (alpha-adrenergic action) in a dose-dependent fashion. Increasing cyclic PIP synthesis with increasing insulin concentrations matches the insulin receptor binding curves. Cyclic PIP levels in blood serum remain low after hormonal stimulation and no cyclic PIP can be detected in urine. As an indication of its ubiquity, cyclic PIP was even detected in yeast. Prostaglandin E (as shown by incorporation of [3H]PGE into cyclic PIP and demonstration of a constant specific activity), myo-inositol (as shown by acid hydrolysis of the dephosphorylated cyclic PIP and mass spectrometric identification of the products) and one phosphate (as shown by the ionic nature of cyclic PIP and its inactivation by phosphodiesterase plus phosphatase) are components of cyclic PIP. Chemical derivatization experiments of cyclic PIP suggest the phosphate to be bound to myo-inositol and the myo-inositol phosphate to the prostaglandin E by its C15-hydroxyl group.

Protective effect of increased glycolytic substrate against systolic and diastolic dysfunction and increased coronary resistance from prolonged global underperfusion and reperfusion in isolated rabbit hearts perfused with erythrocyte suspensions

Current therapy of myocardial infarction may include early reperfusion. We simulated myocardial perfusion conditions during evolving myocardial infarction in isolated, normothermic, isovolumic rabbit hearts perfused with buffer containing bovine red blood cells (hematocrit of 40%), and we assessed the effects of high levels of glucose and insulin as "therapy" during prolonged (150-minute) severe underperfusion and reperfusion. Protocol 1 consisted of underperfusion at a constant coronary perfusion pressure of 8 mm Hg. The control group (n = 8) received 5.5 mmol/l glucose and 15 microunits/ml insulin; the group treated with high levels of glucose and insulin (G + I) (n = 8) received 19.5 mmol/l glucose and 250 microunits/ml insulin during both underperfusion and reperfusion. Relative to the control group, the G + I group experienced 1) greater developed pressure during underperfusion and increased recovery during reperfusion, 2) preserved diastolic function during underperfusion and reperfusion, 3) lower coronary resistance and greater coronary flow during the underperfusion period, 4) increased glycolytic flux and preserved glycogen stores and high energy phosphate levels, and 5) less loss of myocyte enzymes (creatine kinase and alanine aminotransferase). In protocol 2, coronary flow was kept identical in control (n = 8) and G + I hearts (n = 8) during the underperfusion period, and left ventricular end-diastolic pressure was kept below 10 mm Hg in both groups to minimize subendocardial damage and vascular compression. In this protocol, the effect of the G + I intervention in the prevention of an increase in coronary resistance during the underperfusion period was distinguished from its myocellular metabolic effects; the high G + I substrate had protective effects on mechanical and metabolic function that were less marked than, but similar to, those in protocol 1, indicating that its mechanisms of protection during underperfusion affected both cardiac function and coronary resistance. We conclude that the G + I intervention, in clinically relevant concentrations, markedly protected severely underperfused myocardium for 150 minutes and may be a beneficial intervention in combination with reperfusion therapy in acute myocardial infarction.

Coronary blood flow in chronic insulin-dependent diabetic dogs

Diabetic patients appear to be at an increased risk for perioperative morbidity and mortality following coronary artery bypass grafting. Many have suggested that microangiopathy is a primary cause. Using radionuclide labelled microspheres, we measured the perfusion of the subendocardium, midmyocardium, subepicardium, and the subendocardium/subepicardium ratio in alloxan-induced diabetic and normal dogs. We found no statistical difference in the myocardial perfusion of dogs made diabetic for five months when compared to normal dogs. By using repeated measures two-factor analysis of variance-regression model, changing blood glucose levels had no effect on coronary blood flow in either the diabetic or normal dogs.

Ketone bodies maintain normal cardiac function and myocardial high energy phosphates during insulin-induced hypoglycemia in vivo

It has been suggested that myocardial utilization of ketone bodies might cause deterioration of cardiac function. Therefore, the influence of ketonemia (mean: 1.3 and 3.3 mM) in the presence of hypoglycemia (mean: 33 mg/dl) on cardiac function, substrate utilization and myocardial high energy phosphate levels was studied in 10 mongrel dogs. Hypoglycemia alone led to a significant increase of mean aortic pressure, total peripheral resistance and myocardial oxygen consumption, but other hemodynamic parameters and regional myocardial function were not changed. Additional infusion of 3-hydroxybutyrate did not affect hemodynamic variables significantly. During both metabolic interventions in vivo phosphorus-31 nuclear magnetic resonance (NMR) spectroscopy showed stable levels of myocardial Pi, PCr, ATP, as well as PCr/Pi (3.2-3.4) and PCr/ATP (3.0-3.2) ratios. Biochemical measurements revealed that ketonemia led to significant alterations in arterial concentrations and arterio-coronary venous differences of selected citric acid cycle intermediates, thus confirming previous reports which suggested a blockade of the 2-oxoglutarate-dehydrogenase reaction induced by ketone body oxidation. However, despite this blockade, the energy supply to the heart was not impaired as shown by normal NMR spectroscopy and cardiac performance. It is speculated that the blockade might be due to an enhanced NADH/NAD ratio.

The effects of alpha- and beta-adrenergic agents, Ca2+ and insulin on 2-deoxyglucose uptake and phosphorylation in perfused rat heart

Insulin (0.1 microM) and 1 microM epinephrine each increased the uptake and phosphorylation of 2-deoxyglucose by the perfused rat heart by increasing the apparent Vmax without altering the Km. Isoproterenol (10 microM), 50 microM methoxamine and 10 mM CaCl2 also increased uptake. Lowering of the perfusate Ca2+ concentration from 1.27 to 0.1 mM Ca2+, addition of the Ca2+ channel blocker nifedipine (1 microM) or addition of 1.7 mM EGTA decreased the basal rate of uptake of 2-deoxyglucose and prevented the stimulation due to 1 microM epinephrine. Stimulation of 2-deoxyglucose uptake by 0.1 microM insulin was only partly inhibited by Ca2+ omission, nifedipine or 1 mM EGTA. Half-maximal stimulation of 2-deoxyglucose uptake by insulin occurred at 2 nM and 0.4 nM for medium containing 1.27 and 0.1 mM Ca2+, respectively. Maximal concentrations of insulin (0.1 microM) and epinephrine (1 microM) were additive for glucose uptake and lactate output but were not additive for uptake of 2-deoxyglucose. Half-maximal stimulation of 2-deoxyglucose uptake by epinephrine occurred at 0.2 microM but maximal concentrations of epinephrine (e.g., 1 microM) gave lower rates of 2-deoxyglucose uptake than that attained by maximal concentrations of insulin. The addition of insulin increased uptake of 2-deoxyglucose at all concentrations of epinephrine but epinephrine only increased uptake at sub-maximal concentrations of insulin. The role of Ca2+ in signal reversal was also studied. Removal of 1 microM epinephrine after a 10 min exposure period resulted in a rapid return of contractility to basal values but the rate of 2-deoxyglucose uptake increased further and remained elevated at 20 min unless the Ca2+ concentration was lowered to 0.1 mM or nifedipine (1 microM) was added. Similarly, removal of 0.1 microM insulin after a 10 min exposure period did not affect the rate of 2-deoxyglucose uptake, which did not return to basal values within 20 min unless the concentration of Ca2+ was decreased to 0.1 mM. Insulin-mediated increase in 2-deoxyglucose uptake at 0.1 mM Ca2+ reversed upon hormone removal. It is concluded that catecholamines mediate a Ca2+-dependent increase in 2-deoxyglucose transport from either alpha or beta receptors. Insulin has both a Ca2+-dependent and a Ca2+-independent component. Reversal studies suggest an additional role for Ca2+ in maintaining the activated transport state when activated by either epinephrine or insulin.

Stimulation of Na+-Ca2+ exchange in heart sarcolemma by insulin

Insulin was found to stimulate Na+-dependent Ca2+ uptake in dog heart sarcolemma in a concentration dependent manner (0.001 to 1 milliunits/ml). Maximal stimulation (160 to 170%) was seen at 0.1 to 1 milliunits/ml of insulin. Unlike Na+-dependent Ca2+ uptake, ATP-dependent Ca2+ uptake was unaltered by 1 microunit/ml of insulin. However, high concentrations of insulin (0.01 to 1 milliunits/ml) significantly increased the ATP-dependent Ca2+ uptake activity of heart sarcolemma; maximal increase (60%) was observed at 1 milliunit/ml of insulin. The Na+ K+-ATPase activity did not change upon incubating sarcolemma with insulin. The membrane preparation exhibited specific insulin binding characteristics. The Scatchard plot analysis of the data indicated two binding sites for insulin; the association constants for the high and low affinity sites were 2 X 10(9) M-1 and 4.4 X 10(8) M-1, respectively. These results support the view regarding the presence of insulin receptors in the heart cell membrane and indicate a dramatic effect of insulin on the sarcolemmal Ca2+ transport systems.

Increase in atrial contractility induced by PGE2 in diabetic rats

Contractile response to exogenous prostaglandin E2 (PGE2) was studied in auricles from normal and acutely-diabetic (streptozotocin-treated) rats. In normal atria, PGE2 induced a biphasic inotropic effect negative at low concentrations and positive at higher ones. In diabetic, PGE2 only elicited a positive inotropic action which was greater in efficacy and potency than in normal controls. Incubation of diabetic atrial preparations with alpha-adrenoceptor antagonists (phentolamine, phenoxybenzamine or Prazosin) diminished the prostaglandin effect. However, blockade of beta-adrenoceptors with propranolol did not modify the response. Blockers of arachidonic acid metabolism via cyclo-oxygenase (indomethacin and acetylsalicylic acid) or via lipoxygenase(s) (nordihydroguaiaretic acid and dithizone) were able to reduce the positive inotropism of PGE2. A significant blockade of the stimulant action of PGE2 was seen in the presence of inhibitors of thromboxane synthesis (L-8027 and imidazole). These results suggest that in diabetic atria PGE2 effect could be associated to an involvement of cardiac alpha-adrenergic stimulation which promotes endogenous arachidonic acid release with diversification of its metabolism towards cyclo- and lipoxygenase(s)- pathway and direct to an increased thromboxane formation which could account for the positive inotropic effect induced by PGE2.

Intravenous insulin has no effect on myocardial contractility or heart rate in healthy subjects

To evaluate the acute effects of intravenous insulin on myocardial contractility and heart rate, echocardiography was performed in 12 healthy subjects and continuous heart rate recording in 11 healthy subjects before and during euglycaemic insulin and glucose infusion. The rate of insulin infusion was 0.5-1.0 mU X kg-1 X min-1. Serum insulin concentration was increased from 14.1 +/- 5.5 (mean +/- SD) to a plateau level of 91.3 +/- 22.8 mU/l. Left ventricular end-diastolic diameter, ejection phase indices and the heart rate remained at basal levels during the intervention. Thus moderate hyperinsulinaemia, induced by euglycaemic insulin and glucose infusion, has no inotropic or chronotropic effects in healthy supine subjects.