Preservation of myocyte contractile function after hypothermic, hyperkalemic cardioplegic arrest with 2, 3-butanedione monoxime

One proposed contributory mechanism for depressed ventricular performance after hypothermic, hyperkalemic cardioplegic arrest is a reduction in myocyte contractile function caused by alterations in intracellular calcium homeostasis. Because 2,3-butanedione monoxime decreases intracellular calcium transients, this study tested the hypothesis that 2,3-butanedione monoxime supplementation of the hyperkalemic cardioplegic solution could preserve isolated myocyte contractile function after hypothermic, hyperkalemic cardioplegic arrest. Myocytes were isolated from the left ventricles of six pigs. Magnitude and velocity of myocyte shortening were measured after 2 hours of incubation under normothermic conditions (37 degrees C, standard medium), hypothermic, hyperkalemic cardioplegic arrest (4 degrees C in Ringer's solution with 20 mEq potassium chloride and 20 mmol/L 2,3-butanedione monoxime). Because beta-adrenergic agonists are commonly employed after cardioplegic arrest, myocyte contractile function was examined in the presence of the beta-agonist isoproterenol (25 nmol/L). Hypothermic, hyperkalemic cardioplegic arrest and rewarming reduced the velocity (32%) and percentage of myocyte shortening (27%, p < 0.05). Supplementation with 2,3 butanedione monoxime normalized myocyte contractile function after hypothermic, hyperkalemic cardioplegic arrest. Although beta-adrenergic stimulation significantly increased myocyte contractile function under normothermic conditions and after hypothermic, hyperkalemic cardioplegic arrest, contractile function of myocytes exposed to beta-agonist after hypothermic, hyperkalemic cardioplegic arrest remained significantly reduced relative to the normothermic control group. Supplementation with 2,3-butanedione monoxime restored beta-adrenergic responsiveness of myocytes after hypothermic, hyperkalemic cardioplegic arrest. Thus, supplementation of a hyperkalemic cardioplegic solution with 2,3-butanedione monoxime had direct and beneficial effects on myocyte contractile function and beta-adrenergic responsiveness after cardioplegic arrest. A potential mechanism for the effects of 2,3-butanedione monoxime includes modulation of intracellular calcium transients or alterations in sensitivity to calcium. Supplementation with 2,3-butanedione monoxime may have clinical utility in improving myocardial contractile function after hypothermic, hyperkalemic cardioplegic arrest.     

Adrenergic processess and partial secretion of the stomach

The stimulation of alpha- and beta-adrenergic processes by epinephrine, phenylephrine and isoproterenol increases the hydrochloric acid and gastric juice secretion (as well as the secretion of gastric juice components is decreased under the influence of the alpha-adrenergic blocking agents dehydrobenzperidol and beta-adrenergic blocking agent propranolol. However, propranolol essentially reduces the acid components secretion not affecting greatly the alkaline components secretion of the patients with a high basal secretion. As a result the P/NP-ration is decreased.     

Modulation of the stress-induced synthesis of hsp27 and alpha B-crystallin by cyclic AMP in C6 rat glioma cells

The possible participation of cyclic AMP in the stress-induced synthesis of two small stress proteins, hsp27 and alpha B-crystallin, in C6 rat glioma cells was examined by specific immunoassays, western blot analysis, and northern blot analysis. When C6 cells were exposed to arsenite (50-100 microM for 1 h) or heat (42 degrees C for 30 min), expression of hsp27 and alpha B-crystallin was stimulated, with levels of the two proteins reaching a maximum after 10-16 h of culture. Induction of hsp27 was markedly enhanced when cells were exposed to arsenite in the presence of isoproterenol (20 microM) or epinephrine (20 microM) but not in the presence of phenylephrine. The stimulatory effects of isoproterenol and epinephrine were blocked completely by propranolol, an antagonist of beta-adrenergic receptors. Cholera toxin (2 micrograms/ml), forskolin (20 microM), and dibutyryl cyclic AMP (2.5 mM), all of which are known to increase intracellular levels of cyclic AMP, also stimulated the arsenite- or heat-induced accumulation of hsp27. Treatment of cells with each of these modulators alone did not result in the induction of hsp27. The level of hsp70 in C6 cells, as estimated by western blot analysis, was also enhanced by arsenite or heat stress. However, induction of hsp70 by stress was barely stimulated by isoproterenol. By contrast, induction of alpha B-crystallin by heat or arsenite stress was suppressed when isoproterenol, cholera toxin, forskolin, or dibutyryl cyclic AMP was present during the stress period. Northern blot analysis of the expression of mRNAs for hsp70, hsp27, and alpha B-crystallin showed that the modulation of the stress-induced accumulation of the three hsps by the various agents was regulated at the level of the corresponding mRNA. These results indicate that stress responses of hsp70, hsp27, and alpha B-crystallin in C6 rat glioma cells are regulated differently and, moreover, that when the level of cyclic AMP increases in cells, the response to stress of hsp27 is stimulated but that of alpha B-crystallin is suppressed.     

Triiodothyronine reverses depressed contractile performance after excessive catecholamine stimulation

BACKGROUND: Conflicting results have been reported regarding the acute effects of triiodothyronine (T3) on myocardial contractile performance. The present study analyzes the role of T3 in reversing the depressant effect of excessive catecholamine stimulation in isolated porcine left ventricular myocardium. METHODS: Thirty-six left ventricular trabeculae (0.4 x 6.0 mm) obtained from 6 pigs were used for measurements of isometric force development, isotonic shortening, and intracellular calcium in three experimental series (measurement conditions: 37 degrees C; optimal length; supramaximal electrical stimulation, 1 Hz; calcium measurement, fura-2 ratio method; frequency, 225 Hz). In series 1, isometric force development was measured before and after a 60-minute incubation with 10(-7) mol/L epinephrine in preparations with (n = 6) and without (n = 6) preceding fura-2 loading for calcium measurements. In series 2, the acute effects of a 30-minute administration of T3 (10(-9) mol/L) on isometric force and intracellular calcium were analyzed (n = 6). In series 3, after simultaneous fura-2 loading and a 6-hour 10(-7) mol/L epinephrine exposure the effects of T3 (10(-9) mol/L, 30 minutes) on force development, shortening, and intracellular calcium transient were analyzed. RESULTS: Long-term and high-dose epinephrine exposure induced a severe contractile depression with a significant reduction of isometric force development (p < 0.05) and increased diastolic (p < 0.001) and systolic calcium (p < 0.001). In normal porcine myocardium T3 had no effect on the extent of isometric force generation but accelerated the time course of force development (p < 0.05) and increased the calcium transient (p < 0.001). After induction of myocardial depression by epinephrine exposure T3 accelerated the intracellular calcium transients and reduced diastolic calcium. Triiodothyronine increased the shortening amplitude and the force amplitude (p < 0.01). CONCLUSIONS: Triiodothyronine reverses depressed contractile performance after preceding high-dose epinephrine exposure in isolated porcine myocardium. Increased force amplitudes and unaltered or even reduced intracellular calcium transients argue in favor of a resensitization of the contractile apparatus for calcium by T3. The study supports a potential role for T3 treatment in depressed myocardium after previous excessive catecholamine exposure (eg, brain death, catecholamine treatment, ischemia).     

Differential sensitivity to the wake-promoting actions of norepinephrine within the medial preoptic area and the substantia innominata.

Mapping studies were conducted to delineate the site(s) of action for the arousal-enhancing actions of norepinephrine (NE) within the basal forebrain region encompassing the medial preoptic area (MPOA) and the substantia innominata (SI). Varying doses of NE, the β-agonist, isoproterenol, or the α?-agonist, phenylephrine, were infused into the MPOA or SI in the resting rat. Infusions of NE (4 nmol, 16 nmol/150 nl), isoproterenol (15 nmol/150 nl), and phenylephrine (40 nmol/250 nl) into the MPOA elicited robust increases in waking. In contrast, neither isoproterenol or phenylephrine infusions into the SI altered behavioral state. NE infusions into the SI increased waking only at the highest dose, and at this dose there was an anatomical gradient for NE-induced waking, with infusions placed farther from the MPOA, producing smaller increases in waking. Thus, in contrast to the MPOA, the SI is relatively insensitive to the wake-promoting actions of NE. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neurocardiogenic syncope in children with a normal heart

OBJECTIVES: The purpose of this study was to review the results of investigation and management of children with syncope and a structurally normal heart. BACKGROUND: Syncope is a common clinical problem and has many etiologies. Autonomic testing and, in particular, the tilt/orthostatic test have helped to positively diagnose neurocardiogenic syncope in a high proportion of such patients. METHODS: Patient case notes and autonomic test charts were reviewed in 162 children aged 1 to 20 years (mean age 12.8 years) with syncope. The autonomic test consisted of orthostatic maneuver, carotid sinus massage, diving reflex, Valsalva maneuver and dose response to intravenous boluses of isoproterenol and phenylephrine. Serum levels of epinephrine and norepinephrine were drawn during the orthostatic test. After confirmation of neurocardiogenic syncope, treatment was begun with fludrocortisone and salt, and beta-adrenergic blocking agents were used as a second line of therapy when indicated. RESULTS: The orthostatic test was positive for neurocardiogenic syncope in 100 patients (62%) and negative in 62 (38%). Patients in the former group were older, were more often female and had a diminished response to carotid sinus massage, a higher Valsalva ratio and a higher supine epinephrine level. Both groups showed an increase in epinephrine and norepinephrine levels at 5 min of standing. In the orthostatic positive group at the time of syncope, norepinephrine levels decreased, whereas epinephrine levels increased. Patients in this group were also more sensitive to the vasodilating effect of isoproterenol but not to its chronotropic effects. Eleven patients had cardioinhibitory syncope (asystole > or = 3 s). Of these, three had pacemaker implantation. Fludrocortisone and salt used in 84 patients in the orthostatic positive group produced resolution of symptoms in 55 patients (65%) and improvement in 14 (17%). Ten patients received beta-blockers, with resolution in four and improvement in four. CONCLUSIONS: Patients with orthostatic test-proved neurocardiogenic syncope show evidence of autonomic dysfunction. They also show beta-adrenergic hypersensitivity. Treatment initiated on the basis of the protocol was associated with amelioration of symptoms in the majority of patients.     

The effect of triiodothyronine on myocardial contractile performance after epinephrine exposure: implications for donor heart management

BACKGROUND: This study analyzes in the experimental model of isolated human atrial myocardium whether the myocardial contractile depression occurring after high-dose/long-term catecholamine exposure (as typically occurring in brain-dead organ donors) can be reversed by thyroid hormone administration. METHODS: Isolated trabeculae were prepared from atrial myocardium from patients undergoing coronary artery bypass (n = 15). Initial measurements of isometric force were carried out (measurement conditions of 37 degrees C, Krebs Henseleit solution, supramaximal electrical stimulation, 1 Hz, at optimal length). Then the trabeculae were incubated for 6 hours at 26 degrees C in a Krebs Henseleit solution containing epinephrine 10(-7) mol/L and the fluorescent dye FURA-2/AM for calcium measurements. At the end of the incubation period, isometric force, isotonic shortening, and intracellular calcium transient (FURA-2 "ratio method") were measured. After 30 minutes administration of triiodothyronine (5 x 10(-9) mol/L), the measurements were repeated. Control groups included 6 hours incubation in 4 degrees C Krebs Henseleit solution (n = 5); 6 hours incubation in 26 degrees C FURA-2/AM (n = 5); and 6 hours incubation in epinephrine 10(-7) mol/L (n = 5). RESULTS: After 6 hours catecholamine exposure isometric force declined significantly to 56.8% (p < .0001) and isotonic shortening to 54% of its initial value (p < .01). Administration of triiodothyronine was associated with a significant recovery of the isotonic shortening amplitude (p < .005), of isometric force development (p < .01), an increased velocity of force development (p < .0001), and of diastolic force decay (p < .005). At the same time the shape of the intracellular calcium transient became smaller as a result of an accelerated diastolic decay. The amplitude of the calcium transient remained unaltered, whereas the calcium time integral was reduced (p < .05). CONCLUSION: In the model of isolated human myocardium, experimental depression of the contractile performance resulting from long-term catecholamine exposure could be reversed by a 30-minute triiodothyronine incubation. The experimental data showing increased force amplitudes at unaltered amplitudes of the intracellular calcium transient and an even-reduced calcium time integral provide strong evidence for a sensitization of the contractile apparatus for calcium by triiodothyronine. The data provide additional knowledge to explain the successful administration of triiodothyronine in donor heart management.     

Effect of hypoglycemia on beta-adrenergic sensitivity in normal and type 1 diabetic subjects

OBJECTIVE: The purpose of this study was to assess the potential role of reduced tissue sensitivity to catecholamines in the pathogenesis of hypoglycemia unawareness in patients with type 1 diabetes. RESEARCH DESIGN AND METHODS: The effect of a single episode of hypoglycemia on beta-adrenergic sensitivity was studied in 10 type 1 diabetic patients with apparently normal awareness of hypoglycemia (age 29 +/- 5 years, diabetes duration 13 +/- 8 years, HbA1c 7.3 +/- 0.9%) and 10 age-matched healthy control subjects. Beta-adrenergic sensitivity was measured with the isoproterenol test after a hyperinsulinemic euglycemic clamp and after a hyperinsulinemic hypoglycemic clamp. Beta-adrenergic sensitivity was expressed as the dose of intravenous isoproterenol that increased the heart rate by 25 beats/min (IC25). RESULTS: During hypoglycemia, diabetic subjects had an impaired plasma epinephrine response compared with that of the control subjects (16.7 +/- 5.0 vs. 40.1 +/- 6.8 ng/ml, P = 0.02). In control subjects, the IC25 was lower after hypoglycemia than after euglycemia (0.83 +/- 0.22 vs. 1.13 +/- 0.21 microg, P = 0.02) indicating an increase in beta-adrenergic sensitivity. In diabetic subjects, on the other hand, the IC25 was greater after hypoglycemia than after euglycemia (1.00 +/- 0.26 vs. 0.65 +/- 0.14 microg, P = 0.04), indicating a decrease in beta-adrenergic sensitivity. CONCLUSIONS: In normal subjects, a single episode of hypoglycemia increases beta-adrenergic sensitivity. In diabetic subjects, in contrast, hypoglycemia reduces beta-adrenergic sensitivity. These results provide evidence that in type 1 diabetic patients, some maladaptation of tissue sensitivity to catecholamines contributes to the development of hypoglycemia unawareness. A unifying hypothesis is presented for the pathogenesis of hypoglycemia unawareness in type 1 diabetic patients incorporating the concepts of both a reduced catecholamine response and reduced adrenergic sensitivity     

Activation of the Na+-K+(NH4+)-2Cl(-)- cotransporter from rat submandibular glands in response to VIP

A cellular suspension from rat submandibular glands was prepared with collagenase. The intracellular pH (pHi) was estimated with 2',7'-bis-(2-carboxy-ethyl)-5(6)-carboxyfluorescein (BCECF). After exposure to NH4Cl, the pHi transiently increased (diffusion of NH3) and then dropped (influx of NH4+). Isoproterenol increased 2.5-fold the rate of NH4+ influx; bumetanide, an inhibitor of the Na+-K+-2Cl(-)-cotransporter blocked the response to isoproterenol, confirming that the beta-adrenergic agonist stimulated the cotransporter. Forskolin (1 micromol/L) mimicked the response to isoproterenol. VIP (1 nmol/L(-1) micromol/L) also increased the activity of the cotransporter. Cyclic AMP rather than calcium was the mediator of this activation since 1) carbachol which increased the [Ca2+]i fivefold increased the uptake of NH4+ by only 50%; 2) only high concentrations of VIP significantly increased the [Ca2+]i; 3) incubation in the presence of EGTA had no effect on the response to VIP; 4) low concentrations (nmol/L) of the neuropeptide increased the intracellular level of cAMP; and 5) the stimulation of the cotransporter by VIP, forskolin, and isoproterenol was inhibited by H8, an inhibitor of cAMP-dependent protein kinase. It is concluded that the Na+-K+-2Cl(-)-cotransporter of rat submandibular glands is activated by isoproterenol, forskolin, and neuropeptides of the VIP family by a mechanism involving cAMP-dependent processes. The activation of the cotransporter by VIP could partly explain the potentiating effect of VIP on the response to sialagogues like substance P or muscarinic agonists.     

Effects of alpha 1-adrenoreceptor subtype blockade on ischemia-reperfusion injury

To clarify the roles of subclasses of alpha 1-adrenoreceptors in ischemic-reperfused myocardium, we compared the effect of the nonselective alpha 1-blocker bunazosin with that of the alpha 1A-blocker WB4101 and the alpha 1B-blocker chlorethylclonidine (CEC) in isolated rat hearts. After 30 min of preperfusion, Langendorff-perfused hearts were subjected to 25 min of global ischemia followed by 30 min of reperfusion. Hearts were randomly divided into 4 groups, with one of the following substances being added to the perfusate: buffer alone (control), 10(-6) mol/L bunazosin, 10(-7) mol/L WB4101, or 10(-7) mol/L CEC. Bunazosin had a negative inotropic effect and preserved the postischemic ATP content, reduced the postischemic increase in intracellular Na+ content and then enhanced postreperfusion recovery of creatine phosphate. Bunazosin also reduced myocardial 45Ca2+ uptake during reperfusion (control 5.2 vs bunazosin 2.5 mumol/g dry weight of tissue (dwt), p < 0.01). However, the recovery of left ventricular developed pressure (DP) was not improved when bunazosin was added to the perfusate during reperfusion. WB4101 had neither a negative inotropic nor an energy-sparing effect, but it improved the recovery of DP (control 43% vs WB4101 56% of preischemic value, p < 0.05) with no reduction in myocardial 45Ca2+ uptake. CEC had a negative inotropic and energy-sparing effect and then reduced myocardial 45Ca2+ uptake (CEC 3.1 mumol/g dwt, p < 0.05), but it did not improve the recovery of DP. These results suggest that the preischemic administration of an alpha 1B-adrenoreceptor subtype blocker protected ischemic-reperfused myocardium via reduction of Ca2+ overload, whereas the selective blockade of the alpha 1A-adrenoreceptor subtype reduced myocardial damage via mechanism(s) other than Ca2+ metabolism.     

Endotoxin differentially impairs receptor-mediated relaxation in rat isolated pulmonary and thoracic aortic vessels

PURPOSE: The purpose of this study was to determine the effect of endotoxin on vasorelaxation in the pulmonary and systemic circulations in response to the following agonists that require generation of cyclic adenosine monophosphate: (1) beta-adrenergic receptor stimulation with isoproterenol; (2) H2 receptor stimulation with dimaprit; and (3) adenylate cyclase stimulation with forskolin. METHODS: Male Sprague-Dawley rats weighing 250 to 350 g were injected with endotoxin (20 mg/kg intraperitoneal) or saline. Six hours later, the cumulative dose response to beta-adrenergic receptor stimulation (isoproterenol), H2 receptor stimulation (dimaprit), and adenylate cyclase stimulation (forskolin) was determined in isolated rat pulmonary artery and thoracic aortic rings preconstricted with phenylephrine. RESULTS: Endotoxin caused significant impairment of relaxation to isoproterenol in the pulmonary artery, but the response in the aorta was not different from the control response. In the pulmonary circulation, endotoxin converted the response to dimaprit from vasorelaxation to vasoconstriction. On the other hand, dimaprit resulted in vasorelaxation in the thoracic aorta after endotoxin; however, the response was impaired compared with the control response. Endotoxin did not affect the dose response to forskolin in either the pulmonary artery or the thoracic aorta. CONCLUSION: From these data, we conclude that endotoxin causes regional specific changes in vascular reactivity. These changes in vascular reactivity result in preserved vasorelaxation in the systemic circulation and impairment of vasorelaxation in the pulmonary circulation in response to endotoxin.     

The effect of coenzyme Q10 and cold cristalloid cardioplegia on hypothermic global ischemia

Coenzyme Q10 (CoQ10, ubiquinone) has been shown to be protective against myocardial ischemia/reperfusion induced injury. The purpose of this study was to investigate the effect of CoQ10 added to cold cristalloid cardioplegia on hypothermic ischemia and normothermic reperfusion using an isolated working rat heart. Hearts (n = 6-9/group) from male Wistar rats were aerobically (37 degrees C) perfused (20 min) with bicarbonate buffer. This was followed by a 3-min infusion of St. Thomas' Hospital cardioplegic solution containing various concentrations of CoQ10 (0, 1, 3, 6, 12, and 58 mumol/L). Hearts were then subjected to 180 min of hypothermic (20 degrees C) global ischemia and 35 min of normothermic (37 degrees C) reperfusion (15 min Langendorff, 20 min working). Ventricular fibrillation (Vf) upon reperfusion was irreversible in the 12 and 58 mumol/ L CoQ10 groups (4/6 and 3/6, respectively). In the hearts which Vf upon reperfusion was not irreversible, the percent recovery of aortic flow (%AF) was 43.3 +/- 5.4% (n = 9) in the control group versus 31.6 +/- 7.7% (n = 6), 38.0 +/- 12.0% (n = 6), 27.2 +/- 6.9% (n = 6), 31.3% (n = 2), and 30.4 +/- 14.2% (n = 3) in the 1, 3, 6, 12, and 58 mumol/L CoQ10 groups, respectively. Creatine kinase leakage during Langendorff reperfusion tended to be greater in the 12 and 58 mumol/L CoQ10 groups than in the control group. Thus, CoQ10 in the cold cristalloid cardioplegic solution induced irreversible Vf upon reperfusion and failed to improve functional recoveries following hypothermic global ischemia.     

Use of immunoblot assay to define serum antibody patterns associated with Helicobacter pylori infection and with H. pylori-related ulcers

OBJECTIVE: We evaluated the effect of pretreatment with nitric oxide precursor before ischemia on recovery with reperfusion in rat hearts. METHODS: Isolated rat hearts were perfused with Krebs-Henseleit buffer without (C group) or with 3 mmol/L L-arginine (A group) before 30 minutes of ischemia. The left ventricular function, including heart rate, developed pressure, maximal dp/dt, and coronary flow, were measured before pretreatment and after 10 and 30 minutes of reperfusion. Cyclic guanosine monophosphate (by radioimmunoassay), calcium (by absorption spectrophotometry), and inositol 1,4,5-triphosphate synthesized from tritiated myo-inositol (by ion-exchange chromatography preceding counting) were measured at the same times and immediately after ischemia. RESULTS: Recovery of ventricular function was significantly greater in the A group than in the C group. Pretreatment increased postischemic cyclic guanosine monophosphate content compared with the preischemic level (from 1.06 +/- 0.12 to 1.94 +/- 0.09 pmol/mg protein, p < 0.05). No change in cyclic guanosine monophosphate was evident in the C group. In the C group, inositol triphosphate content increased after 10 minutes of reperfusion beyond the preischemic level (from 0.53 +/- 0.023 to 1.15 +/- 0.045 cpm x 10(-3)/gm, p < 0.05) as did calcium at 30 minutes (from 4.12 +/- 0.164 to 6.86 +/- 0.544 mmol/gm dry weight). In the A group, both of these increases were significantly attenuated. CONCLUSION: These data suggest that L-arginine pretreatment may reduce calcium overload by increasing cyclic guanosine monophosphate production, which in turn downregulates inositol triphosphate synthesis during reperfusion.     

Pyruvate potentiates beta-adrenergic inotropism of stunned guinea-pig myocardium

This study tested the hypotheses that the sensitivity of stunned myocardium to beta-adrenergic stimulation is diminished, and that metabolic intervention with pyruvate can restore beta-adrenergic responsiveness to pre-ischemic levels. Isolated working guinea-pig hearts metabolizing 10 mM glucose were stunned by 45 min of low flow ischemia, and pyruvate and/or isoproterenol treatments were initiated 15 and 30 min after reperfusion, respectively. The dose: response for cardiac power from 0.1-100 nM isoproterenol was significantly shifted to the right in stunned hearts: EC50 (nm) increased from 0.3 +/- 0.06 to 5.2 +/- 1.86. Pyruvate (5 mM) largely restored isoproterenol responsiveness of stunned myocardium, lowering EC50 to 1.1 +/- 0.34 nM. Maximum power was similar in each group. Additional stunned hearts were treated with intermediate (2 nM) or high (30 nM) isoproterenol concentrations with or without pyruvate. Combining treatments produced a significant interaction at the low dose of isoproterenol, increasing cardiac power (mJ x min(-1) x g(-1)) to 149 +/- 20, twice the sum of the individual treatments (2 nM isoproterenol: 34 +/- 11; pyruvate: 33 +/- 8). Cyclic AMP content was unaltered by isoproterenol or pyruvate alone but was increased 41% by the combination. Power was maximized by 30 nM isoproterenol, which tripled cyclic AMP content; pyruvate did not augment these responses, but lessened the isoproterenol-induced decline in cytosolic phosphorylation potential. Conclusions: Beta-adrenergic inotropism is attenuated in stunned myocardium, although the maximal response is unchanged. Pyruvate potentiated the effects of sub-maximal doses of isoproterenol without depleting cellular energy reserves further, and attenuated energy depletion by high doses of isoproterenol. Pyruvate may allow restoration of contractile performance with lower, energetically less costly doses of beta-adrenergic agents.     

Beta-adrenergic regulation of the eosinophil respiratory burst as detected by lucigenin-dependent luminescence

Because beta-adrenoceptor agonists are commonly used in the treatment of disease states associated with eosinophil activation, beta-adrenergic regulation of the eosinophil respiratory burst (as monitored with lucigenin-dependent luminescence) was evaluated. Normodense, nonprimed eosinophils from healthy volunteer subjects were potently inhibited by very low concentrations of isoproterenol. The inhibitory concentration of 50% for isoproterenol was approximately 2 nmol/L. The beta-agonist was able to inhibit the eosinophil respiratory burst induced by receptor-mediated (chemotactic peptide) and nonreceptor-mediated (calcium ionophore and phorbol ester) stimuli. Thus beta-agonist inhibition was unlikely to be isolated to an effect at the receptor or G protein linkage. To determine whether cyclic adenosine 3',5' monophosphate (cAMP) may mediate beta-agonist effects, studies were performed with the type IV cAMP phosphodiesterase inhibitor Ro-201724. beta-Agonist inhibition of the respiratory burst was clearly synergistic with effects of Ro-201724. We conclude that beta-adrenoceptor agonists can regulate the eosinophil respiratory burst at least partially through an effect mediated by cAMP. Because regulation of the eosinophil by isoproterenol was observed at very low concentrations, these results may be relevant to pharmacologic effects of beta-agonists in disease states complicated by eosinophil activation during asthma.     

Differentiation of smooth muscle cells from undifferentiated cells of chicken gizzard occurs on the layer of fibroblast-like cells

Conflicting results have been reported in literature about the influence of beta-adrenergic stimulation on the fast cardiac sodium current (INa+). To elucidate these mechanisms in multicellular preparations we used the loose-patch-clamp technique to evaluate the effect of the beta-adrenergic agonist isoproterenol 1-1000 nmol/l. Isoproterenol enhanced INa+ at all membrane potentials by elevation of the maximal available INa+ . Only at the high concentration of 1 micromol/l was INa+ slightly depressed after depolarizing conditioning clamps. The most marked increase of the maximal available INa+ was 30+/-9% after application of 100 nmol/l isoproterenol. To learn about the mechanisms in view of sodium channel modulation we combined isoproterenol with the sodium channel blocker lidocaine (47 micromol/l). Under these circumstances the effects of both drugs were completely independent. This investigation shows clearly that low concentrations of isoproterenol increase INa+ in multicellular preparations by a gating-independent mechanism.     

The guanylate cyclase-coupled natriuretic peptide receptor: a new target for prevention of cold ischemia-reperfusion damage of the rat liver

The aim of our studies was to investigate hormonal prevention of hepatic preservation damage by the atrial natriuretic peptide (ANP) and the mechanisms involved. Isolated perfusion of rat livers was performed in a nonrecirculating fashion. Twenty minutes of preischemic perfusion was performed with or without different concentrations of ANP, followed by 24-hour storage in cold University of Wisconsin (UW) solution. Two hundred nanomoles of ANP prevented hepatocellular damage during a 2-hour reperfusion period as indicated by a marked attenuation of the sinusoidal efflux of lactate dehydrogenase (LDH) and purine nucleoside phosphorylase (PNP), and by reduced Trypan blue uptake. Furthermore, postischemic bile flow as an indicator of liver function was significantly improved by about 60% with 200 nmol/L ANP. No protection was conveyed by 20 nmol/L ANP nor by pretreatment with 200 nmol/L ANP for only 10 minutes. The effects of ANP seemed to be mediated by the guanylate cyclase-coupled A (GC-A) receptor and cyclic guanosine monophosphate (cGMP): whereas expression of both GC-A and GC-B receptors as well as of the GC-C receptor was found, cGMP did protect from ischemia-reperfusion damage, but selective ligands of the B and C receptor did not. To begin to determine the mechanisms of ANP-mediated protection, different parameters were investigated: ANP had no effect on portal pressure as an indicator of hepatic circulation, nor on intracellular energy depletion determined by adenosine nucleotide concentration. However, the marked augmentation of nuclear factor kappaB (NF-kappaB) binding activity during reperfusion was prevented in ANP-pretreated livers. In conclusion, pretreatment with ANP protects the rat liver from cold ischemia-reperfusion damage. This effect is mediated via the GC-A receptor and cGMP, and may be linked to an influence of ANP on NF-kappaB activation. Thus, ANP signaling via the GC-A receptor should be considered as a new pharmacological target to prevent preservation injury of the liver.     

Evidence for the presence of adrenergic receptors in 3-day-old chick embryo

Effects of sympathomimetic amines without and with alpha and beta-adrenergic blocking agents on the heart rate and arterial and venous blood pressures in the 3-day-old chick embryo were studied. No chronotropic effect was observed. Norepinephrine caused a biphasic change in systolic and diastolic arterial pressures, the lower doses effecting a fall, and the higher doses a rise in these pressures. With phenylephrine a sharp rise in systolic, diastolic, and pulse pressures was seen. Isoproterenol caused a dramatic fall in systolic, diastolic, and pulse pressures. In the presence of phenoxybenzamine, the pressor effect of high doses of norepinephrine was reversed, the pressor effect of phenylephrine was abolished, and the hypotension with isoproterenol was enhanced. After propranolol, the hypotensive effect of low doses of norepinephrine was reversed, the pressor response to phenylephrine was unchanged, and the depressor effect of isoproterenol was abolished. These findings suggest the presence of functioning alpha- and beta-receptors in the 3-day-old chick embryo. Additionally, they suggest that the alpha-receptors develop more slowly in the chick embryo.     

Translocation of bacteria due to direct mucosal damage caused by Gastrografin. An experimental study in newborn rats

The aim of this study was to investigate the role of heat-shock proteins after heat-shock stress on the post-ischemic recovery of cardiac mechanical and endothelial function following a prolonged cardiac arrest. Isolated working rat hearts were subjected to a cardioplegic arrest for 4 hours at 4 degrees C. Three groups (n = 8 in each) were studied: (1) control, (2) sham-treated, and (3) heat-shocked rats. Postischemic recovery of cardiac output and endothelial function (as percent of preischemic control values) was 57.8% +/- 2.8% and 20.8% +/- 3.9% in group 1, 50.9% +/- 4.0% and 26.3% +/- 5.9% in group 2, and 74.0% +/- 2.4% and 51.2% +/- 8.0% in group 3, respectively. Both postischemic myocardial and endothelial function were improved by heat stress.     

Protective effect of clentiazem against epinephrine-induced cardiac injury in rats

We investigated the effects of clentiazem, a 1,5-benzothiazepine calcium antagonist, on epinephrine-induced cardiomyopathy in rats. With 2-week chronic epinephrine infusion, 16 of 30 rats died within 4 days, and severe ischemic lesions and fibrosis of the left ventricles were observed. In epinephrine-treated rats, left atrial and left ventricular papillary muscle contractile responses to isoproterenol were reduced, but responses to calcium were normal or enhanced compared to controls. Left ventricular alpha and beta adrenoceptor densities were also reduced compared to controls. Treatment with clentiazem prevented epinephrine-induced death (P < .05), and attenuated the ventricular ischemic lesions and fibrosis, in a dose-dependent manner. Left atrial and left ventricular papillary muscle contractile responses to isoproterenol were reduced compared to controls in groups treated with clentiazem alone, but combined with epinephrine, clentiazem restored left atrial responses and enhanced left ventricular papillary responses to isoproterenol. On the other hand clentiazem did not prevent epinephrine-induced down-regulation of alpha and beta adrenoceptors. Interestingly, clentiazem, infused alone, resulted in decreased adrenergic receptor densities in the left ventricle. Clentiazem also did not prevent the enhanced responses to calcium seen in the epinephrine-treated animals, although the high dose of clentiazem partially attenuated the maximal response to calcium compared to epinephrine-treated animals. In conclusion, clentiazem attenuated epinephrine-induced cardiac injury, possibly through its effect on the adrenergic pathway.