The effect of tolbutamide on contractility and cyclic adenosine 3':5'-monophosphate concentration in the intact beating rat heart.

The effect of tolbutamide on contractility and the concentration of cyclic adenosine 3':5'-monophosphate (cyclic AMP) in ventricular muscle was examined in the intact beating rat heart. The hearts were perfused in a nonrecirculated (Langendorff) fashion. Bolus injections of tolbutamide caused an increase in cardiac contractility. This increase in contractility was markedly inhibited when bovine albumin (3 g/100 ml) was present in the perfusing fluid. The increase in contractility caused by tolbutamide was not preceded by or associated with any change in the concentration of cyclic AMP in the ventricular muscle. Further studies utilizing a simultaneous injection of norepinephrine and tolbutamide demonstrated no significant effect of this combination on the concentration of cardiac cylcic AMP produced by an injection of norepinephrine alone. Our findings suggest that in the intact beating rat heart the positive inotropic effect of tolbutamide is not mediated via an increase in the concentration of cardiac cyclic AMP and that tolbutamide does not significantly potentiate the effect of catecholamines on cardiac cyclic AMP concentration.     

Acute effects of iron on contractile function in isolated rabbit myocardium

Changes in contractile function following exposure to iron (Fe) salts were evaluated in isolated isometrically contracting rabbit left atrial strips and right ventricular papillary muscles. Fe acutely depressed myocardial contractility as evidenced by dose-related declines in developed force and maximal rate of force development. There were no significant changes in duration of contraction or resting force. The tissue Fe content was increased nearly 3-fold after a 60 min exposure to Fe and subsequently was not decreased by repeated washing or by treatment with deferoxamine. Isoproterenol, but not deferoxamine, reversed the Fe-mediated impairment of myocardial contractility. These findings suggest that in cases of severe acute iron poisoning, depression of cardiac contractility might occur which may be improved by treatment with isoproterenol.     

Effects of platelet-activating factor on β- and H2-receptor-mediated increase of myocardial contractile force in isolated perfused guinea pig hearts

Platelet-activating factor (PAF) has been termed an important mediator of cardiovascular shock due to immunological reactions, including anaphylaxis and endotoxic reactions. Previous studies have shown that PAF is a potent cardiodepressive agent inducing a drastic coronary constriction and a sustained impairment of myocardial contractility. In this study, an attempt was made to further characterize the prolonged PAF effects on coronary circulation and myocardial contractile force in the isolated guinea pig heart perfused at constant pressure. An intracoronary PAF bolus (0.18 nmol, related to coronary flow rates of 1 ml/min) induced a precipitous decrease of coronary flow rates, left ventricular pressure, and left ventricular contraction (peak positive dP/dt), which was followed by a slow increase reaching new steady state after 15 min (-48%, -40%, -42% below baseline, respectively). If the specific PAF antagonist WEB 2086 (3.65 nmol/min, related to coronary flow rates of 1 ml/min) was infused 30 min after PAF administration, the prolonged PAF-mediated cardio-depressive effects were rapidly reversed. Several studies indicate that PAF induces a down regulation of beta-adrenoreceptors in different cell types, including human lung tissue. Therefore, a further objective of the study was to evaluate whether PAF selectively impairs the positive inotropic effects of beta-receptor agonists or also inhibits the contractile effects of inotropic drugs, which are known to enhance cardiac contractility independently of beta-receptors. In these experiments, the beta-agonist isoproterenol and the H2-agonist impromidine were administered as intracoronary boluses (0.35 nmol and 0.14 nmol, respectively, related to coronary flow rates of 1 ml/min) prior to PAF injection and 30 min after PAF.(ABSTRACT TRUNCATED AT 250 WORDS)     

Insulin worsens ischemia-induced myocardial contracture in the isolated rat heart

We used a modification of Langendorff's isolated perfused nonworking rat-heart model to study the effects of diabetes, insulin-treated diabetes, and hyperinsulinemia on left ventricular pressure, force of ventricular contraction, and myocardial contracture, before, during, and after 20 min of complete normothermic global ischemia. Untreated diabetic rat hearts behaved the same as normal hearts, but insulin-treated diabetic hearts had more ischemic and postischemic contracture (p less than .01), and less return of left ventricular function. Chronic insulin treatment potentiated ischemic contracture in diabetic and nondiabetic rat hearts. These results support the hypotheses that insulin can increase Ca++ actin-myosin ATPase activity, and increase the affinity of myofibrillar receptors for calcium, which may lead to increased ischemic contracture. Insulin as a risk factor in myocardial ischemia, cardiothoracic surgery and cardiac resuscitation, and other pathogenetic factors of "stone heart" development, deserve further investigation.     

Cardiac conditioning ameliorates cardiac dysfunction associated with renal hypertension in rats

To explore the effect of physiologic hypertrophy superimposed on pathologic hypertrophy, hearts from female control rats (C), renal hypertensive rats (H), rats conditioned with a 10-12 wk swimming program (Sw), and hypertensive rats trained by the swimming program (H-Sw) were perfused in an isolated working rat-heart apparatus. Systolic blood pressure was approximately 100 mmHg in C and Sw and was 160 mmHg in H and H-Sw. The swimming program had no effect on blood pressure. Compared with C, heart weight was increased by 30% in Sw, 47% in H, and 77% in H-Sw. At high preload and afterload, cardiac output (milliliters per gram dry LV weight) was decreased in H, increased in Sw, and partially restored towards normal in H-Sw. Ejection fraction, percent fractional shortening, and mean velocity of circumferential fiber shortening were enhanced in Sw, depressed in H, and normalized in H-Sw when compared with C. Coronary flow and myocardial oxygen consumption in this series of hearts were depressed in H, with no restoration in H-Sw, but coronary effluent lactate/pyruvate ratios were only elevated in the hearts of H-Sw. Coronary vascular responses were examined in a second series of experiments which used microspheres. In this series, the depressed coronary flow observed in H was partially restored towards normal in H-Sw and the inner/outer myocardial flow ratio was normal when hearts were perfused at 140 cm aortic pressure but was somewhat depressed in both H and H-Sw when the hearts were perfused at 80 cm aortic pressure. These studies demonstrate that hypertrophic hearts from renal hypertensive rats have diminished coronary flow and depressed cardiac function when they are studied in the isolated working heart apparatus, yet there is no evidence of myocardial ischemia. Superimposition of a chronic swimming program results in increased hypertrophy but restoration of cardiac function partially or completely to normal. Thus, pathologic and physiologic hypertrophy are biologically distinct entities. Physiologic hypertrophy may partially ameliorate the defects associated with pathologic hypertrophy.     

Inhibition of nitric oxide synthase enhances the myocardial toxicity of phenylpropanolamine

OBJECTIVE: To investigate the direct and indirect effects of the anorexic agent phenylpropanolamine (PPA) on the heart and to determine whether nitric oxide deficiency exacerbates the myocardial toxicity of PPA. DESIGN: Dose response effects using sequential drug administration. SETTING: Animal research laboratory of a large tertiary academic medical center. SUBJECTS: Isolated hearts (n = 8) from male Sprague-Dawley rats weighing 300-400 g. INTERVENTIONS: Measurement of heart rate, maximal change in pressure over time (dP/dtmax), -dP/dtmax, and coronary blood flow in isolated hearts perfused on a Langendorff apparatus. PPA was infused through the aortic cannula at 0.05, 0.125, 0.25, 0.5, and 1.25 mmol/L before and after inhibition of nitric oxide synthesis with N-nitro-L-arginine methyl ester (L-NAME). RESULTS: PPA had little effect on myocardial contractility of normal hearts until the highest dose of PPA (1.25 mmol/L). However, after L-NAME, PPA significantly depressed contractility at a dose of 0.25 mmol/L. PPA had no significant effects on coronary blood flow. PPA failed to induce arrhythmias in normal hearts. However, after L-NAME, PPA induced ventricular fibrillation in 50% of the hearts. CONCLUSION: PPA causes myocardial contractile depression without altering global coronary artery blood flow. Inhibition of nitric oxide synthesis sensitizes the heart to the myocardial depressant effects of PPA and increases the risk for ventricular fibrillation.     

Myocardial contractility after brain injury

Cardiac contractile function in the acute period after brain injury (BI) was studied on 158 non-inbred male albino rats, by using the isolated isovolumetrically contracted heart according to the procedure described by Fallen et al. The injured rats showed a significantly depressed left ventricular myocardial contractility during the hypoxic test, followed by reoxygenation, a lower positive chronic inotropic effect, and an increased diastolic defect with an enhanced rate of cardiac stimulation rates. Brain injury increased the dependence of cardiac performance on the concentration of Ca2+ in the perfused solution. The findings suggest the decreased resistance of the hearts of the rats that had sustained BI to pathogenetic factors.     

Regulation of cyclic nucleotide levels and glycogen phosphorylase activity by acetylcholine and epinephrine in perfused rat hearts.

Acetylcholine (ACh) produced a time and dose-dependent increase in cyclic 3',5'-guanosine monophosphate (cyclic GMP) levels in perfused rat hearts without any significant (P greater than .05) change in cyclic 3',5'-adensoine monophosphate (cyclic AMP) level or glycogen phosphorylase activity. Epinephrine produced a dose-dependent increase in both cyclin AMP and phosphorylase activity but no significant (P greater than .05) change in cyclic GMP levels. When ACh (10(-6) M) was infused into hearts during the infusion of epinephrine (10(-6) M), a time-dependent increase in cyclic GMP and decrease in cyclic AMP occurred, both of which preceded a significant (P less than .05) decrease in glycogen phosphorylase activity. In epinephrine-stimulated hearts, ACh produced a dose-dependent increase in cyclic GMP levels. Similar concentrations produced a fall in cyclic AMP levels and phosphorylase activity. No condition tested resulted in a significant (P greater than .05) change in glycogen synthase activity. It is concluded that ACh can reduce cyclic AMP levels and phosphorylase activity only when they have been elevated above basal values. These changes are associated with an increase in cyclic GMP. The reduction in phosphorylase produced by ACh may be the result of either or both of the changes in cyclic nucleotide levels.     

Responsiveness to glucagon in fetal hearts. Species variability and apparent disparities between changes in beating, adenylate cyclase activation, and cyclic AMP concentration.

Previous studies of the ability of the immature heart to respond to glucagon have yielded conflicting results. To test the possibility that the apparent discrepancies might be explained in part by species variability, isolated hearts of fetal mice and rats (13-22 days' gestational age) were studied under identical conditions in vitro. Changes in atrial rate and ventricular contractility were measured in spontaneously beating hearts exposed to glucagon, and activation of adenylate cyclase was assayed in cardiac homogenates. In mice of 16 days' gestational age or less, there was no change in heart rate in response to glucagon; at 17-18 days, minimal responsiveness was present; and after 19 days, 10muM glucagon caused an increase in spontaneous atrial rate of 30 +/- 4% (SEM) (P less than 0.001). Measurement of the extent and speed of volume displacement of the isotonically contracting hearts with a specially constructed capacitance transducer revealed that ventricular inotropic responsiveness also appeared after 17-19 days. Cardiac stores of glycogen were reduced in older hearts exposed to glucagon, but not in those aged less than 16 days. In contrast, glucagon failed to activate adenylate cyclase in homogenates of hearts of fetal mice at any age. Furthermore, glucagon failed to elicit an increase in the concentration of cyclic AMP in spontaneously beating hearts that developed tachycardia. Responses in hearts of fetal rats were distinctly different from those in mouse hearts: at no age was there any change in heart rate, strength of contraction, glycogen content, or adenylate cyclase activation. Thus, there are major species differences in cardiac pharmacological maturation. Although the mouse heart develops the ability to increase its rate and strength of contraction and to undergo glycogenolysis in response to glucagon well before birth, the rat heart does not. In addition, there is an apparent disparity in late fetal mouse hearts between the ability of glucagon to induce functional responses and its ability to stimulate adenylate cyclase and increase cyclic AMP levels. It is impossible, of course, to rule out absolutely the possibility that localized increases in a critical cyclic AMP pool were present but too small to measure in the entire tissue. Nevertheless, the most obvious interpretation of our results is that they are compatible with the hypothesis that glucagon may exert some of its hemodynamic effects independently from the adenylate cyclase-cyclic AMP system in the late-fetal mouse heart.     

Pharmacology of LY175326: a potent cardiotonic agent with vasodilator activities

Compound LY175326 is one of a series of novel cardiovascular agents with both inotropic and vasodilator activities. In cat papillary muscles, LY175326 increased contractility in a concentration-dependent manner; these actions were not blocked by prazosin, propranolol or cimetidine. Inotropic responses were observed in unpaced, perfused guinea-pig hearts and these effects were associated with modest increases in heart rate and coronary flow. An i.v. dose of 0.1 mg/kg of LY175326 caused 54 and 95% increases in contractility in either the anesthetized cat or dog, respectively; corresponding heart rates were increased by less than 10%. Oral administration of 0.5 mg/kg to dogs was associated with an inotropic response that was maximal between 60 and 90 min and lasted in excess of 3 hr. These effects were not accompanied by increases in heart rate, gross behavioral changes or emesis. The pharmacology of LY175326 was evaluated in a propranolol-induced heart failure model using anesthetized beagle dogs. A bolus injection of 0.15 mg/kg of LY175326 followed by an infusion of 0.4 mg/kg/hr reversed the hemodynamic symptoms of heart failure by increasing left ventricular dP/dt60, cardiac output and stroke volume and reducing left atrial filling pressure and vascular resistance; heart rate was unchanged and calculated myocardial oxygen consumption was reduced. This balance of inotropic:vasodilator activities may provide a means of improving cardiac function while maintaining the myocardial oxygen supply:demand.     

Glucose,insulin and potassium (GIK) during reperfusion mediates improved myocardial bioenergetics

Previous studies suggest glucose, insulin and potassium (GIK) infusion during ischemia reduces infarct size and improves post-ischemic myocardial function in acute myocardial infarction and following surgical revascularization of the heart. The potential use of GIK when given only during reperfusion after a period of global ischemia, as might occur during cardiac arrest, is unclear. To test the hypothesis that GIK reperfusion improves post-ischemic myocardial bioenergetics and function, we utilized a perfused heart model. Hearts from Sprague-Dawley rats (350-450 g) were perfused at 85 mmHg with oxygenated Krebs-Henseleit bicarbonate containing 5.5 mM glucose and 0.2 mM octanoic acid. Following 20 min of global ischemia, hearts were reperfused for 30 min with original solution (control) or GIK in two different doses (10 or 20 mM glucose each with insulin 10 U/l and K(+) 7 meq/l). Hearts perfused with GIK solutions had significantly higher ATP, creatine phosphate, energy charge, and NADP(+) and lower AMP and inosine levels compared with control after 30 min of reperfusion. Hearts reperfused with GIK had significantly higher developed pressure and higher dP/dt than control reperfused hearts. Reperfusion with GIK improved post-ischemic recovery of both contractile function and the myocardial bioenergetic state. GIK may be a viable adjunctive reperfusion therapy following the global ischemia of cardiac arrest to improve post-resuscitation cardiac dysfunction.     

Isoproterenol-induced relaxation, phosphorylase activation and cylic adenosine monophosphate levels in the polarized and depolarized rat uterus.

There is some evidence in the literature that catecholamines relax uterine and other types of smooth muscle by increasing tissue levels of cyclic adenosine monophosphate (cyclic AMP). In the present study, isoproterenol completely relaxed uterine strips obtained from estrogen-primed rats and also increased tissue levels of cyclic AMP and phosphorylase a. In uterine strips depolarized and put into contracture for 15 minutes by 127 mM K+, isoproterenol did not increase phosphorylase a or cyclic AMP but was still capable of producing relaxation. When uterine strips were exposed to the methoxy derivative of verapamil, D-600, a compound known to prevent the influx of calcium, the uterus relaxed completely without an increase in cyclic AMP. The addition of isoproterenol at this stage resulted in an increase in cyclic AMP similar to that noted in nondepolarized uterine strips. The addition of 127 mM K+ also resulted in time-dependent biochemical changes as well as contracture. Cyclic AMP was increased 3-fold after 2 minutes of K+ depolarization and phosphorylase a was increased as well. The increase in cyclic AMP was prevented by propranolol but propranolol did not affect the contracture response to K+. D-600 prevented contracture but did not affect the K+-induced increase in cyclic AMP. The data suggest that an increase in whole tissue levels of cyclic AMP are not necessary in order for isoproterenol to relax depolarized rat uterine strips. The data also suggest that intracellular calcium levels can affect the level of cyclic AMP in the rat uterus.     

Global ischemic duration and reperfusion function in the isolated perfused rat heart

Post-ischemic myocardial dysfunction has been observed in a variety of clinical situations including cardiac arrest. Potentially survivable cardiac arrest following short-term global myocardial ischemia may be of insufficient duration to cause irreversible myocyte injury, but still results in contractile and bioenergetic dysfunction. The purpose of this study was to characterize the ischemic transition from reversible to irreversible injury in the isolated perfused rat heart. Isolated, buffer perfused, male Sprague-Dawley rat hearts underwent normothermic ischemia of 15, 20, 25 or 30 min with or without 30 min of reperfusion and were freeze clamped in liquid nitrogen for bioenergetic analysis of LV tissue. Post-ischemic LV function and measurements of bioenergetic recovery were made between groups and with non-ischemic controls. Baseline LV function was similar in all groups. Post-ischemic contractile function was markedly depressed in the 25 and 30 min ischemia groups with persistent depression of high-energy phosphates, total adenine nucleotide pool, myocardial oxygen consumption, elevated CK release and evidence of significant mitochondrial edema in the 30 min group. In contrast with longer ischemic periods, the reduction in LV contractile function after 15 and 20 min of ischemia was mild, with more complete bioenergetic recovery, minimal CK release, and normal appearing mitochondrial. This data suggests a period of transition from reversible to irreversible injury occurring at approximately 20 min of normothermic global ischemia in the isolated perfused rat heart.     

Cardioprotective action of alpha-blocking agents, phentolamine and bunazosin, on hypoxic and reoxygenated myocardium

The present study was undertaken to determine whether alpha-blocking agents, phentolamine and bunazosin, may exert a cardioprotective effect on hypoxic and subsequently reoxygenated hearts. For this purpose, rabbit hearts were perfused for 20 min under hypoxic conditions, followed by a 45 min-reoxygenation. Agents were administered between the 8th and 20th min of hypoxic perfusion. Hypoxic perfusion for 8 min resulted in a decline of cardiac contractile force and myocardial high-energy phosphates and a loss of adenine nucleotide metabolites from the heart, whereas a rise in resting tension was not observed. Neither increase in perfusion pressure, release of creatine kinase from hearts nor increase in tissue calcium was observed. At 20 min-hypoxia, significant changes in resting tension and perfusion pressure of the heart and release of creatine kinase from the heart were observed. Cardiac contractile force after 45 min of reoxygenation was less than 10% of the initial value. Treatment with 83 microM phentolamine or 46 microM of bunazosin resulted in a significant suppression of hypoxia-induced increase in tissue calcium, release of creatine kinase and adenine nucleotide metabolites and rise in perfusion pressure and resting tension. Treatment with either phentolamine or bunazosin resulted in appreciable recovery of cardiac contractile force. Reoxygenation-induced release of creatine kinase was also suppressed significantly. Two possible mechanisms for the protective effect of this treatment are considered; 1) preservation of ATP metabolites which may be utilized as substrates for a salvage synthesis of ATP during reoxygenation and 2) prevention of a nonselective transmembrane flux of cellular constituents due to changes in cell membrane permeability.     

Effect of endothelin on the function of the isolated perfused working rat heart

1. The effect of endothelin on the performance of the isolated perfused working rat heart has been examined. 2. A low concentration of endothelin (60 pmol/l) produced a gradual but sustained increase in cardiac output; coronary vascular resistance was unaffected. 3. A high concentration of endothelin (600 pmol/l) produced a rapid increase in cardiac output, followed by a marked fall in cardiac output as progressive, severe coronary vasoconstriction developed. 4. The coronary vasoconstriction induced by endothelin (600 pmol/l) was partially blocked by nicardipine (0.5 mumol/l). 5. In the presence of either nicardipine (0.5 mumol/l) or verapamil (0.2 mumol/l), the increment in cardiac output induced by endothelin (600 pmol/l) was greater than that induced by the addition of the same concentration of endothelin to hearts which had not been exposed to calcium-entry blockers. 6. The effect of endothelin on myocardial contractility has a different time course, concentration dependence and response to calcium-entry blockade than the effect on the coronary vasculature. This suggests that different mechanisms are involved in the generation of the myocardial and vascular responses to endothelin.     

Possible mechanism by which coenzyme Q10 improves reoxygenation-induced recovery of cardiac contractile force after hypoxia

To elucidate possible mechanisms by which coenzyme Q10 enhances reoxygenation-induced recovery of cardiac contractile force after hypoxia, rabbit hearts were subjected to hypoxic perfusion for 20 min, followed by 45 min-reoxygenation with or without pretreatment with coenzyme Q10. Hypoxia induced a decline in cardiac contractile force, a decrease in myocardial high-energy phosphates and a release of ATP metabolites and creatine phosphokinase from the perfused heart. Upon reoxygenation the rate of release of ATP metabolites subsided, but no appreciable recovery of the loss of contractile force and the reduction of myocardial ATP content was seen, and the release of creatine phosphokinase was increased further. Pretreatment of rabbits with coenzyme Q10 resulted in an appreciable recovery of cardiac contractile force and of myocardial ATP content upon reoxygenation. The release of creatine phosphokinase from hearts during hypoxia and reoxygenation was inhibited completely by the pretreatment. Changes in the UV absorbance of the perfusate suggested that coenzyme Q10 reduced the loss of ATP metabolites from hypoxic hearts. Furthermore, high-performance liquid chromatographic analysis indicated that coenzyme Q10 attenuated the release of inosine and hypoxanthine from the hearts and decreased myocardial inosine and adenosine content of the hypoxic heart, suggesting that coenzyme Q10 retards the breakdown of ATP metabolites which are possible substrates for a salvage synthesis of ATP, when oxygen is replenished. This could account for an appreciable restoration of ATP, and eventually provide a significant recovery of cardiac contractile force upon reoxygenation.     

Glucagon antagonism of calcium channel blocker-induced myocardial dysfunction

Calcium channel blockers (CCBs) may produce profound myocardial depression. Glucagon antagonized verapamil-induced hypotension and bradycardia in rats; however, glucagon's ability to antagonize other CCBs is unexplored. This study determined: a) if glucagon reverses verapamil-induced depression by a direct cardiac effect, b) if myocardial depression induced by diltiazem and nifedipine (representing different classes of CCBs) is also reversed by glucagon, and c) the glucagon concentration needed to reverse myocardial depression. Isolated rat hearts were perfused at a constant flow rate in a Langendorff preparation. Developed pressure (dP), contractility (+dP/dtmax), relaxation (-dP/dtmax), heart rate, and coronary vascular resistance were recorded. A CCB (n = 6, each blocker) was infused until greater than 50% depression of contractility was achieved. Glucagon was then simultaneously infused (perfusion concentration of 0.6-1.1 x 10(-7) M), and repeat cardiac variables were recorded. In a separate group of 36 hearts, glucagon dose response was determined. After producing a greater than 50% depression in dP/dtmax with 3 mumol of diltiazem, a single concentration of glucagon was infused simultaneously into each heart (perfusion concentrations between 10(-6) and 10(-9) M) and percent recovery of baseline function was determined. Glucagon restored baseline contractility and dP with all three CCBs. Complete reversal of diltiazem-induced myocardial depression occurs at glucagon concentrations greater than or equal to 5 x 10(-7) M. We conclude that a) glucagon directly reverses myocardial depression from three classes of CCBs at concentrations achieved in vivo, and b) glucagon may be useful in the treatment of CCB-induced myocardial toxicity.     

The Rapid Changes of Hepatic Glycolytic Enzymes and Fructose-1, 6-Diphosphatase Activities after Intravenous Glucagon in Humans

Glucagon (0.04-0.09 mg/kg/min) was given intravenously for either 2 or 3 min to eight patients with fasting-induced hypoglycemia. One child had hepatic phosphorylase deficiency, two children had glucose-6-phosphatase deficiency, two children had debrancher enzyme (amylo-1,6-glucosidase) deficiency, and two children and one adult had decreased hepatic fructose-1,6-diphosphatase (FDPase) activity. Liver biopsy specimens were obtained before and immediately after the glucagon infusion. The glucagon caused a significant increase in the activity of FDPase (from 50+/-10.0 to 72+/-11.7 nmol/mg protein/min) and a significant decrease in the activities of phosphofructokinase (PFK) (from 92+/-6.1 to 41+/-8.1 nmol/mg protein/min) and pyruvate kinase (PK) (from 309+/-39.4 to 165+/-23.9 nmol/mg protein/min). The glucagon infusion also caused a significant increase in hepatic cyclic AMP concentrations (from 41+/-2.6 to 233+/-35.6 pmol/mg protein). Two patients with debrancher enzyme deficiency who had biopsy specimens taken 5 min after the glucagon infusion had persistence of enzyme and cyclic AMP changes for at least 5 min. One child with glucose-6-phosphatase deficiency was given intravenous glucose (150 mg/kg/min) for a period of 5 min after the glucagon infusion and biopsy. The plasma insulin concentration increased from 8 to 152 muU/ml and blood glucose increased from 72 to 204 mg/100 ml. A third liver biopsy specimen was obtained immediately after the glucose infusion and showed that the glucagon-induced effects on PFK and FDPase were completely reversed. The glucagon infusion caused an increase in hepatic cyclic AMP concentration from 38 to 431 pmol/mg protein but the glucose infusion caused only a slight decrease in hepatic cyclic AMP concentration (from 431 to 384 pmol/mg protein), which did not appear to be sufficient to account for the changes in enzyme activities. Hepatic glucose-6-phosphatase and fructose-1,6-diphosphate aldolase activities were not altered by either the glucagon or the glucose infusion in any patients. Cyclic AMP (0.05 mmol/kg) was injected into the portal vein of adult rats and caused enzyme changes similar to those seen with glucagon administration in humans. Our findings suggest that rapid changes in the activities of PFK, PK, and FDPase are important in the regulation of hepatic glycolysis and gluconeogenesis, respectively, in humans and that cyclic AMP may mediate the glucagon- but probably not the glucose-insulin-induced changes in enzyme activities.     

Concentration-dependent effects of prostacyclin on the response of the isolated guinea pig heart to ischemia and reperfusion: possible involvement of the slow inward current

Isolated guinea pig hearts were subjected to 40 min of low flow global ischemia followed by 30 min of reperfusion. The effects of prostacyclin (PGI2) (10 pg/ml-10 ng/ml) on the response of hearts to ischemia and reperfusion were studied. Ischemia caused a 55% decline in contractile force and the development of contracture. Sinus bradycardia and varying degrees of atrioventricular conduction block were observed. Reperfusion was associated with rapid recovery of contractile force and a gradual decline in resting tension. PGI2 (1 ng/ml) enhanced ischemic contracture significantly at 10 and 20 min (P less than .05). Hearts made ischemic in the presence of PGI2 developed higher degrees of atrioventricular conduction block when compared to controls. Reperfusion in the presence of 1 or 10 ng/ml of PGI2 caused a significant decline in recovery of force (P less than .05) and enhanced reperfusion-associated contracture. We examined the influence of verapamil (100 ng/ml) and lowering external calcium to 1.25 mM on hearts subjected to ischemia and reperfusion in the absence of presence of PGI2 (1 ng/ml). Neither verapamil nor 1.25 mM calcium exerted significant effects on the decline of contractile force during ischemia or on recovery of contractility upon reperfusion. However, verapamil did reverse the reperfusion-associated cardiodepressant effects of PGI2. Verapamil abolished contracture in control hearts after 5 and 10 min of reperfusion and prevented the enhancement of contracture in hearts reperfused in the presence of PGI2.(ABSTRACT TRUNCATED AT 250 WORDS)     

Neutrophils delay functional recovery of the post-hypoxic heart of the rabbit

A postischemic contractile dysfunction termed myocardial stunning has been described in vivo and is attributed, in part, to the generation of oxygen-derived free radicals and the presence of neutrophils. An analogous contractile derangement occurs in the posthypoxic heart in vitro. This study determined the role of neutrophils in hypoxia/reoxygenation-induced cardiac dysfunction in the isolated buffer-perfused rabbit heart utilizing a recirculating system with or without neutrophils present. In control hearts perfused with a neutrophil-free buffer, reoxygenation after 20 min of hypoxia was associated with a slow recovery of contractility which returned to prehypoxic values by 30 to 45 min. Although perfusion with buffer-containing neutrophils did not affect the hypoxia-induced decrease in myocardial contractility, the recovery of contractile function during subsequent reoxygenation was significantly diminished (P less than .01 vs. control), remaining depressed by 30 to 35% at 45 min. The myocardial neutrophil content increased approximately 2-fold in response to hypoxia and reoxygenation, as assessed using 51Cr-labeled neutrophils. The deleterious effects of neutrophil perfusion on cardiac function could not be attributed to neutrophil-mediated plugging of coronary vessels or enhanced myocellular damage. These results support the concept that neutrophils contribute to the cardiac dysfunction described in this model.