Characterization of a calcium-activated chloride channel as a shared target of Th2 cytokine pathways and its potential involvement in asthma.

Interleukin (IL)-9 is a T helper (Th) 2 cytokine recently implicated as an essential factor in determining susceptibility to asthma. Transgenic mice overexpressing IL-9 exhibit many features that are characteristic of human asthma. To better understand the mechanism by which IL-9 mediates the various biologic activities in asthma, we performed suppressive subtraction hybridization with whole lung from IL-9 transgenic and control mice. Here we report the identification of mCLCA3, a calcium-activated chloride channel that was specifically induced in the lung epithelium of IL-9 transgenic mice. Expression of mCLCA3 could also be induced by intratracheal administration of IL-9 or other Th2 cytokines (IL-4, IL-13), but not by interferon-gamma. Moreover, expression of mCLCA3 was induced in the lung of antigen-exposed mice, and this induction could be suppressed by neutralizing IL-9 antibody treatment, indicating IL-9 is both necessary and sufficient to induce mCLCA3 in this experimental model of asthma. Finally, we demonstrate that hCLCA1 is the human counterpart to mCLCA3 and is also induced in vitro in human primary lung cells by Th2 cytokine treatment. Together, these data strongly implicate the involvement of mCLCA3 (in mice) and hCLCA1 (in humans) in the pathogenesis of Th2 cytokine-mediated asthmatic disorders.

Squalamine treatment of human tumors in nu/nu mice enhances platinum-based chemotherapies.

Squalamine, an antiangiogenic aminosterol, is presently undergoing Phase II clinical trials in cancer patients. To broaden our understanding of the clinical potential for squalamine, this agent was evaluated in nu/nu mouse xenograft models using the chemoresistant MV-522 human non-small cell lung carcinoma and the SD human neuroblastoma lines. Squalamine was studied alone and in combination with either cisplatin or paclitaxel plus carboplatin. Squalamine alone produced a modest MV-522 tumor growth inhibition (TGI) and yielded a TGI with cisplatin that was better than cisplatin alone. Squalamine also significantly enhanced the activity of paclitaxel/carboplatin combination therapy in the MV-522 tumor model. Squalamine similarly improved the effectiveness of cisplatin in producing TGI when screened against the SD human neuroblastoma xenograft. Xenograft tumor shrinkage was seen for the MV-522 tumor in combination treatments including squalamine, whereas no tumor shrinkage was seen when squalamine was omitted from the treatment regimen. To gain a greater understanding of the mechanism by which squalamine inhibited tumor growth in the xenograft studies, in vitro experiments were carried out with vascular endothelial growth factor-stimulated human umbilical vein endothelial cells in culture exposed to squalamine. Squalamine treatment was found to retard two cellular events necessary for angiogenesis, inducing disorganization of F-actin stress fibers and causing a concomitant reduction of detectable cell the surface molecular endothelial cadherin (VE-cadherin). We propose that the augmentation by squalamine of cytotoxicity from platinum-based therapies is attributable to interference by squalamine with the ability of stimuli to promote endothelial cell movement and cell-cell communication necessary for growth of new blood vessels in xenografts after chemotherapeutic injury to the tumor.

IL-9 pathway in asthma: new therapeutic targets for allergic inflammatory disorders.

BACKGROUND: Asthma is a complex heritable inflammatory disorder of the airways associated with clinical signs of allergic inflammation and bronchial hyperresponsiveness (BHR). The incidence of asthma continues to rise in industrialized countries despite advances in the identification of cellular and molecular mediators that are associated with the disease. Because of its importance in human health, additional research and alternative therapeutic strategies are justified to create more effective treatments for this debilitating disease. OBJECTIVE: Studies use recombinant inbred mice to demonstrate that BHR in mouse models of asthma is associated with a genetic alteration at the IL-9 locus, where IL-9 expression in lung is strongly associated with bronchial responsiveness. We have investigated the ability of intratracheal instilled IL-9 to induce asthmatic-like responses in naive C57BL/6 (B6) mice, which express very low levels of IL-9. METHODS: IL-9 or vehicle was intratracheal instilled in naive B6 mice for 10 days. Mice were analyzed for effects on BHR, lung eosinophilia, and serum total IgE levels. RESULTS: Phenotypic effects of B6 mice instilled with IL-9 were increased eosinophils in the bronchoalveolar lavage and significantly elevated serum total IgE. Moreover, IL-9 was found to induce IL-5Ralpha in vivo and in vitro, suggesting a potential mechanism for the novel actions described for IL-9 on eosinophils. CONCLUSION: Increased levels of IL-9 in the airway of naive B6 mice induced lung eosinophilia and serum total IgE levels, which are 2 clinical features of asthma. These data support a central role for the IL-9 pathway in the complex pathogenesis of allergic inflammation.

Interleukin-9 promotes allergen-induced eosinophilic inflammation and airway hyperresponsiveness in transgenic mice.

Human atopic asthma is a complex heritable inflammatory disorder of the airways associated with clinical signs of allergic inflammation and airway hyperresponsiveness. Recent studies demonstrate that the degree of airway responsiveness is strongly associated with interleukin (IL)-9 expression in murine lung. To investigate the contribution of IL-9 to airway hyperresponsiveness, and to explore directly its relationship to airway inflammation, we studied transgenic mice overexpressing IL-9. In this report we show that IL-9 transgenic mice (FVB/N-TG5), in comparison with FVB/NJ mice, display significantly enhanced eosinophilic airway inflammation, elevated serum total immunoglobulin E, and airway hyperresponsiveness following lung challenge with a natural antigen (Aspergillus fumigatus). These data support a central role for IL-9 in the complex pathogenesis of allergic inflammation.

Squalamine inhibits angiogenesis and solid tumor growth in vivo and perturbs embryonic vasculature.

The novel aminosterol, squalamine, inhibits angiogenesis and tumor growth in multiple animal models. This effect is mediated, at least in part, by blocking mitogen-induced proliferation and migration of endothelial cells, thus preventing neovascularization of the tumor. Squalamine has no observable effect on unstimulated endothelial cells, is not directly cytotoxic to tumor cells, does not alter mitogen production by tumor cells, and has no obvious effects on the growth of newborn vertebrates. Squalamine was also found to have remarkable effects on the primitive vascular bed of the chick chorioallantoic membrane, which has striking similarities to tumor capillaries. Squalamine may thus be well suited for treatment of tumors and other diseases characterized by neovascularization in humans.

Adrenergic, insulin, and work interactions with adenosine's effects on in situ myocardial glucose uptake.

We have demonstrated that adenosine enhances insulin-stimulated myocardial glucose uptake in situ. In the present study we determined the role of adrenergic influences and myocardial work on insulin-stimulated myocardial glucose uptake while varying intracoronary adenosine concentrations. Under pentobarbital anesthesia we instrumented mongrel dogs to obtain blood pressure, heart rate, and arterial and coronary sinus blood samples for measuring oxygen and glucose concentrations. An electromagnetic blood flow probe around the circumflex coronary artery allowed determinations of blood flow, and calculation of myocardial oxygen (MVO2) and glucose (MGU) uptakes. Somatostatin was infused i.v. (0.8 microgram/kg.min-1) along with 10 mU/kg.min-1 regular insulin, and variable quantities of glucose to maintain euglycemia. Adenosine was infused at logarithmic incremental rates (0, 0.01, 0.1, 1.0, and 10 mumoles.min-1) for 30 min each into the main left coronary arteries. Adrenergic blockade was achieved with i.v. propranolol (70 micrograms/kg bolus followed by 5 micrograms/kg.min-1 infusion), and phentolamine (95 micrograms/kg bolus followed by 9.5 micrograms/kg.min-1 infusion). Insulin infusion significantly increased MGU. Adenosine increased the maximal value for insulin-stimulated glucose uptake. Adrenergic blockade alone did not alter insulin-stimulated MGU, but reduced heart rate and MVO2. When evaluated relative to MVO2 1.0 mumoles/ml adenosine infusion increased MGU independent of work-related changes in the presence or absence of adrenergic blockade. With an adenosine infusion rate of 10 mumoles/ml myocardial glucose uptake returned to baseline. These data also support our earlier speculation that the MGU response to adenosine may be biphasic. These results suggest that antagonism of adrenergic effects by adenosine cannot account for adenosine's ability to enhance insulin's effects on glucose uptake in the heart, but that work-related influences should be accounted for in interpreting results of this kind.

Hepatic insulin resistance during chronic hyperdynamic sepsis.

Disturbances in normal glucose metabolism and homeostasis which manifest as hyperglycemia and glucose intolerance are often observed during clinical sepsis. Skeletal and myocardial muscle as well as whole body insulin resistance have been demonstrated in this laboratory and others during experimental and clinical sepsis. The existence of hepatic insulin resistance in sepsis has yet to be fully elucidated. This study was undertaken to assess hepatic insulin resistance during chronic hyperdynamic sepsis. Animals were randomly assigned to a septic (n = 7), sham (n = 7), or control (n = 7) group. Sepsis was induced in anesthetized dogs via a midline laparotomy whereby a fecal-soaked gauze sponge was placed amid the intestines. Sham animals underwent a laparotomy with mechanical manipulation of the intestines but no fecal implant. Control animals had no previous surgery. Sham and control dogs were pair-fed with the septic dogs. On postoperative day 7, after an overnight fast, animals were anesthetized, intubated, and ventilated. Via a left subcostal laparotomy, electromagnetic flow probes were placed to measure hepatic arterial and portal venous blood flows. Cannulae were placed in femoral, portal, and hepatic veins and femoral artery and used to calculate hepatic outputs of glucose, lactate, and oxygen during a basal period and hyperinsulinemic-euglycemic clamps which used intravenous insulin infusions which ranged from 0.4 to 4,000 mU/min. Mean arterial blood pressure decreased with increasing insulin concentrations in septic animals while no change was seen in control or sham animals. In control and sham animals, net hepatic glucose output (NHGO) decreased in response to increasing insulin levels. Septic animals showed no such inverse relationship and, moreover, showed no change in glucose output response to any insulin infusion, i.e., hepatic insulin unresponsiveness during sepsis. Net hepatic lactate output during basal pre-insulin period during sepsis was negative. This was in contrast to the positive outputs in control and sham animals. Glucose infusion rates (GIR) increased during insulin infusion but were not different between groups at any insulin infusion rate. These data demonstrated a hepatic insulin resistance (unresponsiveness) during chronic hyperdynamic, hypermetabolic sepsis.

Improved cerebral blood flow and CO2 reactivity after microvascular anastomosis in patients at high risk for recurrent stroke.

The medical community has not yet identified cerebrovascular pathophysiological factors that distinguish patients at high risk for stroke or aid in selecting patients for microvascular cerebral bypass. In this study, we describe the courses of 13 patients, all of whom suffered recurrent episodes of transient cerebral ischemia after previous cerebral infarction. These patients underwent regional cerebral blood flow studies using xenon inhalation with a CO2 challenge before and at various times after extracerebral-to-intracerebral microvascular anastomosis. Collateral circulation was assessed in all patients before surgery using four-vessel cerebral angiography. Patients were followed for a mean of 30 months (range, 1-7 yr) after the anastomosis. Measurements of mean cortical cerebral blood flow, as measured using the initial Slope Index, and CO2 cerebrovascular reactivity of these 13 patients were compared with those in a group of 20 patients designed as controls. Hemispheric cortical blood flow was significantly depressed in these patients before surgery compared with those in the control group (P less than 0.05). After the bypass, the mean resting Initial Slope Index in these patients increased 14% (P = 0.0005). Cerebral blood flow both before and after CO2 inhalation improved significantly in these patients after surgery (P = 0.001). Detectors bordering computed tomographic or magnetic resonance image documented infarctions, identified as peri-infarct regions, and demonstrated significant mean increases in both cerebral blood flow (38.8-43.2 ml/min/100 g, P = 0.05) and CO2 cerebrovascular reactivity in these patients after bypass (1.71 + 1.91% to 4.00 + 2.38% change Initial Slope Index/mm Hg CO2, P = 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular sequelae of endotoxin shock in diabetic dogs.

Diabetic patients exhibit a higher incidence of post-surgical sepsis, as well as a higher rate of mortality from sepsis, than their non-diabetic counterparts. This may be a result of cardiovascular deterioration associated with diabetes mellitus. This study was designed to characterize the cardiovascular sequelae associated with endotoxin shock in a canine model of diabetes. Diabetes was induced with alloxan (50 mg/kg) and streptozotocin (30 mg/kg) in dogs weighing 19-25 kg. Thirty days later, anaesthetized dogs were instrumented to obtain blood pressures, blood samples, left ventricular chamber diameter, circumflex arterial blood flow, and aortic blood flow. Metabolic parameters were calculated according to the Fick principle, and myocardial inotropic state assessed with the end-systolic pressure-diameter relationship. After stable baseline measurements, Escherichia coli endotoxin (1 mg/kg) was infused over 1 h, and measurements were obtained every 30 min. After endotoxin administration diabetic dogs became more hypotensive than the non-diabetic dogs. Cardiac performance parameters were also depressed to a greater degree. These changes could be attributed to depressions in vascular resistance and myocardial inotropic state in diabetic dogs. Cardiac dysfunction occurred in association with a relative decrease in the supply to demand ratio for oxygen in the diabetic dogs, suggesting functional ischemia. Data indicating a decrease in pre-load and vascular resistance in the diabetic group suggest a greater degree of vascular collapse, vascular pooling, or extravasation of fluid than occurred in the non-diabetic group. These data support the hypothesis that the cardiovascular system of diabetic subjects cannot tolerate a septic insult as well as their non-diabetic counterparts.

Adenosine enhances myocardial glucose uptake only in the presence of insulin.

Better understood in other tissues, the effects of adenosine on insulin-stimulated glucose uptake in the heart are poorly understood. Under pentobarbital anesthesia, we instrumented mongrel dogs to obtain general hemodynamics (blood pressure and heart rate), and arterial and coronary sinus blood samples for measuring oxygen and glucose concentrations. An electromagnetic blood flow probe around the circumflex coronary artery allowed determinations of blood flow, and calculation of substrate uptake by the heart (Fick principle). Somatostatin (SRIF) was infused intravenously (0.8 micrograms/kg/min) along with 0, 0.5, 1.0, 5.0, or 10 mU/kg/min regular insulin, and variable quantities of glucose to maintain euglycemia. Concomitant with the SRIF, insulin, and glucose infusions, adenosine was infused in logarithmically increasing rates (0, 0.01, 0.1, 1.0, 10 or 100 mumol/min) for 30 minutes each into the main left coronary arteries. Insulin infusions increased myocardial glucose uptake in a dose-dependent manner. The heart displayed exquisite sensitivity to insulin, with an ED50 of approximately 14 microU/mL (serum insulin). Adenosine infusions in the absence of insulin (SRIF infusion) increased coronary blood flow, but did not alter myocardial glucose uptake. In the presence of insulin, adenosine increased the maximal value for glucose uptake without changing sensitivity to insulin. These results indicate that adenosine enhances myocardial responsiveness to insulin, with respect to glucose uptake, independent of changes in blood flow. Since glucose can be used for anaerobic metabolism, and adenosine levels are known to increase under situations in which myocardial oxygenation is inadequate, these data have serious implications for conditions such as myocardial ischemia or hypoxia, when glycolytic substrate availability is vital.

Hepatic insulin resistance during canine sepsis.

Glucose dyshomeostasis and insulin resistance are well-documented characteristics of sepsis. The insulin resistance could be manifested in a decreased peripheral glucose uptake and/or an increased hepatic glucose output. To investigate the hepatic and peripheral responses to insulin in a three-day model of sepsis, 14 mongrel dogs were studied. Animals were randomly assigned to a SEPTIC (n = 5), SHAM (n = 4), or CONTROL (n = 5) group. Sepsis was induced in anesthetized dogs via a midline laparotomy with subsequent placement of a fecal-soaked gauze sponge around intestines. SHAM and CONTROL dogs were pair-fed with the SEPTIC dogs. On the third day, animals were anesthetized, intubated, and ventilated. Via a left-side laparotomy, electromagnetic flow probes were placed to measure hepatic arterial and portal venous blood flows. Cannulas were placed in femoral, portal, and hepatic veins and femoral artery to measure hepatic outputs of glucose, lactate, and oxygen during hyperinsulinemic-euglycemic clamps ranging from 0.4 to 4,000 mU insulin/min. Portal venous insulin concentrations in SEPTIC animals were significantly increased compared to CONTROL animals during 0.4 and 4 mU insulin/min infusions. An insulin infusion rate of 40 mU/min significantly decreased net hepatic glucose output (NHGO) in CONTROL animals but did not affect NHGO in SHAM or SEPTIC animals. An insulin infusion rate of 4,000 mU/min significantly decreased NHGO in all groups. An attempt to analyze the ED50 of the three dose-response curves was inconclusive. Glucose infusion rates (GIR) increased during insulin infusion but the GIR were not different between groups at any insulin infusion rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of adenosine on the stimulatory effect of isoprenaline and insulin on myocardial contractility in vivo.

STUDY OBJECTIVE: In vitro investigations have indicated that adenosine can inhibit beta adrenergic stimulated increases in cardiac contractility. The present study was designed to determine the ability of adenosine to inhibit isoprenaline induced increases in contractility in vivo. Adenosine has been reported to exert its inhibitory effects on contractility by inhibiting adenylate cyclase. Thus, adenosine should have no effect on positive inotropic agents that act independently of adenylate cyclase. We therefore assessed the ability of this nucleoside to inhibit the positive inotropic effect of insulin, a hormone that exerts a positive inotropic effect independently of alterations in cyclic AMP. DESIGN: Saline or adenosine (10 mumol.ml-1) was infused into the circumflex artery at 1 ml.min-1 as a background. Isoprenaline (20 or 200 pmol.min-1) was infused into the artery during saline or adenosine infusion. The response to insulin was determined during hyperinsulinaemic euglycaemic clamp. SUBJECTS: 16 adult mongrel dogs were anaesthetised with pentobarbitone. Five dogs were used in isoprenaline studies, and 11 dogs in insulin studies. MEASUREMENTS AND MAIN RESULTS: Dogs were instrumented to obtain measurements of mean arterial blood pressure, heart rate, circumflex artery blood flow (Q), instantaneous left ventricular pressure, and posterior left ventricular wall thickness. We used the slope of the end systolic pressure-dimension relationship (Ees) as an index of myocardial contractility, previously shown to reflect changes in myocardial inotropic state independent of influence from afterload and preload. Left ventricular dP/dtmax was derived from left ventricular pressure with respect to time, and Ees was determined from left ventricular pressure and wall thickness. Neither adenosine, isoprenaline, nor insulin alone caused any significant changes in mean arterial pressure or heart rate. Adenosine caused a significant increase in Q. Both left ventricular dP/dtmax and Ees were significantly increased by either insulin or both doses of isoprenaline. Adenosine inhibited the increases in these indices caused by isoprenaline, but not those caused by insulin. CONCLUSIONS: Adenosine is capable of inhibiting the positive inotropic effect of isoprenaline in vivo. The results suggest that adenosine does not inhibit positive inotropic responses that act independently of the stimulation of adenylate cyclase.

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.

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.

Adenosine restores myocardial responsiveness to insulin during acute endotoxin shock in vivo.

We recently reported that adenosine potentiated insulin-stimulated myocardial glucose uptake (MGU) in vivo and that adenosine receptor blockade resulted in myocardial insulin resistance. Since myocardial insulin resistance has been reported to occur during endotoxin shock, we decided to investigate whether infusion of adenosine could ameliorate this condition. Studies were performed in pentobarbital-anesthetized dogs that were instrumented to measure mean arterial blood pressure (MAP), circumflex arterial blood flow (Q), myocardial glucose uptake (MGU), and oxygen uptake (MVO2). Endotoxin shock was induced by administration of an intravenous bolus of Salmonella typhymurium endotoxin (1 mg/kg). The response to insulin was determined during hyperinsulinemic (4 U/min), euglycemic clamp (INS). The ability of adenosine to potentiate insulin-stimulated glucose uptake was measured during sequential infusions of adenosine (0.01 mumol/min to 10 mumol/min) or during infusion of a single concentration of adenosine (1.0 mumol/min) into the circumflex artery. In control dogs INS resulted in an approximate twofold elevation of myocardial glucose uptake over basal values (2.6 +/- 0.4 to 4.9 +/- 0.7 mg/min; mean +/- S.E.M.). There was no significant effect of INS on MAP, Q, or MVO2 in this group. Adenosine infusions resulted in potentiation of insulin-stimulated MGU. During shock INS elevated MAP, Q, and MVO2 to levels that were not significantly different from the control group, but did not raise MGU above the pre-endotoxin level. Adenosine infusions elevated insulin-stimulated MGU during shock to levels similar to those observed in the control group during respective adenosine infusion rates. MAP and MVO2 were not significantly altered by INS + adenosine in the shock group as compared with the effect of INS alone. From these results we conclude that adenosine restored the myocardial glucose uptake response to insulin during endotoxin shock. The response of the oxygen supply to demand ratio to INS suggests that myocardial adenosine production may be reduced during endotoxin shock.

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.

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.

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.

Aspartame use by persons with diabetes.

Sixty-two subjects having either insulin-dependent or non-insulin-dependent diabetes completed a randomized, double-blind study comparing effects of aspartame or a placebo on blood glucose control. Twenty-nine subjects consumed 2.7 g aspartame per day for 18 wk, given as aspartame-containing capsules with meals, while 33 subjects took identical appearing placebo capsules. After 18 wk, no changes were seen in fasting or 2-h postprandial blood glucose levels or glycohemoglobin levels in either the aspartame- or placebo-treated groups. Adverse reactions were no more common in the group taking aspartame. We conclude that use of aspartame as a low-calorie sweetener does not adversely affect glycemic control of persons with diabetes.