Surgical implications of vascular endothelial physiology.
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Animals↗
Biomedical subjects
D R Meldrum
Publications and source records attributed to D R Meldrum.
Adenosine decreases post-ischaemic cardiac TNF-alpha production: anti-inflammatory implications for preconditioning and transplantation.
Tumour necrosis factor-alpha (TNF-alpha) is an autocrine contributor to myocardial dysfunction and cardiomyocyte death in ischaemia-reperfusion injury (I/R), sepsis, chronic heart failure and cardiac allograft rejection. Cardiac resident macrophages, infiltrating leucocytes, and cardiomyocytes themselves produce TNF-alpha. Although adenosine reduces macrophage TNF-alpha production and protects myocardium against I/R, it remains unknown whether I/R induces an increase in cardiac TNF-alpha in a crystalloid-perfused model (in the absence of blood), and, whether adenosine decreases cardiac TNF-alpha and protects function after I/R. To study this, isolated rat hearts were crystalloid-perfused using the Langendorff method and subjected to I/R, with or without adenosine pretreatment. Post-ischaemic cardiac TNF-alpha (enzyme-linked immunosorbent assay and bioassay) and function were determined (Langendorff). I/R increased cardiac TNF-alpha and impaired myocardial function. Adenosine decreased cardiac TNF-alpha and improved post-ischaemic functional recovery. This study demonstrates that: first, I/R induces an increase in cardiac tissue TNF-alpha in a crystalloid-perfused model: second, adenosine decreases cardiac TNF-alpha and improves post-ischaemic myocardial function; third, decreased cardiac TNF-alpha may represent a mechanism by which adenosine protects myocardium; and fourth, adenosine-induced suppression of cardiac TNF-alpha may provide an anti-inflammatory link to preconditioning and have implications for cardiac allograft preservation.
Adenosine↗
Adaptive and maladaptive mechanisms of cellular priming.
OBJECTIVE: The mechanisms of cellular priming resulting in both adaptive and maladaptive responses to subsequent injury and strategies for manipulating this priming to constructive therapeutic advantage are explored. BACKGROUND DATA: A cell is prepared or educated by an initial insult (priming stimulus). Investigations in both laboratory animals and humans indicate that cells, organs, and perhaps even whole patients respond differently to a proximal second insult ("second hit") by virtue of this prior environmental history. The opportunity to achieve the primed state appears to be conserved across almost all cell types. The initial stimulus transmits a message to the cellular machinery that influences the cell's response to a subsequent challenge. This response may result in an exaggerated inflammatory response in the case of the neutrophil (an often maladaptive process) or an improved tolerance to injury by the myocyte (adaptive response). Our global hypothesis is that cellular priming is a conserved, receptor-dependent process that invokes common intracellular targets across multiple cell types. We further postulate that these targets create a language based on the transient phosphorylation and dephosphorylation of intracellular enzymes that is therapeutically accessible. CONCLUSIONS: Priming is a conserved, receptor-dependent process transduced by means of intracellular targets across multiple cell types. The potential therapeutic strategies outlined involve the receptor-mediated manipulation of cellular events. These events are transmitted through an intracellular language that instructs the cell regarding its behavior in response to subsequent stimulation. Understanding these intracellular events represents a realistic goal of priming and preconditioning biology and will likely lead to clinical control of the primed state.
Adaptation, Physiological↗
Neutrophils mediate pulmonary vasomotor dysfunction in endotoxin-induced acute lung injury.
BACKGROUND: The major hemodynamic feature of endotoxin (ETX)-induced acute lung injury is pulmonary hypertension secondary to increased pulmonary vascular resistance. Endotoxin causes dysfunction of pulmonary vasorelaxation, which is associated with increased lung neutrophil accumulation. We hypothesized that neutrophils mediate the dysfunction of cGMP-mediated pulmonary vasorelaxation in acute lung injury. In a rat model of ETX-induced lung injury, our purpose was to determine the effect of neutrophil depletion on the following mechanisms of pulmonary vasomotor control: endothelium-dependent cGMP-mediated relaxation (response to acetylcholine) and endothelium-independent relaxation (response to sodium nitroprusside). METHODS: Rats were studied 6 hours after ETX (20 mg/kg). Neutropenia (< 75 neutrophils/microL) was induced with anti-neutrophil serum 24 hours before ETX. Saline injected rats were controls. Dose-response curves to acetylcholine and sodium nitroprusside were generated in isolated pulmonary artery rings preconstricted with phenylephrine (n = 10 rings/5 rats per group). Lungs were harvested (n = 4 rats/group) and lung neutrophil accumulation was assessed with a myeloperoxidase assay. RESULTS: Endothelium-dependent and -independent cGMP-mediated pulmonary vasorelaxation was dysfunctional in ETX-induced ALI. Neutrophil depletion prevented lung neutrophil accumulation and attenuated pulmonary vasomotor dysfunction after endotoxin. CONCLUSIONS: These data suggest that neutrophils contribute to pulmonary endothelium and smooth muscle dysfunction in acute lung injury induced by endotoxemia.
Acetylcholine↗
L-arginine decreases alveolar macrophage proinflammatory monokine production during acute lung injury by a nitric oxide synthase-dependent mechanism.
BACKGROUND: Recent clinical reports indicate that inhaled nitric oxide (NO) reduces lung parenchymal inflammation during acute lung injury; however, the mechanism of its protective effects remains incompletely understood. We hypothesized that the provision of substrate for local NO production (L-arginine) would reduce alveolar macrophage proinflammatory monokine production during endotoxin (ETX)-induced acute lung injury. Our purposes were to (1) determine alveolar macrophage tumor necrosis factor alpha (TNFalpha) and interleukin 1beta (IL-1beta) production after ETX-induced acute lung injury; (2) determine the effect of L-arginine on alveolar macrophage TNFalpha and IL-1beta production in ETX-induced acute lung injury; and (3) determine whether L-arginine's effects on the alveolar macrophage are mediated by NO. METHODS: Rats received ETX (0.5 mg/kg intraperitoneal (i.p.)) or vehicle, with or without (1) L-arginine supplementation (300 mg/kg i.p.) and (2) nitric oxide synthase inhibition (N(G)-monomethyl-L-arginine, 30 mg/kg i.p.). Four hours later, alveolar macrophage were harvested by bronchoalveolar lavage and incubated at 10(6) cells/mL + 1 microg/mL phorbol myristase acetate for 24 hours. Cell-free supernatants were collected and assayed (enzyme-linked immunosorbent assay) for TNFalpha and IL-1beta. RESULTS: Sublethal ETX increased alveolar macrophage capacity to produce TNFalpha and IL-1beta (p < 0.05, analysis of variance and Bonferroni/Dunn). L-Arginine decreased alveolar macrophage TNFalpha and IL-1beta release during acute lung injury. Concurrent inhibition of nitric oxide synthase abrogated L-arginine's protective effects, suggesting that L-arginine's anti-inflammatory effects are mediated by NO. CONCLUSIONS: (1) L-Arginine is an immunomodulating nutritional supplement; (2) L-arginine decreases alveolar macrophage proinflammatory monokine production during ETX-induced acute lung injury by a nitric oxide synthase-dependent mechanism; and (3) the provision of exogenous substrate for local NO production may reduce inflammation during acute lung injury.
Analysis of Variance↗
Endotoxin stuns cGMP-mediated pulmonary vasorelaxation.
Net pulmonary vascular tone is determined by the balance of pulmonary vasorelaxation and vasoconstriction. In endotoxemic rats, cGMP-mediated pulmonary vasorelaxation is impaired through neutrophil-dependent mechanisms, yet agonist stimulated vasoconstriction remains intact. Endotoxin-induced lung neutrophil accumulation is a transient response. In models of myocardial ischemia-reperfusion injury, "stunning" or reversible cardiac dysfunction is also associated with a reversible neutrophil presence. We hypothesized that lung neutrophil accumulation and dysfunction of cGMP-mediated pulmonary vasorelaxation is reversible after an endotoxin challenge. Our purpose was to examine lung neutrophil accumulation and endothelium-dependent and -independent mechanisms of cGMP-mediated pulmonary vasorelaxation 4 and 48 h after endotoxin challenge. Rats (n = 5 per group) were studied 4 and 48 h after injection of saline or endotoxin (500 micrograms/kg, intraperitoneal). Endothelium-dependent relaxation by receptor-dependent (acetylcholine) and -independent (A23187) mechanisms and endothelium-independent (sodium nitroprusside) relaxation were studied in isolated pulmonary artery rings preconstricted with phenylephrine. Lung neutrophil accumulation was examined by lung myeloperoxidase assay. Lung neutrophil accumulation was increased at 4 h (p < .05 vs. control) and was attenuated by 48 h (p < .05 vs. endotoxin x 4 h) following endotoxin challenge. Similarly, the endotoxin-induced dysfunction of endothelium-dependent and -independent cGMP-mediated pulmonary vasorelaxation at 4 h normalized by 48 h. Endotoxin appears to induce reversible dysfunction of pulmonary vasorelaxation through stunning of vascular endothelial and smooth muscle cells.
Acetylcholine↗
LPS-induced delayed myocardial adaptation enhances acute preconditioning to optimize postischemic cardiac function.
Myocardial tolerance to ischemia and reperfusion (I/R) injury can be achieved by either acute or delayed cardioprotective mechanisms. Ischemic preconditioning has been demonstrated to be a powerful acute cardioprotective stimulus. We have reported that lipopolysaccharide (LPS) pretreatment induces delayed myocardial adaptation to I/R injury. To optimize myocardial protection, we examined the ability of delayed myocardial adaptation to enhance acute ischemic preconditioning in the isolated working rat heart. Male Sprague-Dawley rats were divided into control, acute [transient ischemia (TI); 5-min global ischemia, 37 degrees C], delayed (LPS; 500 micrograms/kg i.p.), or combined (LPS + TI) cardioprotective groups. Delayed cardioprotection involved LPS injection 72 h before heart isolation. All hearts were subjected to 20-min global ischemia (37 degrees C) and 30-min reperfusion. Coronary effluent collected during reperfusion was assayed for creatine kinase (CK) activity. Both TI and LPS treatment improved postischemic aortic flow recovery (29 +/- 4.5 and 44 +/- 4.0%, respectively; P < 0.05, LPS vs. TI) compared with control hearts (11 +/- 2.2%; P < 0.05, TI or LPS vs. control). When TI was applied to LPS-treated hearts (LPS + TI), aortic flow recovery was further enhanced (57 +/- 3.8%; P < 0.05 vs. TI or LPS alone). CK release during 20 and 30 min of reperfusion was decreased in all treated hearts compared with control hearts (P < 0.05). These results indicate that delayed myocardial adaptation and acute ischemic preconditioning independently activate protective mechanisms against ischemia. Enhanced protection occurs when induced delayed mechanisms are combined with acute cardioprotective stimuli, which optimize postischemic myocardial function and reduce myocellular necrosis.
Adaptation, Physiological↗
Early and delayed preconditioning: differential mechanisms and additive protection.
The purposes of this study were to determine whether 1) 24-h endotoxin (ETX) pretreatment induces delayed ("second window") myocardial protection against ischemia-reperfusion (I/R), 2) acute adenosine (Ado) or phenylephrine (PE) pretreatment confers similar protection, 3) the mechanisms of Ado- and PE-induced early protection remain intact after endotoxemia, 4) Ado- and PE-induced protection may combine with ETX-induced delayed protection to optimize cardiac protection, and 5) these strategies of early and/or delayed myocardial protection require de novo protein synthesis. Rats (n = 6-8/group) were treated with ETX (0.5 mg/kg i.p.) or vehicle, with or without prior inhibition of protein synthesis. Twenty-four hours later, the hearts were isolated, perfused, and acutely pretreated with Ado or PE before I/R (20-min ischemia and 40-min reperfusion). Developed pressure, coronary flow, compliance (end-diastolic pressure), and reperfusion creatine kinase leak were measured. Results indicated that 1) Ado, PE, and ETX independently induced myocardial functional protection; 2) either Ado or PE acutely enhanced ETX induced protection; and 3) cycloheximide abolished delayed, but not acute, protection. We conclude that early and delayed forms of protection 1) may be combined to optimize protection and 2) differentially rely on de novo protein synthesis.
Adenosine↗
Ischemic preconditioning of human myocardium: protein kinase C mediates a permissive role for alpha 1-adrenoceptors.
The purposes of this study were to determine whether ischemic preconditioning (IPC) in human atrial trabeculae is mediated by alpha 1-adrenoceptors and protein kinase C (PKC) and whether the protection of IPC is replicated with alpha 1-adrenoceptor stimulation [alpha 1-adrenoceptor preconditioning (alpha 1-PC)]. Atrial trabeculae were obtained during coronary bypass surgery. The trabeculae were suspended in organ baths containing Tyrode solution and field stimulated at 1 Hz, and developed force was recorded. The trabeculae underwent 45 min of simulated ischemia (SI) and 120 min of reperfusion (I/R injury). IPC trabeculae received transient SI before I/R injury, alpha 1-Adrenoceptor blockade with BE-2254 and PKC inhibition with chelerythrine were independently combined with IPC before I/R injury. alpha 1-PC before I/R was examined with alpha 1-adrenergic agonist (phenylephrine) pre-treatment. Improved recovery of developed force and higher tissue creatine kinase activity were present in IPC trabeculae, and the protective effect of IPC was eliminated with either alpha 1-adrenoceptor blockade or PKC inhibition. alpha 1-PC trabeculae also exhibited enhanced functional recovery after I/R injury but lacked preservation of tissue creatine kinase activity. PKC inhibition eliminated the functional protection of alpha 1-PC. These results suggest that, in human atrial trabeculae, alpha 1-adrenoceptors and PKC mediate, in part, the functional and tissue CK preservation conferred by IPC, but alpha 1-PC does not replicate the protection of IPC.
Creatine Kinase↗
LPS induces late cardiac functional protection against ischemia independent of cardiac and circulating TNF-alpha.
Lipopolysaccharide (LPS) and tumor necrosis factor (TNF)-alpha independently induce cardioprotection against ischemia in the rat at 24 h after administration, suggesting that endogenously synthesized TNF-alpha may play a role in LPS-induced protection. The purposes of this study were 1) to delineate the time course of LPS-induced cardiac functional protection against ischemia and its relation with myocardial and circulating TNF-alpha profile, 2) to examine whether prior protein synthesis inhibition abrogates the protection, and 3) to assess the effects of TNF-alpha inhibition and neutralization on the protection. Rats were treated with LPS (0.5 mg/kg i.p.). Cardiac functional resistance to normothermic global ischemia-reperfusion was examined at sequential time points after LPS treatment in isolated hearts by the Langendorff technique. Myocardial and circulating TNF-alpha was determined by enzyme-linked immunosorbent assay at 1-24 h after LPS treatment. Protection was apparent at 24 h, 3 days, and 7 days but not at 2 or 12 h. Maximal protection at 3 days was abolished by cycloheximide pretreatment (0.5 mg/kg i.p. 3 h before LPS treatment). Increases in myocardial and circulating TNF-alpha preceded the acquisition of protection. Dexamethasone pretreatment (4.0 or 8.0 mg/kg i.p. 30 min before LPS treatment) abolished peak increase in myocardial TNF-alpha and substantially suppressed circulating TNF-alpha (54.3 and 85.9% inhibition, respectively) without an influence on the maximal protection. Similarly, maximal protection was not affected by TNF binding protein (40 or 80 microg/kg i.v. immediately after LPS treatment). The results suggest that LPS-induced cardiac functional protection against ischemia is a delayed and long-lasting protective response that may involve de novo protein synthesis. Although LPS-induced increase in myocardial and circulating TNF-alpha precedes the delayed protection, it may not be required for the delayed protection.
Animals↗
KATP channels contribute to beta- and adenosine receptor-mediated pulmonary vasorelaxation.
ATP-sensitive K+ (KATP) channels have been implicated in the regulation of vasomotor tone in aortic, mesenteric, and pulmonary vascular smooth muscle. Several investigators have described an association between KATP channels and isoproterenol (Iso)-stimulated relaxation responses. To study the relationship between receptor-dependent pulmonary vasorelaxation and KATP channels, we examined the response to agonists that generate adenosine 3',5'-cyclic monophosphate at two distinct levels of the signal transduction pathway after inhibition or activation of KATP channels in isolated rat pulmonary artery rings. Cumulative concentration responses to beta-adrenergic receptor stimulation (Iso), purinergic receptor stimulation [adenosine (Ado)], and direct stimulation of adenylate cyclase [forskolin (FSK)] were studied with and without concurrent inhibition of KATP channels (glibenclamide or tolbutamide). In addition, the effect of direct KATP channel activation (cromakalim) on the response to beta-adrenergic and purinergic receptor stimulation was determined. Last, we investigated the influence of KATP channel inhibition on endothelium-dependent and -independent mechanisms of pulmonary vasorelaxation linked to guanosine 3',5'-cyclic monophosphate production. KATP channel inhibition impaired the response to Iso and Ado. Activation of KATP channels caused a leftward shift in the dose responses of Iso and Ado, with a significant decrease in the 50% effective concentration for each agent. KATP channel inhibition did not impair the pulmonary arterial vasorelaxation response to FSK, acetylcholine, or sodium nitroprusside. KATP channels appear to contribute to beta-adrenergic and purinergic receptor-stimulated vasorelaxation in rat pulmonary arteries.
ATP-Binding Cassette Transporters↗
Hemorrhage induces acute cardioadaptation to ischemia-reperfusion by an alpha1-adrenoceptor-mediated, protein synthesis-independent mechanism.
Hemorrhage and resuscitation (H-R) has been recognized as an exclusively destructive process that results in multiple organ dysfunction. Although it is well established that endogenous adaptation mechanisms exist, it is unknown whether H-R induces endogenous adaptive/protective mechanisms. Furthermore, alpha1-adrenoceptors and de novo protein synthesis have been variably implicated in myocardial adaptation responses. This study tests the hypothesis that H-R results in myocardial adaptation by a mechanism mediated by alpha1-adrenoceptors and requiring de novo protein synthesis. The aims of the present study were to determine 1) whether H-R stress results in acute cardioadaptation to subsequent global, normothermic ischemia-reperfusion (I-R); 2) whether H-R-induced endogenous adaptation is mediated by alpha1-adrenoceptors; and 3) whether H-R-induced endogenous adaptation requires de novo protein synthesis. Rats were hemorrhaged and resuscitated, sham operated, or neither, with and without prior alpha1-adrenoceptor or protein synthesis inhibition. Hearts were then isolated and subjected to a second insult consisting of global, normothermic I-R (20 min ischemia-40 min reperfusion). The results show that antecedent H-R improved post-I-R left ventricular developed pressure, compliance, coronary flow, and decreased reperfusion creatine kinase loss (P < 0.05, analysis of variance with Bonferroni-Dunn). H-R-induced adaptation was abolished by prior alpha1-adrenoceptor blockade (prazosin, 0.5 mg/kg ip); however, inhibition of de novo protein synthesis (cyclohexamide, 1.0 mg/kg ip) did not affect H-R-induced acute adaptation. This study constitutes the initial demonstration that H-R induces endogenous cardioadaptation, which is mediated by an alpha1-adrenergic signaling pathway, but does not require de novo protein synthesis.
Adaptation, Physiological↗
Stress-induced cardioadaptation reveals a code linking hormone receptors and spatial redistribution of PKC isoforms.
Extracellular agents, including growth factors, cytokines and hormones, transmit their information into cells utilizing a balanced mosaic of intracellular phosphatases and kinases. How do these agonists select the correct substrates and modify them in order to produce defined physiological responses? Our studies have centered on the mechanisms of stress-induced cardioprotection (preconditioning) against postischemic dysfunction. In several species, the ischemia-reperfusion resistant phenotype appears to be induced by metabotropic-receptor pathways linked to PKC. Our results on the isolated rat heart show that each protective stimulus involves a characteristic mosaic of PKC isoforms, translocating into distinct cellular compartments. The distinct receptor-stimulated PKC isoform profile engaged by each extracellular metabotropic agent could allow the heart several overlapping modes of phenotypic adaptation to ischemia.
Animals↗
Calcium-induced inotropy is in part mediated by protein kinase C.
Protein kinase C (PKC) is an ubiquitous regulatory enzyme with dense myocardial distribution and activity; however, its physiologic relevance to myocardial function remains poorly understood. Although endogenous Ca2+ is a potent stimulus of PKC isoforms alpha and beta (cPKCs) it remains unknown whether exogenous Ca2+ activates these PKC isoforms, and if so, whether PKC plays any role in Ca2+-induced myocardial inotropy. To study this, ventricular sections from isolated rat hearts, with and without Ca2+-induced inotropy (CaCl2, 0.5 mM coronary concentration x 2 min), were probed for cPKC isoform translocation using immunofluorescence in order to determine if exogenous Ca2+ indeed activates cPKCs. We further examined the effects of exogenous Ca2+, with and without concurrent PKC inhibition (chelerythrine, 20 microM coronary concentration x 2 min), on fundamental physiologic parameters of myocardial developed pressure (DP), dP/dt, and coronary flow (CF) in the isolated rat heart to determine if Ca2+-induced inotropy involves PKC. Results indicated that exogenous Ca2+ results in translocation of PKC a from the cytoplasm to the sarcolemma and intercalated discs, as well as the translocation of PKC beta from the perinuclear to the intranuclear compartment. This dose of exogenous Ca2+ resulted in myocardial inotropy as determined by DP, dP/dt, and CF. Furthermore, myocardial inotropy was attenuated with concurrent inhibition of PKC activity. These findings link the physiologic effects of exogenous Ca2+ to PKC, providing a better understanding of the physiologic mechanism of Ca2+-induced inotropy.
Animals↗
Neutrophils are required for endotoxin-induced myocardial cross-tolerance to ischemia-reperfusion injury.
BACKGROUND: Although polymorphonuclear neutrophilic leukocytes (PMNs) contribute to oxidative stress after endotoxemia, it is unknown whether preischemic PMN induction is required for endotoxin-mediated myocardial resistance to ischemia-reperfusion (I/R). OBJECTIVE: To determine whether neutrophils mediate endotoxin-induced myocardial cross-tolerance to I/R. DESIGN AND INTERVENTIONS: Rats received sublethal endotoxin (0.5 mg/kg intraperitoneally) with and without rabbit anti-rat PMN antibody (anti-PMN antibody, 0.15 mL intravenously, to achieve an absolute neutrophil count of < 200/microL) or antibody alone, 24 hours prior to global myocardial I/R (20-40 minutes, Langendorff mode). SETTING: The University of Colorado Surgical Research Laboratories, Denver. MAIN OUTCOME MEASURES: Myocardial developed pressure, coronary flow, end diastolic pressure, and time to ischemic contracture were recorded with a pressure amplifier-digitizer (MacLab, AD Instruments Inc, Milford, Mass). Myocyte damage was assessed by determining creatine kinase leakage in the coronary flow effluent by creatine kinase assay. RESULTS: Sublethal endotoxin induced cross-tolerance to I/R, as demonstrated by improved recovered developed pressure and coronary flow, and decreased time to ischemic contracture, end diastolic pressure, and creatine kinase leak (P < .05, analysis of variance and Bonferroni-Dunn). Anti-PMN antibody administered prior to sublethal endotoxin abolished these protective effects (P < .05). Polymorphonuclear neutrophil leukocyte depletion alone failed to abrogate the deleterious effects of I/R. CONCLUSIONS: (1) Sublethal endotoxin induces myocardial cross-tolerance to I/R; (2) PMN induction is required for endotoxin-mediated myocardial resistance to I/R; and (3) while myocardial I/R injury is equally severe after antibody-mediated PMN depletion, endotoxin-induced tolerance to I/R does not occur in the neutropenic host.
Animals↗
Antibody-mediated neutrophil depletion preserves pulmonary vasomotor function.
Neutrophil depletion is commonly used to examine the role of neutrophils in lung injury. However, the effect of neutrophil depletion per se on mechanisms of pulmonary vascular smooth muscle relaxation is unknown. The purpose of this study was to examine the effect of neutropenia on the following mechanisms of cGMP-mediated pulmonary vasorelaxation: (1) receptor-dependent endothelium-dependent relaxation (response to acetylcholine (ACh)), (2) receptor-independent endothelium-dependent relaxation (response to the calcium ionophore A23187), and (3) endothelium-independent relaxation (response to sodium nitroprusside (SNP)). Neutropenia (<75 neutrophils/mu l) was induced with anti-neutrophil antibody serum 24 hr prior to lung harvest in five rats. Saline-injected rats were controls (n = 5). Dose-response curves to ACh, A23187, and SNP were generated in isolated pulmonary artery rings preconstricted with phenylepherine. Statistical comparison was performed using one-way ANOVA with post-hoc Bonferroni-Dunn, and P < 0.05 was accepted as significant. Relaxation to ACh, A23187, and SNP was complete in both control and neutropenic rats. Thus, antibody-mediated depletion does not impair endothelial-dependent or -independent cGMP-mediated pulmonary vasorelaxation.
Acetylcholine↗
Microtubules regulate pulmonary vascular smooth muscle contraction.
Microtubules are ubiquitous in eukaryotic cells. However, the role of microtubules in the mechanisms of pulmonary vascular smooth contraction has not previously been described. The purpose of this study was to examine the effect of microtubular inhibition (vinblastine) on the following mechanisms of pulmonary vascular smooth muscle contraction in rats using isolated pulmonary artery rings: (1) receptor-independent, calcium-dependent contraction via smooth muscle cell depolarization (response to KCl); (2) receptor-dependent, calcium-dependent contraction via alpha 1-adrenergic receptor stimulation (response to phenylephrine, PE); (3) receptor-dependent, calcium-independent contraction via thromboxane A2 receptor stimulation (response to the thromboxane mimetic, U-46619). Rats were studied 4 days after administration of vinblastine (750 micrograms/kg i.v.). Concentration-response curves were generated for KCl (5 mM to 100 mM) and for PE and U-46619 (10(-9) to 10(-4) M) (n = 8 rings/4 rats per group). Saline injected rats were controls. Pulmonary vascular smooth muscle contraction by calcium-dependent and -independent mechanisms was significantly increased following microtubular inhibition. These findings suggest that microtubules have an important role in the response of pulmonary vascular smooth muscle to vasoconstricting agonists.
15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
Differential effects of adenosine preconditioning on the postischemic rat myocardium.
Ischemic preconditioning describes the phenomenon of endogenous myocardial protection against sustained ischemia-reperfusion injury (I/R). Although the complex stimulus of transient ischemia induces global myocardial protection against acidosis, infarction, and stunning, it is unknown whether select components of transient ischemia (e.g., adenosine) are responsible for different aspects of protection. To study this, isolated rat hearts were treated with adenosine (125 microM coronary concentration) or vehicle 10 min prior (preconditioning) to global myocardial I/R (20 min/40 min; 37 degrees C). To determine whether adenosine affects stunning, continuous functional data (rate pressure product and coronary flow) were obtained. To determine whether adenosine affects necrosis, creatine kinase (CK) loss into the coronary effluent was determined during postischemic reflow. To determine whether adenosine affects pH, continuous pH measurements were made using NMR. Results indicate that adenosine protects against stunning but provides only minimal protection against acidosis. Adenosine's protection of function occurs despite severe acidosis. Adenosine does not limit CK loss. We conclude that (1) adenosine preconditioning, a component of ischemic preconditioning, protects myocardial function following I/R, but does not provide global myocardial protection against I/R in the rat; (2) protection of function can occur despite severe ischemic acidosis; and (3) protection of function occurs despite equivalent postischemic CK loss. These results suggest that pharmacologic preconditioning may require multiple agents in order to provide global myocardial protection.
Acidosis↗