Sustained effect of glucose-insulin-potassium on myocardial performance during regional ischemia. Role of free fatty acid and osmolality

Titin and CK2α are New Intracellular Targets in Acute Insulin Application-Associated Benefits on Electrophysiological Parameters of Left Ventricular Cardiomyocytes From Insulin-Resistant Metabolic Syndrome Rats

BACKGROUND

Previous studies have demonstrated that a high-carbohydrate intake could induce metabolic syndrome (MetS) in male rats with marked cardiac functional abnormalities. In addition, studies mentioned some benefits of insulin application on these complications, but there are considerable disagreements among their findings. Therefore, we aimed to extend our knowledge on the in-vitro influence of insulin on left ventricular dysfunction and also in the isolated cardiomyocytes from MetS rats.

RESULTS

At the organ function level, an acute insulin application (100-nM) provided an important beneficial effect on the left ventricular developed pressure in MetS rats. Furthermore, to treat the freshly isolated cardiomyocytes from MetS rats with insulin provided marked recoveries in elevated resting intracellular Ca²⁺-level, as well as significant prevention of prolonged action potential through an augmentation in depressed K⁺-channel currents. Insulin also normalized the cellular levels of increased ROS and phosphorylation of PKCα, together with normalizations of apoptotic markers in MetS cardiomyocytes through the insulin-mediated regulation of phospho-Akt. Since not only elevated PKCα-activity but also reductions in phospho-Akt are key modulators of titin-based cardiomyocyte stiffening in hyperglycemia, insulin treatment of the cardiomyocytes prevented the activation of titin via the above pathways. Furthermore, CK2α-activation and NOS-phosphorylation could be prevented with insulin treatment. Mechanistically, we found that impaired insulin signaling and elevated PKCα and CK2α activities, as well as depressed Akt phosphorylation, are key modulators of titin-based cardiomyocyte stiffening in MetS rats.

CONCLUSION

We propose that restoring normal kinase activities and also increases in phospho-Akt by insulin can contribute marked recoveries in MetS heart function, indicating a promising approach to modulate titin-associated factors in heart dysfunction associated with type-2 diabetes mellitus. Graphical Abstract.

The effect of insulin on the heart : Part 1: Effects on metabolism and function

Positive inotropic effects of insulin were described early after the isolation of insulin from the pancreas but data on the effect of insulin on the heart are conflicting. Systemic insulin administration results in a reduction in circulating free fatty acids and an improvement in myocardial glucose uptake, which causes an efficiency improvement in the myocardial cell. There is strong evidence that insulin administration results in functional improvement in dysfunctional myocardium. (Neth Heart J 2010;18:197-201.).

The effect of insulin on the heart: Part 2: Effects on function during and post myocardial ischaemia

Insulin infusion has been advocated in the treatment of myocardial ischaemia and myocardial infarction. There is evidence from experimental animal studies for a protective effect of high-dose insulin administration in myocardial ischaemia and myocardial infarction. In some relatively small study populations a reduction in mortality was reported in those patients who received glucose-insulin-potassium (GIK) during myocardial infarction, which was confirmed in two meta-analyses. However, it has not been possible to reproduce these positive results in large randomised clinical trials. (Neth Heart J 2010;18:255-9.).

Effects of high-dose insulin infusion on left ventricular function in normal subjects

Background. Only a few studies have reported on the effect of high-dose insulin (HDI) infusion on cardiac function in healthy volunteers. Methods. We studied ten healthy volunteers with low-dose dobutamine (LDD, 10 mug/kg/min) echo-cardio-graphy and HDI echocardiography (insulin administration for one hour) by volume and Doppler analysis. Results. During LDD, cardiac output increased from 5.7+/-1.3 l/min to 9.0+/-2.1 l/min (p<0.001) and during HDI from 5.5+/-1.2 l/min to 6.2+/-1.1 l/min (p=0.048). Increase was not only due to increase in frequency, which was only present in the LDD study, but also due to increase in stroke volume (from 82+/-15 ml to 110+/-23 ml, p<0.001 during LDD and from 82+/-16 ml to 93+/-24 ml, p=0.014 during HDI). The increase in stroke volume was the result of a decrease in end-systolic volume with an unchanged end-diastolic volume. Conclusion. High-dose insulin infusion results in increased cardiac output by improving systolic myocardial function. (Neth Heart J 2010;18:183-9.).

Effects of GIK (glucose-insulin-potassium) on stress-induced myocardial ischaemia

Despite the evidence in experimental animal models that insulin, or GIK (glucose-insulin-potassium), improves left ventricular function and perfusion during both acute and chronic ischaemia, clinical studies have generated conflicting results. We tested the hypothesis that pretreatment with GIK attenuates the vascular and functional effects of stress-induced myocardial ischaemia in humans. Twenty-two patients with evidence of inducible myocardial ischaemia were enrolled; 11 patients with normal ventricular function underwent two dipyridamole echocardiography tests, and 11 with regional contractility defects from previous myocardial infarction were submitted to two ECG exercise tests combined with 201Tl myocardial perfusion scintigraphy; the tests were preceded by 60 min of either normal saline or an isoglycaemic GIK infusion. On a stress echocardiogram, a 30% reduction in the severity of ischaemia was observed. On ECG ergometry, GIK infusion slightly increased the time to ischaemia (+0.6 min, P=0.07); however, the higher workload (+8%, P=0.07) was achieved at a similar rate-pressure plateau. On scintigraphy, an increase in ischaemic segments (+48%, P<0.001) was imaged mainly at the expense of viable (but non-ischaemic) and non-viable segments, which were reduced by 60%. GIK affected stress-induced left ventricular underperfusion only marginally (GIK: 39.7+/-2.5 compared with saline: 35.4+/-2.2 units, P<0.05), but significantly improved its acute reversibility (-42+/-4 compared with -25+/-4%, P<0.001). We conclude that GIK pretreatment attenuates the effect of ischaemia on myocardial contractility, slightly improves exercise tolerance and causes a more rapid and diffuse recovery of post-ischaemic reperfusion.

Glucose-insulin-potassium-albumin infusion in the early phase of acute myocardial infarction--a controlled study

Fifty consecutive patients with acute myocardial infarction admitted to a coronary care unit within 6 hours from onset of symptoms were randomly assigned either to a treatment group (n=27) receiving glucose-insulin-potassium-albumin (GIKA) or to a control group (n=23), comparable regarding clinical data, receiving 5.5% glucose. Both infusions were given intravenously at a rate of 1.2 ml/kg b.wt./hour during 48 hours. The GIKA solution contained 40 mEq K+, 10 ml 20% albumin and 16 IU regular crystalline insulin per 1000 ml 10% glucose. Before the infusion, the treatment group received an i.v. loading dose of 50 ml 50% glucose. Serum time activity curves for creatine kinase (CK) and myoglobin (MG) were established from frequent blood level determinations. A 15-minute single-lead ECG was recorded every fourth hour and subsequently analysed for ventricular arrhythmias. The two patient groups did not differ regarding cumulative MG and CK release. The GIKA group had significantly more patients with high MG/CK ratios (p less than 0.02). No clinically significant difference was found between the two patient groups regarding ventricular arrhythmias, even if ventricular extrasystoles tended to occur less frequently in the GIKA group.

Glucose-insulin-potassium echocardiography detects improved segmental myocardial function and viable tissue shortly after acute myocardial infarction

Previous studies showed that glucose-insulin-potassium (GIK) increases cardiac output in patients after cardiac surgery and improves segmental myocardial wall motion. We hypothesized that GIK improves regional wall motion, detects contractile reserve, and predicts functional recovery at follow-up to a similar extent as low-dose dobutamine (LDD) in patients with recent myocardial infarction. Forty-one patients underwent LDD and GIK echocardiography. Data were analyzed according to a 13-segment model. Segments were scored from 0 (normokinesia) to 2 (a-/dyskinesia). Wall motion score index was calculated for baseline and intervention. During GIK, wall motion score index improved from 0.60 +/- 0.25 to 0.39 +/- 0.20 (P < .0001) and from 0.58 +/- 0.25 to 0.39 +/- 0.21 (P < .0001) during LDD. Overall agreement between GIK and LDD echocardiography to detect contractile reserve (improvement of segmental function by >or= 1 point) was 93% with a kappa value of 0.88. Sensitivity, specificity, and positive and negative predictive values of GIK echocardiography to predict functional recovery at follow-up (mean time to follow-up, 13 months) were 74%, 84%, 85%, and 72% respectively, and values were similar to LDD echocardiography. Thus, GIK infusion improves regional left ventricular function and allows the detection of myocardial viability to a similar extent as LDD in patients shortly after infarction.

Effects of glucose-insulin-potassium infusion on chronic ischaemic left ventricular dysfunction

BACKGROUND

Glucose-insulin-potassium (GIK) infusion improves cardiac function and outcome during acute ischaemia.

OBJECTIVE

To determine whether GIK infusion benefits patients with chronic ischaemic left ventricular dysfunction, and if so whether this is related to the presence and nature of viable myocardium.

METHODS

30 patients with chronic ischaemic left ventricular dysfunction had dobutamine echocardiography and were given a four hour infusion of GIK. Segmental responses were quantified by improvement in wall motion score index (WMSI) and peak systolic velocity using tissue Doppler. Global responses were assessed by left ventricular volume and ejection fraction, measured using a three dimensional reconstruction. Myocardial perfusion was determined in 15 patients using contrast echocardiography.

RESULTS

WMSI (mean (SD)) improved with dobutamine (from 1.8 (0.4) to 1.6 (0.4), p < 0.001) and with GIK (from 1.8 (0.4) to 1.7 (0.4), p < 0.001); there was a similar increment for both. Improvement in wall motion score with GIK was observed in 55% of the 62 segments classed as viable by dobutamine echocardiography, and in 5% of 162 classed as non-viable. There was an increment in peak systolic velocity after both dobutamine echocardiography (from 2.5 (1.8) to 3.2 (2.2) cm/s, p < 0.01) and GIK (from 3.0 (1.6) to 3.5 (1.7) cm/s, p < 0.001). The GIK effects were not mediated by changes in pulse, mean arterial pressure, lactate, or catecholamines, nor did they correlate with myocardial perfusion. End systolic volume improved after GIK (p = 0.03), but only in 25 patients who had viable myocardium on dobutamine echocardiography.

CONCLUSIONS

In patients with viable myocardium and chronic left ventricular dysfunction, GIK improves wall motion score, myocardial velocity, and end systolic volume, independent of effects on haemodynamics or catecholamines. The response to GIK is observed in areas of normal and abnormal perfusion assessed by contrast echocardiography.

Identification of viable myocardium in patients with chronic coronary artery disease and myocardial dysfunction: comparison of low-dose dobutamine stress echocardiography and echocardiography during glucose-insulin-potassium infusion

Low-dose dobutamine stress echocardiography (LDDSE) is one of the methods most used to assess myocardial viability. Glucose-insulin-potassium (GIK) has been shown to increase contraction of the ischemic zone. The aim of this study was to compare LDDSE and echocardiography during GIK infusion for detection of myocardial viability in patients with chronic coronary artery disease (CAD) and myocardial dysfunction. Twenty-one patients who had chronic CAD and myocardial dysfunction were included in the study. Glucose-insulin-potassium protocol consisted of a fixed dose of insulin (100 microU/kg/hour IV) and a variable glucose/potassium infusion rate. GIK echocardiography was made at baseline and after 60 minutes of GIK infusion. During continuous electrocardiographic, blood pressure, and echocardiographic monitoring, an intravenous infusion of dobutamine (3 microg/kg body weight/min) was started with an infusion pump and continued for 5 minutes and then increased to 5 microg/kg/min and 10 microg/kg/min for another 5 minutes. The detected viable myocardium was defined as 1 or 2 scores decreasing in at least 2 adjacent abnormal segments during LDDSE and GIK echocardiography. Viability was detected in 19% (52 segments) of the asynergic segments at baseline with GIK echocardiography and 16% (44 segments) of those segments with LDDSE (p>0.05). Left ventricular wall motion score index at baseline was 2.24+/-0.35 and it decreased significantly during both LDDSE (p=0.004 vs 2.11+/-0.36) and GIK echocardiography (p=0.001 vs 2.09+/-0.32). The agreement between LDDSE and GIK echocardiography for detection of myocardial viability was 95%. This study shows that GIK echocardiography is similar to LDDSE for detection of myocardial viability. With the support of further clinical studies GIK echocardiography can be used to detect myocardial viability in patients with chronic CAD.

Comparison of low-dose dobutamine stress echocardiography and echocardiography during glucose-insulin-potassium infusion for detection of myocardial viability after anterior myocardial infarction

BACKGROUND

Low-dose dobutamine stress echocardiography (LDDSE) is one of the methods most used to assess myocardial viability. Glucose-insulin-potassium (GIK) infusion has been shown to increase contraction of the ischemic zone. The aim of this study was to compare LDDSE and echocardiography during GIK infusion for detection of myocardial viability.

METHODS

Thirty-two patients who had first anterior myocardial infarction (MI) without previous MI were included in the study. Echocardiographic evaluation was carried out on the 7th +/- 2 days after MI. During continuous electrocardiographic, blood pressure and echocardiographic monitoring, an intravenous infusion of dobutamine (3 microg/kg body weight/min) was started with an infusion pump, continued for 5 min and then increased to 5 microg/kg/min and 10 microg/kg/min for another 5 min. The GIK protocol consisted of a fixed dose of insulin (100 microU/kg/h intravenously) and a variable glucose/potassium infusion rate. GIK echocardiography was done at baseline and after 60 min of GIK. The detected viable myocardium was defined as one or two scores decreasing in at least two adjacent abnormal segments during LDDSE and GIK echocardiography.

RESULTS

Under resting conditions 225 segments (44%) were normokinetic, 21 segments (4%) dyskinetic, 117 segments (23%) akinetic and 149 segments (29%) hypokinetic. Viability was detected in 20% (57 segments) of the asynergic segments at baseline with GIK echocardiography and in 22% (62 segments) of those segments with LDDSE (P < 0.05). Left ventricular wall motion score index at baseline was 1.87 and it decreased significantly indicating improvement in left ventricular systolic function during both LDDSE and GIK echocardiography (P < 0.001, versus 1.75 and 1.76 respectively). The agreement between LDDSE and GIK echocardiography for detection of myocardial viability was 96%.

CONCLUSION

We have shown that GIK echocardiography is similar to LDDSE for detection of myocardial viability. With the support of further clinical studies GIK echocardiography could be used to detect myocardial viability after acute MI.

Glucose-insulin-potassium preserves systolic and diastolic function in ischemia and reperfusion in pigs

Clinical and experimental studies have suggested benefit of treatment with intravenous glucose-insulin-potassium (GIK) in acute myocardial infarction. However, patients hospitalized with acute coronary syndromes often experience recurrent myocardial ischemia without infarction that may cause progressive left ventricular (LV) dysfunction. This study tested the hypothesis that anticipatory treatment with GIK attenuates both systolic and diastolic LV dysfunction resulting from ischemia and reperfusion without infarction in vivo. Open-chest, anesthetized pigs underwent 90 min of moderate regional ischemia (mean subendocardial blood flow 0.3 ml x g(-1) x min(-1)) and 90 min reperfusion. Eight pigs were treated with GIK (300 g/l glucose, 50 U/l insulin, and 80 meq/l KCl; infused at 2 ml x kg(-1) x h(-1)) beginning 30 min before ischemia and continuing through reperfusion. Eight untreated pigs comprised the control group. Regional LV wall area was measured with orthogonal pairs of sonomicrometry crystals. GIK significantly increased myocardial glucose uptake and lactate release during ischemia. After reperfusion, indexes of regional systolic function (external work and fractional systolic wall area reduction), regional diastolic function (maximum rate of diastolic wall area expansion), and global LV function (LV positive and negative maximum rate of change in pressure with respect to time) recovered to a significantly greater extent in GIK-treated pigs than in control pigs (all P < 0.05). The findings suggest that the clinical utility of GIK may extend beyond treatment of acute myocardial infarction to anticipatory metabolic protection of myocardium in patients at risk for recurrent episodes of ischemia.

Insulin improves contractile function during moderate ischemia in canine left ventricle

This study determined the effects of insulin on myocardial contractile function and glucose metabolism during moderate coronary hypoperfusion. Coronary perfusion pressure (CPP) was lowered from 100 to 60, 50, and 40 mmHg in the left anterior descending coronary artery of anesthetized, open-chest dogs. Regional glucose uptake (GU), lactate uptake, myocardial O2 consumption, and percent segment shortening (%SS) were measured without (n = 12) or with intravenous (4 U/min, n = 12) or intracoronary insulin (4 U/min, n = 6). Glucose metabolites were also measured in freeze-clamped biopsies of control heart (n = 6) and hearts treated with intravenous insulin (n = 6) at the completion of the protocol (40 mmHg CPP). GU increased with intravenous and intracoronary insulin (P < 0.01). In all groups, GU was unaffected by reduced CPP, although lactate uptake decreased significantly (P < 0.01). Myocardial O2 consumption fell (P < 0.05) as CPP was lowered in all groups and was not altered significantly by intravenous or intracoronary insulin treatment. Without insulin, %SS decreased 72% (P < 0.05) at 40 mmHg CPP, but in hearts treated with intravenous and intracoronary insulin, %SS was not reduced (P > 0.05). Myocardial glycogen, alanine, lactate, and pyruvate contents were not significantly different in untreated hearts and hearts treated with intravenous insulin. Thus, in moderately ischemic canine myocardium, insulin markedly improved regional contractile function and did not appreciably increase the products of anaerobic glucose metabolism.

Normalization of impaired response of platelets to prostaglandin E1/I2 and synthesis of prostacyclin by insulin in unstable angina pectoris and in acute myocardial infarction

The minimal inhibitory concentration of prostaglandin E1 (used as a probe for prostacyclin [PGI2]) needed to inhibit platelet aggregation (36 +/- 16 nM) in normal volunteers (n = 40) increased (64 +/- 30 nM) in patients (n = 46) with acute coronary artery disease. Bolus injection of insulin in 20 patients, 0.1 U/kg body weight 4 times a day (every 6 hours) for 7 days decreased the minimal inhibitory concentration of prostaglandin E1 from 64 +/- 30 to 26 +/- 12 nM (p less than 0.001). Twenty other patients who received only saline solution had no decrease in minimal inhibitory concentration of the prostanoid. The bolus injection of insulin also increased the plasma level of PGI2 (9 +/- 2 pM) two-fold in these patients (28 +/- 10 pM). Administration of aspirin inhibited the insulin-induced increase of plasma prostanoid level. Patients in the placebo group had no increase in plasma PGI2 level. The bolus injection of insulin administered only once to another group of patients (n = 6) demonstrated that the hormonal effects were maximally increased within an hour of insulin administration, and were directly related to the increased insulin level in plasma. These results indicated the feasibility of using physiologic quantities of insulin for controlling of platelet aggregation through resensitization of platelet response to prostaglandin and increased synthesis of PGI2 in vivo in acute coronary artery disease.

An algorithm for tight glycaemic control in diabetic infarct survivors

An algorithm has been developed to provide predictable control of blood glucose for 48 h following acute myocardial infarction. In 29 diabetic patients intravenous infusion of soluble insulin was started upon admission to hospital and the rate adjusted hourly on the basis of bedside capillary glucose estimations. Insulin infusion rates related to glycaemia were higher in obese patients and those with severe cardiac failure. For all patients mean admission glucose levels were reduced from 18.3 +/- 5.9 mmol l-1 to 9.1 +/- 3.3 mmol l-1 at 4 h and to 8.8 +/- 2.5 mmol l-1 at 6 h. Mean glucose concentrations for 48 h after admission were 8.2 +/- 1.3 mmol l-1 for all patients. Admission glucose levels were slightly higher in patients with severe, compared to those without or mild, cardiac failure (P less than 0.1), but levels over the following 48 h were similar. Doubling insulin infusion rates before meals did not achieve tighter glycaemic control. Hypoglycaemia (glucose less than 3 mmol l-1) occurred on 11 occasions in six patients; only two episodes were symptomatic and only two episodes occurred when the insulin rates were doubled before meals. This algorithm produced tighter glycaemic control than previously published protocols, particularly in patients with severe cardiac failure. Hypoglycaemia is uncommon and the algorithm easy to administer by nursing staff.

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.

Enhanced utilization of exogenous glucose improves cardiac function in hypoxic rabbit ventricle without increasing total glycolytic flux

The effects of elevated glucose on cardiac function during hypoxia were investigated in isolated arterially perfused rabbit interventricular septa. Rest tension, developed tension, intracellular potential, 42K+ efflux, lactate production, exogenous glucose utilization, and tissue high-energy phosphate levels were measured during a 50-min period of hypoxia with 4, 5, or 50 mM glucose present (isosmotically balanced with sucrose) and during reoxygenation for 60 min with perfusate containing 5 mM glucose/45 mM sucrose. At physiologic (4 or 5 mM) and supraphysiologic glucose (50 mM), lactate production and high-energy phosphate levels during hypoxia were equally well maintained, yet cardiac dysfunction was markedly attenuated by 50 mM glucose. Despite identical rates of total glycolytic flux, exogenous glucose utilization was enhanced by 50 mM glucose so that tissue glycogen levels remained normal during hypoxia, whereas glycogen became depleted with 4 or 5 mM glucose present during hypoxia. Most of the beneficial effects of 50 mM glucose occurred during the first 25 min of hypoxia. Prior glycogen depletion had no deleterious effects during hypoxia with 50 mM glucose present, but exacerbated cardiac dysfunction during hypoxia with 5 mM glucose present. These findings indicate that enhanced utilization of exogenous glucose improved cardiac function during hypoxia without increasing total glycolytic flux or tissue high-energy phosphate levels, suggesting a novel cardioprotective mechanism.

Improved myocardial contractility with glucose-insulin-potassium infusion during pacing in coronary artery disease

The metabolic and mechanical effects of a solution of glucose-insulin-potassium (G-I-K) were investigated in 18 patients who underwent diagnostic cardiac catheterization for coronary artery disease. All patients were paced at a rate of approximately 140 beats/min before and after infusion of G-I-K. Basal and paced left ventricular (LV) end-diastolic pressure, dP/dt, arterial substrate levels and osmolarity were measured in all 18 patients. In 13 patients cardiac index was also measured. In 5 patients arterial-coronary sinus measurements of oxygen, carbon dioxide, glucose, free fatty acids, lactate, alanine, glutamate, glutamine, ammonia and urea were made, in addition to coronary sinus blood flow. G-I-K increased the blood sugar level to approximately 200 mg/dl and raised the serum osmolarity 9 mosmol. Pacing alone raised the cardiac index 4% and pacing with G-I-K increased the cardiac index 6% (p less than 0.05). Pacing before G-I-K augmented dP/dt (21%) and pacing with G-I-K increased it (30%) (p less than 0.01). The metabolic changes noted included a shift in the respiratory quotient from 0.77 to 0.96 with G-I-K infusion (p less than 0.05). During G-I-K infusion the myocardial oxygen consumption at rest increased from 17.1 to 21.8 ml/min (23%, p less than 0.05). Myocardial oxygen consumption during pacing was similar before and after G-I-K infusion. Before G-I-K infusion nitrogen balance was slightly positive; after G-I-K infusion it was negative with regard to the nitrogen-containing compounds measured.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of beta-adrenergic inhibition on scar formation after myocardial infarction

In view of clinical interest in the efficacy of beta-adrenergic blockade during acute myocardial infarction (AMI), we have determined the long-term effect of therapy on scar formation after experimental myocardial ischemia. Intact anesthetized dogs underwent acute occlusion of the left anterior descending coronary artery, by means of a balloon catheter, which permitted monitoring of the aortic-peripheral coronary artery pressure gradient during the 4-hour period of balloon inflation. Practolol administration was begun 15 minutes after the onset of ischemia in group A. Control animals (group B) received procainamide to approximate the antiarrhythmic action of beta blockade. Only group A exhibited significant reduction in the ST segments during acute ischemia. Chronic therapy was maintained for 1 month and the mature scar formed in the myocardium was assessed after 4 months. The extent of subendocardial scar was similar in both groups but subepicardial scar formation was significantly less in group A. There was also a significant decrease in the percentage of total myocardium involved with scar in this treatment group. Although thinning of the left ventricular wall was similar for both groups in the central scar region, this process was significantly reduced at the lateral margin in group A. Thus, specific beta-receptor blockade during acute myocardial ischemia and sustained during the repair process can result in a reduced quantity and altered distribution of mature scar.

Management of acute myocardial infarction with natural physiological agents

A number of natural physiological agents deserve evaluation in the treatment of acute myocardial infarction. Prostacyclin and magnesium dilate large coronary arteries and could promote collateral circulation to ischemic regions, especially if used in conjunction with alpha-agonists to prevent a drop in coronary perfusion pressure. In addition, prostacyclin has anti-aggregatory and de-aggregatory effects on platelets and a stabilizing action on hypoxic tissue, while magnesium has anti-arrhythmic, potassium-retaining, and fibrinolytic effects, all of which could improve the outcome in acute MI. Adenosine or ribose infusion could be used to promote rapid repletion of adenine nucleotides in reperfused tissue, but unfortunately arteriolar vasodilation by adenosine might reduce collateral perfusion by "coronary steal". High-dose insulin has positive-inotropic (at minimal oxygen cost) and potent anti-arrhythmic actions that have not been adequately tested in previous clinical trials of "polarizing solutions". Carnitine infusion could improve the bioenergetics of ischemic myocardium by relieving inhibition of mitochondrial adenine nucleotide translocase.

Intra-aortic balloon counterpulsation in an experimental model of myocardial infarction

The efficacy of intra-aortic balloon counterpulsation for heart failure during acute myocardial infarction has been controversial, and early intervention has been suggested as crucial. We have examined this type of therapy in the intact anesthetized dog during complete occlusion of the proximal left anterior descending coronary artery with a balloon-tipped catheter. Group 1 (n = 8) represented untreated animals undergoing four hours of ischemia. Group 2 (n = 7) consisted of animals undergoing counterpulsation with an intra-aortic balloon after 15 minutes of ischemia. Initially, stroke volume and the mean rate of left ventricular fiber shortening were similarly diminished in both groups, while filling pressure rose proportionately. After four hours, the mean rate of fiber shortening, stroke volume, and left ventricular filling pressure rose to a greater extent in untreated compared to treated animals (p less than 0.01). The degree of swelling in ischemic tissue and the number of sites with ST-segment elevation and their sums were comparable in the two groups. Thus, intra-aortic counterpulsation applied early in the course of ischemia can improve global left ventricular dysfunction without affecting the extent of myocardial injury.

Termination of cardiopulmonary bypass facilitated by insulin

A 61-year old woman with severe coronary artery disease underwent three-vessel coronary bypass surgery. Difficulty was encountered in terminating cardiopulmonary bypass, but there was dramatic improvement following the administration of intravenous insulin. The use of insulin to facilitate termination of cardiopulmonary bypass is discussed.

Extra-adrenergic mechanisms responsible for the effects of glucose-insulin-potassium solution on vulnerability to ventricular fibrillation

In 53 chloralose-anesthetized dogs, the actions of glucose (10 mg/kg per min), insulin (0.025 U/kg per min) and potassium (0.025 mEq/kg per min) on the ventricular fibrillation and repetitive extrasystole thresholds were examined. Measurements were initially made in the control state and then repeated at 30, 60 and 120 minutes of infusion of glucose-insulin-potassium solution at a constant rate of 1.23 ml/min. The dogs received on the average 36 g of glucose, 44 U of insulin and 44 mEq of potassium over a 2 hour period. In the nonischemic myocardium, the infusion raised the threshold for ventricular fibrillation and repetitive extrasystole to a peak of 94 and 61 percent, respectively, without significantly changing serum potassium or circulating catecholamine concentration. In the ischemic myocardium, the incidence of spontaneous ventricular fibrillation during 10 minutes of coronary occlusion was reduced from 83 percent in the control state to 17 percent with glucose-insulin-potassium infusion. However, the infusion did not alter the incidence of ventricular fibrillation associated with reperfusion. Because cardio-cardiac sympathetic reflexes are elicited in response to coronary occlusion, the effect of glucose-insulin-potassium infusion on ventricular vulnerability during left stellate ganglion stimulation and norepinephrine infusion was investigated. The infusion completely prevented the reduction in the vulnerable period threshold during stellate stimulation and norepinephrine infusion. Furthermore, the peak protection afforded by the infusion was greater than that achieved with beta adrenergic blockade and was still present in catecholamine-depleted hearts. It is concluded that infusion of glucose-insulin-potassium solution protects against ventricular fibrillation in the normal and ischemic canine heart but not during reperfusion. This protection may be due in part to antagonism of adrenergic activity; however, the primary influence of the solution is mediated by extra-adrenergic mechanism.

Evaluation of thallium-201 imaging in nontransmural ischemia and infarction

To assess the validity of thallium-201 myocardial imaging in the diagnosis of nontransmural ischemia and infarction, the proximal left anterior descending coronary artery was partially occluded for 60 minutes with a balloon-tip catheter in intact anesthetized dogs in a basal state or during atrial pacing. In vivo scintigrams of myocardium were compared with those obtained in the isolated heart and in the incised ventricle spread flat. None of the animals with partial occlusion with or without pacing demonstrated abnormal scintiscans in vivo. Removal of background by isolating the heart increased positive images to 30%; positive images were associated with an isotope count ratio between ischemic and normal muscle of less than 0.67. Removal of superimposed nonischemic muscle in the heart enface increased image detection after pacing to 11 of 15. Since animals with subendocardial scar failed to demonstrate a "cold area" in vivo, unfavorable geometry as well as extent and degree of ischemia appear to be important. Thus, thallium radioactivity in superimposed and adjacent myocardium, as well as background, may limit the detection of nontransmural ischemia and scar.

The therapeutic potential of glucose tolerance factor

Glucose Tolerance Factor (GTF) is synthesized in vivo from absorbed dietary chromium, and acts as a physiological enhancer of insulin activity, binding to insulin and potentiating its action about three-fold. Since GTF is well absorbed orally, the development of sufficiently concentrated and stable supplementary sources of this agent may enable convenient and physiologically appropriate pharmacological modulation of insulin activity. A review of the numerous physiological actions of insulin suggests a number of therapeutic applications for GTF, in such diverse ailments as diabetes mellitus, hyperlipidemia, reactive hypoglycemia, obesity, cancer, protein malnutrition or malabsorption, endogenous depression, Parkinsonism, hypertension and cardiac arrhythmias. GTF supplementation may also have value in preventive medicine.

Dose-response relationship for a positive inotropic effect of insulin on isolated papillary muscle

Beneficial effect of glucose and insulin on the myocardium are still a matter of discussion. The influence of insulin on isometric force of contraction of right ventricular papillary muscles of guinea pigs was studied. The papillary muscles were mounted vertically in a 95% O2, 5% CO2 modified Krebs-Hensuleit solution (31.5 degrees C, 5.5 mM glucose) and stimulated l/s. A positive inotropic effect of insulin was dedectable at a concentration of 5 x 10(-4) IU/ml insulin, was half maximal (52% above controle force of contraction) at 8 x 10(-3) IU/ml and maximal at 10(-1) IU/ml. The maximal positive inotropic effect was observed 4.7 +/- 0.6 min after addition of insulin. After the maximum there was a decrease to a steady state level of 109.8 +/- 8.5% of control (p less than 0.05) in 14.6 +/- 1.3 min. Higher glucose (16.5 mM) only shifted the half maximal positive inotropic effect to 5.5 x 10(-3) IU/ml insulin (n.s.). Inhibition of glycolysis with hypoxia or jodoacetate (5 x 10(-5) M) did not prevent the positive inotropic effect as known as 75% of control force was retained. When glucose transport was blocked with phlorizin (5 x 10(-3) M) or phloritin (5 x 10(-4) M) no positive inotropic action of insulin was observed. Therefore we conclude that the positive inotropic effect of insulin in isolated papillary muscles is mediated by inhanced glucose transport.