Dissecting x-ray-emitting gas around the center of our galaxy

Most supermassive black holes (SMBHs) are accreting at very low levels and are difficult to distinguish from the galaxy centers where they reside. Our own Galaxy's SMBH provides an instructive exception, and we present a close-up view of its quiescent x-ray emission based on 3 megaseconds of Chandra observations. Although the x-ray emission is elongated and aligns well with a surrounding disk of massive stars, we can rule out a concentration of low-mass coronally active stars as the origin of the emission on the basis of the lack of predicted iron (Fe) Kα emission. The extremely weak hydrogen (H)-like Fe Kα line further suggests the presence of an outflow from the accretion flow onto the SMBH. These results provide important constraints for models of the prevalent radiatively inefficient accretion state.

A faint discrete source origin for the highly ionized iron emission from the Galactic Centre region

The origin of the X-ray emission for the central region of our Galaxy has remained a mystery. In particular, the relative spectral contributions of the diffuse emission and discrete sources, which are critical to understanding the high-energy phenomena in this environment, have been unclear because of the lack of sufficient spatial resolution. Here we report the results of a large-scale imaging survey of the Galactic Centre that resolves these components. We find that the Kalpha emission from iron that has been highly ionized (so that it has only two electrons left), which has previously been attributed to the diffuse component, actually arises mainly from discrete sources. This suggests that the presence of a large amount of hot gas (T approximately 108 K) is no longer required to explain the iron line emission. The spectra of the discrete sources indicate the presence of numerous accreting white dwarfs, neutron stars, and/or black holes in the region. The diffuse emission dominates over the contribution from the faint point sources, and is shown to be associated globally with interstellar features that have been observed at radio and mid-infrared wavelengths, suggesting that it is the product of recent massive star formation.

Endothelin in myocardial ischaemia and reperfusion

Endothelin-1 (ET-1) is an extremely potent vasoconstrictor peptide derived from vascular endothelial cells. ET-1 can also be produced by other cell types such as smooth muscle cells and cardiomyocytes. Plasma levels of ET-1 are elevated during several different cardiovascular disorders like atherosclerosis, myocardial infarction and congestive heart failure. During and following myocardial ischaemia and reperfusion, the myocardial production and release of ET-1 is stimulated and the coronary constrictor response to ET-1 is enhanced. These findings all favour a pathophysiological role for ET-1 in the development of ischaemia/reperfusion injury. Accordingly, by using different pharmacological tools (monoclonal antibody, ET converting enzyme inhibitor or ET receptor antagonists) that block the biological actions of ET-1, myocardial ischaemia/reperfusion injury has been demonstrated to be reduced in experimental animal models, in terms of both reduction in final infarct size and improved recovery of myocardial performance and coronary flow. However, some studies have shown no cardioprotective effects of ET receptor antagonists. Possible explanations for these apparently conflicting results are differences in animal species used, route and timing of drug administration, experimental protocol and chemical nature of the antagonists. The potential mechanisms underlying the cardioprotective effects of ET antagonists are discussed and include prevention of no-reflow, inhibition of ET-induced neutrophil activation, abolishment of direct pro-ischaemic actions of ET on myocytes, and interruption of interference of ET with the renin-angiotensin system.

Sensitization of human colon cancer cells to TRAIL-mediated apoptosis

TNF-related apoptosis-inducing ligand (TRAIL), a novel member of the tumor necrosis factor (TNF) family, is thought to induce apoptosis preferentially in cancer cells; however, increasing evidence suggests that a number of cancers are resistant to TRAIL treatment. FLICE-like inhibitory protein (FLIP), which structurally resembles caspase-8, can act as an inhibitor of apoptosis when expressed at high levels in certain cancer cells. The purpose of our present study was to determine whether human colon cancer cells are sensitive to TRAIL treatment and, if not, to identify potential mechanisms of resistance. Colon cancer cells of different metastatic potential (KM12C, KML4A, and KM20) were found to be resistant to the effects of TRAIL when used as a single agent. FLIP expression levels were increased in all three KM cell lines. Treatment with either actinomycin D (Act D;10 :g/ml) or cycloheximide (CHX; 10 :g/ml) decreased FLIP expression levels in all three cell lines. The decrease in cellular levels of FLIP was associated with sensitization to TRAIL-mediated apoptosis, as demonstrated by enhanced cell death and caspase-3 activity compared with either Act D or CHX alone. Our findings suggest that reduction of FLIP levels by Act D or CHX renders TRAIL-resistant human colon cancer cells sensitive to TRAIL-mediated apoptosis. The combination of TRAIL along with agents such as Act D or CHX, which target proteins that prevent cell death, may provide a more effective and less toxic regimen for treatment of resistant colon cancers.

Daidzin, an antioxidant isoflavonoid, decreases blood alcohol levels and shortens sleep time induced by ethanol intoxication

The extract from an edible vine, Pueraria lebata, has been reported to be efficacious in lessening alcohol intoxication. In this study, we have tested the efficacy of one of the major components, daidzin, from this plant extract. When ethanol (40% solution, 3 g/kg body weight) was given to fasted rats intragastrically, blood alcohol concentration (BAC) peaked at 30 min after alcohol ingestion and reached 1.77 +/- 0.14 mg/ml (mean values +/- SD, n = 6). If daidzin (30 mg/kg) was mixed with the ethanol solution and given to animals intragastrically, BAC was found to peak at 90 min after alcohol ingestion and reached only 1.20 +/- 0.30 mg/ml (n = 6) (p < 0.05 vs. controls). The ability of daidzin to delay and decrease peak BAC level after ethanol ingestion was also observed in fed animals. In both fasted and fed rats given alcohol without daidzin, BAC quickly declined after reaching its peak at 30 min. By contrast, BAC levels receded more slowly if daidzin was also fed to the animals. Daidzin showed a chronic effect. Rats fed daidzin for 7 days before ethanol challenge, but not on the day of challenge, also produced lower and later peak BAC levels. Interestingly, daidzin, whether fed to rats only once or chronically for 7 days, did not significantly alter activities of either alcohol dehydrogenase or mitochondrial aldehyde dehydrogenase in the liver. Further experiments demonstrated that daidzin shortened sleep time for rats receiving ethanol intragastrically (7 g/kg) but not intraperitoneally (2 g/kg). To test whether daidzin delayed stomach-emptying, [14C]polyethylene glycol was mixed with ethanol and fed to rats.(ABSTRACT TRUNCATED AT 250 WORDS)

The protective effect of L-arginine on myocardial injury and endothelial function following ischaemia and reperfusion in the pig

The protective effect of the nitric oxide (NO) substrate L-arginine on myocardial ischaemial/reperfusion injury was studied in pigs. Four groups were subjected to 45 min ischaemia and 4 h reperfusion. One control group received coronary venous retroinfusion of saline, the second retroinfusion of L-arginine (1 mg.kg-1.min-1), the third retroinfusion of L-arginine plus the NO synthase inhibitor N omega-nitro-L-arginine (L-NNA), and the fourth systemic i.v. infusion of L-arginine (1 mg.kg-1.min-1). The infarct size in the L-arginine retroinfusion group was 35 +/- 5% of the myocardial area at risk compared to 76 +/- 5% in saline treated controls (P < 0.001). In pigs receiving the combination of retroinfused L-arginine and L-NNA the infarct size was similar to that of controls (79 +/- 4%). Systemic i.v. infusion of L-arginine did not influence the infarct size. Administration of L-NNA+L-arginine slightly increased arterial blood pressure during ischaemia but the groups did not differ in blood pressure, heart rate, rate-pressure product, left ventricular dP/dt or coronary blood flow during the reperfusion period. Coronary vasodilatation by acetylcholine was significantly compromised in the saline retroinfusion group, but not in the L-arginine retroinfusion group as compared to pigs not subjected to myocardial ischaemia. The results show that coronary venous retroinfusion of L-arginine reduces myocardial infarct size and preserves endothelial function via a local action which seems to be related to maintained nitric oxide formation.

L-arginine enhances functional recovery and Ca(2+)-dependent nitric oxide synthase activity after ischemia and reperfusion in the rat heart

The effects of L-arginine on ischemia/reperfusion-induced myocardial dysfunction as well as the tissue activity of nitric oxide synthase (NOS) were investigated in rat isolated Langendorff-perfused hearts. Hearts were subjected to nonischemic perfusion or 30 min of global ischemia followed by 30 min of reperfusion. The hearts subjected to ischemia/reperfusion received either vehicle, L-arginine (1 mM), D-arginine (1 mM), the NOS inhibitor NG-nitro-L-arginine (L-NNA, 1 mM), or L-arginine (1 mM) plus L-NNA (1 mM) at the beginning of ischemia. L-Arginine but not D-arginine significantly enhanced the recoveries of left ventricular double product and coronary flow compared with the vehicle group. There was a substantial activity of Ca(2+)-dependent NOS but no significant Ca(2+)-independent NOS activity in the hearts undergoing 60 min of nonischemic perfusion. After ischemia/reperfusion, Ca(2+)-dependent NOS activity significantly decreased (by > 90%) in comparison with that of nonischemic hearts. L-Arginine increased the Ca(2+)-dependent NOS activity compared with the vehicle group to a level that was similar to that observed in nonischemic hearts. There was no difference in Ca(2+)-dependent NOS activity between vehicle- and D-arginine-treated groups. Administration of L-NNA abolished the beneficial effects of L-arginine on functional recovery and on Ca(2+)-dependent NOS activity. There were no significant Ca(2+)-independent NOS activities in any of the ischemic groups. These results suggest that myocardial ischemia/reperfusion reduces Ca(2+)-dependent NOS activity in the heart. Administration of L-arginine enhances myocardial function and preserves Ca(2+)-dependent NOS activity after ischemia/reperfusion through a pathway involving NOS activity.

Beneficial effects of the endothelin receptor antagonist bosentan on myocardial and endothelial injury following ischaemia/reperfusion in the rat

The effects of bosentan, a nonpeptide endothelin receptor antagonist, on endothelin-induced changes in coronary flow and myocardial ischaemic and reperfusion injury were investigated in the Langendorff perfused rat isolated heart. Endothelin-1 (0.012-0.4 nmol) evoked dose-dependent reduction in coronary flow, which was attenuated by bosentan (1.0-10 microM) in a concentration-related fashion. The inhibitory effect of bosentan lasted more than 30 min. The endothelin ETB receptor agonist Suc-[Glu9,Ala11,15]endothelin-1-(8-21) (IRL 1620) increased coronary flow in the absence but not in the presence of bosentan. In hearts subjected to 30 min of global ischaemia followed by 30 min of reperfusion, the recoveries of the left ventricular developed pressure, dP/dtmax, and coronary flow were significantly larger in a group given bosentan 10 microM at the start of ischaemia (92 +/- 7%, 98 +/- 8% and 83 +/- 5%, respectively) than in a vehicle-treated group (70 +/- 4%, 70 +/- 6% and 42 +/- 2%, respectively) at the end of the reperfusion period. During the reperfusion period, left ventricular end diastolic pressure was significantly lower in the bosentan group than in the vehicle group. The area of no-reflow in the bosentan group was 7 +/- 3% of left ventricle compared to 21 +/- 2% in the vehicle group (P < 0.01). Acetylcholine-induced endothelium-dependent vasodilatation was significantly reduced after ischaemia and reperfusion in the vehicle group but not in the bosentan group. It is concluded that bosentan attenuates the coronary vasoconstrictor effect elicited by endothelin and reduces ischaemia/reperfusion-induced myocardial and endothelial injury in the rat isolated heart.(ABSTRACT TRUNCATED AT 250 WORDS)

Myocardial release of endothelin (ET) and enhanced ET(A) receptor-mediated coronary vasoconstriction after coronary thrombosis and thrombolysis in pigs

We investigated changes in vascular reactivity to endothelin (ET) and local release of ET-like immunoreactivity (ET-LI) induced by myocardial ischemia and reperfusion in a pig model of coronary thrombosis and thrombolysis and studied the possible mechanisms producing the changed vascular reactivity to ET-1. We induced coronary thrombosis by inserting a copper coil into the left anterior descending coronary artery (LAD) and achieved thrombolysis with tissue plasminogen activator (t-PA). Vascular reactivity to ET-1 in the nonischemic and ischemic/reperfused LAD diagonal branches was evaluated in vitro. ET-LI was analyzed in plasma from the great cardiac vein and aorta for estimation of local release. The vasoconstrictor response to ET-1 was enhanced twofold (p < 0.01) in the ischemic/reperfused arteries as compared with the nonischemic arteries. The vasoconstriction induced by the ETB receptor agonist [Ala 1,3,11,15] ET-1 or serotonin was not significantly affected by ischemia/reperfusion. The ETA receptor antagonist BQ-123 reversed the ET-1-induced vascular contraction to a similar degree in ischemic/reperfused and control arteries. The ET-1-induced vasoconstriction of control arteries was not affected by inhibition of nitric oxide (NO) synthase with NG-nitro-L-arginine (L-NNA) or cyclooxygenase with indomethacin. During reperfusion, the myocardial venoarterial plasma concentration difference of ET-LI and blood flow increased, resulting in an increased overflow of ET-LI. Our results demonstrate that coronary thrombosis and thrombolysis evokes enhanced local release of ET-LI during the reperfusion period and increases the vasoconstrictor effects of ET-1 through a mechanism related to ETA receptor activation but unrelated to altered endothelial function. These changes may play a role in the development of ischemic/reperfusion injury and no-reflow phenomenon.

Role of L-arginine in preventing myocardial and endothelial injury following ischaemia/reperfusion in the rat isolated heart

The protective effect of L-arginine on ischaemia/reperfusion-induced myocardial injury was investigated in the rat isolated Langendorff perfused heart. Six groups of hearts subjected to 30 min global ischaemia and 30 min reperfusion received either vehicle, D-arginine, L-arginine, the nitric oxide (NO)-donor S-Nitroso-N-Acetyl-D, L-Penicillamine (SNAP), the inhibitor of NO formation NG-nitro-L-arginine (L-NNA), or L-arginine plus L-NNA. The recoveries of left ventricular double product and coronary flow at the end of reperfusion were significantly higher in the L-arginine group (85 +/- 5 and 75 +/- 6%, respectively) than in the vehicle group (37 +/- 6 and 34 +/- 5%, respectively, P < 0.05). During both the ischaemic and reperfusion periods, left ventricular end diastolic pressure was lower in the L-arginine group than in the vehicle group. Creatine kinase outflow and the area of no-reflow were smaller in the L-arginine treated hearts (P < 0.01). There were no differences between vehicle and D-arginine treated groups. L-NNA did not affect recovery per se but abolished the protective actions of L-arginine. SNAP produced the same protective effects as L-arginine. Acetylcholine-induced endothelium-dependent vasodilation was reduced after ischaemia and reperfusion in the vehicle group but not in the L-arginine group. It is concluded that L-arginine reduces ischaemia/reperfusion-induced myocardial and endothelial injury. The results suggest that the beneficial effects of L-arginine are related to preserved synthesis and release of NO.

The endothelin A receptor antagonist LU 135252 protects the myocardium from neutrophil injury during ischaemia/reperfusion

OBJECTIVE

Endothelin-1 (ET-1) is not only a potent vasoconstrictor but also a stimulator of polymorphonuclear leukocyte (PMN) aggregation and adhesion. The aim of this study was to investigate whether an ETA receptor antagonist attenuates the PMN-mediated contractile dysfunction following myocardial ischaemia.

METHODS

Isolated rat hearts were perfused according to the Langendorff method. The hearts were subjected to global ischaemia and reperfused with buffer solution only, or human PMNs dissolved in rat plasma (HNRP).

RESULTS

In an initial study, the ETA receptor antagonist LU 135252 (1 and 10 mumol/l) or ET-1 (1 and 10 nmol/l) did not significantly affect the recovery of left ventricular developed pressure (LVDP), end-diastolic pressure (LVEDP), the first derivative of left ventricular pressure (dP/dt) or the rate pressure product (RPP) during reperfusion with buffer solution only compared to a vehicle group. In a second study on hearts reperfused with HNRP, administration of LU 135252 (10 mumol/l) significantly enhanced the recovery of LVDP, dP/dt and RPP in hearts reperfused with HNRP. LVEDP was 20 mmHg lower in hearts given LU 135252 than vehicle in combination with HNRP (P < 0.05). The outflow of PMNs in the coronary effluent during reperfusion was 41 +/- 8% in hearts given LU 135252 compared to 9 +/- 5% in vehicle-treated hearts (P < 0.01). There was a significant correlation between the myocardial functional recovery and the outflow of PMNs. Administration of ET-1 (0.1 and 1 nmol/l) in combination with HNRP resulted in complete loss of contractile function and no outflow of PMNs during reperfusion.

CONCLUSION

The ETA receptor antagonist LU 135252 protects from ischaemia/reperfusion injury in the isolated rat heart in the presence of PMNs. It is suggested that inhibition of PMN-induced injury during reperfusion is an important cardioprotective action of LU 135252.

Characterization of endothelin-1-induced vascular effects in the rat heart by using endothelin receptor antagonists

The coronary vasoconstrictor effect of endothelin-1 was characterized in the isolated rat heart by using the endothelin ETA receptor antagonist D-Asp-L-Pro-D-Val-L-Leu-D-Trp (BQ-123) and the endothelin ETB receptor antagonist [Cys11-Cys15]endothelin-1-(11-21) (IRL 1038). In addition, the involvement of nitric oxide and cyclooxygenase products was investigated. Endothelin-1 (0.012-0.4 nmol) dose dependently reduced coronary flow, which reached a maximum reduction of 83% at 0.4 nmol. BQ-123 (1 microM) attenuated the responses to all doses of endothelin-1, whereas a lower concentration of BQ-123 (0.1 microM) only reduced the vasoconstriction due to the lower doses of endothelin-1 (0.012-0.12 nmol). In contrast, IRL 1038, which markedly antagonized the vasodilator response to the endothelin ETB receptor agonist Suc-[Glu9,Ala11,15]endothelin-1-(8-21) (IRL 1620), significantly enhanced the endothelin-1-evoked coronary vasoconstriction. Endothelin-1 (0.04 nmol) reduced coronary flow by 61% in the presence of IRL 1038 as compared to 30% in the absence of the endothelin ETB receptor antagonist. The endothelin-1-evoked reduction in coronary flow was also significantly enhanced by the nitric oxide synthesis inhibitor NG-nitro-L-arginine but was unaffected by the cyclooxygenase inhibitor diclofenac. IRL 1038 did not affect the response to endothelin-1 after blockade of nitric oxide synthesis. These results demonstrate that the coronary vasoconstriction induced by endothelin-1 in the isolated rat heart is a net effect of the stimulation of both endothelin ETA and endothelin ETB receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Contribution of endothelin to the coronary vasoconstriction in the isolated rat heart induced by nitric oxide synthase inhibition

The possible involvement of endothelin-1 (ET-1) and angiotensin II in the coronary vasoconstriction induced by nitric oxide synthase (NOS) inhibition was investigated in isolated Langendorff-perfused rat hearts. Fifteen minutes of perfusion with the NOS inhibitor NG-nitro-L-arginine (L-NNA, 0.1 mM) reduced coronary flow by 31%. Pre-treatment with the non-selective ETA/ETB receptor antagonist bosentan (1 and 10 microM) attenuated this reduction in coronary flow to 16% (P < 0.05) and 8% (P < 0.01), respectively. The selective ETA receptor antagonist BQ-123 (1 microM) induced a similar inhibitory action, whereas the selective ETB receptor antagonist BQ-788 and the angiotensin II type 1 receptor antagonist candesartan did not affect the vasoconstrictor response to L-NNA. In addition, bosentan administered after 15 min of L-NNA perfusion reversed the L-NNA-induced reduction in coronary flow in a dose-dependent manner. The high concentration of bosentan (10 microM) increased the basal coronary flow by 17%, while the lower concentration of bosentan, BQ-123, BQ-788 and candesartan did not affect basal coronary flow. Bosentan (10 microM) increased the level of ET-like immunoreactivity (-LI) in the coronary effluent twofold. L-NNA did not affect ET-LI level. These results indicate that ET-1 contributes to the coronary vasoconstrictor effect of L-NNA in the isolated rat heart, and that this action of ET-1 is mediated through ETA receptor activation. Angiotensin II does not seem to contribute to L-NNA-induced vasoconstriction under the present condition.

Calcium antagonist protects the myocardium from reperfusion injury by interfering with mechanisms directly related to reperfusion: an experimental study with the ultrashort-acting calcium antagonist clevidipine

To test the hypothesis that calcium antagonists protect the myocardium from reperfusion-induced damage by local myocardial mechanisms just at the time of reperfusion, the myocardioprotective effects of the dihydropyridine clevidipine were investigated, taking advantage of its ultrashort-acting effect. Pigs were subjected to 45 min of myocardial ischemia by occlusion of the left anterior descending coronary artery followed by 4 h of reperfusion. Either clevidipine (0.3 nmol/kg/min, n = 6) or the corresponding amount of vehicle (n = 6) was administered to the ischemic myocardium by retrograde coronary venous infusion over a 30-min period starting 10 min before reperfusion. Hemodynamic variables (heart rate, left ventricular systolic and end-diastolic pressure, max dP/dt, and mean arterial blood pressure) as well as coronary blood flow were measured throughout the experiment. At the end of reperfusion, the area at risk (percentage of left ventricle) was determined by infusion of Evans blue into the left atrium, and the infarct size, by triphenyl tetrazolium chloride (TTC) staining. The plasma level of endothelin-like immunoreactivity (ET-LI) was analyzed in blood from the aorta and the anterior coronary vein before ischemia and at different times during reperfusion. The area at risk was similar in the vehicle and the clevidipine groups. The infarct size, expressed as a percentage of the area at risk, was 80 +/- 9.2 in the vehicle group, whereas it was significantly reduced to 51 +/- 9.2% in the clevidipine group (p < 0.01). Clevidipine did not influence any of the hemodynamic variables measured throughout the study. A nonsignificant trend toward decreased total ET-LI overflow during 4-h reperfusion was observed in the clevidipine-treated pigs compared with vehicle-treated ones (5.3 +/- 1.4 vs. 7.1 +/- 3.4 pmol). These results demonstrate that, in this model of ischemia/reperfusion-induced myocardial infarction, clevidipine reduced the damage to the myocardium when given in association with reperfusion. The local administration of the compound together with its short blood half-life shows that clevidipine reduces reperfusion-induced damage by local mechanisms within the ischemic tissue rather than by peripheral mechanisms.

The role of the L-arginine/nitric oxide pathway in myocardial ischaemic and reperfusion injury

Myocardial ischaemia followed by reperfusion (I/R) is associated with impaired endothelial function including diminished release and/or effects of nitric oxide (NO) which may contribute to the development of I/R injury. The aim of the present study was to investigate the role of the L-arginine/NO pathway in myocardial I/R injury. In isolated rat hearts subjected to global ischaemia followed by reperfusion L-arginine and the NO donor S-nitroso-N-acetyl-D,L-penicillamine (SNAP), but not D-arginine, significantly enhanced the recoveries of mycardial performance and coronary flow, and reduced the area of no-reflow and creatine kinase outflow. The NO synthase inhibitor NG-nitro-L-arginine (L-NNA) abolished the protective effects of L-arginine. Endothelium-dependent vasodilatation after I/R was preserved in L-arginine treated but not in vehicle hearts. Following I/R Ca2+-dependent NO synthase activity was reduced by 90% in comparison with non-ischaemic hearts. L-arginine but not D-arginine significantly increased NO synthase activity. In anaesthetized pigs, L-arginine given by local coronary venous retroinfusion reduced myocardial infarct size induced by 45 min of coronary artery ligation and 4 h of reperfusion to 35% of the area at risk from 76% in controls. The protective effect of L-arginine was blocked by L-NNA. Acetylcholine-induced coronary vasodilatation following I/R was attenuated in controls but not in L-arginine treated pigs. It is concluded that L-arginine or the NO donor SNAP reduces I/R-induced myocardial and endothelial injury. The protective effect of L-arginine seems to be mediated through maintained production of NO by preserving the function of Ca2+-dependent NO synthase in the heart.

Relationship between ischaemic time and ischaemia/reperfusion injury in isolated Langendorff-perfused mouse hearts

Myocardial functional recovery and creatine kinase (CK) release following various periods of ischaemia were investigated in isolated mouse hearts. The hearts were perfused in the Langendorff mode with pyruvate-containing Krebs-Hensleit (KH) buffer under a constant perfusion pressure of 80 mmHg, and were subjected to either continuous perfusion or to 5, 15, 20, 25, 30, 45 or 60 min of global ischaemia followed by 45 min of reperfusion. In hearts subjected to ischaemic periods of 5, 15 or 20 min, there was a transient reduction in the left ventricular (LV) dP/dt max during the early phase of reperfusion, while the recovery at the end of reperfusion reached a level similar to that in hearts subjected to continuous perfusion. In hearts subjected to longer ischaemic periods, i.e. 25, 30, 45 or 60 min, the decrease in the cardiac performance was more pronounced and persistent, with significantly lower recovery in LV dP/dt max and higher LV end diastolic pressure (LVEDP) at the end of reperfusion than in the non-ischaemic hearts. There were no significant differences in the recoveries in coronary flow or in heart rate (HR) between groups. Similarly to the functional recovery, the release of CK showed a clear ischaemic length-related increase. In conclusion, the Langendorff-perfused isolated mouse heart could be a valuable model for studies of myocardial ischaemia/reperfusion injury. Future studies using gene-targeted mice would add valuable knowledge to the understanding of myocardial ischaemia/reperfusion injury.

Differential circRNA expression profiles in latent human cytomegalovirus infection and validation using clinical samples

Human cytomegalovirus (HCMV) is an opportunistic prototypic beta-herpesvirus that can cause severe and even fatal diseases in immune-naive newborns and immunocompromised adults. Host-virus interactions occurring at the transcriptional and posttranscriptional levels are critical for establishing an HCMV latent or lytic infection, but the mechanisms remain poorly understood. Herein, we investigated the expression of circRNAs in human leukemia monocytes (THP-1 cells) latently infected with HCMV and explored the diagnostic value of circRNAs in children with HCMV infection. A total of 2,110 and 1,912 circRNAs were identified in mock-infected and HCMV latent-infected THP-1 cells, respectively. Of these, we identified 1,421 differently expressed circRNAs, of which 650 were upregulated and 771 were downregulated. The host genes corresponding to the differentially expressed circRNAs were mainly involved in the regulation of host cell secretion pathways, cell cycle, and cell apoptosis. The differentially expressed circRNAs had binding sites for microRNAs, suggesting an important role in the mechanism of HCMV latent infection. Furthermore, a clinical analysis showed that the expression levels of hsa_circ_0001445 and hsa_circ_0001206 were statistically significantly different in HCMV-infected patients vs. normal controls, suggesting that these circRNAs could potentially serve as biomarkers of HCMV-infection.

Angiotensin II type 1 receptor blockade with candesartan protects the porcine myocardium from reperfusion-induced injury

Angiotensin-converting enzyme (ACE) inhibitors reduce myocardial ischemia/reperfusion injury. It is unclear whether reduced formation of angiotensin II or attenuated degradation of bradykinin is responsible for the beneficial effects. We investigated the role of endogenous angiotensin II in ischemia/reperfusion injury by studying the effects of the angiotensin II type 1 receptor antagonist candesartan on myocardial function, infarct size, and perfusion after ischemia/reperfusion. Anesthetized pigs were subjected to 45 min of regional ischemia and 240 min of reperfusion. Starting 5 min before reperfusion, four groups of pigs (n = 6 in each) received coronary venous retroinfusion of candesartan (0.2, 2, or 20 microg/kg) or vehicle for 30 min. Myocardial regional blood flow was measured with radioactive microspheres in two separate groups (n = 6 in each) given 20 microg/kg candesartan or vehicle. Retroinfusion of 20 microg/kg of candesartan improved recovery of left ventricular systolic segment shortening measured by sonomicrometry in the ischemic area compared with 0.2 microg/kg of candesartan and vehicle. Infarct size, as a percentage of the area at risk, was smaller in the 2 and 20 microg/kg groups than in the vehicle group (39.1 +/- 11.6% and 34.8 +/- 10.2% vs. 78.3 +/- 8.9%, p < 0.01). There was no difference between candesartan and vehicle in their effects on regional myocardial blood flow. Angiotensin II type 1 receptor blockade supports myocardial functional recovery and reduces infarct size. This effect is not related to improved regional myocardial blood flow during reperfusion.

Antithrombotic activity of inogatran, a new low-molecular-weight inhibitor of thrombin, in a closed-chest porcine model of coronary artery thrombosis

OBJECTIVE

To characterize the antithrombotic activity of inogatran per se in a porcine model of copper-coil-induced coronary artery thrombosis and to compare its effect with that of heparin and ASA.

METHODS

Forty-eight pigs were assigned to one of the following groups: (1) saline; (2) heparin, (a) 75 and (b) 150 IU/kg/h; (3) acetylsalicylic acid (ASA), 12.5 mg/kg; (4) ASA 12.5 mg/kg + inogatran, 0.06 mg/kg/h; (5) ASA 12.5 mg/kg + inogatran, 0.30 mg/kg/h; (6) inogatran, 0.30 mg/kg/h; (7) inogatran, 0.60 mg/kg/h; (8) inogatran, 1.5 mg/kg/h. Computerized vectorcardiography was applied to monitor coronary occlusion and reperfusion.

RESULTS

Cumulative time in which coronary arteries were patent, expressed as a percentage of the treatment time (i.e., 90 min) in heparin- and ASA-treated pigs, was 8 +/- 6 and 14 +/- 7%, respectively. This is not significantly different from placebo-treated pigs. Inogatran-treated pigs showed a dose-dependent antithrombotic effect, and the average patency rates were 34 +/- 39, 54 +/- 37 and 80 +/- 32%, in groups 6, 7 and 8, respectively. Combined treatment with inogatran and ASA did not significantly improve the antithrombotic effect. A partial antithrombotic effect of inogatran was maintained for, on average, at least 150 min after the end of treatment, as evidenced by patency rates of 31 +/- 43, 52 +/- 48 and 62% +/- 44, in groups 6, 7, and 8, respectively.

CONCLUSION

Inogatran inhibits the formation of arterial thrombosis more effectively than heparin or ASA. Inhibition of clot-bound thrombin and thrombin-induced platelet activation may be the mechanisms behind this effect. Our findings also suggest that a thrombus formed in the presence of inogatran is more susceptible to spontaneous endogenous fibrinolysis.

The novel non-peptide selective endothelin A receptor antagonist LU 135,252 protects against myocardial ischaemic and reperfusion injury in the pig

The aim of the study was to investigate the efficacy of the novel non-peptide selective endothelin A (ETA) receptor antagonist LU 135,252 to limit the extent of myocardial ischaemic and reperfusion injury. Administration of LU 135,252 (1 and 5 mg kg-1 i.v.) to anaesthetised pigs reduced mean arterial pressure (MAP) from 91 +/- 4 to 79 +/- 3 mmHg (P < 0.05) and 96 +/- 3-82 +/- 3 mmHg (P < 0.01), respectively. Heart rate, coronary blood flow and coronary vascular resistance were not affected by LU 135,252. The infarct size induced by 45-min ligation of the left anterior descending coronary artery (LAD) followed by 4-h reperfusion in pigs was 81 +/- 5% of the area at risk in control animals given vehicle (n = 8). In pigs receiving 1 mg kg-1 (n = 6) or 5 mg kg-1 (n = 8) of LU 135,252 i.v. 20 min before ischaemia the infarct size was reduced to 64 +/- 3% (P < 0.05) and 35 +/- 4% (P < 0.001), respectively, of the area at risk. During the reperfusion period there was a non-significant trend towards a higher coronary blood flow and a lower coronary vascular resistance in the groups given LU 135,252 compared to controls. Myocardial overflow of ET-like immunoreactivity was increased during the reperfusion period but it was not affected by administration of LU 135,252. It is concluded that administration of the selective ETA receptor antagonist LU 135,252 effectively protects the myocardium from ischaemia/reperfusion injury, indicating that the ETA receptor subtype is involved in the development of ischaemia/reperfusion injury.

Effects of the insurmountable angiotensin AT1 receptor antagonist candesartan and the surmountable antagonist losartan on ischemia/reperfusion injury in rat hearts

Two angiotensin AT1 receptor antagonists with different receptor binding characteristics, candesartan (insurmountable antagonism) and losartan (surmountable antagonism), were compared as regards their effects on angiotensin II-induced vasoconstriction and on myocardial ischemia/reperfusion injury. In isolated rat hearts perfused under constant flow, it was found that at equipotent concentrations candesartan (10 nM) and losartan (3 microM) almost completely inhibited the angiotensin II-induced increase in coronary perfusion pressure. However, if a washout period was introduced before the angiotensin II challenge, the effect of losartan quickly vanished, while that of candesartan remained. In hearts subjected to 25 min of global ischemia and 45 min of reperfusion, pre-treatment with candesartan (10 nM) or losartan (3 microM) immediately prior to ischemia improved the recovery of left ventricular developed pressure as compared to the effect of vehicle (69 +/- 3.2 and 64 +/- 2.3 vs. 44 +/- 6.2%, respectively; mean +/- S.E.M, P < 0.05). When ischemia was initiated following 30 min of washout after drug administration, the recovery of left ventricular developed pressure was higher in the candesartan group (73 +/- 3.2%, P < 0.05), but not in the losartan group (63 +/- 2.8%), than in the vehicle group (58 +/- 4.8%). The cumulative creatine kinase release during the first 30 min of reperfusion in the washout experiments was lower in the candesartan group (28.5 +/- 2.30 U, P < 0.05), but not in the losartan (40.8 +/- 6.73 U) group, than in the vehicle group (48.1 +/- 4.35 U). No significant difference between groups in left ventricular end-diastolic pressure and coronary perfusion pressure was found. The present results demonstrate that angiotensin AT1 receptor antagonists at equipotent concentrations could differ in their cardioprotective effects in hearts subjected to ischemia/reperfusion. It is suggested that the insurmountable AT1 receptor characteristics of candesartan could provide more persistent cardioprotection than the surmountable receptor characteristics of losartan.

The angiotensin II AT1-receptor antagonist candesartan improves functional recovery and reduces the no-reflow area in reperfused ischemic rat hearts

It is not yet clear if cardiac angiotensin II is involved in the pathophysiology of myocardial ischemia/ reperfusion injury. The aim of this study was to investigate the effect of the angiotensin II AT1-receptor antagonist candesartan on myocardial functional recovery in isolated rat hearts subjected to ischemia and reperfusion. Three groups of hearts perfused in the Langendorff mode with Krebs-Henseleit buffer under constant pressure received either vehicle (n = 7), candesartan, 1 nM (n = 6), or 100 nM (n = 7) at the start of 30 min of global ischemia. The recovery of the double product was significantly higher in the candesartan, 100 nM, group (75+/-9.2%) than in the vehicle group (40+/-5.1%; p < 0.05). At the end of 30 min of reperfusion, left ventricular end diastolic pressure was lower in rats given candesartan, 100 nM, than in rats given vehicle (10+/-4.3 vs. 38+/-4.8 mm Hg; p < 0.05). After ischemia and reperfusion, there was a large no-reflow area in the vehicle group (28+/-3.1% of the left ventricle), which was reduced by candesartan, 100 nM (12+/-1.3%; p < 0.05). In rats given candesartan, 1 nM, there was a trend toward a higher recovery of the double product (73+/-13.4%), a lower left ventricular end-diastolic pressure (29+/-6.6 mm Hg), and a smaller no-reflow area (19+/-3.5% of the left ventricle) compared with the rats receiving vehicle. These trends did, however, not reach statistical significance. Our results demonstrate that candesartan reduces myocardial ischemia/reperfusion injury, thus indicating that endogenous cardiac angiotensin II is involved in the tissue injury after myocardial ischemia and reperfusion.

Cardiac inotropic vs. chronotropic selectivity of isradipine, nifedipine and clevidipine, a new ultrashort-acting dihydropyridine

Cardiac effects of clevidipine, a new ultrashort-acting dihydropyridine Ca2+ channel antagonist were investigated in Langendorff-perfused rat hearts and compared to those of nifedipine and isradipine. The aim was to determine and compare the negative inotropic vs. chronotropic potency of these drugs. The hearts were perfused with oxygenated Krebs-Henseleit buffer at a perfusion pressure of 90 cm H2O. After stabilization, one concentration of each drug was administered for 45 min followed by a higher concentration for an additional 45 min. The concentrations of each drug in this study were 10(-9), 3 x 10(-9), 10(-8), 10(-7), 10(-6.5) and 10(-6) M for clevidipine and nifedipine, and 10(-10), 3 x 10(-10), 10(-9), 10(-8), 10(-7.5) and 10(-7) M for isradipine. Each concentration of each drug was tested in six hearts. Coronary flow, left ventricular dP/dt max, left ventricular systolic pressure and heart rate were recorded when the hearts were beating spontaneously and during pacing at a constant rate for 1 min. Spontaneous heart rate and atrio-ventricular conduction were not affected by clevidipine at any of the concentrations studied, while nifedipine and isradipine caused a concentration-dependent decrease. These two drugs caused atrio-ventricular block at high concentrations. All three compounds reduced cardiac contractility in a concentration-dependent manner. When isradipine was administered, at a given concentration, heart rate and contractility decreased proportionately. When clevidipine or nifedipine was given, at a given concentration, the proportionate reduction in left ventricular dP/dt max was greater than that in heart rate, resulting in a high inotropic vs. chronotropic selectivity. It is concluded that in contrast to nifedipine and isradipine, clevidipine does not impair atrio-ventricular conduction. Like nifedipine, clevidipine is selective for inotropic vs. chronotropic cardiac effects.

Effects of dietary protein levels and protease supplementation on growth performance, carcass traits, meat quality, and standardized ileal digestibility of amino acid in Pekin ducks fed a complex diet

This study aimed to investigate to the effects of dietary CP levels and protease supplementation on growth performance, carcass traits, meat quality, nutrients utilization, and standardized ileal digestibility of amino acid in Pekin ducks fed a complex diet. A total of 960 14-day-old male ducks were weighed and randomly allotted to a 2 × 5 factorial arrangement of 10 treatments with 6 replicate pens per treatment and 16 ducks per pen fed to 49 D of age. Experimental factors included five dietary CP levels ranging from 13.5 to 17.5% and with or without protease (200 mg/kg) supplementation. Between day 28 to 34, the digestible and metabolizable trials were performed. Significant CP × protease interactions (P < 0.05) on breast meat yield, DM, energy and nitrogen utilization, as well as standardized ileal digestibility values of 7 amino acids were observed. Regardless of protease supplementation, ducks fed 13.5, 14.5, and 15.5% CP had a poorer (P < 0.05) growth performance and breast meat yield than ducks fed with 16.5 and 17.5% CP. Ducks fed 13.5% CP had a positive effect (P < 0.05) on meat quality, dietary DM, energy and nitrogen utilization as well as standardized ileal digestibility of amino acids. Protease supplementation increased (P < 0.05) DM and phosphorus retention and decreased (P < 0.05) shear force of breast meat, regardless of CP level; when CP = 14.5%, protease significantly increased (P < 0.05) breast muscle yield. The optimal CP requirement without or with protease supplementation for BWG and FI were 17.02 or 16.53% and 16.64 or 16.75%, respectively, based on linear broken-line regression.

The angiotensin II AT1 receptor antagonist candesartan at antihypertensive plasma concentrations reduces damage induced by ischemia-reperfusion

The aim of this study was to investigate if the angiotensin II AT1 receptor antagonist candesartan in antihypertensive plasma concentrations improves myocardial function and limits infarct size in anesthetized pigs. Animals were subjected to 45 min of regional ischemia and 240 min of reperfusion. Starting 60 min before ischemia, two groups of pigs (n = 6 in each) received either candesartan (25 micrograms/kg bolus followed by a continuous infusion at a rate of 14 micrograms/kg/h) or the corresponding volume of vehicle throughout the study period. Left ventricular systolic segment shortening (%SS) was measured by sonomicrometry, and infarct size was determined by triphenyl tetrazolium chloride staining. The plasma concentration of candesartan during the experiment was between 100 and 150 nmol/L, which was considered to be within the therapeutic range. Neither candesartan nor vehicle affected hemodynamics or coronary blood flow prior to ischemia. Compared to vehicle, candesartan improved recovery of %SS in the ischemic area. At 240 min of reperfusion, the %SS was significantly higher in pigs given candesartan than in pigs given vehicle (7.1 +/- 0.87% vs-1 +/- 1.79%; p < 0.01). In both groups the area at risk was approximately 20% of the left ventricle. Infarct size as a percentage of the area at risk was significantly smaller in the candesartan group than in the vehicle group (46 +/- 3.0 vs 73 +/- 3.6%; p < 0.01). The results suggest that angiotensin II AT1 receptor blockade, obtained in antihypertensive plasma concentrations, supports myocardial functional recovery and limits infarct size.