Adenosine reversal of in vivo hepatic responsiveness to insulin.

Modulation by adenosine of hepatic responsiveness to insulin was investigated in vivo in 10 healthy mongrel dogs of both sexes by determining net hepatic glucose output (NHGO) in response to insulin during the presence or absence of exogenous adenosine infusion. In addition, two separate series of experiments were performed to study the effect of adenosine (n = 7) or glucagon (n = 5) on NHGO. Basal NHGO, quantitated via the Fick principle, was significantly decreased by insulin infusion (4 U/min; 4.8 +/- 0.6 vs. -1.7 +/- 2.6 mg.kg-1.min-1, P less than 0.05). The addition of an intrahepatic arterial infusion of adenosine (10 mumol/min) during insulin infusion caused glucose output to return to basal levels (insulin, -1.7 +/- 2.6 mg.kg-1.min-1; insulin + adenosine, 3.8 +/- 1.6 mg.kg-1.min-1, P less than 0.05). The addition of intrahepatic arterial saline (control) during insulin infusion had no effect on insulin's action (insulin, -1.0 +/- 1.9 mg.kg-1.min-1; insulin + saline, -1.2 +/- 1.6 mg.kg-1.min-1, P greater than 0.05). Hepatic glucose, lactate, and oxygen deliveries were not affected during either insulin or insulin plus adenosine infusion. Intrahepatic arterial infusion of adenosine alone had no effect on NHGO, whereas intrahepatic arterial infusion of glucagon alone stimulated glucose output approximately fivefold (basal, 2.7 +/- 0.4 mg.kg-1.min-1; glucagon, 15.5 +/- 1.2 mg.kg-1.min-1, P less than 0.01). These results show that adenosine completely reversed the inhibition by insulin of NHGO. These data suggest that adenosine may act as a modulator of insulin action on the liver.

Adenosine is required for myocardial insulin responsiveness in vivo.

The adenosine-receptor antagonist 8-phenyltheophylline (8-PTH) was used to study the role of endogenous adenosine in modulating insulin-stimulated myocardial glucose uptake (MGU) in vivo. Dogs were surgically instrumented under pentobarbital sodium anesthesia to measure hemodynamics and obtain blood samples for determinations of oxygen and glucose concentrations. Myocardial uptake of these substances was calculated as the product of the appropriate arterial-coronary sinus differences and circumflex blood flow. The response to insulin was determined with the hyperinsulinemic-euglycemic clamp technique. During insulin infusion, MGU increased from 3.12 +/- 0.8 to 9.20 +/- 1.8 mg/min (mean +/- SE). In contrast, insulin failed to increase MGU when 8-PTH was being infused into the circumflex artery. These results demonstrate that some degree of adenosine-receptor-mediated activity is required for insulin to stimulate myocardial glucose uptake. It is suggested that the presence of adenosine at its receptor may be an important factor during conditions in which myocardial insulin resistance may develop.

Myocardial insulin resistance during acute endotoxin shock in dogs.

Myocardial insulin responsiveness was determined in open-chest pentobarbital sodium-anesthetized dogs before and after endotoxin administration. Animals were instrumented to measure mean arterial blood pressure (MABP), heart rate (HR), and coronary blood flow. Myocardial glucose uptake and myocardial oxygen uptake (MVO2) were determined during a basal control period and after a hyperinsulinemic-euglycemic clamp procedure over a wide range of insulin concentrations. The clamp was accomplished by intravenously infusing insulin (0-4000 mU/min) and 20% glucose in sufficient amounts to maintain arterial glucose concentrations within 5 mg/dl of the control value. In a separate series of experiments, myocardial insulin responsiveness was determined by use of a single dose of insulin (4000 mU/min). This was done to determine whether antecedent insulin infusions during the sequential clamp procedure would affect the responsiveness of the heart. In control experiments, myocardial glucose uptake increased without any changes in HR, MVO2, or MABP. Maximum myocardial glucose uptake occurred at an insulin infusion rate between 400 and 4000 mU/min. A single concentration of insulin resulted in similar increases in myocardial glucose uptake as with the sequential clamp protocol. Acute endotoxin shock was induced by bolus injection of 1 mg/kg Salmonella typhimurium endotoxin (Difco Labs, Detroit, MI). One hour after administration of endotoxin, basal myocardial glucose uptake was decreased compared with the control animals. After 1 h of endotoxin shock, the heart was refractory to all concentrations of insulin, suggesting the site for altered insulin response was being mediated by a postreceptor mechanism.

Aminophylline fails to improve the outcome of cardiopulmonary resuscitation from prolonged ventricular fibrillation: a placebo-controlled, randomized, blinded experimental study.

OBJECTIVES: The purpose of this study was to evaluate systematically the effects of the adenosine antagonist aminophylline on resuscitation outcome in a canine model of postcardioversion nonperfusing rhythm. BACKGROUND: Theoretic considerations and experimental studies indicate that myocardial adenosine accumulation during prolonged ventricular fibrillation might play a significant role in postcardioversion asystole and electromechanical dissociation. A recent uncontrolled clinical trial has suggested that the adenosine antagonist aminophylline might improve the outcome of cardiopulmonary resuscitation from refractory bradyasystolic cardiac arrest. METHODS: Two placebo-controlled, randomized, blinded experimental studies were performed. In protocol 1 (20 dogs), ventricular fibrillation was induced and maintained for 7.5 min. Sixty seconds before cardioversion, dogs received 1 mg of epinephrine followed by 250 mg of aminophylline or placebo. In protocol 2 (20 dogs), dogs were cardioverted to electromechanical dissociation after 5 min of unsupported ventricular fibrillation. Sixty seconds later, all dogs received 1 mg of epinephrine followed by 250 mg of aminophylline or placebo. In both experiments, resuscitation efforts were continued until return of spontaneous circulation, or up to 30 min. The primary end point was survival to 1 h. RESULTS: In protocol 1, 4 of 10 dogs survived in the aminophylline group, whereas 7 of 10 dogs survived in the placebo group, a nonsignificant trend toward unfavorable outcome from aminophylline. Pretreatment with aminophylline increased the number of cardioversion applications required to terminate ventricular fibrillation. In protocol 2, 5 of 10 and 6 of 10 dogs survived in the aminophylline and placebo groups, respectively. CONCLUSIONS: The results of this study suggest that aminophylline fails to improve the outcome of resuscitation from prolonged ventricular fibrillation. It does not reverse established electromechanical dissociation and may in fact increase the number of cardioversion applications required to terminate ventricular fibrillation. The rationale for conducting clinical trials with aminophylline during cardiopulmonary resuscitation is questionable.

The effect of hypodynamic endotoxin shock on myocardial high energy phosphates in the rat.

High energy phosphate concentrations were determined in the isolated perfused (in vitro) and intact (in situ) heart preparations in the rat during a control period and at various time intervals (1,2,4,8 or 16 h) following the intraperitoneal injection of 4 mg.kg-1 E coli endotoxin. Arterial glucose and lactate concentrations were determined just prior to excising the hearts. Following the induction of endotoxin shock, myocardial ATP and creatine phosphate decreased in both the in situ and in vitro preparations, while AMP increased only in the in situ group. There was no significant alteration in ADP in either group throughout the 16 h experimental period. Myocardial energy charge decreased at 1 h following endotoxin shock and remained depressed throughout the 16 h study period. Total heart weights as well as the wet/dry ratio were unaltered throughout the experiment. The reductions in ATP and creatine phosphate during endotoxin shock were a direct result of the shock state and not due to the loss of myocardial mass or the presence of oedema. One hour following the induction of endotoxin shock plasma glucose increased then returned to the control value by 2 h and remained at the pre-endotoxin level throughout the experimental protocol. Arterial lactate concentration increased following endotoxin administration and remained elevated until 16 h, where it was not different from the control value. Data from the present study clearly indicate a myocardial energy deficit during acute hypodynamic endotoxin shock in the rat and may provide a mechanism for the cardiac dysfunction normally associated with this shock paradigm.

Insulin and beta adrenergic effects during endotoxin shock: in vivo myocardial interactions.

STUDY OBJECTIVE - Catecholamine concentrations are raised during endotoxin shock and may be responsible for myocardial insulin resistance in such a condition. The purpose of the investigation was to examine the effect of insulin on myocardial contractility and glucose uptake in the presence of beta adrenergic blockade during endotoxin shock. DESIGN - Endotoxin shock was obtained in dogs by giving S Typhimurium endotoxin intravenously (1 mg.kg-1) and the cardiac responses to insulin were determined under hyperinsulinaemic (4 U.min-1) euglycaemic clamp conditions during continuous beta adrenergic blockade (propranolol 150 micrograms.kg-1 + 5 micrograms.kg-1.min-1). SUBJECTS - 19 mongrel dogs of either sex, weight 20-25 kg, were studied under pentobarbitone anaesthesia. Seven dogs received endotoxin plus propranolol, and seven others received propranolol alone (control group). Five dogs received endotoxin but no propranolol or insulin. All other procedures were the same in each group. MEASUREMENTS and RESULTS - The exposed heart was prepared for coronary sinus blood sampling and measurements of circumflex artery blood flow (Q), instantaneous left ventricular pressure, and left ventricular wall thickness. Glucose uptake was calculated from product of Q and aortic-coronary sinus concentration difference. End systolic pressure-dimension relationship was used to assess contractility. Myocardial performance was assessed from left ventricular dP/dtmax. Basal shock measurements were made 60 min post endotoxin. beta Adrenergic blockade did not interfere with insulin stimulated glucose uptake in controls, but was unable to restore the uptake response during endotoxin shock. Contractility was increased during endotoxin shock and this effect was abolished by beta adrenergic blockade. In controls the only variable affected by beta adrenergic blockade was left ventricular dP/dtmax (decreased). Insulin increased contractility during beta adrenergic blockade in controls but not in shock. Myocardial performance was depressed during shock. In controls, insulin increased myocardial performance; in shock this response was attenuated. CONCLUSIONS - The findings confirm that the myocardium becomes less responsive to the glucose uptake stimulating and positive inotropic effects of insulin during endotoxin shock. The data show that beta adrenergic activity is responsible for the increased contractile state of the heart during acute endotoxin shock, but is not the cause of the observed insulin resistant state.

Effect of insulin on myocardial contractility during canine endotoxin shock.

During endotoxin shock the heart becomes less responsive to the stimulatory effect of insulin on glucose uptake. In the present study we sought to determine if the heart was also less responsive to the positive inotropic effect of insulin during non-cardiogenic endotoxin shock. Responses of the heart to insulin were assessed under conditions of hyperinsulinaemic (4U.min-1), euglycaemic clamp (INS). Adult mongrel dogs, weighing 20-25 kg, were anaesthetised and instrumented to measure differences in substrate concentrations between arterial and coronary sinus blood, circumflex artery blood flow (using electromagnetic flow probe), haemodynamic variables, and left ventricular posterior wall thickness (using sonomicrometry). The first derivative of left ventricular pressure with respect to time was measured and its maximal value (LV dP/dtmax) used as an index of cardiac performance. Myocardial contractility was measured using the end systolic pressure-dimension relationship. Endotoxin shock was induced by Salmonella typhimurium (1 mg.kg-1 intravenously), and resulted in depression of myocardial performance but increased contractility. INS caused a twofold elevation in myocardial glucose uptake in control animals while in endotoxin shocked dogs it was unable to elevate glucose uptake above the pre-endotoxin level. In control animals INS caused both increased cardiac contractility and performance. In the endotoxin shock group INS was unable to increase LVdP/dtmax above the basal, pre-endotoxin level and did not cause any significant change in myocardial contractility. We suggest that the heart becomes less responsive to the positive inotropic as well as metabolic effects of insulin during endotoxin shock. Changes in LV dP/dtmax can be attributed to the changing loading conditions that occur during endotoxin shock.

Insulin improves heart function and metabolism during non-ischemic cardiogenic shock in awake canines.

OBJECTIVES: This study was undertaken to examine in-situ heart function and metabolism during insulin treatment of verapamil-induced cardiogenic shock in awake canines. METHODS: Twenty mongrel canines were instrumented to monitor myocardial substrate uptakes (glucose, lactate, free fatty acids, oxygen [MVO2]), as well as ventricular (LV) end-systolic elastance (Emax), LV efficiency (LV minute work/MVO2), and Tau. Shock was induced by graded intraportal verapamil infusion followed by randomized assignment to one of 4 treatment groups: saline control (3.0 ml/kg/min, n = 5), epinephrine (5 micrograms/kg/min, n = 5), glucagon (10 micrograms/kg/min, n = 5) or insulin (1000 mU/min, n = 5) with dextrose to clamp arterial [glucose] +/- 10% of basal concentrations. RESULTS: Insulin treatment significantly increased Emax (34 +/- 3 vs. 17 +/- 3 mmHg/mm, saline control), and shortened Tau (9 +/- 3 ms) compared to saline control (42 +/- 5 ms), epinephrine (20 +/- 4 ms) and glucagon (35 +/- 8 ms). With insulin treatment, mechanical efficiency increased to 20,097 +/- 2070 vs. 12,424 +/- 1615 mmHg.mm/ml/O2/100 g in controls. Simultaneously, insulin increased myocardial lactate uptake (35 +/- 2 vs. 17 +/- 4 mumol/min/100 g. saline control), but did not increase glucose uptake. Epinephrine and glucagon decreased mechanical efficiency compared to saline controls, coincident with increased myocardial fatty acid consumption, but without increasing lactate uptake. One dog died early with glucagon treatment before the first death in the saline-treated group. CONCLUSIONS: Insulin improves systolic and diastolic heart function during aerobic shock and accelerates in-vivo myocardial lactate oxidation.

Effect of amiloride on age-dependent cardiac dysfunction after ischemia/reperfusion in the isolated, perfused rat heart.

This study was intended to compare the cardiac consequences of ischemia/reperfusion and amiloride treatment in immature (2-3 wk), juvenile (4-6 wk), and adult (3-5 mo) rats using an isolated, perfused heart model. Male immature, juvenile, and adult rats were anticoagulated and anesthetized. Hearts were harvested and coronary arteries were perfused on a Langendorff apparatus via retrograde perfusion of the aorta at a constant coronary flow (initially determined by perfusing the heart at 50 mm Hg perfusion pressure) with oxygenated Krebs-Henseleit-Bicarbonate (KHB) solution. Left ventricular peak systolic (LVPSP) and end diastolic (LVEDP) pressures were measured via a balloon-tipped catheter placed in the left ventricle through the mitral valve. Following a 20-30 min stabilization period, hearts underwent 30 min of normothermic ischemia and were then reperfused with Krebs-Henseleit-Bicarbonate alone for 30 min, or Krebs-Henseleit-Bicarbonate containing 500 microM amiloride for 5 min followed by Krebs-Henseleit-Bicarbonate alone for 25 min (n = 6/age group). Left ventricular generated pressure was calculated (left ventricular peak systolic-left ventricular end diastolic) and used as a measure of ventricular function. All hearts demonstrated a decrease in generated pressure, respectively, from preischemic levels at 15 and 30 min of reperfusion, although this decrease was significantly less for the immature hearts. Ischemia/reperfusion injury was attenuated by amiloride in adult and juvenile hearts, whereas ischemia/reperfusion injury was worsened by amiloride in immature hearts. Although immature hearts were relatively resistant to ischemia/reperfusion injury compared with adult and juvenile hearts, the presence of amiloride during reperfusion resulted in more severe ventricular dysfunction in immature hearts. These data suggest a differential age-dependent mechanism of sarcolemmal ion exchange in response to ischemia/reperfusion.

Contrast media-induced ventricular fibrillation. A comparison of Hypaque-76, Hexabrix, and Omnipaque.

Contrast media occasionally produce ventricular fibrillation during coronary angiography. We compared the fibrillatory propensity of the conventional ionic contrast medium, Hypaque-76 (H76) to the low osmolar ionic dimer Hexabrix (HB) and to the nonionic agent Omnipaque (OM) in 20 open chest anesthetized dogs. Intracoronary injection of 6 mL of contrast medium produced spontaneous ventricular fibrillation in four of ten dogs with H76, compared with two of ten with HB, and zero of ten with OM (P = .07). The induction of two premature beats by programmed stimulation of the myocardium during injection of 4 mL of contrast medium produced ventricular fibrillation in ten of ten dogs with H76, compared with three of ten with HB, and zero of ten with OM (P less than .001). Both H76 and HB produced ventricular fibrillation in ten of ten dogs when three premature beats were induced, compared with two of ten dogs with OM (P less than .001). Four mL H76 produced a 109 +/- 18 msec increase in the QT interval, compared with an 82 +/- 17 msec increase with HB, and a 45 +/- 12 msec increase with OM. We conclude that both low osmolar HB and OM are less fibrillatory than the conventional ionic medium H76, and that the nonionic medium OM is less fibrillatory than the ionic dimer contrast medium HB.

The effect of sodium on the fibrillatory propensity of nonionic contrast media.

Removing sodium from standard ionic contrast media markedly increases the incidence of ventricular fibrillation in patients undergoing coronary angiography. Newer nonionic contrast media, iopamidol, iohexol, and ioversol contain only trace amounts of sodium. To determine whether sodium attenuates or potentiates ventricular fibrillation from nonionic contrast media, we measured the prolongation in QT interval and performed programmed electrical stimulation with one, two and three extra ventricular stimuli in 40 dogs during 4-mL intracoronary injections of iopamidol, iohexol, and ioversol. Solutions of each contrast medium with added NaCl at concentrations of 0.225%, 0.45%, and 0.9% were compared with standard contrast media. The addition of NaCl markedly increased the amount of QT interval prolongation produced by each contrast medium. With iopamidol, the amount of QT interval prolongation was 40 +/- 11 msec with standard iopamidol, but was 58 +/- 11 msec with 0.225% NaCl/iopamidol, 84 +/- 17 msec with 0.45% NaCl/iopamidol, and 132 +/- 42 msec with 0.9% NaCl/iopamidol (P less than .001). Similar results were seen with iohexol and ioversol. Ventricular fibrillation was difficult to induce with standard solutions of these agents (even with three extra stimuli), but became progressively easier to induce when NaCl was added. Three extra stimuli produced ventricular fibrillation in zero of 11 dogs with standard iopamidol, zero of 11 with 0.225% NaCl/iopamidol, three of 11 with 0.45% NaCl/iopamidol, and eight of 11 with 0.9% NaCl/iopamidol (P less than .001). Similar results were observed with iohexol and ioversol. The addition of choline chloride or dextrose did not increase ventricular fibrillation and QT interval prolongation. It is concluded that standard preparations of nonionic contrast media have a very low fibrillatory propensity.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of contrast media on the conducting system of the heart during coronary angiography. A comparison of Renografin-76 to Hypaque-76.

Electrocardiographic changes induced by ionic contrast media can cause complications during coronary angiography. A conduction delay through various parts of the heart is one factor in the genesis of asystole or ventricular fibrillation. Hypaque-76 (H76) and Renografin-76 (R76) are nearly identical ionic contrast media except that R76 binds more calcium than H76 because of the presence of sodium citrate and EDTA in R76. To determine whether the calcium binding additives in ionic contrast media contribute to the cardiac conduction abnormalities, we examined conduction time through the atrioventricular (AV) nodal tissue (via bipolar His bundle electrograms) and through the distal part of the conduction system (recording the QRS complex from the ECG) during coronary angiography. We injected 10 mL of H76 and R76 in 19 closed chest dogs in a blinded, randomized fashion during coronary angiography. The effects of H76 and R76 on heart rate, AH interval, HV interval, V interval and PR interval, and QRS complex duration were recorded. In 14 nonatrial pacing dogs, compared with H76, R76 produced a greater increase in the AV interval (32.9 +/- 6 milliseconds vs 12.4 +/- 2 milliseconds, P less than .01) and the PR interval (29.6 +/- 6 milliseconds vs 11.9 +/- 4 milliseconds, P less than .02). Additionally, the heart rate decreased 13.9 +/- 3.5 beats/minute from control with R76 compared with a decrease of 4.2 +/- 2.6 beats/minute from control with H76 (P less than .05). There was no significant difference between the prolongation of the HV interval and V interval, or QRS complex duration generated by R76 and H76.(ABSTRACT TRUNCATED AT 250 WORDS)

Skeletal muscle insulin resistance during Escherichia coli bacteremic shock in the dog.

Skeletal muscle glucose uptake during close, intra-arterial insulin infusion was studied before and during live Escherichia coli bacteremic shock in the dog. An in vivo, constant-flow perfused gracilis muscle preparation was used. Insulin infusion before shock resulted in a 395% increase in muscle glucose uptake, which was independent of changes in muscle lactate production or oxygen uptake. At 1, 2, and 3 hours of shock, insulin infusion had no effect on gracilis muscle glucose uptake. This loss of responsiveness to insulin occurred with no change in muscle oxygen uptake, muscle venous PO2, or muscle blood flow (held constant). On the other hand, during nonshock control experiments, muscle glucose uptake in response to insulin infusion was maintained during the 3-hour protocol. These data demonstrate that skeletal muscle insulin resistance develops early during bacteremic shock.

Myocardial depression during acute pancreatitis: fact or fiction?

Clinical and experimental evidence suggests that myocardial depression occurs during severe pancreatitis, but this evidence is derived from techniques that are not optimal for assessing myocardial contractility (e.g., rate of rise in ventricular pressure [dP/dt]). The slope of the left ventricular (LV) and systolic pressure dimension relationship (Ees), a better indicator of myocardial function, has not been measured in pancreatitis. Ten mongrel dogs underwent surgical instrumentation to monitor systemic arterial and LV pressure, cardiac output, LV dP/dt, and anterior LV wall thickness. End of systole was defined by the peak negative dP/dt. The end-systolic points used to calculate Ees were obtained by aortic and vena caval occlusion. After surgical recovery, pancreatitis was induced via cannulation of the pancreatic duct and injection of autologous bile (1 ml/kg) at 200 mm Hg perfusion pressure. All measurements were taken during a control period and daily after pancreatitis was induced. Pancreatitis was confirmed by a significant increase in serum amylase throughout the study and by autopsy finding of hemorrhagic necrosis. Ees was increased throughout the experimental protocol (1 to 7 days) (p less than 0.05). Myocardial performance as assessed by Ees was significantly increased and myocardial depression did not occur in untreated, conscious dogs with severe pancreatitis. Peak positive LV dP/dt was a poor index of contractility during pancreatitis since it decreased while myocardial contractility was increased. Cardiac depression in pancreatitis noted in other reports was likely due to decreased preload and not to intrinsic cardiac dysfunction.

Arterial regeneration over polydioxanone prostheses in the rabbit.

We analyzed histologic, ultrastructural, and functional characteristics of rabbit aortic conduits regenerated over absorbable polydioxanone prostheses. Twenty-eight polydioxanone-elicited prosthesis/tissue complexes harvested two weeks to 12 months following implantation were analyzed grossly; photographed; sectioned for light, scanning, and transmission electron microscopy; and studied for compliance, bursting strength, and prostacyclin and thromboxane metabolite contents. No aortic-related deaths or hemorrhages occurred. Smooth regenerated conduits without stenoses were seen in 27 of 28 specimens, with one small aneurysm. Transprosthetic myofibroblast migration and proliferation paralleled the kinetics of macrophage-mediated prosthetic dissolution, which was consequently delayed compared with polyglycolic acid prostheses. Confluent endothelial-like luminal surfaces were present after two weeks. Progressive inner capsular thickening ended after three months at 420 micron. Ex vivo compliance curves resembled arterial elasticity. Regenerated tissue withstood 1200 mm Hg of systolic pressure, and 6-keto-prostaglandin F1 alpha to thromboxane B2 ratios did not differ from normal control specimens.

A novel nonsense mutation in the EYA1 gene associated with branchio-oto-renal/branchiootic syndrome in an Afrikaner kindred.

Branchio-oto-renal (BOR) syndrome is an autosomal dominant disorder characterized by the associations of hearing loss, branchial arch defects and renal anomalies. Branchiootic (BO) syndrome is a related disorder that presents without the highly variable characteristic renal anomalies of BOR syndrome. Dominant mutations in the human homologue of the Drosophila eyes absent gene (EYA1) are frequently the cause of both BOR and BO syndromes. We report a South African family of Afrikaner descent with affected individuals presenting with pre-auricular abnormalities and either hearing loss or bilateral absence of the kidneys. Genetic analysis of the pedigree detected a novel EYA1 heterozygous nonsense mutation in affected family members but not in unaffected family members or a random DNA panel. Through mutational analysis, we conclude that this particular mutation is the cause of BOR/BO syndrome in this family as a result of a truncation of the EYA1 protein that ablates the critical EYA homologous region. To the best of our knowledge, this is the first case of BOR/BO syndrome reported in Africa or in those of the Afrikaner descent.