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.

COS cells expression cloning of tyrosine-phosphorylated proteins by immunocytochemistry

Tyrosine phosphorylation is an important post-translational modification of proteins, essential in many aspects of the cell economy, particularly in signal transduction pathways. Despite the importance of protein tyrosine phosphorylation, the approaches available for molecular cloning remain limited. We have developed a COS cell-based eukaryotic expression cloning procedure for phosphotyrosine-containing proteins by immunocytochemistry of cell monolayers. The approach takes advantage of the low basal levels of tyrosine phosphorylated, robust transient expression, availability of specific antibodies against tyrosine-phosphorylated residues, and rescue of episomal DNA after immunocytochemistry. The technique is validated by cloning the rat proto-oncogene c-fgr in its tyrosine-phosphorylated form out of a rat kidney cDNA library containing over 10(6) primary recombinants. This technique set the grounds for expression cloning of tyrosine-phosphorylated proteins in eukaryotic cells, and it is anticipated that further modifications and refinements will allow the identification of protein tyrosine phosphatase substrates.

Dilation by isoflurane of preconstricted, very small arterioles from human right atrium is mediated in part by K(+)-ATP channel opening

The adenosine triphosphate (ATP)-sensitive potassium channels (K(+)-ATP channels) are activated by decreases in intracellular ATP and help to match blood flow to tissue needs. Such metabolism-flow coupling occurs predominantly in the smallest arterioles measuring 50 microm or less in diameter. Previous studies demonstrated that isoflurane may activate the K(+)-ATP channels in larger arteries. We examined whether isoflurane also activates the channels in the smallest arterioles of approximately 50 microm. Microvessels of approximately 50 microm were dissected from right atrial appendages from patients undergoing coronary artery bypass surgery and were monitored in vitro for diameter changes by videomicroscopy. With or without preconstriction with the thromboxane analog U46619 1 microM, vessels were exposed to isoflurane 0%-3% either in the presence or absence of the K(+)-ATP channel blocker glibenclamide 1 microM. Without preconstriction, isoflurane neither dilated nor constricted the vessels significantly. After preconstriction, isoflurane had a concentration-dependent dilation of the small arterioles (39 +/- 13% [mean +/- SD] dilation at 3% isoflurane) (P < 0.001), and this effect was significantly attenuated by glibenclamide (18 +/- 5% dilation at 3% isoflurane) (P < 0.01). In comparison, nitroprusside 10(-4) M produced 79 +/- 6% dilation, and adenosine diphosphate 10(-4) M produced 29 +/- 7% dilation. We conclude that isoflurane-mediated dilation of the smallest resistance arterioles may be in part based on activation of the K(+)-ATP channels when the arterioles are relatively constricted.

IMPLICATIONS

Vasodilation of very small coronary arterioles by isoflurane depends on preexisting tone and may in part be mediated by the K(+)-ATP channels.

Epithelium-dependent bronchodilatory activity is preserved in pig bronchioles after normothermic cardiopulmonary bypass

Analogous to vascular endothelium, bronchial epithelium modulates bronchomotor activity by releasing epithelium-derived relaxing factors. Cardiopulmonary bypass (CPB) is associated with endothelial dysfunction. We examined whether CPB may be associated with bronchiolar epithelial dysfunction in pigs. Pigs were exposed to normothermic CPB for 1.5 h and then separated from CPB. Lung tissues were biopsied before and 30 min after CPB. For time control, lung tissues were biopsied at baseline and after 2 hr of anesthesia. Bronchioles measuring about 100 microm were dissected, and the epithelium was either left intact or denuded. Each bronchiolar segment was preconstricted with 10 microM 5-hydroxytryptamine and relaxation responses to nitroprusside 10(-9)-10(-4) M, isoproterenol 10(-9)-10(-4) M, or the inhaled anesthetics halothane or isoflurane 0-2.5 minimum alveolar anesthetic concentration were examined in vitro by videomicroscopy. Bronchiolar segments demonstrated concentration-dependent relaxation responses to each of the dilators examined. Epithelial denudation reduced bronchodilation to isoproterenol, isoflurane, and halothane, but not to nitroprusside. Bronchodilation was not significantly affected by CPB. We conclude that, unlike vascular endothelial function, porcine bronchiolar epithelium-modulated bronchomotor activity is not significantly affected by normothermic CPB.

IMPLICATIONS

Normothermic cardiopulmonary bypass does not result in epithelial dysfunction in pigs. Epithelium-dependent and epithelium-independent bronchodilators may be equally effective before and after cardiopulmonary bypass.

Mesenteric dysfunction after cardiopulmonary bypass: role of complement C5a

BACKGROUND

We investigated the effects of cardiopulmonary bypass (CPB) on ileal homeostasis, and the influence of functional inhibition of complement C5a on CPB-induced mesenteric injury.

METHODS

Pigs were perfused on CPB for 1 hour and then perfused off CPB for an additional 2 hours. Antiporcine C5a monoclonal antibody (C5a MAb) was administered 20 minutes before onset of CPB to 6 pigs; 6 controls received saline vehicle. Total complement activity, ileal myeloperoxidase, and indices of ileal integrity were examined.

RESULTS

Treatment with C5a MAb ameliorated CPB-induced abnormalities in endothelium-dependent relaxation to ADP and substance P, and the hypercontractile response to phenylephrine of ileal microvessels (88 to 168 microm). Ileal myeloperoxidase activity [units/g protein] was 41 +/- 11 in the C5a MAb group, compared to 83 +/- 13 in the saline group (19 +/- 10 base line). Total hemolytic complement activity was similar in the C5a MAb and saline groups (0.6 +/- 0.2 and 0.7 +/- 0.2 CH50 units). During CPB, ileal mucosal blood flow and mucosal pH, edema formation, and epithelial permeability deteriorated similarly in saline and C5a MAb groups. Inducible nitric oxide synthase (iNOS) mRNA expression was similar before and after CPB.

CONCLUSIONS

CPB is associated with significant physiologic alterations in mucosal perfusion, epithelial permeability, edema formation, and blood flow regulation. Inhibition of C5a limits neutrophil-mediated impairment of ileal microvascular regulation after bypass, but does not improve extravascular mesenteric dysfunction after CPB.

Intrapericardial delivery of fibroblast growth factor-2 induces neovascularization in a porcine model of chronic myocardial ischemia

Therapeutic angiogenesis is a novel approach to the treatment of myocardial ischemia based on the use of proangiogenic growth factors to induce the growth of new blood vessels to supply the myocardium at risk. This study was designed to assess the safety and efficacy of a single intrapericardial injection of basic fibroblast growth factor (FGF-2) in a porcine model of chronic myocardial ischemia. Yorkshire pigs underwent ameroid placement around the left circumflex coronary artery. At 3 weeks, animals were randomized to receive a single intrapericardial injection of either saline (n = 10), 3 mg of heparin (n = 9), 3 mg of heparin + 30 microgram of FGF-2 (n = 10), 200 microgram of FGF-2 (n = 10), or 2 mg of FGF-2 (n = 10). Coronary angiography, microsphere flow, magnetic resonance functional, and perfusion imaging were performed before and 4 weeks after treatment, at which time histologic analysis was also performed on 3 animals in each group. In ischemic pigs, FGF-2 treatment resulted in significant increases in left-to-left angiographic collaterals and left circumflex coronary artery blood flow. These benefits were accompanied by improvements in myocardial perfusion and function in the ischemic territory, as well as histologic evidence of increased myocardial vascularity without any adverse effects. Not one of these benefits was seen in saline- or heparin-treated ischemic animals. A single intrapericardial injection of FGF-2 in a porcine model of chronic myocardial ischemia results in functionally significant myocardial angiogenesis, without any adverse outcomes. This mode of FGF-2 administration may prove to be a useful therapeutic strategy for the treatment of patients with ischemic heart disease.

Serotonin-induced coronary contraction increases after blood cardioplegia-reperfusion: role of COX-2 expression

BACKGROUND

Coronary contraction has been implicated in causing suboptimal myocardial function after coronary bypass surgery. Addition of blood to cardioplegic solutions has been shown to improve endothelial function after cardioplegia. In this study, the effects of blood cardioplegia and brief reperfusion on vascular reactivity in patients with coronary artery disease and the expression (mRNA and protein) of enzymes involved in vasomotor regulation were examined.

METHODS AND RESULTS

The atrial appendages of patients undergoing coronary artery surgery were harvested before cardiopulmonary bypass (control, n=8) and after bypass from a nonischemic tissue atrial segment exposed to cold, hyperkalemic blood cardioplegia (mean, 60 minutes) and a brief period (10 minutes) of reperfusion (CP-Rep, n=8). Responses of atrial arterioles were studied in vitro with video-microscopy. Reverse-transcriptase polymerase chain reaction and Western blotting were used to examine the expressions and protein content, respectively, of enzymes involved in vasomotor regulation. Serotonin caused a minimal dilation under baseline conditions but after CP-Rep elicited a potent contractile response that was inhibited in the presence of the selective inducible cyclooxygenase (COX-2) inhibitor NS398. Substance P caused an endothelium-dependent relaxation of atrial arterioles through release of nitric oxide, and ADP caused relaxation mediated through release of prostaglandins. After CP-Rep, relaxation to substance P was impaired, whereas endothelium-independent relaxation to nitroprusside and response to ADP were unchanged. Expression and protein level of COX-2 were significantly increased after CP-Rep. In contrast, expression of inducible (nitric oxide synthase-2) or constitutive endothelial (nitric oxide synthase-3) nitric oxide synthase, prostacyclin synthase, and constitutive cyclooxygenase (COX-1) were not altered after CP-Rep.

CONCLUSIONS

CP-Rep increases serotonin-induced contraction of human microvessels caused by the release of products of COX-2 and the impaired release of nitric oxide. These findings have implications regarding altered coronary microvascular regulation and the cause of coronary spasm after cardiac surgery.

Local perivascular delivery of basic fibroblast growth factor in patients undergoing coronary bypass surgery: results of a phase I randomized, double-blind, placebo-controlled trial

BACKGROUND

Angiogenesis is a promising treatment strategy for patients who are not candidates for standard revascularization, because it promotes the growth of new blood vessels in ischemic myocardium.

METHODS AND RESULTS

We conducted a randomized, double-blind, placebo-controlled study of basic fibroblast growth factor (bFGF; 10 or 100 microg versus placebo) delivered via sustained-release heparin-alginate microcapsules implanted in ischemic and viable but ungraftable myocardial territories in patients undergoing CABG. Twenty-four patients were randomized to 10 microg of bFGF (n=8), 100 microg of bFGF (n=8), or placebo (n=8), in addition to undergoing CABG. There were 2 operative deaths and 3 Q-wave myocardial infarctions. There were no treatment-related adverse events, and there was no rise in serum bFGF levels. Clinical follow-up was available for all patients (16.0+/-6.8 months). Three control patients had recurrent angina, 2 of whom required repeat revascularization. One patient in the 10-microg bFGF group had angina, whereas all patients in the 100-microg bFGF group remained angina-free. Stress nuclear perfusion imaging at baseline and 3 months after CABG showed a trend toward worsening of the defect size in the placebo group (20.7+/-3.7% to 23.8+/-5.7%, P=0.06), no significant change in the 10-microg bFGF group, and significant improvement in the 100-microg bFGF group (19.2+/-5.0% to 9.1+/-5.9%, P=0.01). Magnetic resonance assessment of the target ischemic zone in a subset of patients showed a trend toward a reduction in the target ischemic area in the 100-microg bFGF group (10.7+/-3.9% to 3. 7+/-6.3%, P=0.06).

CONCLUSIONS

This study of bFGF in patients undergoing CABG demonstrates the safety and feasibility of this mode of therapy in patients with viable myocardium that cannot be adequately revascularized.

Vascular changes after cardiopulmonary bypass and ischemic cardiac arrest: roles of nitric oxide synthase and cyclooxygenase

Cardiac surgery involving ischemic arrest and extracorporeal circulation is often associated with alterations in vascular reactivity and permeability due to changes in the expression and activity of isoforms of nitric oxide synthase and cyclooxygenase. These inflammatory changes may manifest as systemic hypotension, coronary spasm or contraction, myocardial failure, and dysfunction of the lungs, gut, brain and other organs. In addition, endothelial dysfunction may increase the occurrence of late cardiac events such as graft thrombosis and myocardial infarction. These vascular changes may lead to increased mortality and morbidity and markedly lengthen the time of hospitalization and cost of cardiac surgery. Developing a better understanding of the vascular changes operating through nitric oxide synthase and cyclooxygenase may improve the care and help decrease the cost of cardiovascular operations.

Angiogenesis in cardiovascular disease: current status and therapeutic potential

Therapeutic angiogenesis, in the form of growth factor protein administration or gene therapy, has emerged as a new method of treatment for patients with severe, inoperable coronary artery disease. Improved myocardial perfusion and function after the administration of angiogenic growth factors has been demonstrated in animal models of chronic myocardial ischaemia. Recently, preliminary clinical trials using growth factor proteins or genes encoding these angiogenic factors have demonstrated clinical and other objective evidence of relevant angiogenesis. Thus, therapeutic angiogenesis has the potential to extend treatment options to patients who are not optimal candidates for conventional methods of myocardial revascularisation.

Surgical ICU recidivism after cardiac operations

BACKGROUND

Decreasing the ICU length of stay (LOS) after cardiac operations may increase ICU recidivism, obviating the benefit of early discharge.

METHODS

From January 1, 1994 to January 1, 1998, there were 2,388 consecutive cardiac operations, from which 2,228 patients were discharged alive from the ICU and had sufficient information to determine their incidence of ICU return, the reasons for their return, their ICU LOS (initial and secondary LOS), and mortality.

RESULTS

A decrease occurred in the initial ICU LOS from 1994 through 1997 (medians for 1994, 1995, 1996, and 1997, respectively: 31 h, 26.4 h, 24.5 h, and 24 h; and means, respectively: 69.4 +/- 139.8, 62.8 +/- 114.1, 52.5 +/- 104.0, and 56.2 +/- 103.4 h; p = 0.048). In association with this, however, ICU recidivism increased (as percentage of discharges, respectively: 3.9%, 4.2%, 6.1%, and 8.4%; p = 0.005). Inclusive of secondary ICU LOS, the total ICU LOS hours still decreased over the 4-year period. Most notably, the incidence of readmission increased with longer initial LOS (initial LOS quartiles from shortest to longest: 3.9%, 5.2%, 4.7%, and 9.2%; p = 0.0008). Predictors of ICU recidivism included preoperatively, a history of congestive heart failure, and a lower mean left ventricular ejection fraction (52.7 +/- 19.3% vs 49.8 +/- 21.5%; p = 0.0080); and, postoperatively, an increased mean weight gain (8.5 +/- 5.6 kg vs 10.3 +/- 4.7 kg; p = 0.040) and longer mean initial ventilator time (157 +/- 299 h vs 35 +/- 107 h; p = 0.038). The most common reason for readmission was pulmonary problems.

CONCLUSIONS

Over the years studied, the initial ICU LOS after cardiac operations has decreased in association with a significant increase in ICU recidivism. Importantly, however, patients readmitted to the ICU are those with longer initial LOSs. Decreased initial stay does not account for our increased ICU recidivism, and efforts to decrease ICU recidivism can focus on the patients with poor preoperative cardiac function and longer initial ICU stays.

Preconditioning improves cardioplegia-related coronary microvascular smooth muscle hypercontractility: role of KATP channels

OBJECTIVES

The effect of preconditioning before hyperkalemic cardioplegia on the coronary smooth muscle remains to be elucidated. We tested the hypothesis that hypoxic preconditioning could protect coronary smooth muscle against subsequent hyperkalemic cardioplegia-induced coronary vasospasm and that this preconditioning effect could be mediated by K(ATP) channels.

METHODS

Rat coronary arterioles (endothelium-denuded) were studied in a pressurized, no-flow, normothermic state. Simultaneous monitoring of luminal diameter and intracellular calcium concentration of vascular smooth muscle loaded with fura-2 was made with microscopic image analysis. All vessels were subjected to 60 minutes of hypoxic hyperkalemic cardioplegia (K(+) = 25.0 mmol/L) and were then reperfused. Six groups were studied: (1) controls, no precardioplegic intervention; (2) preconditioning, achieved with 10 minutes of hypoxia (PO2 < 30 mm Hg) and 10 minutes of reoxygenation; (3) preconditioning plus glibenclamide (10 micromol/L), achieved with 10 minutes of preconditioning in the presence of K(ATP) channel blocker glibenclamide; (4) pretreatment with K(ATP) channel opener pinacidil (100 micromol/L); (5) pretreatment with pinacidil (100 micromol/L) plus glibenclamide (10 micromol/L); and (6) pretreatment with glibenclamide (10 micromol/L) alone.

RESULTS

Hypoxic preconditioning significantly (P <.01) reduced hyperkalemic cardioplegia-induced intracellular calcium concentration accumulation and prevented the hypercontractility during and after hyperkalemic cardioplegia compared with control vessels. Pinacidil provided effective microvascular protection similar to hypoxic preconditioning. These vasoprotective effects of preconditioning were significantly antagonized in glibenclamide-treated vessels.

CONCLUSIONS

Hypoxic preconditioning can prevent coronary microvascular hypercontractility during and after subsequent cardioplegia by a K(ATP ) channel mechanism that regulates intracellular calcium concentration of the vascular smooth muscle.

Influence of oxygenation on endothelial modulation of coronary vasomotor function during hyperkalemic cardioplegia

BACKGROUND

The purpose of this study was to determine the influence of oxygenation of a hyperkalemic cardioplegic solution (K-CP) on endothelial modulation of vasomotor tone and to correlate these changes with the intracellular calcium concentration ([Ca++]i) in microvascular smooth muscle.

METHODS

Rat coronary arterioles were studied in a pressurized, no-flow normothermic state. Simultaneous monitoring of luminal diameter and [Ca++]i (fura-2) was performed with use of microscopic image analysis. Vessels were subjected to 60 minutes of oxygenated or hypoxic K-CP (K+ = 25.0 mmol/L) and were then reperfused with oxygenated Krebs-physiologic saline solution for 60 minutes.

RESULTS

In oxygenated K-CP, the K-CP-induced contraction and [Ca++]i accumulation were significantly increased in endothelium-denuded (ED) vessels compared with endothelium-intact vessels. The effect of ED in oxygenated K-CP was mimicked by administration of the nitric oxide synthase inhibitor NG-monomethyl-L-arginine. Conversely, in hypoxic K-CP the contraction was significantly attenuated in ED vessels compared with endothelium-intact vessels, although there was no significant difference in [Ca++]i. Indomethacin did not affect the endothelium-dependent contraction during hypoxic K-CP.

CONCLUSIONS

Endothelium-derived nitric oxide modulates the vascular tone during K-CP by regulating the vascular smooth muscle [Ca++]i, whereas endothelium-derived contracting factor(s), which is not predominantly a product of cyclo-oxygenase, may play a prominent role under hypoxic K-CP by increasing vascular smooth muscle Ca++ sensitivity.

Attenuation of endothelium-dependent dilation of pig pulmonary arterioles after cardiopulmonary bypass is prevented by monoclonal antibody to complement C5a

We examined whether pulmonary endothelial dysfunction associated with cardiopulmonary bypass (CPB) may be mediated by complement C5a in pigs. Pigs were placed on normothermic CPB for 1 h with or without a previous administration of 1.6 mg/kg anti-C5a monoclonal antibody (MAb), then reperfused for 2 h. Pulmonary tissue myeloperoxidase activity was measured. Expression of nitric oxide synthase (NOS) was measured by reverse transcriptase polymerase chain reaction and Western blotting. Pulmonary arterioles approximately 100 microm in diameter were preconstricted with the thromboxane analog U46619 1 microM, and relaxation responses to adenosine diphosphate 10(-9)-10(-4) M, substance P 10(-12)-10(-6) M, and sodium nitroprusside 10(-9)-10(-4) M were examined in vitro by videomicroscopy. Relaxation to the endothelium-dependent dilators adenosine diphosphate and substance P was attenuated after CPB; this attenuation was prevented by the previous administration of MAb. Relaxation to sodium nitroprusside was not affected by CPB. Neutrophil sequestration, as measured by MPO activity, increased after CPB, either with or without MAb. Transcription of NOS was unchanged by CPB, but translation of constitutive NOS was decreased after CPB, and this decrease was prevented by a previous administration of MAb. We conclude that pig pulmonary endothelial dysfunction associated with CPB may be mediated by C5a. The mechanism may involve changes in NOS translation.

IMPLICATIONS

In pigs, pulmonary endothelial dysfunction may occur after cardiopulmonary bypass due to product(s) of complement activation.

Intracoronary and intravenous administration of basic fibroblast growth factor: myocardial and tissue distribution

Therapeutic angiogenesis using various heparin-binding growth factors is a promising treatment for ischemic heart disease. Single dose intracoronary (IC) or i.v. delivery are most practical for clinical use. This study was designed to investigate the myocardial and tissue deposition of basic fibroblast growth factor (bFGF) after IC and i.v. administration in normal and chronically ischemic animals. Twenty-four Yorkshire pigs were used (12 normal and 12 ischemic animals) with IC and i.v. administration of 125I-bFGF (25 microCi) combined with cold bFGF (30 microg) and heparin (3 mg). Tissue and myocardial distribution was determined at 1 and 24 h by measuring 125I-bFGF specific activity and by organ and light level autoradiography. The liver accounted for the majority of 125I-bFGF activity at 1 h (37.6 +/- 17.1% for IC and 42.1 +/- 17.7% for i.v. delivery), with a reduction to 2.8 +/- 1.5% for IC and 1.5 +/- 0.9% for i.v. delivery by 24 h. Total cardiac specific activity at 1 h was 0.88 +/- 0.89% for IC and 0.26 +/- 0.08% for i.v. administration (p =.12) and decreased to 0.05 +/- 0.04% (p =.05, versus 1 h) and 0. 04 +/- 0.01% (p <.001, versus 1 h) at 24 h, respectively. IC but not i.v. delivery resulted in higher deposition in ischemic than normal myocardium. IC delivery resulted in enhanced bFGF deposition only in myocardial territories subtended by the infused artery. Intravenous delivery compares favorably with IC delivery with a 3- to 4-fold reduction in myocardial deposition at 1 h and with similar solid organ deposition. The less invasive nature of i.v. delivery, its potential for repeat administration, and its applicability to a larger population may offset its resultant reduced myocardial deposition. Efficacy studies are ongoing.

Intracellular free calcium accumulation in ferret vascular smooth muscle during crystalloid and blood cardioplegic infusions

OBJECTIVE

The effects of magnesium- and potassium-based crystalloid and blood-containing cardioplegic solutions on coronary smooth muscle intracellular free calcium ([Ca2+]i) accumulation and microvascular contractile function were examined.

METHODS

Isolated ferret hearts were subjected to hyperkalemic (25 mmol/L K+) blood cardioplegic infusion, hypermagnesemic (25 mmol/L Mg2+, K+-free) crystalloid cardioplegic infusion, or hyperkalemic crystalloid cardioplegic infusion for 1 hour. Coronary arterioles were isolated, cannulated, and loaded with fura 2. Reactivity and [Ca2+]i were assessed with videomicroscopy. [Ca2+]i was measured at baseline and after application of 50 mmol/L KCl. In addition, [Ca2+]i and vascular contraction were measured during exposure to Mg2+ and K+ cardioplegic solution at both 4 degrees C and 37 degrees C.

RESULTS

From a baseline [Ca2+]i of 177 +/- 52 nmol/L, K+ cardioplegic infusion (302 +/- 80 nmol/L potassium) markedly increased [Ca2+]i, whereas blood cardioplegic infusion (214 +/- 53 nmol/L) and Mg2+ cardioplegic infusion (180 +/- 42 nmol/L) did not alter [Ca2+]i. Although a difference between groups in percentage contraction after application of 50 mmol/L KCl was not observed, [Ca2+]i increased significantly more in vessels in the control group (764 +/- 327 nmol/L) and the K+ crystalloid cardioplegic infusion group (698 +/- 215 nmol/L) than in vessels in the blood cardioplegic infusion group (402 +/- 45 nmol/L) and the Mg2+ cardioplegic infusion group (389 +/- 80 nmol/L). Mg2+ cardioplegic solution induced no microvascular contraction at either 4 degrees C or 37 degrees C, nor was an increase in [Ca2+]i observed. K+ cardioplegic solution induced microvascular contraction at 37 degrees C but not at 4 degrees C; it increased [Ca2+]i at both 4 degrees C and 37 degrees C.

CONCLUSION

An Mg2+-based cardioplegic solution, or appropriate Mg2+ or blood supplementation of a K+ crystalloid cardioplegic solution, may decrease the accumulation of [Ca2+]i in the vascular smooth muscle during ischemic arrest.

Effect of sevoflurane and desflurane on the myogenic constriction and flow-induced dilation in rat coronary arterioles

BACKGROUND

Determinants of myocardial blood flow distribution include metabolic, myogenic, endothelial, and neurohumoral control mechanisms. The authors studied the effect of sevoflurane and desflurane on the myogenic and endothelial mechanisms.

METHODS

Wistar rat subepicardial microvessels, approximately 100 microm in diameter, were monitored for diameter changes in vitro using a video detection system. Myogenic vasomotion was studied by varying the intraluminal pressure from 10 mmHg to 120 mmHg. Flow-induced, endothelium-dependent dilation was evaluated in U46619-preconstricted vessels by varying the pressure gradient across the isolated vessel from 10 mmHg to 80 mmHg, while maintaining the midpoint luminal pressure constant at 40 mmHg to avoid myogenic effects. Myogenic and flow-induced vasomotion both were studied in the presence of sevoflurane, 1 or 2 minimum alveolar concentration (MAC) (MAC is a unit of inhalational anesthetic potency), desflurane, 1 or 2 MAC, or no anesthetic (control).

RESULTS

Myogenic constriction was shown above intraluminal pressures of 70 mmHg. Myogenic constriction was unchanged by sevoflurane, 1 MAC (P = 0.24), but was mildly enhanced by sevoflurane, 2 MAC (P < 0.05), or desflurane, 1 (P < 0.05) or 2 MAC (P < 0.01). Flow-induced dilation was shown over the pressure gradient range of 10-80 mmHg. Flow-induced dilation was not altered significantly by sevoflurane, 1 or 2 MAC (P > 0.3 each), but was significantly attenuated by desflurane, 1 or 2 MAC (P < 0.001 each).

CONCLUSIONS

Sevoflurane maintains myogenic and endothelial determinants of myocardial blood flow distribution. Conversely, desflurane attenuates endothelium-dependent flow-induced dilation while mildly enhancing myogenic constriction.

Receptor-type protein-tyrosine phosphatase mu is expressed in specific vascular endothelial beds in vivo

We investigated the localization of receptor-type protein-tyrosine phosphatase mu (RPTPmu) in tissues by immunofluorescence. RPTPmu immunoreactivity was found almost exclusively within vascular endothelial cells. RPTPmu was more abundant in the arterial tree than in the venous circulation. This pattern of expression was opposite to that of the von Willebrand factor and demonstrated a lack of difference in expression of VE-cadherin. RPTPmu was undetectable in the endocardium. In agreement with previous work on nonendothelial cell lines, RPTPmu was exclusively at the lateral aspects of endothelial cells in vivo and at cell-cell contacts as well as ex vivo in two- or three-dimensional endothelial cell cultures, and expression levels were upregulated by cell density. RPTPmu was detected in few other cells: bronchial and biliary epithelia and cardiocytes (intercalated discs). Our results identify RPTPmu as a new marker of endothelial cell heterogeneity and suggest a possible role in endothelial-specific functions, involving cell-cell contact.

Coronary microvascular protection with mg2+: effects on intracellular calcium regulation and vascular function

The use of Mg2+-supplemented hyperkalemic cardioplegia preserves microvascular function. However, the mechanism of this beneficial action remains to be elucidated. We investigated the effects of Mg2+ supplementation on the regulation of intracellular calcium concentration ([Ca2+]i) and vascular function using an in vitro microvascular model. Ferret coronary arterioles (80-150 micrometer in diameter) were studied in a pressurized (40 mmHg) no-flow, normothermic (37 degrees C) state. Simultaneous monitoring of internal luminal diameter and [Ca2+]i using fura 2 were made with microscopic image analysis. The microvessels (n = 6 each group) were divided into four groups according to the content of MgCl2 (nominally 0, 1.2, 5.0, and 25.0 mM) in a hyperkalemic cardioplegic solution ([K+] 25.0 mM). After baseline measurements, vessels were subjected to 60 min of hypoxia with hyperkalemic cardioplegia (equilibrated with 95% N2-5% CO2) containing each concentration of Mg2+ ([Mg2+]) and were then reoxygenated. During hyperkalemic cardioplegia, [Ca2+]i increased in a time-dependent manner in all groups. In the lower [Mg2+] cardioplegia groups, [Ca2+]i was significantly increased at the end of the 60-min cardioplegic period (247 +/- 44 nM and 236 +/- 49 nM in [Mg2+] 0 and 1.2 mM groups, respectively; both P < 0.05 vs. baseline) with 19.6-17.2% vascular contraction. Conversely, there was no significant [Ca2+]i increase in the higher [Mg2+] cardioplegia groups and less vascular contraction (5.4-4.1%, both P < 0.05 vs. [Mg2+] 1.2 mM group). After reperfusion, agonist (U-46619, thromboxane A2 analog)-induced vascular contraction was significantly enhanced in the lower [Mg2+] cardioplegia groups (both P < 0.05 vs. control) but was normalized in the higher [Mg2+] cardioplegia groups. Intrinsic myogenic contraction was significantly decreased in the lower [Mg2+] cardioplegia groups (both P < 0.05 vs. control) but was preserved in the higher [Mg2+] cardioplegia groups. These results suggest that supplementation of the solution with >5.0 mM [Mg2+] may prevent hyperkalemic cardioplegia-related intracellular Ca2+ overloading and preserve vascular contractile function in coronary microvessels.

Effect of sialyl Lewis(x) oligosaccharide on myocardial and cerebral injury in the pig

BACKGROUND

Although administration of the sialyl Lewis(x) oligosaccharide may reduce myocardial injury after ischemia-reperfusion, its effect on coronary and cerebral microvascular regulation and its clinical application during cardiac operation have not been examined.

METHODS

Pigs were placed on normothermic cardiopulmonary bypass after 30 minutes of left anterior descending coronary artery occlusion. The hearts were then arrested with cold high potassium cardioplegia. After 1 hour the cross-clamp was removed and the pigs were weaned from cardiopulmonary bypass and perfused for an additional 1 hour. CY-1503 (a sodium salt of the sialyl Lewis(x) oligosaccharide, n = 6) was administered before reperfusion. Six other pigs received saline vehicle. Endothelium-dependent relaxation of precontracted coronary and brain arterioles (70 to 180 microm) to adenosine 5'-diphosphate and endothelium-independent relaxation to sodium nitroprusside were studied in vitro with videomicroscopy. Control values were obtained from uninstrumented pigs. Myeloperoxidase activity in the myocardium and brain was measured to quantify neutrophil infiltration. Cardiac function and perfusion were assessed by left ventricular systolic pressure, maximum rate of increase of left ventricular pressure, left anterior descending coronary artery blood flow and percent segmental shortening, and cerebral vascular resistance, internal carotid artery blood flow, and the constitutively expressed and inducible isoform of nitric oxide synthase mRNA were measured.

RESULTS

The impaired myocardial contractile function after ischemia and cardioplegia was not improved by administration of CY-1503. The reduced endothelium-dependent relaxation responses of coronary and brain arterioles during ischemia followed by cardioplegia and cardiopulmonary bypass were improved with CY-1503, but the altered pattern of organ perfusion was not improved. Myeloperoxidase activity was increased in the heart after ischemia-cardioplegia and in the brain after cardiopulmonary bypass. CY-1503 reduced myeloperoxidase activity in both the myocardium and in the brain. Expressions of myocardial inducible isoform or constitutively expressed nitric oxide synthase were not altered in the heart.

CONCLUSIONS

Although the sialyl Lewis(x) oligosaccharide does reduce neutrophil infiltration and endothelial injury in the coronary and cerebral microcirculation after cardiopulmonary bypass, it does not have significant beneficial acute effects on organ perfusion or function in the myocardium or brain.

Anti-C5a monoclonal antibody reduces cardiopulmonary bypass and cardioplegia-induced coronary endothelial dysfunction

OBJECTIVE

Because C5a induces tissue injury by activating polymorphonuclear leukocytes, the hypothesis was that inhibition of C5a activity would reduce cardioplegia-related injury.

METHODS

Pigs were placed on cardiopulmonary bypass. The hearts were arrested for 1 hour with hyperkalemic cardioplegia. Pigs were then separated from bypass, and the hearts were reperfused for 2 hours. Anti-porcine C5a monoclonal antibody (1.6 mg/kg, intravenously; n = 6) was administered 20 minutes before the onset of cardiopulmonary bypass. Six pigs received saline solution vehicle. Reactivity of coronary arterioles was studied in vitro with videomicroscopy. Microvessels from uninstrumented pigs served as controls for vascular studies.

RESULTS

Endothelium-dependent relaxation to adenosine diphosphate (percent relaxation of precontraction) was reduced after cardioplegic reperfusion (63% +/- 14% vs 77% +/- 10% in control at 10 micromol/L; P =.01). This impairment in endothelium-dependent relaxation was improved with anti-porcine C5a monoclonal antibody (80% +/- 22%; P =.01 vs saline solution), as was the impaired endothelium-dependent relaxation to clonidine (64% +/- 12% control; 26% +/- 17% saline solution; 55% +/- 24% anti-porcine C5a monoclonal antibody at 10 micromol/L; P =.01 saline solution vs control or anti-porcine C5a monoclonal antibody). Myeloperoxidase activity was significantly decreased (0.2 +/- 0.2 units/g protein; P =.04) in the anti-porcine C5a monoclonal antibody group compared with 5.2 +/- 2.7 in the saline solution group. CH50 2 hours after bypass was not statistically different (0.57 +/- 0.41 unit and 0.65 +/- 0.41 unit, respectively) between the anti-porcine C5a monoclonal antibody and saline solution groups. Despite less myocardial polymorphonuclear leukocyte infiltration after C5a inhibition, maximum rate of rise of left ventricular pressure, percent segmental shortening, and blood flow through the left anterior descending coronary artery were similar in the anti-porcine C5a monoclonal antibody and saline solution groups.

CONCLUSIONS

Inhibition of C5a limits neutrophil-mediated impairment of endothelium-dependent relaxation after cardiopulmonary bypass and cardioplegic reperfusion, but it has no effect on short-term myocardial functional preservation.

Twenty-four-hour heart preservation using continuous cold perfusion and copper (II) complexes

BACKGROUND

During long-term in vitro heart preservation and subsequent reperfusion, irreversible tissue damage occurs in part due to reactive oxygen species. Therefore, inhibition of generation of oxygen-derived free radicals and the related oxidative damage of ischemic tissue may be useful in maintaining heart function after long-term preservation. Complexes of Cu(II) may cause disproportionation of superoxide and thus may function as an inhibitor of the effects of oxygen-derived free radicals.

METHODS

In this study, 24-h preservation of isolated rat hearts was performed. Using the Langendorff technique, hearts were perfused for 24 h with a hypothermic, moderately hyperkalemic (15 mM KCl) solution containing various metabolic and membrane-stabilizing additives at constant low pressure. In addition, the potential benefit of the addition of two Cu(II) compounds (Cu(II) Cl2 and Cu(II)2Asp4) to the perfusion solution was examined.

RESULTS

The Cu(II)Cl2-treated hearts were significantly better preserved than control hearts after 24 h of preservation with regard to recovery of systolic pressure, coronary flow, max +dP/dt, and max -dP/dt. Lipid peroxidation as estimated by myocardial malonaldehyde (both P < 0. 001) and myocardial creatine kinase release (both P < 0.05 vs control) were significantly reduced in the Cu(II)Cl2 and Cu(II)2Asp4 groups. Overall, Cu(II)Cl2 best preserved the heart after 24 h of cold preservation with respect to indices of functional recovery, whereas Cu(II)2Asp4 did not significantly improve functional recovery compared to control.

CONCLUSION

Low-pressure, cold perfusion with an enhanced solution is a potential method to preserve donor hearts in preparation for transplantation. The beneficial effect of Cu(II)Cl2 was attributed to (i) SOD activity of the Cu2+ species and/or (ii) termination of chain carriers in the lipid peroxidations by aqueous Cu2+ and Cu+ species. The negation of some of the positive effects of Cu2+ species by the introduction of acetylsalicylate was tentatively assigned to potentiation of the Ca2+ modality for reperfusion injury.

Modulation of myocardial perfusion and vascular reactivity by pericardial basic fibroblast growth factor: insight into ischemia-induced reduction in endothelium-dependent vasodilatation

OBJECTIVES

The present study was designed to study the effects of a single intrapericardial injection of basic fibroblast growth factor on myocardial vascular resistance and endothelium-dependent microvascular dilatation in a porcine model of chronic myocardial ischemia and to investigate the mechanism of ischemia-induced impairment of endothelium-dependent vasodilatation.

METHODS

Yorkshire pigs underwent ameroid constrictor placement on the left circumflex coronary artery. At 3 weeks, animals were randomized to a single intrapericardial injection of saline solution (n = 10), 30 micrograms basic fibroblast growth factor (n = 10), or 2 mg basic fibroblast growth factor (n = 10). Myocardial vascular resistance in the normal (left anterior descending) and ischemic collateral-dependent (left circumflex artery) territories (using colored microspheres) and microvascular reactivity to adenosine diphosphate and sodium nitroprusside were measured before treatment and 4 weeks after treatment. The expression of inducible and endothelial nitric oxide synthase was determined in normal and ischemic myocardium by means of reverse transcriptase-polymerase chain reaction and Western analysis, and the effect of nitric oxide on endothelium-dependent vasodilatation was determined.

RESULTS

Compared with results in the control group, treatment with basic fibroblast growth factor resulted in significant improvement in left circumflex artery resistance and endothelium-dependent vasodilatation, reflecting increased collaterals. Myocardial ischemia was associated with increased expression of inducible nitric oxide synthase with no change in endothelial nitric oxide synthase. However, the nitric oxide donor sodium nitroprusside did not affect endothelium-dependent vasodilatation to adenosine diphosphate.

CONCLUSIONS

A single intrapericardial bolus of basic fibroblast growth factor may be a useful therapeutic strategy for the treatment of myocardial ischemia in patients with coronary artery disease. Although chronic myocardial ischemia is associated with increased expression of inducible nitric oxide synthase, it does not appear to be the cause of altered endothelial function.