Effect of isoflurane on the beta-adrenergic and endothelium-dependent relaxation of pig cerebral microvessels after cardiopulmonary bypass

We examined the direct vasomotor effect of isoflurane as well as its effect on endothelium-dependent and beta-adrenergic vasodilation of cerebral microcirculation following either normothermic cardiopulmonary bypass (CPB) or profoundly hypothermic CPB with circulatory arrest. Pigs were placed on CPB; the systemic temperature was either maintained at 37 degrees C or lowered to 15 degrees C with 60 minutes of circulatory arrest. After 2 hours of CPB, the animals were separated from CPB; 15 minutes later the brain was quickly harvested in cold Krebs solution. Control animals were not instrumented and their brains were similarly harvested. Arteries of approximately 100 microm were dissected and changes in diameter monitored by in vitro videomicroscopy. Following preconstriction with the thromboxane analogue U46619 1 micromol/L, percent relaxation to the endothelium-dependent dilator adenosine diphosphate (ADP) 10(-9) to 10(-4) mol/L, the endothelium-independent dilator sodium nitroprusside (SNP) 10(-9) to 10(-4) mol/L, or the beta-adrenergic agonist isoproterenol 10(-12) to 10(-4) mol/L was measured either in the presence or absence of isoflurane 2%. Additionally, with or without preconstriction with U46619 1 micromol/L, vessel diameter changes were monitored with increasing concentrations of isoflurane 0-3%. Dose-response curves were compared by two-way analysis of variance. Vasodilation to ADP or isoproterenol, but not SNP, was attenuated after normothermic CPB (N-CPB) or profoundly hypothermic CPB (PH-CPB). Although isoflurane attenuated vasodilation of control vessels to ADP or isoproterenol, isoflurane did not further attenuate vasodilation to ADP or isoproterenol after N-CPB or PH-CPB. The direct vasomotor effect of isoflurane depended on the preexisting tone of the vessels, constricting vessels without preconstriction and dilating them after preconstriction. These findings may have implications on the incidence of neuropsychological dysfunction after CPB and use of isoflurane.

CaMKIIT287 and T305 regulate history-dependent increases in alpha agonist-induced vascular tone

CaMKII is a calcium and calmodulin-activated kinase that has been shown to regulate learning and memory in the brain, and contractility in blood vessels. Following Ca activation, CaMKII autophosphorylates, gaining a calcium-independent autonomous activity that reflects a molecular memory of having previously come into contact with calcium. The present study addresses whether the molecular memory properties of CaMKII are involved in the modulation of sustained vascular tone. We demonstrate a history-dependence of α agonist-induced vascular tone and show that CaMKII activation in vascular cells is also history dependent. Autophosphorylation of Thr287, which is classically associated with autonomous activity, does not persist during tone maintenance after transient increases in intracellular calcium levels. However, we have found that another site, Thr305, known from in vitro studies to be inhibitory, is regulated by α agonists in that the inhibitory action is removed, thus leading to a delayed reactivation of CaMKII as measured by Thr287 phosphorylation. By the use of a small molecule CaMKII inhibitor (KN93) as well as a decoy peptide (autoinhibitory peptide; AIP) we show a cause and effect relationship between CaMKII reactivation and sustained vascular tone maintenance. Thus, it appears that a complex interplay between the regulation of Thr305 and Thr287 provides a novel mechanism by which a history-dependence is developed and contributes to a new facet of molecular memory for CaMKII of relevance to vascular tone maintenance.

Salvage or planned esophagectomy after chemoradiation therapy for locally advanced esophageal cancer--a review

Definitive chemoradiation (without esophagectomy) and neoadjuvant chemoradiation followed by planned esophagectomy are commonly used treatments for locally advanced esophageal cancer. These two treatment strategies have similar survival outcomes, so the value of planned esophagectomy is debated. However, persistence or recurrence of local disease is not uncommon after definitive chemoradiation. Salvage esophagectomy for isolated local failures of definitive chemoradiation is an option for selected patients. In this article we review the debate over definitive chemoradiation versus neoadjuvant chemoradiation and surgery, and then restate the argument in terms of salvage versus planned esophagectomy. Although both forms of esophagectomy are done in the setting of previous chemoradiation, they are different in several ways. Salvage esophagectomy appears to be a more morbid operation than planned esophagectomy. Surgeons supportive of the salvage esophagectomy strategy face the challenge of reducing its postoperative mortality.

Gene therapy progress and prospects: therapeutic angiogenesis for limb and myocardial ischemia

After extensive investigation in preclinical studies and recent clinical trials, gene therapy has been established as a potential method to induce therapeutic angiogenesis in ischemic myocardial and limb disease. Advancements in viral and nonviral vector technology including cell-based gene transfer will continue to improve transgene transmission and expression efficiency. An alternative strategy to the use of transgenes encoding angiogenic growth factors is therapy based on transcription factors such as hypoxia-inducible factor-1alpha (HIF-1alpha) that regulate the expression of multiple angiogenic genes. Further understanding of the underlying biology of neovascularization is needed to determine the ability of growth factors to induce functionally significant angiogenesis in patients with atherosclerotic disease and associated comorbid conditions including endothelial dysfunction, which may inhibit blood vessel growth. The safety and tolerability of therapeutic angiogenesis by gene transfer has been demonstrated in phase I clinical trials. However, limited evidence of efficacy resulted from early phase II studies of angiogenic gene therapy for ischemic myocardial and limb disease. The utility of therapeutic angiogenesis by gene transfer as a treatment option for ischemic cardiovascular disease will be determined by adequately powered, randomized, placebo-controlled phase II and III clinical trials.

Rat aortic smooth muscle cell density affects activation of MAP kinase and Akt by menadione and PDGF homodimer BB

Mitogen-activated protein kinases (MAPK) and protein kinase B (PKB or Akt) are major signal transduction molecules regulating cell proliferation, differentiation, and apoptosis. We examined how cultured rat aortic vascular smooth muscle cells (VSMC) at different cell densities respond to selected stimuli and how this is reflected in the two distinct (MAPK and Akt) and yet cross-talking signaling pathways. VSMC were cultured to 100% confluence, reaching contact inhibition, and to 60-70% confluence, as sparse, proliferating cells. They were treated with menadione (an intracellular generator of O(-2)) and/or platelet-derived growth factor homodimer BB (PDGF). In sparse cells, menadione or PDGF alone activated ERK, and together the effect was synergistic, whereas in confluent cells menadione's and PDGF's activations of ERK were, at most, additive. Activation of the upstream ERK kinase (MEK-1) paralleled ERK activation except in sparse cells in which the synergistic effects of menadione and PDGF on ERK could not be fully accounted for by MEK-1 activation. Another member of the MAPK family, p38, did not show significant changes. Akt activation by PDGF alone was present under both cell culture conditions; Akt activation is blocked by menadione. Co-incubation with the reducing agent dithiothreitol or calcium chelators (EDTA/EGTA) inhibited partially or completely menadione's effects on MEK/ERK and Akt pathways, as well as menadione's effects on PDGF-induced ERK and Akt activations. These data suggest that in VSMC, the state of cell confluence determines how distinct pathways of MAPK activation cross talk. In addition while PDGF may function as a survival factor by inducing Akt activation, menadione could promote apoptosis by inhibiting PDGF-induced Akt activation independent of cell density. The effects of menadione, but not those of PDGF, are more dependent on the cellular redox status and extracellular calcium.

Biochemical and structural evidence for pig myocardium adherens junction disruption by cardiopulmonary bypass

BACKGROUND

Given that cardiopulmonary bypass (CPB) is associated with edema and heart dysfunction and that adherens junctions may regulate vascular permeability barrier integrity and cardiomyocyte function, we investigated adherens junction protein steady-state levels in a pig model of CPB.

METHODS AND RESULTS

Pigs were subjected to normothermic CPB for 90 minutes, followed by post-CPB perfusion for 90 minutes. Atrial and ventricular myocardium tissue samples were harvested before institution of bypass (basal levels) and at the end of post-CPB perfusion. Adherens junctions were analyzed by either total lysate or cadherin immunoprecipitates that were immunoblotted for pan-cadherin, VE-cadherin, beta-catenin, and gamma-catenin. Adherens junction solubility was addressed with Triton X-100 extraction. Frozen tissue sections were labeled with the same antibodies, and adherens junctions were visualized by confocal microscopy. Immunoblotting of total lysates revealed an increase in smaller-molecular-weight fragments of VE-cadherin, beta-catenin, and gamma -catenin after post-CPB perfusion, indicating partial protein degradation. Smaller-molecular-weight fragments recognized by VE-cadherin and beta-catenin antibodies were also obtained from VE-cadherin immunoprecipitation, indicating degradation of endothelial cell adherens junctions. A prominent increase in adherens junction complex solubility was observed in post-CPB perfusion samples. Confocal microscopy of hearts obtained before CPB showed a continuous, homogeneous pattern of cell-cell labeling that contrasted with an irregular, discontinuous, punctuate, or zigzag pattern observed in post-CPB perfusion samples, corroborating biochemical data.

CONCLUSIONS

These results indicate that CPB is associated with signs of degradation of endothelial and cardiomyocytes adherens junctions, pointing to a molecular mechanism leading to increased vascular permeability and cardiomyocyte dysfunction.

Oscillation in the activities of MEK/ERK1/2 during cardiopulmonary bypass in pigs

BACKGROUND

Because cardiopulmonary bypass (CPB) is associated with edema and vasoreactive dysfunction and ERK1/2 pathway is involved in vascular contractility and permeability, a time course study was performed to monitor MEK/ERK1/2/Elk-1 activities during CPB.

METHODS

Pigs were subjected to normothermic CPB for 90 minutes followed by post-CPB perfusion for 180 minutes. Atrial myocardium was sampled before CPB, 5 minutes after CPB onset, 5 minutes after weaning from CPB, and at the end of post-CPB. Skeletal muscle and mesenteric vessels samples were harvested before CPB, 5 minutes after CPB institution, and every 30 minutes thereafter to the end of post-CPB. Samples were analyzed by immunoblotting and immunofluorescence microscopy with the use of specific antibodies against active (phosphorylated) forms of ERK1/2, MEK1/2, and Elk-1.

RESULTS

Pigs that were subjected to CPB showed an increase in phospho-ERK1/2 after 30 minutes of CPB, followed by a decrease after 90 minutes. Another phosphorylation peak was observed 30 to 60 minutes of post-CPB, followed by a decrease to below baseline at the end of reperfusion. MEK1/2 and Elk-1 activation profiles paralleled ERK1/2 activity peaks. Control samples showed no significant increase above basal levels.

CONCLUSIONS

Activation of MEK/ERK1/2/Elk-1 pathways closely follows major CPB surgical manipulations (institution and termination) and could be related to morbidity during and after CPB.

Inactivation of the MEK/ERK pathway in the myocardium during cardiopulmonary bypass

OBJECTIVES

A general pro-inflammatory response after cardiopulmonary bypass (CPB) may involve changes in signal transduction and in part be responsible for arrhythmias and myocardial dysfunction after cardiac surgery. The MEK/ERK (mitogen-activated protein kinase kinase/extracellular regulated kinase) pathway is common to many stimuli and may play a pivotal role in morbidity associated with CPB. We investigated the changes in MEK/ERK pathway and related enzymes after CPB in pigs.

METHODS

We examined ventricular and atrial tissue from pigs before 90 minutes of normothermic CPB and after 90 minutes of post-CPB perfusion. The activities and protein levels of kinases MEK1/2, ERK1/2, a cellular tyrosine kinase (c-Src), protein kinase B (Akt), and the protein levels of mitogen-activated protein kinase phosphatase (MKP-1) were studied by immunoblotting ventricular and atrial myocardium lysates and labeling sections with antibodies that recognize the activated forms of the kinases and the phosphatase. Control pigs were subjected to sternotomy and heparinization but not CPB.

RESULTS

We found a consistent inactivation of MEK/ERK pathway in both ventricular and atrial myocardium with an increase in MKP-1, a negative regulator of ERK1/2. The activities and protein levels of c-Src and Akt were not significantly modified before or after CPB, suggesting a certain degree of specificity for the MEK/ERK pathway. Such changes were not observed in controls. The decrease of ERK1/2 and MEK1/2 phosphorylation 90 minutes after termination of CPB (as well as the increase of nuclear MKP-1 protein levels) was also apparent by confocal microscopy.

CONCLUSIONS

These results collectively reveal a prevalence of inhibitory mechanisms in the MEK/ERK signal transduction machinery in myocardium subjected to CPB.

Expression of vascular endothelial growth factor and its receptors is increased, but microvascular relaxation is impaired in patients after acute myocardial ischemia

BACKGROUND

Vascular endothelial growth factor, a specific endothelial mitogen, plays an important role in myocardial angiogenesis. Previous work has demonstrated increased expression of vascular endothelial growth factor and its receptors in a rat myocardial infarction model, as well as in a pig model of chronic ischemia. The expression of vascular endothelial growth factor and other growth factors after acute myocardial ischemia in patients has not been examined. In this study we examined the expression of vascular endothelial growth factor and its receptors and the responsiveness of human atrial microvessels to vascular endothelial growth factor before and after acute ischemia.

METHODS

Paired specimens of human atrial tissue were harvested before and after atrial devascularization (ligation) in 16 patients undergoing coronary bypass operations.

RESULTS

The messenger RNA (reverse transcriptase-polymerase chain reaction) level of vascular endothelial growth factor and vascular endothelial growth factor receptor 1 were increased by 22.2% +/- 4.2% and 30.7% +/- 7.6%, respectively (P <.05), in the ischemic specimens as compared with the control specimens. Protein expression (Western blotting) of vascular endothelial growth factor and that of vascular endothelial growth factor receptor 1 also were increased significantly by 71.7% +/- 27.8% and 68.2% +/- 27.6%, respectively (P <.05). However, both RNA and protein expressions of another vascular endothelial growth factor receptor, vascular endothelial growth factor receptor 2, and fibroblast growth factor and fibroblast growth factor receptor 1 were unchanged. Reactivity of precontracted atrial vessels was examined with video microscopy. Vascular endothelial growth factor-induced (33.9% +/- 2.4% vs 18.3% +/- 2.8% in control and ischemic vessels, respectively; P <.05), fibroblast growth factor-induced (31.6% +/- 3.2% vs 15.8% +/- 4.1%, P <.05), and substance P-induced (84.5% +/- 3.7% vs 54.3% +/- 9.0%, P <.05) microvascular relaxations were decreased in ischemic samples and in the presence of N (G)nitro-L -arginine, whereas responses to sodium nitroprusside were unchanged (90.9% +/- 2.2% vs 91.2% +/- 2.0%).

CONCLUSIONS

This study suggests that acute myocardial ischemia in patients results in increased expression of vascular endothelial growth factor but not fibroblast growth factor and that the functional activity of vascular endothelial growth factor receptors and that of other growth factors may be impaired.

Microvascular endothelial dysfunction and its mechanism in a rat model of subarachnoid hemorrhage

After subarachnoid hemorrhage (SAH), large cerebral arteries are prone to vasospasm. Using a rat model of SAH, we examined whether cortical microvessels demonstrate vasomotor changes that may make them prone to spasm and whether endothelial dysfunction may account for any observed changes. Two days after percutaneous catheterization into the cisterna magna, 0.3 mL of autologous blood was injected into the subarachnoid space. The brain tissue was harvested 20 min later, and microvessels were dissected from the parietal cortex. Vasomotor responses to the thromboxane analog U46619, the protein kinase C agonist phorbol acetate, endothelin-1, adenosine diphosphate, nitroprusside, and isoproterenol were examined in vitroin cerebral arterioles from the control, sham-operated, and SAH animals. Endothelial nitric oxide synthase (NOS3) messenger RNA and protein concentration was measured by northern and western blotting, respectively. Arterioles from the SAH animals demonstrated attenuated dilation to the endothelium-dependent dilator adenosine diphosphate and accentuated constriction to endothelin-1, while responses to the other agents tested were unchanged. NOS3 protein concentration was decreased, but NOS3 messenger RNA was increased after SAH. After SAH, cortical arterioles demonstrate endothelial dysfunction, which may be the basis for microvascular spasm. This is in part related to decreased NOS3, which occurs despite an increase in its transcription.

IMPLICATIONS

Acute microvascular endothelial dysfunction may occur after subarachnoid hemorrhage and contribute to microvascular spasm.

Therapeutic angiogenesis in cardiology using protein formulations

Therapeutic angiogenesis in cardiovascular disease aims at improving myocardial function by increasing blood flow to ischemic myocardium that is not amenable to traditional forms of revascularization. Preclinical data have provided proof of the concept that angiogenic growth factors such as fibroblast growth factor 2 (FGF-2) and vascular endothelium growth factor (VEGF) may indeed improve myocardial flow and function when administered in ways that ensure prolonged tissue exposure to these short-lived molecules. Although other cytokines have been shown to enhance angiogenesis in vivo, FGF-2 and VEGF have been most widely studied and may serve as prototype proangiogenic drugs. Currently, several delivery techniques that are clinically applicable are being studied with respect to tissue distribution and retention as well as angiogenic efficacy of FGF-2 and VEGF. Although tissue distribution and retention of FGF-2 after intramyocardial injection compares favorably with other routes of administration, efficacy studies are not yet conclusive. At the same time, different protein- and gene-based formulations are being investigated. Arguments for and against protein and gene therapy are presented, showing that protein-based therapy seems to have advantages over gene therapy at the present time, although continuous efforts should be made to increase the tissue exposure time after a single administration of protein. While delivery systems and growth factor formulations are being improved, double-blind, placebo-controlled trials designed with existing animal data in mind, are needed to firmly establish the utility of therapeutic angiogenesis in cardiovascular disease.

Efficacy of intracoronary or intravenous VEGF165 in a pig model of chronic myocardial ischemia

OBJECTIVES

We sought to optimize vascular endothelial growth factor (VEGF) treatment for therapeutic angiogenesis in myocardial ischemia, we explored the efficacy of five different regimens.

BACKGROUND

Although VEGF165 is one of the most potent pro-angiogenic growth factors, VEGF165 treatment for myocardial ischemia has been hampered by low efficacy and dose-limiting hypotension after systemic or intracoronary delivery.

METHODS

This study evaluated the effect of intravenous or intracoronary rhVEGF165 in the presence or absence of nitric oxide (NO) synthase inhibition in a porcine model of chronic myocardial ischemia. Forty-two Yorkshire pigs with chronically occluded left circumflex coronary arteries were randomly assigned to receive 10 microg/kg of VEGF165: 1) rapid (40 min) intravenous VEGF165 0.25 microg/kg/min, 2) slow (200 min) intravenous VEGF165 0.05 microg/kg/min, 3) rapid intracoronary VEGF165 0.25 microg/kg/min, 4) rapid intracoronary VEGF165 0.25 microg/kg/min + nitro-L-arginine methyl ester hydrochloride (L-NAME) or 5) rapid vehicle infusion.

RESULTS

Intracoronary and intravenous VEGF165 induced hypotension. Intracoronary VEGF-induced hypotension was blocked by L-NAME. Coronary angiography three weeks after treatment showed improvement in collateral index in both intracoronary groups but not the intravenous VEGF165 groups. Likewise, myocardial blood flow and microvascular function in the ischemic territory improved in both intracoronary groups but not in the intravenous groups. Global and regional myocardial function showed no significant improvements in any groups.

CONCLUSIONS

Intracoronary infusion of VEGF165 significantly improves blood flow to the ischemic myocardium. Concomitant administration of L-NAME inhibits VEGF-induced hypotension while most likely preserving VEGF-induced angiogenesis. Intravenous infusion of VEGF165 was not effective in augmenting either myocardial flow or function in this model.

Serotonin-induced human coronary microvascular contraction during acute myocardial ischemia is blocked by COX-2 inhibition

Since serotonin (5-HT) is implicated in exacerbating acute coronary syndromes, we studied the reactivity of atrial coronary arterioles (70-140 microm) of atherosclerotic patients undergoing cardiac surgery to 5-HT, substance P (Sub P), and sodium nitroprusside by video-microscopy. Before ischemia, 5-HT-induced relaxation was not affected by NS398 (cyclooxygenase inhibitor), H2O2 or U63557A (thromboxane A2 synthase inhibitor), but was reduced by L-NNA. 5-HT elicited a potent contractile response after ischemia that was inhibited by NS398, Indo, and U63557A. While Sub P relaxation was decreased after ischemia, SNP relaxation was unchanged. The mRNA steady-state levels of NOS-3, NOS-2, prostacyclin synthase, and COX- 1 were not altered by ischemia. COX-2 mRNA and protein levels (Westernblotting), however, were increased (mean +/- SEM) 2.4 +/- 0.4 and 3.2 +/- 0.7 fold, respectively, in ischemic atrium corroborating with the immunohistochemistry of atrial tissue. It is concluded that myocardial ischemia enhanced contractile response of coronary arterioles to 5-HT maybe due to the stimulated prostaglandin release (likely thromboxane A2) secondary to induction of COX-2 expression. These findings may have implications regarding the cause of coronary spasm during acute myocardial ischemia.

Efficacy of intracoronary versus intravenous FGF-2 in a pig model of chronic myocardial ischemia

BACKGROUND

Therapeutic angiogenesis in ischemic myocardium has been shown to be a feasible and effective strategy to improve regional blood flow and myocardial function. However, the optimal mode of growth factor administration still needs to be established.

METHODS

Using a pig model of chronic myocardial ischemia, we evaluated the efficacy of intravenous and intracoronary infusion of FGF-2 at 2 and 6 microg/kg compared with a vehicle control. Improvement in myocardial perfusion and function was assessed by angiography, colored microspheres, and function and perfusion magnetic resonance imaging.

RESULTS

Intracoronary 6-microg/kg FGF-2 increased angiographic collaterals (p = 0.046) and increased regional blood flow to the ischemic area from 0.36 +/- 0.07 to 0.59 +/- 0.08 mL/min/g at stress (vs control, p = 0.032). Also, after 6 microg/kg intracoronary FGF-2, ejection fraction, regional wall motion, and thickening improved significantly by 9.9% +/- 1.9%, 126% +/- 39%, and 13.8% +/- 3.6%, respectively. Intravenous FGF-2 and intracoronary 2 microg/kg FGF-2 were ineffective.

CONCLUSIONS

A single 6-microg/kg intracoronary treatment with FGF-2 resulted in significant improvement in collateralization and regional and global function of chronically ischemic myocardium. Single intravenous infusion of FGF-2 was not effective in this model.

Clinical trials in coronary angiogenesis: issues, problems, consensus: An expert panel summary

The rapid development of angiogenic growth factor therapy for patients with advanced ischemic heart disease over the last 5 years offers hope of a new treatment strategy based on generation of new blood supply in the diseased heart. However, as the field of therapeutic coronary angiogenesis is maturing from basic and preclinical investigations to clinical trials, many new and presently unresolved issues are coming into focus. These include in-depth understanding of the biology of angiogenesis, selection of appropriate patient populations for clinical trials, choice of therapeutic end points and means of their assessment, choice of therapeutic strategy (gene versus protein delivery), route of administration, and the side effect profile. The present article presents a summary statement of a panel of experts actively working in the field, convened by the Angiogenesis Foundation and the Angiogenesis Research Center during the 72nd meeting of the American Heart Association to define and achieve a consensus on the challenges facing development of therapeutic angiogenesis for coronary disease.

Evidence for involvement of the PKC-alpha isoform in myogenic contractions of the coronary microcirculation

The role of protein kinase C (PKC) isoforms in myogenic tone of the ferret coronary microcirculation was investigated by measuring fura 2 Ca(2+) signals, PKC immunoblots, contractile responses, and confocal microscopy of PKC translocation. Phorbol ester-evoked contractions were completely abolished in the absence of extracellular Ca(2+) but involved a Ca(2+) sensitization relative to KCl contractions. Immunoblotting using isoform-specific antibodies showed the presence of PKC-alpha and -iota and traces of PKC-epsilon and -mu in the ferret coronary microcirculation. PKC-beta was not detectable. When intraluminal pressure (40 to 60 and 80 mmHg) was increased, ferret coronary arterioles showed a transient increase in fura 2 Ca(2+) signals, whereas the myogenic tone remained sustained. The increase in Ca(2+) and tone was sustained at 100 mmHg. Isolated ferret coronary arterioles were fixed and immunostained for PKC-alpha at 40 and 100 mmHg intraluminal pressure. PKC translocation was determined by confocal microscopy. Increased PKC translocation was observed when vessels were exposed to 100 mmHg relative to that at resting pressure (40 mmHg). These results suggest a link between the Ca(2+) sensitization that occurs during the myogenic contraction and activation of the alpha-isoform of PKC.

Effects of pinacidil on coronary Ca(2+)-myosin phosphorylation in cold potassium cardioplegia model

The effects of the potassium (K(+)) channel opener pinacidil (Pin) on the coronary smooth muscle Ca(2+)-myosin light chain (MLC) phosphorylation pathway under hypothermic K(+) cardioplegia were determined by use of an in vitro microvessel model. Rat coronary arterioles (100-260 microm in diameter) were subjected to 60 min of simulated hypothermic (20 degrees C) K(+) cardioplegic solutions (K(+) = 25 mM). We first characterized the time course of changes in intracellular Ca(2+) concentration, MLC phosphorylation, and diameter and observed that the K(+) cardioplegia-related vasoconstriction was associated with an activation of the Ca(2+)-MLC phosphorylation pathway. Supplementation with Pin effectively suppressed the Ca(2+) accumulation and MLC phosphorylation in a dose-dependent manner and subsequently maintained a small decrease in vasomotor tone. The ATP-sensitive K(+) (K(ATP))-channel blocker glibenclamide, but not the nitric oxide (NO) synthase inhibitor N(omega)-nitro-L-arginine methyl ester, significantly inhibited the effect of Pin. K(+) cardioplegia augments the coronary Ca(2+)-MLC pathway and results in vasoconstriction. Pin effectively prevents the activation of this pathway and maintains adequate vasorelaxation during K(+) cardioplegia through a K(ATP)-channel mechanism not coupled with the endothelium-derived NO signaling cascade.

Regulation of coronary myoplasmic Ca(2+)-myosin light chain phosphorylation pathway and vasomotor tone: hyperpolarizing versus depolarizing cardioplegia

BACKGROUND

This study was designed to compare the effects of hyperpolarizing versus depolarizing cardioplegic solutions on the coronary vasomotor regulation, specifically focusing on coronary myoplasmic Ca2+-myosin light chain (MLC) phosphorylation pathway and beta-adrenergic signal transduction.

METHODS

With the use of an in vitro cardioplegic model, rat coronary microvessels loaded with fura-2 were subjected to simulated cold (20 degrees C) cardioplegia and reperfused with Krebs solution for 60 minutes at 37 degrees C. Cardioplegia consisted of either (1) Krebs solution alone (control), (2) Krebs plus adenosine triphosphate-sensitive potassium channel opener (100 micromol/L pinacidil [PCO-CP]), (3) hyperkalemic cardioplegia (K(+) = 25 mmol/L [K-CP]), or (4) K-CP plus magnesium (Mg(2+) = 25 mmol/L; [K/Mg-CP]).

RESULTS

At the endpoint of the cardioplegic period, K-CP resulted in a significant increase both in [Ca(2+)](i) and in MLC phosphorylation compared with control (both P <.05). In contrast, PCO-CP did not make any significant difference in these indices compared with control. After reperfusion, the relaxation responses to isoproterenol and forskolin after K-CP were significantly reduced (both P <.05 vs control) but were preserved after PCO-CP. K/Mg-CP provided comparable effects to PCO-CP.

CONCLUSIONS

These results suggest that neither an activation of the coronary myoplasmic Ca(2+)-MLC phosphorylation pathway nor beta-adrenergic desensitization seen after exposure to depolarizing cardioplegia occurs with exposure to hyperpolarizing cardioplegia and magnesium-supplemented depolarizing hyperkalemic cardioplegia.

Sialyl lewis oligosaccharide preserves cardiopulmonary and endothelial function after hypothermic circulatory arrest in lambs

OBJECTIVE

Neutrophil adhesion to endothelium contributes to cardiopulmonary dysfunction after cardiac surgical procedures. Initial neutrophil-endothelial interactions involve selectins, which bind carbohydrate ligands, such as sialyl-Lewis(X). Blockade of selectin-mediated neutrophil interactions with CY1503, a synthetic oligosaccharide analog of sialyl-Lewis(X), could limit neutrophil-mediated injury after cardiopulmonary bypass.

METHODS

The efficacy of CY1503 treatment was tested in a lamb model of cardiopulmonary bypass with hypothermic circulatory arrest. Neonatal lambs received CY1503 (n = 6, CPB-CY1503) or saline solution vehicle (n = 7, CPB-saline) into the pump prime before bypass and as a continuous infusion throughout reperfusion. Five lambs served as control animals for in vitro microvessel studies. Indexes of myocardial function (preload recruitable stroke work index, and rate of pressure rise) and pulmonary function (compliance, airway resistance, and arterial PO (2)) were measured before bypass and during reperfusion. The effect of CY1503 on endothelium-dependent vascular reactivity was assessed by means of in vitro pulmonary and coronary microvessel studies.

RESULTS

Myocardial function was depressed after circulatory arrest, but CY1503 preserved function near baseline (36% +/- 25% vs 99% +/- 19% of baseline at 3 hours of reperfusion). CY1503-treated animals also demonstrated improved pulmonary function during reperfusion. In vitro microvessel analysis of vascular reactivity revealed endothelial dysfunction after circulatory arrest compared with control lambs. CY1503-treated lambs (CPB-CY1503) had intact endothelial function, as demonstrated by normal vasodilatory responses to endothelium-dependent vasodilators.

CONCLUSIONS

CY1503 preserves cardiopulmonary and endothelial function after cardiopulmonary bypass and hypothermic circulatory arrest in neonatal lambs. This suggests a role for selectin-mediated, neutrophil-endothelial interactions in the inflammatory response after cardiac operations.